Synopsis of Biological Data on Skipjack Tuna, Katsuwonus Pelamis

Synopsis of Biological Data on Skipjack Tuna, Katsuwonus pelamis

WALTER M. MATSUMOTO,’ ROBERT A. SKILLMAN,’ and ANDREW E. DIZON’

INTRODUCTION 1 IDENTITY

There has been a major expansion in the world’s skipjack 1. I Nomenclature tuna, Karsuwonus pelamis, fisheries in the past decade or so with the catch increasing better than twofold, from 320,000 1.1 I Valid name metric tons (t) in 1969 to 699,000 t in 1979. While catches increased in both the Atlantic and Pacific Oceans, the most strik- Kutsuwonus pelamis (Linnaeus 1758) ing increase has been in the western central Pacific, which includes the Japanese southern water fishery and the fisheries of 1.12 ObjectiLe synoiiymy Papua New Guinea and the Solomon Islands. In this area the catches have risen over sevenfold. from 41,500 t in 1969 to Scornberpelamis Linnaeus 1758 (original description); Osbeck 316,000 t in 1979. 1765; Bonnaterre 1788; Gmeliri 1788; Rafinesque 1810 The catch of skipjack tuna can probably be increased over Scotnber pelaniys Bloch and Schneider 1801; Kino 1810: present levels, but by how much is uncertain. To deal with the Cuvier 1829; Valenciennes 1836 rational utilization of this resource as it approaches the level of Scomher pe/uniides 1.ac;p;de 1802 full exploitation, it is imperative to have in hand all informa- Thynnus pelamis. Risso 1826; Steindachner 1868: Hoek 1904 tion concerning the biology, physiology, and various other T/iynnus vagans Lescon 1828 (original description). 1830 factors relating to the fish and fishery. Th-vnnus pdaniys. Cuvier and Valenciennes 183 I ; Temminck Synopses of biological and technical data and information and Schlegel 1842: Cantor 1850; Bleeker 1856; Ci”ut1it.r on the skipjack tuna by oceans were first compiled by Waldron 1860, 1876; Playfair and Cibthcr 1866; Day 1878; Liitken (1963) for the Pacific Ocean, Postel (1963) for the Atlantic 1880; Macleay 1881; Eigenmann and Eigenmann 1891; Ocean and Mediterranean Sea, and Jones and Silas (1963) for Richard 1905; Cunningham 1910; Parona 1919 the Indian Ocean, and were presented at the Food and Pelarnvs pelam.vs. Bleeker 1862, 1865 Agriculture Organization of the United Nations (FAO)-spon- OrcXnnu.5 pelun?.vs. Poey 1868; Goode and Bean 1879; Goode sored World Scientific Meeting on the Biology of Tunas and 1884 Related Species, 2-14 July 1962, at La Jolla, Calif. Forsbergh Eurh.vnnus pelumys. Jordan and Gilbert 1882: Carus 1893; (1980) completed a synopsis of the species for the Pacific Jouhin and Le Danois 1924 Ocean. Gymnosardu pelanits. Dresslar and Fesler 1889: Jordan and This paper reports current knowledge of the species in all Evermann 1898; Jenkins 1904; Snodgrass and Heller 1905; oceans and reviews and evaluates, where\er appropriate, the Evermann and Seale 1907; Jordan 1907; de Miranda Ribeiro results of past and recent research on the skipjack tuna 1915; Meek and Hildebrand 1923; Breder 1929; Hornell through 1980. 1935; Palnia 1941 Euth.i.nnk pelumic. Smitt 1893; Stark< 1910; Tanaka 1912; Jordan and Jordan 1922; Bizelow and Welch 1925; Fouler 1928, 1938; Herre 1932; Deraniyagala 1933; Nobre 1935: Smith 1949: de Beaufort and Chapman 1951; Bigelou and Schroeder 1953: Steinitz and Ben-Tuvia 1955: Fourmanoir 1957; Bailey et al. 1960, 1970; Collette and Gibh 1963; 1. Nakamura 1965; Robins et al. 1980 Karwwonus pelanyc. Kishinouye 1915; Frade and de Buen 1932; Le Gall 1934; Morro\\ 1957 GymnosUrdu pelarnys. Thompson 1918; Barnard 1925 harciin~onirspr/uint\. Ki\hinouye 1923; de Buen 1926, 1930, Stearn 1948: Smith 1949; Frarer-Brunner 1950; de Beaufort 1935, 1958; Jordan et ai. 1930: SoIdato\ arid Lindberg 1930: and Chapman 1951; Rivas 1951; Jones and Silas 1960, 1963, klirenbaurn 1936; Scale 1940; Serventy 1941; God\il and 1964; Schultz 1960; Collette and Gibbs 1963; Waldron 1963; Bqcri 1944: Nichols and Murphy 1944: Fonler 1945; La- I. Nakamura 1965; Gibbs and Collettc 1967: Collette and hlonte 1945; Clcmen\ and M'ilby 1946: Hildebrand 1946; Chao 1975; Collette 1978). Frater-Brunner (1950) recognized Brock 1949; Ri\a\ 1949. 1951: Herre 1953; Belloc 1955: only the subfamilies Gasterochimatinae and Scombrinae. I. Munro 1955, 195X: Brigs\ 1960; Jones and Silac 1960, 1963, Nakamura (1965) added a third subfamily, Thunninae, but 1964; ScIiuIt7 1960; Postel 1963. 1964: Talbot 1964; Whit- Colletre and Chao (1975) reberted to tun subfamilies, as pro- ley 1964; Williams 1964; Collette 1978 posed by Fraser-Brunner, and split the Scombrinae into two Kur.su~vonirsi'qqunr. Jordan et al. 1930; Barnhart 1936; Ohada tribes, placing Scombrini (the more primitive mackerels) and and Matsubara 1938: Fomler 1949 Scomberomorini (the Spanish mackerels) in one group and Karsuwonis pelumis. Herre 1933 (typographical error?] Sardini (the bonito,) and Thunnini in the other (Fig. I). Eur/?.vnnw (Kut.wwonur)prlaniis. Fraser-Brunner 1950; Men- Opinion on the generic name also has differed over the dis 1954: Bini and Tortonese 1955: Williams 1956; Scaccini years and the differences continue to this day. Jordan and et al. 1975 Gilbert (1882) credit Liltken for establishing the genus Eu- rhynnus and separating alliterarus and pelamys from the other 1.2 lawnomq tunas largely on the basis of an important osteological character, the trellis formed on a portion of the abdominal vertebrae. 1.21 Affinities Kishinouye (1915) established the genus Katsuwonus and separated it from Eurhynnirs based on differences in internal Phylum Vertebrata characters. Since then many others have recognized Katsu- Subph\luni Craniata wonus (de Buen 1930; Jordan et al. 1930; Herre 1932; Ser- Superclas\ Gnatlio\tornata venty 1941; Godsil and Byers 1944; Clernens and Wilby 1946; Series Pi\ce\ Hildebrand 1946: Rivas 1951; Godsil 1954; Belloc 1955; Class Teleostoini Munro 1955; Briggs 1960; Gosline and Brock 1960; Jones Sub&\\ Actinopterkgii and Silas 1960; Schultz 1960; Postel 1964; Talbot 1964; Whit- Ordcr Pcrcifornie5 ley 1964; Zharov 1967; Collette and Chao 1975; Collette Suborder Sconibroidei 1978). Family Sconibridac Fraser-Brunner (1950), in his attempt to maintain the Subfaniil) Sconibrinae Family Scombridae as a natural unit, synonymized Katsu- Tribe Thunnini wonus with Euthynnu~,as did other investigators (de Beaufort <;cnti? Ku/sir~wnir.s and Chapman 1921: Bigelou and Schroeder 1953; Mendis Species pe/uinr< 1954; Bini and Tortonese 1955: Williams 1956; Bailey et al.

The Family Scombridae was defined by Regan (1909) and further clarified by Starks (1910), uho divided it into fi\e subfamilies: Scombrinae. Scomberomorinae, Acanthocybinae, Sardinac, and Thunninae. Kishinouye (19 15) divided Regan's Sconihridae into three Families: Scombridae, Cybiidae, and Thunnidae. He subsequently (1917) split Thunnidae into trio Families. Thunnidae and Katsu\+onidae, and placed both into a ne\sly erected Order Plecostei on the basis of their \$ell- debeloped s~bct~taiieous\. ular system. Takahashi (1324), however, rejected Kishinouye's new order, pointing out that the subcutaneous vascular syrtem was not unique to tunas, but \vas also found in swordfish, Xiphius pludius; dolphin, Cor-vphaena hippurus: stargarer, Gnathapus elonparus; goby, Aprocryples chmensir; and puffer, Sphoeroides ruhriceps. These two views have persisted to the present. Berg (1940) followed Kishinouye in placing the tunas into a single Family Thunnidae and renamed the Order Thunni- formes. He relegated Katsuuonidae to subfamily \tatus as Auzidini. Some investigators retained the Family Thunnidae, uliilc rele_eating Kattuuonidae to generic status (Fomler 1945: Herre 1953; Morrow 1954, 1957; Munro 1955). Zharoc (1967) divided the Thunnidae into two subfamilies, Thunninae and Kat\u\voninae, \I hile others recognized the Families Thunni- dae and Kat\u\\onidae (Jordan and Hubbs 1925; Barnhart 1936: Kamohara 1941; tvlorice 1953; Godsil 1954). Most other investigators followed Regan and Stark's classi-

fication, maintaining the Family Scombridae as a natural unit Figure I.--The wbfamilir\. tribe,. and genera of the Sromhridsc tfnim C'allrllr (Barnard 1925: Fo\\ler 1928; Hildebrand 1946; Schultz and 2nd C'hm IY7Sl. 1960, 1970; Collette and Gibbs 1963; I. Nakamura 1965; E. linearus and Ausis rhazard \bere about as close to each Robins et al. 1980). Of those who relied heavily upon internal other as were K. pelamis to E. uffinis, but somewhat more characters, I. Nakamura (1965) supported his choice on the distantly related to T. albucures, and, therefore, to thc I(. basis that in both genera the atlas was not reduced in size pelamis-E. uffinis group. The authors indicated that their re- and the alisphenoids did not meet ~entrallyat the median line. sults showed little reason for separating Kutsuwonus from Robins et al. (1980), noting that the structure of the bony Euthynnus. While this reems to be true when coniidering shelf that divides the anterior six vertebrae into dorsal and only E. affinrs, the distance between ufjrinir and lineurus and ventral portions is shared by Auxis, Euthynnus, and Karsu- the latter’s close relationship with A. thoiurd suggest5 other- wonus only, suggested that the latter was more intimately re- wise. lated to Eurhynnus than to Thunnus. We thus agree with Collette’s (1978) view that placing Because of the close relationship of these t%ogenera, simi- Katsuwonus in synonymy with Eurhynnus \\odd obscure the larities in a number of characters such as noted abobe, are relationships of Eurhynnus with Auxis and Karsuwonus with expected; however, the differences pointed out by Kishinouye Thunnus. (1923), Godsil and Byers (1944), Godsil (1954), and Collette (1978) seem large enough to justify their separation. These 1.22 Taxonomic status differences include the following: The name pelamis was established by Linnaeus in 1758 and 1) The dorsal and ventral branches of the cutaneous artery was accepted by workers throughout the remainder of the in Karsuwonus are about equally developed, insread of 18th century. Bloch and Schneider (1801) used the name having the ventral branch short and dendritic as in pelamys and most workers also used this name in the 1800’s Eurhynn us. and early 1900’s. Some of these, notably Cuvier (l829), 2) The trellis on the vertebral column moves the aorta ven- Valenciennes (I 836), Temminck and Schlegel (1842), Cantor trally a distance slightly less than the depth of a centrum (1850), Bleeker (1856), and Ghther (1860), although spelling in Karsuwonus; less than in Airsis and Euthynnus, but the name pelamys, attributed the authorship to Linnaeus. more than in Tlricnnus. Two other names, pelamides by Lac$$ede (1802) and vagans 3) The liver in Katsuwonus resembles that of the yellowfin by Lesson (1828), were used briefly. Both names reflected group of Thunrrus more than Euthynnus and Auxis be- differences in the geographic locality of capture. The name cause the right lobe doe5 not extend the length of the pelamis gained in acceptance between 1890 and 1935, and body cavity. nearly all workers today use this name. 4) Hepatic veins are absent from the ventral surface of the Existing morphological and meristic descriptions of the liver in Karsuwonus, as opposed to Auxis and Eulhyn- skipjack tuna, Karsuwonus pelamis, from all oceank (Jones nus. and Silas 1963; Postel 1963; Waldron 1963) and biochemical 5) The prefontals are smaller in Kursuwonus and do not genetic study by Fujino (1969) indicate that there is but one project into the dorsal outline in dorsal view. worldwide species-Karsuwonus pelamis. 6) The edge of the posterior orifice of the niyodome in Karsuwonus is nearly vertical, whereas it is roughly spherical in Euthynnus. 7) The exoccipital condyle in Euthynnus projects beyond 1.23 Subspecies the transverse margin of the skull a distance approximately equal to the length of the first vertebra, whereas No subspecies are recognized. 1.24 Standard common and vernacular names it is much shorter in Kutsuwonus and equals roughly half the length of the first vertebra. The standard common and vernacular names the skip- 8) Katsuwonus has 41 vertebrae, whereas Euthynnus has of 39 or fewer. jack tuna, obtained from various sources (Herre and Umali 1948; Rosa 1950; Herre 1953; Okada 1955; Van Pel 1960; Attempts to determine generic relationships between Kutsu- Jones and Silas 1963; Postel 1963; Waldron 1963; Moreland 1967; Miyake and Hayasi 1972) are listed in Table wonus and Eurhynnus by serological and immunogenetic I. techniques have also given mixed results. Electrophoretic analyses of hemoglobin (Sharp 1969, 1973) have indicated 1.3 Morphology that Karsuwonus differs from Eurhynnus and Thunnus. Karsuwonus has only two hemoglobin bands; E. allerreruius 1.31 External morphology (and description) and E. affinis have three identical bands; and the four species of Thunnus examined (albacares, alalunpa, sib;, and thynnus) Body robust, rounded in cross-section and full in outline; have at least four bands. One of the bands in Karsuwonus maxillary not concealed by preorbital; about 40 teeth on jaws, and Eurhynnus seems to be identical whereas none of the but absent on vomer and palatines; corselet is well defined hemoglobins in Karsuwonus or Euthynnus is identical to any with hardly any scales visible on rest of body; interspace be- hemoglobin in the four species of Thunnus examined. Analy- tween 1st and 2d dorsal fins hardly exceeding eye diameter; ses of heart, red and white muscle tissues, and enzymes, on lateral line with a decided downward curve below 2d dorsal the other hand, have provided conflicting evidence. Sharp fin; margin of 1st dorsal fin rtrongly concave; pectoral fin and Pirages (1978) found that K. pelamis and E. affinis were short and triangular reaching posteriorly to the 9th or lGth the most closely related of rhe non-Thunnus tunas, that both dorsal spine most commonly, but to only the 8th or as far as species were almost equally close to T. albucares, and that the 1 Ith spine in exceptional specimens (Fig. 2).

3 Table I.-

Standard common Countr\/localit! name \ ernaculai name Aden. CiulCol AI mu\\:ddhub; haighciha >lorocco Li5tao I 'hakoura Alhariia Palamidd Ue\\ Guinea Tjakalang Angd.l BCNlllO heu Zealand Bonito Strtped bonito; \triped 4u\tidIla Strlpcd tuna Uatermeli~n:skipjack tunn); skipjack. slipper Bralll Himto de barriga Bonito rajado horua) Bonit Ii\tadd Peru Barrilete Uritiih C'luiana Oceamc honiio \\bite bonito Philippine I\ Gul)asan Striped tuna: \kiplack; Bllll\h \be51 Oceanic horiiiu Uhitc bonito; banlo; barriolet pundahan; bankulis; sohad; Indm oceanic honito; honiio; Canada Skipjack; thonine\ Skipjack tuna; oceanic honito, palanaban: puyan; tuhngan \entre ray: 5rriped bonito Poland Bonite Canan I\. Bonito Polynesia (except At" Bonito Chlk Atun Cachurreta; cachureta; Tahiti and cachorreta; harriiete Hawaii) Cubd At"" hlernia Portugdl - Gaiado; bonito de ventre Denmark Bug\tiihct honil raiado; bonito; listado; Ea\[ Africa arid SkLpjack \eheua(alw reler\to gayado; sarrajao. serra Laniibar Eirlhvnnus rp , Aurrr 5pp.) Roumania Paiamida Palamida lacherda France I ictao; bonite; Bonitr5 ventre ray/ Senegal Kirt-kin bonitou; boiinicou South Africa S k i pjac k Sklplack Luna; oceanic bonito: Germdny Echter boiiito Bauch5treitiger lesser tunny; bonito; Grrecc Pelam)\ Pelamis; tonina aatermelon; katunkel India Oceanic skipjack Bonito; kali-phila-nia\; Spain 1 istado Skipjack; atun de alfura; bonito barichoora: chooia; metti de veintre rayado; bonito; Indone\ia Cakalang Tjakalang; tjakalang-lelaki; palomida; bonitol; bonito de tjakalang-perempuan ; alrura; lampo; Ilampua; tlakalang-merah; skipjack bonito del wi; boniia Israel Balamida Sri Lanka Bonito Balaya; scorai Ital) Palometid Paamla; paamitun; palametto; Sweden Bonit palarnida; palamaru, palamid; Tahiti Auhopu tonina de dalniana; nzirru; Taiaan Theng chien paiamitu impinah; tonnetfo TunisI a Boussenna Bonite Japan Katruo KatuHo. katauuo; magatsuao. Union of Soviet - Okeanskti bonito; katwo; mandagat\uuo: mandara; Socialist polosatyi tunets honeat suo Republic3 horea Gd-da-ri; )eo-da-raeng-i; United Kingdom Striped bellied Striped bellied tunny; bonito bonito chi; niog-maen-dung- United Statea Skipjack tuna Skipjack; arctic bonito; oceanic da-racng-i of America skipjack; striped tuna; Madagascar Bonitr Bonitc\a \entre ray!; watermelon; rtctor fish; diodar). m'ba\\i striped bonito; oceanic hlddeira Is. Gaiado bonito; rkippy; ocean bonito; hlaldl\er Kaduma\ (\mall); Skipjack luna mushmouth; aku (Hauaii); Godhaa (large) aku kina, (Hawaii) Mc\,co Barrileie Trup prugavac Tun] prugavac Monaco Bonita

Anatomical descriptions of the species may be found in Body color in life is steel blue, tinged with lustrous violet Kishinouye (1923) and Godsil and Byers (1944). The vertebral along the dorsal surface and decreasing in intensity on the column (Fig. 3) differs sufficiently from that of other fishes sides to the level of the pectoral fin base; half of the body, to be worthy of comment. Godsil and Byers (1944) wrote including the abdomen, is whitish to pale yellow; evanescent "The spinal column is extremely complex in this species. In vertical light bars are seen on the sides of the body immedi- the posterior half of the precaudal, and the anterior part of the ately after capture; and a light grayish tinge on the underside caudal region, haemapophyses arise at both ends of each of the mandible merges posteriorly with the whitish color on vertebra, with the anterior haemapophyses of one vertebra the lower half of the body. Four to six black longitudinal articulating with the posterior haemapophyses of the pre- stripes are conspicuous below the lateral line on each side of ceding vertebra. These haemapophyses project far below the the body. Matsumoto et al. (1969) described t\+ospecimens, spinal column and alternate with the longer haemal spines one taken in Hawaiian waters, the other off Honduras, which described below. An osseous bridge roughly parallel with the lacked these stripes. They, however, represent extremely rare spinal column unites the anterior and posterior haemapophyses caw. of each vertebra. Viewing the spinal column laterally, the The counts of body parts for specimens from all oceans bridge and the circular opening it forms may be easily seen. are given in Table 2. There seems to be no difference in the A branch arises from each bridge and extends downward to counts on fish from the Pacific and Indian Oceans and in at unite in the median line with its fellow from the opposite side. least tw'o characters, first dorsal spines and gill rakers, on This forms the haemal arch from the tip of which a single fish from all oceans. haemal spine continues ventralward."

4 Figure 2.-Thr \kipjack luna. harrirwnnrt< pela,ni\ (1.innseusI

Table 2.-Counts of body part, for the skipjack tuna. ti~rrwuonir~pelmrir. from Ihe Parific. Indian. and Allanlic Oceans.

lndiaii Occan

PaciSic Ocean E. ASrica. Sri I ankn. Laccadlie AiianiiL Ocean Japan. Habail. Ii , Indone5ia. E. Paclflc Au\rialia (Jones Cap? Veri Characterr (Waldron 1963) and Sda5 1963) (Portel 1963) All ocean\

I 2.10il I) lit dona1 $pine 14-17 14-17 14-16 14-17 15-16) 2d dorial ra)\ 13-16 13-16 - 13-16 (14-12)

Dorm1 finlet\ 7-10 7-9 ~ 7-10 (8) Anal ray5 13-16 13-17 - 17-17 (14.10 Aria1 fink15 7-x 7~8 - 7-8 17)

Pcctoral ra)\ 24-32 26-30 ~ 24-32 (26-30) GI raker*

t ~ +( R~20) Upper 18-22 18-21 + 16-22 I I.ouer 35-43 33-42 - 33-43 (3R-41) Total 53-63 SO-63 5 1-62 50-63 (56-60)

Figure 3.-Axial skeleton of an adult skipjack luna (from (;odd and 19441

5 Such complex ba\ket\\ork also occur) in the Eurhynnus erythrocytes in normal bovine serum. Subsequently, Sprague (Godsil 1954), hut \\hereas the haemal arch in k. pelamrs and Hollosay (1962) named this cystcm rhe C blood group occurs adjacent to the \ertebral column, that in titfhynnur apparently after Cushing. In the 5ame paper, they published ii positioned a\\aq from the vertebral column (Fig. 4) at the information on another blood group, B, and on blood factors lips of the haemapophysec. Vie\\iiip the vertebral column A, D, and F \\hicli ucre 1101 \honn to belong to any inheri- laterally, the inferior foramina in Eurh~nnirtare elongate tance sysiem. Fujino (1967, 1969) found that the frequency of and about twice as long as those in K. pelamis. the K,-positive phenotype of the B group was related to the The abwnce of con\i\tenl differences in both external and size of skipjack tuna. Several papers were published after this internal morphologic;ii characters of skipjack tuna from purporting to habe found or not to have found evidence of widely separated region> in the Pacific (Godsil and Byers subpopulations from various areas in the Pacific Ocean 1944) indicates that there is but one species of skipjack tuna (Sprague and Nakashima 1962; Sprague et al. 1963; Sprague and that it is not possible to define subpopulations on the 1963; Fujino 1969, 1970b, 1972). Neither the C nor B groups basis of these characters. were shown to be amenable to Hardy-Weinberg analysis, and neither of these blood groups proved useful for population 1.32 Cytomorphology genetics studies. Fujino and Kazama (1968) found another blood group, Y, No information is available on chromosome number of which again did not prove useful in separating subpopulations, skipjack tuna. except when used together with other gene systems (Fujino 1969, 1970a). The Y group is made up of 15 phenotypes, I .33 Protein specificit) coded by 6 codominant alleles; however, only 2 alleles, Y' and Y"', and the 3 resultant phenotypes are abundant enough The inability of standard morphometric analyses to resol\e to be useful in population studies. The system was shown to the problem of subpopulation or stock separation in skipjack be amenable to Hardy-Weinberg analysis and independent of tuna has led to the utilization of population genetic method- sex, sire (age), and the C and B blood groups. Samples from ologies. Initial attempts involved the stud, of blood types various areas in the eastern, central, and western Pacific through antigen-antibody reactions, and this was follohed by Ocean and the Atlantic Ocean failed to show heterogeneity some work on polymorphisms of the protein hemoglobin of genotypic frequencies; however, the lower frequency of using starch-gel electrophoresis. As in other applications of the Y' allele found in the Atlantic Ocean indicates greater population genetics, most work nom involves the study of opportunity for divergence and, therefore, utility in sub- various serum and tissue enzymes, again using starch-gel population differentiation. electrophoresis. Sera are more commonly used because col- Fujino (1970a, 1971) described some preliminary results lecting the sample does not decrease the commercial value of for an H blood group consisting of two phenotypes. While the catch. Early isoenzyme studies involved samples collected there \vas some evidence for the existence of subpopulations from the central Pacific, then rather quickly from the eastern within the east-central Pacific Ocean (by testing phenotypes), Pacific, Atlantic, western Pacific, and finally the Indian the system was not shown to be amenable to Hardy-Weinberg Ocean. analysis.

(I) Blood groups (2) Hemoglobins

Cushing (1956). who pioneered the application of blood Little work has been performed using henioglobins because typing for the study of tuna subpopulations, found two their instability requires preservation techniques that are hard phenotypes on the basis of the agglutination of skipjack tuna to apply at sea and because they are not highly polymorphic.

'..

6 All samples examined by Sharp (1969, 1973) from off Baja three different approaches being followed by various scientists California and Hawaii showed two phenotypic bands; there- and organizations. fore, the author made no inferences regarding subpopulation The first approach was advanced by Kazuo Fujino who differentiation. was associated with the Honolulu Laboratory, National Marine Fisheries Service, and is now with the Kitasato Uni- (3) Serum isoenzymes versity in Japan. Fujino (1970a) showed that the Hardy- Weinberg method is not very sensitive to deviations from ex- While it is true that serum enzymes have provided the rich- pected proportions (genetic nonequilibrium) by employing a est material for differentiating subpopulations of skipjack simple theoretical test. Taking the calculated allelic frequencies tuna, only esterase and transferrin, and recently guamine for the eastern-central and western subpopulations (to be deaminase, have actually been found to be sufficiently poly- described later) and constructing a one-to-one mixture of morphic. In the plid-1960’s while testing a series of tissues these subpopulations, lack of fit to Hardy-Weinberg propor- sampled from skipjack tuna collected off Hawaii, Sprague tions could not be shown with a sample size of 100 individuals (1970) found six electrophoretic zones of esterases, one of (nor, we might add, would have been found if he had used a which he interpreted as serum esterase. He hypothesized that sample of 200 individuals). Later Fujino (1971) presented the four observed phenotypes are coded by three alleles. graphic evidence showing that a mixture of subpopulations Using blood serum, Fujino (1967) and Fujino and Kang could always be detected for a sample of 100 individuals (1968a) found three clear and three faint bands of serum from a one-to-one mixture of subpopulations having a differ- esterase activity resulting in nine observed phenotypes and ence > 0.443 in the frequency of the allele being tested, hypothesized, on the basis of the Hardy-Weinberg law, that whereas a mixture could never be detected if the difference they are coded by six codominant alleles. We follow the con- were < 0.328. For differences falling between 0.328 and ventional allele numbering system based on relative mobility, 0.443, ability to detect a mixture depended on the absolute hence the most abundant allele in the eastern and central allelic frequencies. While an examination of the effect of Pacific is Est 2, rather than number 1 as in Fujino’s papers sample size shows that it is, of course, easier to determine a (the reason for this difference is historical in that the now Est mixture with larger sample sizes, Fujino’s data indicate that 1 is rare and was found after much work was already pub- the differences in the allelic frequencies between the hypothe- lished). Because the faint bands are so rare, the system is sized eastern-central and western subpopulations preclude the usually treated as a six phenotype, three allele system for ability to consistently detect mixtures with a sample size of subpopulation study. The transferrin gene system was first 100 (or as we said, even 200). From this result, Fujino seems described for skipjack tuna by Barrett and Tsuyuki (1967) to have concluded that a reasonable strategy would be to from samples collected in the eastern tropical Pacific. They collect small samples (generally < 100 individuals) and to observed six phenotypes and hypothesized that they are sample more schools. He has then proceeded to search for coded by three codominant alleles. Researchers at the Aus- subpopulations by grouping sample lots (schools) from similar tralian National University (South Pacific Commission (SPC) geographical areas, by testing for intra- and inter-area 1981) have reportedly tested 42 gene loci (proteins) and found homogeneity, and by setting up statistical confidence regions only 3 that were highly polymorphic. Glucose-phosphate for classifying individual school samples into separate sub- isomerase, 6-phosphogluconate dehydrogenase (also reported populations, without considering whether the individual by Sharp and Kane’), and apparently adenosine deaminase schools represented mixtures of genetic units. were variable but at low levels. Research on the esterase, Fujino (1967) and Fujino and Kang (1968a) presented re- transferrin, and guamine deaminase gene systems will be dis- sults from their initial examination of material from the cussed in some detail below. Atlantic, Hawaiian Islands, the northeastern tropical Pacific, After the observed serum esterases were hypothesized to Palau Islands, and Japan. They found no evidence of heter- compose a single gene locus consisting of six codominant ogeneity of samples within these areas, nor between Hawaii alleles, the locus was shown to be independent of sex, size, and the eastern tropical Pacific or between Palau and Japan. blood groups B, C, and Y, and serum transferrin (Fujino However, their tests did show that samples from Hawaii were 1967, 1970a; Fujino and Kang 1968a. b). While these basic different from the combined samples from Palau and Japan; and essentially genetic factors were being established, the and Atlantic material was different from that collected in the search for subpopulations, which was the real purpose of the eastern Pacific. Fujino (1969) used both the esterase system studies, proceeded. Such population genetics studies involve and the Y blood group in attempting to separate subpopula- testing individual sample lots for genetic equilibrium and tions. Using rejection ellipsoids for Y’ and Est 2, he found testing for homogeneity both within and between sample lots that the eastern-central Pacific samples overlapped with those from arbitrary areas. These tests are quite technical since from the western Pacific, and these, in turn, overlapped with they involve inheritance properties of the multinomial Hardy- samples from the Atlantic. Thus, while the Atlantic material Weinberg law, chi-square tests of homogeneity or, more re- was shown to be different from the eastern-central and west- cently, the G-test of Sokal and Rohlf (1969), and considera- ern Pacific material, the employment of these two gene sys- tions of the effect of sample size on these tests. A great deal tems did not contribute to differentiating between eastern- of controversy has surrounded the employment of these tests, central and western Pacific material. He also stated that there i.e., the confidence to be placed on the results, and has led to was no evidence of heterogeneity (for any of the five gene systems, including esterase and blood group Y) between the

7 and restated that he had found no evidence of heterogeneity of samples within these areas, even with the inclusion of new material such as those from Ecuador. Also for the first time, Fujino described the boundary between these IWO subpopulations, and he did this by assigning schools to either of the subpopulations based on rejection limits for Est 2. While the western subpopulation was shown to be present the entire year in inshore waters off the east coast of the main Japanese Islands and around the Ryukyu Islands, the Bonin-northern Mariana Islands chain, and Palau Islands, he stated that the boundary between the subpopulations shifts easterly in the summer and'westerly in the fall and winter in the waters between the Bonin-northern Mariana chain and the international dateline. Then in the same year, Fujino (1970b) presented additional information on these subpopulations, namely, that there was no evidence for seasonal variation in the esterase gene frequency in either Hawaii or Palau, that new material from the Line Islands was not different from the historical Hawaiian material, that there was no evidence for heterogeneity within the western Pacific subpopulation based on samples from Japan, northern Mariana Islands, Ryukyu Islands, and Palau Islands, and further that the relatively low numbers of skipjack tuna larvae found in the area between long. 170"E and the international dateline in the Northern Hemisphere was supportive of the two subpopulation hy- pothesis. On the basis of new samples from schools in the western Pacific. which were assigned to either the eastern- central or western subpopulation based on rejection limits kigure S.--Uistribution and migration route of the western Pacific \kipjack luna for Est 2, Fujino (1972) adjusted the boundary, indicating subpopulation proposed b) kujino (1972). Eastern limits of distrihution during that the range of the western subpopulation extends out to northern winter and summer are indicated b? a did line and a broken line. reapecli\el!. Intensive %pawningground5 are shewn b? horizontal and bertiral long. 165"E (between the eastern Caroline Islands and the hatching and migration route5 are indicated b? curred lines with arrows. Marshall Islands/Gilbert Islands) without marked seasonal variation and hypothesized that the Iru-Bonin-northern Mariana Islands complex acts as a barrier to the eastern- Kishu group had an average ESIR 1 gene frequency of 0.754 central subpopulation. Using the estimated growth rare of and the Bonin-Izu group had an average gene frequency of skipjack tuna (based on Rothschild 1967), Fujino was able to 0.083. The relationship of these new genetic subpopulations separate the western subpopulation into A and B components to the previously described A and B units was not stated. associated with an apparent hatching time in the Northern Three schools assigned to the eastern-central subpopulation Hemisphere summer and winter, respectively. Figure 5 depicts had an average EstR 1 value of about 0.38, thus falling be- the hypothesized range of the western subpopulation, the tween the two hypothesized western subpopulations. overlap of northern sunimer and winter spawning areas, and The second approach of determining subpopulations was the migration routes of the A and B units. Subsequently, advanced by Gary D. Sharp who was associated with the Fujino (1976) rL 7orted some additional results from material Inter-American Tropical Tuna Commission (IATTC) and is collected from itie southwestern Pacific. He classified all four now with FAO. Sharp (1978) pointed out that if replicate schools sampled in New Zealand and one from Tasmania as samples were collected from homogeneous units, one should belonging to the eastern-central subpopulation. From Aus- expect a normal distribution of estimates about whatever tralia, two schools were classified as belonging to the western parameter was being estimated. He stated, however, that thir subpopulation and one to the eastern-central. Likewise for has not resulted for gene frequencies in the extensive, large- the New Hebrides (7 schools) and southern Solomons (12 sized samples of both skipjack tuna and yellowfin tuna, schools), both subpopulations were represented. All schools Thunnus albaeares, and argued that this was due to the genet- from New Caledonia (2) and Papua New Guinea (13) w'ere ic nonhomogeneity of the schools. As evidence that schools classified as being western subpopulation. Finally, Fujino are genetic composites, he referred to his studies on shifts in (1980) presented nonoverlapplng Est 2 frequency ranges, gene frequency and the clumping of rare alleles in individual namely 0.394-0.570 for the eastern-central and 0.578-0.758 for schools (Sharp'; Sharp and Kane footnote 3). While Sharp the western subpopulation. Using these values to classify (footnote 4) was able to show significant differences between schools, Fujino found that 40-5070 of the schools off eastern schools based on morphometric discriminant analysis, these Japan in May-June belonged to the western subpopulation differences seemed unrelated to genetic differences. Based on and averaged 65% for the entire year. Fujino also indicated these considerations, Sharp recommended that sample sizes that he could subdivide the western subpopulation using a new esterase gene system (EstR) from red blood cells. Taking 'Sharp. G. D. Studics OS Paclllc Ocean sklplack tuna (/(aisur,onuspelornrs) samples classified as western subpopulation and testing for genetics through 1978. Manum in prcn. C N.. FAO. Fnh Den.. VLa della Terrne this new esterase, Fujino found that the Satsunan-Tosa- di Caracaila. 00100 Romc. Italy

8 should be on the order of 200 individuals per school. In his study of subpopulations, Sharp placed greater emphasis on the lack of homogeneity of individual schools, compared the distribution of gene frequency estimates among geographical areas, and employed the usual statistical tests for both intra- and inter-area homogeneity. While he indicated that his large-sample data from the eastern tropical Pacific, Papua New Guinea, and New Zea- land fit Hardy-Weinberg expectations in all but two cases (in the former site), Sharp (footnote 4) and Sharp and Kane (footnote 3) showed that nearly all sampled schools exhibited statistically improbable clumping of rare alleles or a shift in the estimated gene frequency midwjay in the length range of the samples, or both. These results indicate not only that the Hardy-Weinberg test is not sensitive to mixtures but that schools tend to be both mixtures of siblings as well as groups with differing gene frequencies. These results cast doubt on FREQUENCY Cf THE ESTERISE 2 4iLELE Cf L4RGE SKIPJICK S4MPLES the utility of computing average gene frequencies for use in classifying schools to hypothesized subpopulations. Also in tigure L.-Frequenc~ dislribulien of Est 1 skipjack luna allele far large sample\ testing for homogeneity within geographical areas (eastern from +arbus (ource? (from Sharp text footnote 4). tropical Pacific, New Zealand, Papua New Guinea, Hawaii) using his own large samples and the larger sized samples of Fujino's, Sharp (1978, footnote 4) found significant hetero- quency in Hawaii. For both Palau and Papua New Guinea, geneity in the esterase system (and in transferrin also, but to there seem to be three groups showing much overlap between a lesser extent). Since tests among areas also show significant the areas. For New Zealand, Sharp says there is one group heterogeneity, Sharp's results are generally supportive of Fu- similar to the eastern Pacific and one unique group, but all jino's results in that there is evidence for subpopulation dif- of these distributions fall into the upper end of the Hawaiian ferentiation between the eastern-central and western Pacific distribution. The distribution for the northern area of the and within the western Pacific; however, they also indicate eastern tropical Pacific is similar to that for Hawaii and con- that subpopulation differentiation within the eastern-central tains some components similar to those from Ecuador. The subpopulation is likely. Sharp's approach then deviates from latter was said to have a unique component (with low gene Fujino's by comparing the similarities of gene-frequency dis- frequency), but this again falls within the range of the Hawai- tributions among the various sample sites rather than assign- ian samples. Based on all of these findings, Sharp (footnote ing schools to hypothesized subpopulations based on rejection 4) hypothesized the existence of six subpopulations in the limits. Thus, Sharp (footnote 4) observed (Fig. 6) that the Pacific (Fig. 7). Considerable overlapping of the subpopula- esterase gene-frequency distribution for Hawaiian samples tion ranges occurs in the central and western equatorial areas. seems to have components similar to those found in samples The third approach was used by the SPC in association off eastern Japan, and other components similar to those in with their Skipjack Survey and Assessment Programme. the northern areas of the eastern tropical Pacific and off Blood samples and various biological information have been Ecuador. Also, the typical gene frequency in the eastern collected fairly uniformly across the South Pacific and into tropical Pacific corresponds to the most common gene fre- the Northern Hemisphere in the western Pacific. With their

~. . .

Figure 7.-Rangc\ of 4%\kipjar!. luna whpopulalicin\ (from Sharp le11 foolnote 4). milh c\ample\ of the mo\emrnl of 1aBEcd fkh.

......

^--_---I. .. .- interest in determining uhat effect, if any, population struc- that the cline may level off. More samples will be needed turing would have on yield and fishery management in the from the Indian Ocean to resolve this issue. SPC area, they have emphasized the analysis of longitudinal While tagged fish were continuing to be recaptured (and gene-frequency \ ariations and of differences among \

(4) Tissue isoenzymes

Figure 8.-Relalion of esterme erne frequent! and longitude. Represcinn line Sprague (1970) found as many as 12 esterase activity bands and 9500 prediction limih indicated. Regre55ion c\clude5 \ample5 from ea51 of Ih? SPC area (east of dulled line). Y is numher of rampler: R i\ correlation in samples of dark and light skeletal muscle, heart muscle, coefficienl (from South Pacific Commi5\ion 19x1). kidney, liver, spleen, gonad, brain, and whole blood collected

10 from skipjack tuna in Hawaiian waters. These 12 bands ap- material for ADA or GDA, but the samples from Indonesia pear to be arranged in 6 regions, but only 2 of the regions seemed to be homogeneous and had a lower gene frequency were hypothesized to compose a genetic system. The fourth than the samples to the east. The South Pacific Commishn region contained serum esterases as described in the previous (1981) found a decreasing cline in gene frequency for the section. Sprague contended that the esterases in region 5 were GDA, allele from west to east (Fig. 9). also usable for subpopulation studies, but insufficient data were available at the time to do so. He hypothesized that the .48 three observed phenotypes in this region are coded by two alleles. McCabe and Dean (1970) also found innumerable .35 bands of esterase activity in samples of liver and skeletal muscle taken from skipjack tuna in the Atlantic Ocean. They . 30 indicated that the esterases in only two activity regions, Est Ib and Est 111, were stable and, therefore, usable for sub- .25 population studies carried out in the field. Region Est 111 .20 seemed to be a dimer system made up of four phenotypes coded by four alleles. Since one of the alleles had a frequency . 15 of 0.964, this esterase system is, for practical purposes, monomorphic and not likely of much use in studying sub- . IB populations in the Atlantic Ocean; however, the situation in the Indian and Pacific Oceans could prove to be different. In .05 region Est Ib, they observed 15 phenotypes in 300 samples and hypothesized that the phenotypes were coded by 7 alleles. .00t No specific data were given, nor was it shown that the system was amenable to Hardy-Weinberg analysis. Nonetheless, Est Ib may have potential for use in determining subspecific differentiation, since no single allele had a frequency > 0.4. Figure P.-Relalion of guanine deaminaw gene frequenc) and lungitude. Regres- sion line and Y5ob prediction limit\ indicated. Regression ewludes 3amples from Unfortunately, the phenotypes must be determined by a two- ea$t of lhe SPC area (east uf dolled line). > is numher of samples: H is correlation stage electrophoresis process, making the process more com- coefficient (from buulh Pacific Commission 1981). plicated and expensive than is the case with serum esterases. McCabe et a]. (1970) tested for dehydrogenase, acid phosphatase, and alkaline phosphatase activity in skeletal muscle 2 DISTRIBUTION sampled from skipjack tuna and reported finding polymorphisms of 6-phosphogluconate dehydrogenase (6-PGD) and 2.1 Total area alpha-glycerophosphate dehydrogenase (a-GPD) polymorphism in liver samples. The 6-PGD system was found to be a Prior to 1959, the occurrence and distribution of the skip- dimer with four phenotypes coded by four alleles, and the a- jack tuna had been determined essentially from records of GPD system was found to consist of three phenotypes coded captures in coastal waters and in those offshore areas sub- by three alleles. Since the frequency of PGD and a-GPD jected to commercial pole-and-line and purse seine fishing. were both over 0.9, both systems are essentially monomorphic Because pole-and-line fisheries were constrained by distance in the Atlantic and would probably not be useful for study- to areas within easy access of bait supplies and purse seine ing population differentiation in that ocean; however, the fisheries were confined to thotc areas with a relatively shal- systems could prove to be useful in the Pacific and Indian low mixed layer, a characteristic of the purse seine fishery in Oceans. the eastern sides of both the Atlantic and Pacific Oceans Lewis (footnote 5) reported preliminary results from his (Brock 1959), there were large gaps in our knowledge about investigation of 21 enzymes, encoded by 25 presumed gene the distribution of skipjack tuna in midoceanic areas of the loci, in liver tissues collected from skipjack tuna in north Pacific Ocean. Even less Bas known about the occurrence Queensland, Australia, and Padang, Indonesia. Only the and distribution of skipjack tuna in the Indian and Atlantic adenosine deaminases ADA1 and ADA2 and guanine Oceans, where fishing for this species on a commercial scale deaminase (GDA) were found to be sufficiently polymorphic had not developed as in the Pacific Ocean. (five, four, and three alleles, respectively) to encourage fur- Since 1959 various authors (Brock 1959; Kasahara 1968; ther research, whereas glucose phosphate isomerase (GPI), Miyake 1968; Marcille and Suzuki 1974; blatsumoro 1974, mannose phosphate isomerase (MPI), 6-PGD, isocitrate de- 1975) have utilized the Japanese tuna longline data to deter- hydrogenase (ICD), a-GPD, sorbitol dehydrogenase (SORD), mine the distribution of skipjack tuna in midoceanic areas. glutamate oxaloacetate transaminase (GOT1 and GOT2), Although the catches made by the longline gear were mall, phosphoglucomutase (PGMI and PGMZ), peptida5e 1 and 2, they constituted proof of the presence of skipjack tuna and malic enzyme (ME1 and ME2). fumarate hydratase (FH), the information thus obtained has expanded our knowledge malic dehydrogenase (MDH), lactic dehydrogenase (LDH), about the distribution of the species. pyruvate kinase (PK), glutamate pyl-uvate IranTaminase The distribution of \kipjack tuna (Fig. IO) was derived (GPT), 6-phosphofructokinase (PFK), phosphoglycerate kin- from atlases of the Japanese tuna longline carch data fol ase (PGK), and superoxide dismutase (SOD) were found IO various years from 1964 to 1979 ([Japan.] Fi\heries Agency be absolutely or essentially monomorphic. No large differ- 1967a, b. 1968, 1969, 1971, 1972, 1973, 1979a, 1980a. 1981), ences were evident between the Australian and Indonesian the Japanese southern water fishery for various year\ from ~ ARE& OF OCCURRENCE

Figure 10.-Skipjack tuna distribution and Fisheries in the major oceans. The mean 1S'C isotherms represent maximum late summer poleward displacement (data from various sources).

1964 to 1979 (Tanaka undated a, b, c, 1978, 1979, 1980; Ocean extend the limits of occurrence northward to lat. Tohoku Regional Fisheries Research Laboratory (Tohoku 49"N in the eastern Pacific and beyond lat. 55"N in the RFRL) undated a, b, c, d) the Japanese skipjack tuna bait eastern Atlantic. Skipjack tuna have been taken as far south boat fishery catch data for 1977 and 1978 ([Japan.] Fisheries as lat. 40" to 45"s in the western Indian Ocean and south of Agency 1979b, 1980b). and other sources (Wade 1950; Australia, and, although not indicated in Figure 10, in the Robins 1952; Brock 1959; Roux 1961; Jones and Silas 1963; eastern part of the Persian Gulf on rare occasions. The Postel 1963; Sakagawa 1974; Calkins 1975; Sakagawa and species occurs also in the Mediterranean Sea, from Gibraltar Murphy 1976; Santos 1978; Kikawa and Higashi 1979; Habib to Italy, but not in large concentrations as in the Atlantic et al. 1980a, b, c; Blackburn and Serventy 1981). The species Ocean (Belloc 1955). occurs continuously from east to west across all oceans, and over a wide latitudinal range from about lat. 45"N to south 2.2 Differential distribution of 45"s in the western Pacific and from about lat. 30"N to 30"s in the eastern Pacific. In the Atlantic Ocean, skipjack 2.21 Spawn, larvae, and juveniles tuna have been caught from about lat. 45"N to 40"s in the western side and from lat. 35"N to south of 40"s in the Larvae of skipjack tuna have been found over a wide area eastern side. Rare captures off Vancouver Island (Clemens in all the major oceans, including the Gulf of Mexico and and Wilby 1946) in the Pacific Ocean and off the British throughout the Indo-Pacific Archipelago (Fig. 11). The known Isles, Scandinavia, and Denmark (Postel 1963) in the Atlantic distribution of skipjack tuna larvae in the western and cen-

Figure 11.-Distribution OF skipjack tuna larvae. 1952-15 (data From various sources).

12 tral Pacific extends from near lat. 35"N off Japan to as far dance at long. 120"-150"E along a band of water from lat. south as lat. 375, off the southeastern part of Australia 10"N to the Equator. Matsumoto (1975), after adjusting the (Matsumoto 1958; Nakamura and Matsumoto 1967; Ueya- catches of larvae made with different sized nets and different nagi 1969, 1970; Mori 1970; Seckel 1972; Chen and Tan towing methods in a band of water from lat. 10"s to 20"N 1973; Nishikawa et al. 1978), and in the eastern Pacific from (Table 3; Fig. 12), reported that the center of larval

Table 3.-Calch rates of larval skipjack tuna in night surface lows from the Pacific Ocean (from Matsumoto 1975).

13 10"s (Richards 1969). There are no other reports from the ro\\s to lat. I0"N and 5"s in the east. In the Atlantic Ocean Atlantic or the Indian Oceans pro~idingrneasiircs ut' ahun- the distribution estends from lat. 40"N in the west to lat. dance. 30"s in the east. In all oceans the pattern of distribution re- Juvenile skipjack tuna are rarely \een at sca and are e\- sembles that of the larvae. From information acquired re- tremely difficult to capture. They have been collected in cently about the extremely rapid growth of skipjack tuna and various types of tra\\l and plankton nets, by dip netting at other tunas reared from artificially fertilized eggs through the night under light, and from stomach contents regurgitated by juvenile stages (Harada et al. 1971; Mori et al. 1971; Harada, seabirdr, but the greatest number ha\e come from stomachs Murata. and Furutani 1973; Harada, Murata, and bliyashita of tunas and billfishes. 1973; Ueyanagi et al. 1973), it would be expected that juve- The relatively small number of recorded capturer attest to niles of skipjack tuna occur in all localities where larvae have the difficulty in capturing the juveniles. Higgins (1967) com- been found. piled all records of 512 juveniles, 1.2 to 30 cm in length, In certain localities, i.e., North and South Atlantic, central taken from the Pacific for the period 1916-66. Yothida (1971) Indian, and northwest and southeast Pacific, the distribution obtained 1,742 juveniles, 1.6 to 40 cm in length, from the of juveniles is shown to extend beyond the range indicated stomach\ of billfishes from Hawaii,, and central South for the larbae. This could be due to juveniles leaving the im- Pacific naters in the period 1962-66. Higgins (1970) examined mediate spawning area as they grew larger and became more 578 "juveniles," 7 mm to 4.7 cni in length. taken in mid- mobile. Mori (1972) suggested that this could occur when the uater trauls in Hawaiian naien. Roughly 40mo of the latter juveniles attain the length of 30 cm. catch consisted of skipjack tuna lar\ae < 1.2 cm in length. Simmons (1969) compiled records of I63 ju\enile\. 13 to 15 2.22 Adults cm in length, taken by variow method\, including samples from stomach content5 regurgitated by seabird\. from the Excluding those areas from \%hichonly rare captures have Atlantic Ocean. Mori (1972) examined 5,851 juveniles and been reported, the distribution of skipjack tuna shown in young. 3 to 35 cm in length including some adults Io 70 cm, Figure 10 (medium shaded areas) shows the maximum north- from stomachs of tuna5 and billfi\hcs taken from the Pacific. nard and southnard limits. Both boundaries vary seasonally Indian, and Atlantic Oceani during the period 1949-69. Of and annually as the skipjack tuna respond to seasonal changes this number, 4.104 were juveniles < 35 cni in length: 3.778 in the environment. The boundaries generally shift poleward fiom the Pacific Ocean, 202 from the Indian Occan, and 124 in the summer and fall as seasonal warming of the water from the Atlantic Ocean. Thus, the total iuvenile ship.iack occurs in higher latitudes and recede toward the Equator in tuna collected from 1916 through 1969 is < 7,000. of nhich winter and spring as the uater cools. However, the northern roughly 300 Mere from the Atlantic Ocean, 2W from the and southern boundaries do not appear to shift in unison Indian Ocean, arid the remainder from the Pacific Ocean. with each other and the north-south shifting of the bound- Despite the small numbers of juvenib coilccted from the In- aries does not occur simultaneously across the ocean, due to dian and Atlantic Oceans, the dispersion of the capture sites the varyin8 effects of warm and cold currents in different presents a fair coLeraye of thc two ocean\. parts of the oceani. The above data 5ho\\ that jmenile skipjack tuna are uidel) Matsumoto (1975) has shown that in the Pacific Ocean the distributed in the tropical and subtropical waters of all oceans northern boundary moves poleward in the third and fourth (Fig. 13). In the Indian Ocean the distribution extends from qnarters and recedes toward the Equator in the first and lat. 15"N to 35"s. In the Pacific Ocean the distribution ex- second quarters (Fig. 14). The shift occurs at about the same tend5 generally from lat. 35"N to 35"s in the nest and nar- time in both the western and eastern halves of the ocean. In

, k c ', ',

e I , ._ ,i

Figure 13.--l.iicaIiona of knmn cspIure\ of juvenile \kipjarb tuna in the major owan\ from 1916 through 1969 (data from various sources).

14 Figure 14.-Oullines of the northern and suulhern houndaria of skipjack luna caught in the Japanese luna lonpline fisher). 1964-67. h) )earl) quarters (shaded area). The broken lines denule the maximum range for all four quarlers (from Matsumolo 1915).

~ .... ._..._ I 16 the Southern Hemisphere. ho\\e\er. the western half of the 2.3 Determinants of distribution changes boundary moies pole\\ard in the second and third quarters and toward the Equator in the fourth and first quarters, 2.31 Larvae and juvenile\ \+hereas in the eastern halt. the shifting ol tlie boundary occurs about 3 nio later. Although similar studies ha\e not Surface current5 influence the distribution of skipjack tuna been made in other ocean\, ue believe that the boundaries of larvae indirectly by modifying the distribution of rea-surface skipjack tuna distribution in those oceans also undergo simi- temperatures (Brock 1959; Blackburn 1965). In botli tlie lar changes. Atlantic and Pacific Oceanr the warm North and South \+?thin this \tide distribur.L>iial range. adult shipjack tuna Equatorial Currents flon westuard and are deflected pole- occur in varying den\itic\ it1 Jifferenr parr\ of the oceans, ward as they reach the coritinents. Cold currents at high lati- with area\ of moderare IO Iii~lidensitic\ quite often bein3 de- tudes flow eastnard and are detlected tonard the Equator fined by the existence 01 a fishery (darkly shaded areas, Fig. upon reaching the v.estern shores of the c9ntinents (Fig. 15). 10). In the Indian Ocean, skipjack tima fidierit.\ occur in the This results in the expansion of the narm nater area falor- Gulf of Aden and the Licinity of Laccadlie I5laiids. Jlaldi\e able for spawning in the and the restriction ol similar I4ands, and Sri Lanka. and \poradically along the coast- area in the east, as s1iotr.n by the 25 "C isotherm in Figure 11. lines of countrie5 bordering tlie ocean frorn Australia across A similar situation esisti in the Indian Ocean, except that it the Indian subcontinent to South Africa. In the \restern applies only to the Southern Hemisphere. Pacific Ocean skipjack tuna fisheries occur in the iicinity of Currents can directly influence the distribution of skipjack Jepm, Ryukyu I

kigure tS.--Orean current r>\lern\ (from Hrrich 1959).

17 sbip.iack tuna larvae are not found in water temperatures below 25" or 24"C, for they have been take at surface temperatures as low as 22. I "C (Matsumoto 1974). Both the optimum and minimum temperatures for \kipjack tuna larvae differ by areas (Table 4). In the werrern Pacific Ocean between lat. 30"N and the Equator, all larvae taken in surface night tows from 10 cruises of the RV Sho.vo Marir (data from Ueyanagi 1969) were from waters 25" to 29°C. The most produit!ve tows, in occurrence and number of larvae, were made in 28°C water. The lowest and highest temperature5 in ahich \kipjack tuna larvae were caught were 23.5" and 30"C, respectiLely. These larvae were taken in subsurface tows at 20-30 m (not included in table). In the vicinity of the Hawaiian Islands between lat. 10" and 26"N (Table 3), nearly all larvae caught in surface night to\\\ from nine cruise? of the RV Torcnsend Crot?7we//in 1964 and 1965 (un- publ. data, Honolulu Laboratory), \\ere from waters 23 o- Figure 16.--lcolherm and thermocline deplhs at clnring net plankton ttatiiin~in 26"C, and the most productive tows, in occurrence and num- thecentral equatorial Pacific Ocean (lal. ll"N-S?j: long. 140%'). IlliRh C1. .hhh ber of larvae, were in 25 and 24°C \\ater. respcctivel!. The cruise 33. Circled number5 denote \kipjack luna lanae. dot\ represenl cloring ne1 to^* )ielding other tuna larvae (modified from Strashurg 19601. coldest water in which skipjack tuna lar\ae were caught \\at 22.1 "C. Strasburg (1960), using opening and cloting plankton nets towed obliquely at 0-60, 70.130, and 140-200 m in producti\e than shallow night tws, and deep morning tows the equatorial central Pacific, reported the capture of a skip- tended to be more productive than deep night tows. Daytime jack tuna larba (Fig. 16) in v.ater \\ell below 6jcF (lR.5"C) catches were about the same in shallo\+ and deep to~t.The and felt that 60°F (15.6"C) \\as the minimum temperature in differences in the catch rates for juvenile skipjack tuna be- Nhich tuna larvae could occur. tueen shallow and deep tow5 at different times of the day Studies of tuna larvae taken in plankton nets b) othert were astumed to be the result of diel vertical migration. (Matsumoto 1958; Strasburg 1960: Klawe 1963: Ueyanagi Higgins (1970) found also that juvenile skipjack tuna were 1969: Richards and Simmons 1971) ha\e 5hown that skipjack significantly larger in deep tows than in shallow tows, and tuna larvae generally are limited to the upper 50 ni of nater, night and morning tows at the deeper depth also tended to that they undergo vertical diel migration, and that the verti- catch larger juveniles than day tows. He tentatively concluded cal migration is most pronounced in the upper 30 m. All of that the smaller juveniles live primarily in the upper isother- thete 5tudiec show that surface to~tat night caught con- mal layer, whereas the larger juveniles tend to occur in or siderably more larvae than day tnw. Although Strasburg's migrate to deeper water. result? (Fig. 16) suggest that larvae may be present below the thermocline, Klawe (1963) reported that none were taken 2.32 Adults belov. the mixed layer in the eastern Pacific Ocean. Ju\enile skipjack tuna (up to about 47 mm) also are found (I) Surface temperature near the surface. Sampling for juvenile tunas with a small mesh midwater trawl, Higgins (1970) found that shalloa to\\s The temperature range within which skipjack tuna appear (maximum depth of 20 m) at night tended to catch the most to be restricted has been reported on a world scale by Laevastu juveniles and deep tows (100 m) at night, the fewest. Catches and Rosa (1963) as 17" to 28°C and 19" to 23°C for the during the morning were not significantly different from major fisheries. Specific regions of the world oceans not only those at night, hut shallow morning tows tended to be less show some variations, but extend the range further. Uda

Tahle 4.-Shipjack tuna lanap taken in wrlare tow\ during IO cruise\ of the .Shii.vo lloru in the western liorth Pacific Ocean (Ile?anagi 1969) and in 9 rrui\e\ of the 7uwnwid (rovinell in the central hrth Pacific Ocean (unpuhl. data. hMFS Honolulu Laboralor)).

Ue\tern Paulic (131 30 K-0") Central Pacific (lat. IO"-26"N)'

Surface humhsr Number Perisni Lar\ar Numher Number Percent Larvae temp ('C) iou\ lanap occurrmcc perioa inn\ lanae nceurrence Der IOU

18 (1957) gake the range off Japan as 17.5" to 30°C for all oc- Sharp (1978) listed the optimum temperature range of com- currences: Broadhead and Barrett (1964) and Williams (1970) mercial activities and rchooling behabior of skipjack tuna lor reported a range of 17" to 30°C in the eastern Pacific Ocean; five hypothesized subpopulations in the Pacific Ocean a\ to- Jones and Silas (1963) reported regular catches ol skipjack low: northeastern Pacific, 20"-26 "C; southeastern Pacific, tuna off southern India from 27" to 30°C {{ater; Robinc 20"-28"C; Ne\\ 7ealand, l7"-23 "C; Papua Ne\\ Guinea- (1952) reported skipjack tuna taken in temperature5 of 14.7" Solomon Islands, 28 "-30°C; and northbbestern Pacific, 20'- to 20.8"C in Tasmanian \\aten: and Eggleston and Paul 28°C. Others who have inrestigated the relationship of skip- (1978) gave a range of 16" to 22°C off Neu' Zealand. Thus, jack tuna and mater temperature include Kuroda (1955). the overall temperature range of skipjack tuna occurrence Katrataki (1958, 1965a). Schaefer (1961b), Radoiich (1963), could be taken as 14.7" to 30°C. Figure IO shon5 that the Kasahara and Tanaka (1968). Uchida (1970), Seckel (1972), 15°C isotherm adequately demarks the range of skipjack and Yasui and Inoue (1977). tuna occurrence. (.Note: The 15°C isotherms shown \\ere for the warmest month of the year in both hemispheres and, hence, represent the ma,ximum average poleward displace- (2) Salinity ment .) As in the distribution of the larxae, temperature plays an According to Blackburn (1965), "Salinity measurements important role in the distribution of the adults. Its influence can be important in characterizing and detecting oceanic is usually not obvious in the tropics, %here the temperature IS features with which tuna are arsociated but salinityperse has relatively uniform throughout the year, but IS most notice- no known direct effect on tuna distribution." Barkley (1969), able at the higher latitudes. This is readily seen in the persis- however, showed that the habitat of adult skipjack tuna in tence throughout the year of high catch rate cells of skipjack the Pacific Ocean appears to coincide geographically with tuna taken on the tuna longline in the equatorial Pacific, as areas where a shallo\\. salinity maximum is present seasonally compared with the latitudinal shifting of such cells near the or throughout the year (Fig. 17). and suggested that the nor- northern and southern boundaries 01 distributlon in response mal habitat of skipjack tuna is the lomer salinity water which to seasonal changes in temperature (Matsumoto 1975), and in overrides the shallow salinity maximum. the marked seasonality seen in the curface fisheries near the Seckel (1972) observed that skipjack tuna landings in the northern and southern limits of distribution in the northeast- Hanaiian skipjack tuna fishery were high in those years when ern and southeastern Pacific, Hamaii, northwestern Pacific, init.ial warming of the water occurred before the end of Feb- Papua New Guinea, and Neu Zealand (Kauasaki 1965b; ruary and the mean monthly salinity during spring was be- Joseph and Calkins 1969; Uchida 1975; Habib 1976. 1978; tween 34.6 and 34.8"/00, the latter value indicating the north- Forsbergh 1980; Habib et al. 1980a, b, c; Wankowski 1980). ern boundary of the California Current Extension v;ater. That skipjack tuna seek preferred temperatures is indicated Yasui and Inoue (1977) also noted good to excellent fishing by catch patterns in the various fisheries. These temperatures off southern Japan in those years when the mean surface vary by regions: 20" to 24°C in the northwestern Pacific salinity was 34.81"/~and the mean surface temperature was fishery (Uda 1957). 20" to 30°C in the easlern Pacific fishery Zf.2"C. In poor years the mean salinity was 34.87"/,,,, and (Williams 1970). 28" to 29°C off southern India (Jones and the mean temperature was 19.8"C. In both instances, good Silas 1963). 16" to 18°C off Tasmania (Robins 1952), and fishing was related to favorable salinities, as well as favorable 19" to 21°C off New Zealand (Eggleston and Paul 1978). water ternperat ures.

Figure 17.-Di~trihution 01' ,kipjack tuna in the Pacific Ocean (after Holhwhild and l'rhidn 1968). 1 he contour\ mark the boundaries of the area where a shallow ruhrurfnrr salinit) maximum ib present either wd\Orla~~>or permanmll? (from Barklet 1969).

19 Ihiig~:! et al. (1978), in comparing chart\ oi shipjack tuna (1963) indicated that tunas are distributed by depth layers catclie\ b) the Japanese in tlie nestern Pacific for the period Mith the tkipjack tuna occupying the shallo\~est layer, fol- 1974-76 and turf'xe dinit) chart\ lor 1957-75. noted that lo\red in order b) the bluefin tuna, Thitnnits rhvnnus; yellou- the catchec of tkipjack tuna were greater 111 naters \rith din- fin tuna: bigeye tuna, T. ohecirs; and the albacore, T. ala- ities 01 35"/,!,, or less in the area east of Papua Ne\\ Guinea. lfmea. Skipjack tuna \\ere assumed to occupy the shallowest In thib instance the 3SL'/,,,! iwhaline in the region uas I'ound depth layer largely on the hasis that the) are taken in com- tn be associated \\ith the pre\ence of a co~verpeiice. mercial quantities almost entirely by fishing gear that require the fish to be at or very near the surface, and that the skip- (3) Surface currents jack tuna are taken only incidentally on the deep-fishing long line. 'The circulation features of the major current\ in both the Rerultc from the use of echo sounders and underwater oh- Pacific and Atlantic Ocean\, described pre\iou\l)- in conncc- wr\ations from small submarines hale sho\rn that ihe rkip- tion uith distribution of laivae, ahaffect the di5tribution jack tuna not only occur o\er a much greater depth range of adults. The flow toward thc Eqiiator of cool \rater on the than previoutly realized, but also in depths occupied by other eastern side of the oceans tends to re\trict tlie distribution of tunas. Kimura et al. (1952) and Yamanaka et al. (1966) ob- fish in that region, and the pole\\ard tlo\b at the \restern side served fish schools at depths of 140 and 120 m,respectively. of the oceans perniitr a broader di5tribution there. uhich they identified as skipjack tuna \\hen the schools sub- Surface currents affect the distribution ol' \kipjach tuna in sequently rose to the surface. Strasburg et al. (1968) encoun- other nays. In currents llouing meridionally, tuna are con- tered skipjack tuna schools at depths of 98 to 152 m in >idered to he distributed along the axit of the current and in Hanailan waters during their numernus dives in a submarine. greater abundance than in adjacent natev (Blachburn 1965). Ti-acking skipjack tuna tagged aith ultrasonic transmitters in Such a relation \\a> noted by Kairasaki (1958) and Uda Hawaiian maters (Dizon et al. 1978) indicated that this species (1962a) in the Kuroshio (n'arm current fi-om the south) off spends its time between the surface and 263 rn during the Japan. Uda obserked that inore skipiach tuna became a~ail- day, but remain5 near the surface (within 75 m) at night. able to the fisher) when the \\arm Kuroshio water extended Thete depths are well Hithin the depth range in which the over a broad area; and conversely, that a strong Oyarhio yello\\fin tuna are usually caught by longline. (cold current from the north) hindered the niovement of fish and catches were Ion. 3 BIONOMICS AND LIFE HISTORY Other effects of currents on the movement of fish have been indicated in the models of migration of skipjach tuna 3.1 Reproduction proposed by Seckel (1972), Williams (1972), Matsumoto (1975), and others. These migration models are described in 3. I1 Sexuality Section 3.51. The skipjack tuna is normally heterosexual; however, a (4) Hydrographic features few instances of hermaphroditism have been recorded (Naka- mura 1935; Raju 1960; Uchida 1961; Thomas and Raju 1964). Fish tend to aggregate in areas where harm and cold water In the two specimens described by Uchida from Hawaiian intrusions are well developed, in eddies, in areas of turbulent waters, the left and right gonads of one fish (Fig. 19) and the mixing, in oceanic fronts, comergences, upuelling, and other left gonad of the second fish were divided into three segments: hydrographic features (Uda 1961, 1962b). Kawasaki (1958) an anterior ovarian section, a middle testicular section, and a noted tha! skipjack tuna fishing grounds developed off Japan posterior ovarian section; whereas the right gonad of the when the warm Kuroshio uater spread thinly over colder second fish was divided into two segments: an anterior two- uater and when tlie Kuroshio meandered in a complicated thirds testicular section and a posterior one-third ovarian pattern. Uda (1962a) reported that good catches were also section. In both fish the anterior ovarian sections contained made when both the Kuroshio and the cold Oyashio currents ripe resorbing ova but not in the posterior ovarian sections, a were strong, under which conditions the skipjack tuna were condition that could result from extrusion of ova from the concentrated along the boundary betueen the Harm and cold latter during spawning but not from the former, due to the water (polar front). Uda (1962b) further reported that in the lack of an adequate oviduct. The testicular portions contained eddies associated with the polar Iront, skipjack tuna were no running milt, but were described as well developed. Based found in the warmer anticyclonic eddies along the front. on the developmental stages of the ovarian and testicular Donguy et al. (1978) showed that \kipjack tuna catches by sections, Uchida believed that both fish were functional the Japanese in the western Pacific, east of Papua New males and females. Guinea, were concentrated along and on the low salinity side of convergences (Fig. 18). Forsbergh (1969) reported that a 3.12 Maturity marked salinity front was found at all seasons in the Panama Bight and that the abundance of skipjack (and yellowfin) The minimum size of skipjack tuna at first spawning has tuna in the northern part of the Bight appeared to he related not been defined, but a reasonable estimate can be made to the seasonal cycle of up\\elling. from the various published reports of fish with mature, ripe and spent ovaries, and of fish with ova diameters approach- (5) Vertical distribution ing 1.0 mm. In the Pacific Ocean, Marr (1948) recorded skipjack tuna Based on studies of tuna 1o:igline catches, Yabe et al. as small as 40 cm fork length (FL) uith spent ovaries from

20 Figure 18.--l)istribution of skipjack luna catches and surfare salinilj in the mestern Pacific: a) JanuarJ-March IV74 h) JuI)-Srplember 1974. c) Octohrr-lkrcmhrr 1974. and dl January-March 1975. No calrh denoted h) 0. catches h) +,and dark squares reprewnl > 7uO I (from Ihngu? el al. 1978).

34.0 to 34.9 cm sire class having ripe ovaries; and Brock (1954) noted that the smallest fish that posessed maturing ova during the spawning season in Hawaiian Haters \\ere around 40 to 45 cm. Raju (1964~)estimated the 5i7e of sexual maturity of skipjack tuna in the Indian Ocean around hlini- coy Island as about 40 to 45 cm. He deribed his estimate from his observations that I) the smallest skipjack tuna that possessed ovaries with maturing ova during the spawning season \+asaround 40 to 45 cm and 2) remnant5 of mature o\a were present in fish abo\e 40 cm but none in fich belo\\ thi\ sire. Stequert (1976) reported first spawning of Yhipjach tiina at 41 to 43 cm off the northwest coast of Madagascar. Sim- mon5 (1969) reported minimum size of females at maturity in the Atlantic Ocean as 41 cm, as determined from ltrh \kith spawned or spent ovaries. From the above, it appeari that [he minimum si7e of fc- male ikipjack tuna at maturity is 40 sm and that initial Figwe 19.-Ovulerlr~ of a hermaphrodilir \kipjack luna (from Urhida 19611. spawning can occur in fish between 40 and 45 cni or larger. The unusuallv small female (34.0-34.9 cni stir cia\\) nith ripe the Marshall Islands; Wade (1950) recorded fish in the 40.0 ovaries reported by \\adc. (1950) could be a rarity or a caw to 40.9 cm size class with ripe and spent ovaries from Philip- of erroneous Ftaeing of the gonads (we Section 3.15 tnr d~\- pine waters, and reported the capture of a female in the cussion of maturity stage5 of gonad\).

21 3.13 and 3.14 Mating and fertilization most used were size of gonad and degree of softness or tur- gidity. Others (Buzag 1956; Raju 1964~;Kawasaki 1965a) felt Iversen et al. (1970) observed what they beliebed to be that these general characters alone were inadequate even for courtship of skipjack luna from an underwater sled towed grots clastification. Some improvements were made by in- from the RV Charles H. Gilbert. While observing a pair of cluding the description of ova in the various stages of de- skipjack tuna approximately 50 cm long, swimming close to- velopment (BuTag 1956; Schaefer and Orange 1956; Raju gether back and forth in front of the sled, they noticed that 1964~;Yoshida 1966; Simmons 1969; Batts 1972c), but the the fish's bodies would tilt about 30" from the vertical in classification still remained subjective and was prone to vari- opposite directions with the ventral portions of their bodies ations caused by the observer's interpretation of the various almost touching each other. At another time they sa\& two st ages. fish swimming in tandem, one ahead of the other. The latter Buiiag (1956) and Raju (1964~)classified sexual maturity fish, tituated slightly below the lead firh, uould approach it on the basis of ovum diameter measurements. Yoshida (1966) closely from the rear, its snout coming within a few centi- and Batts (1972~)provided ovum diameter measurements meters of the caudal fin of the lead fish. At the closest point along Mith descriptions of ova, ovaries, or both. Yet the of approach, the trailing fish uould display dark vertical classification by these authors differed noticeably, since a bars on its side, similar to that displayed during feeding. A standard scale defining the Larious stages of development second pair of skipjack tuna shimming in tandem were ob- had not been established for tunas. BuFiag (1956) attempted served from the deck of the vessel. On two occasions the lead to classify the stages according to the International Maturity fish was seen to wobble from side to side and the trailing fith Scale,' but no one else has followed his example. A summary would exhibit vertical bars along its flanks. These fish showed of the maturity stages of female skipjack tuna based on ova no interest in the baitfish throw'n into the water, so that the diameter and descriptions of ova and ovaries from the pre- appearance of the bars were not likely connected with feed- ceding studies is presented in Table 5. ing (see Section 3.41 on feeding behavior). To aboid measuring ova, some authors have used gonad Observations of similar behavior, believed to be mating or indices (G.1.) to determine maturity (Yabe 1954; Schaefer courting acts, have been observed by longtime skipjack tuna and Orange 1965; Orange 1961; Raju 1964~;Yoshida 1966; fishermen (e.g., R. M. Oka6) in the Hawaiian Islands. Schools Baits 1972~).Schaefer and Orange (1956) obtained a linear of fish displaying such behavior were reported to be reddish- relationship between ovum diameter and (3.1. (Fig. 20) of or purplish-hued and as being disinterested in feeding. The fish taken in the eastern tropical Pacific. They thus concluded senior author has observed similar schools on several occa- that maturity of female skipjack tuna could be determined sions and when the visibility, sea, and light conditions were on the basis of G.I. values. Their data, however, consisted right, whitish trails of spawn could be seen at the point of mainly of G.I. below 50 from samples that included only feu contact when two fish came together. The contacts seemed fish larger than 60 cm. Raju (1964~)also obtained similar to occur randomly throughout the rapidly moving schools. results (Fig. 21) from fish taken off Minicoy Island in the These observations suggest that mating is most likely pro- Indian Ocean; however, his sample included larger fish a.id miscuous, and other observations such as the collection of the largest G.I. was about 66. eggs in various stages of embryonic development in plankton Yoshida (1966), whose study was based on fish from the nets suggest that fertilization occurs externally. Marquesas and Tuamotu Islands in the central Pacific, reported G.I. values ranging from 20 to over 90 for ovaries in 3.15 Gonads the developing stage (ovum diameters 0.5 to 0.6 mm) and from 30 to nearly 100 for ovaries in the advanced stage (ovum In the early years, sexual maturity of the skipjack tuna was diameters 0.6 to 0.7 mm). He noted that there was a large determined by the general appearance of the gonad (Matsui overlap in the G.I. values between these two stages and that 1942; Marr 1948; Yao 1955; Williams 1964). The characters the linear relationship reported by Schaefer and Orange

'Maturity wale adopted by the lniernational Council tor the Exploration ot theSea.a5clted b) Clark(1934).

Table 5.-!wmmar? 01 malurit? stages nf female rhipjack luna.

I Immature 0 IC O\a transparent; uith nucleu\ Slender. elonpate. \ex determinahle II tarl, inaiurine 0 35 OLaopaque: )OIL forming Enlarged: ova !not \Ivble 111 1 ate niatorinp 0 60 Obaopaque: )clk eranular Fnlarged. turgid: oba i:\ible IV hlatittc 0 X5 O\atran\parent: uithoil Enlarged. hesin lo\ing turgidit); cIu5icr or oil droplet ma \~sihle,cavly di4odeed V Ripe I.(N) O\a \\ith )ello\r CUIdroplet Grratl) enlarged. not turgid: ma eaol\ dlclodged. some free In lumen: extruded hy preswre VI Spent 0.55 (ha remnant, I.Onini Flaccid, utth remnant5 of ripe ox a

22 50 I I 1 I I I I I

Figure 2O.-Relationship belween gonad index (ovar, weight relative to fish length') and mean diameter of most advanced group of ova of skipjack tuna from the Marquesas and Tuamotu Islands (from Yorhida 1%).

(1956) was not applicable to (3.1. values above 36 (Fig. 20). 0 70 We should also add that the linear relationship shown by 40 ~ Raju (1964~)in Figure 21 does not seem valid either. Because of the wide range of (3.1. values for ovaries in the same developmental stage, the gonad index does not seem to be a sound measure of maturity for skipjack tuna.

3.16 Spawning

(1) Fecundity , 0 IO Relatively little has been published concerning the fecundity of skipjack tuna. The fecundity range has been reported as 0 '0 lo 20 M 40 M 60 70 100,OOO to 2 million ova for fish 43.0 to 87.0 cm long from GONAD INMX the Pacific Ocean, 87,600 to 1,977,000 ova for fish 41.3 to 70.3 cm long from the Indian Ocean, and 141,000to 1,331,OOO ova for fish 46.5 to 80.9 cm long from the Atlantic Ocean Figure 21.-Relalionship between gonad index (ovar) weigh1 relalive to fish length') and modal length of largest group of ova of \kipjack tuna from Minico) (Table 6). Plots of number of ova in the most advanced (from Raju 1964~). mode against fish size by Joseph (1963),Raju (1964a),Sim-

Table 6.--Obserred fecundilr e,timatea for skipjack luna. Fi\h length Source of Numher (range) Estirnaied ova data Localit\ oi fi,h (mm) (ranee)

~~ ~ Pacific Ocean Yabe (19%) Ryukyu Islands S 468-6 10 I13.364-854,897 Rothschild (1963) Hawaiian Islands 3 W-870 280,000-I ,900,wo Joseph (1963) Eastern Pacific 42 614-715 210,000-1.4w.wo Yoshida (1966) Marquesas Islands 4 430-750 100.ooo-2,ooo.ooo Indian Ocean Raju (1964a) Minicoy Island 63 418-703 ISI.Y00-1,977.900 Stequert (1976) Madagascar 64 44-565 87,600-824.000 Atlantic Ocean Simmons (1969) Caribbean Sea 13 46s-809 262.(xx)-1,331.00 Batts (1972~) North Carolina, 31 498.704 I4I .ooO- I ,200,000 U.S.A

23 mons (1969), and Batts (1972~)shorn considerable variation also. Both reported smaller standard error of estimates than among fish of the same size. All four authors fitted regrec- those obtained from any of the fecundity-length rslationship5, sion lines to the relationship between fecundity and length Nhereas the latter obtained a coefficient of correlation only (Table 7; Fig. 22), but due either to inadequate sample size slightly higher than that of the fecundity-length cubed rela- or to samples of limited size ranges, the regression lines \dried tionship. The closeness of the coefficients of correlation is noticeably. Raju (1964a) fitted regression lines also to the re- understandable, since weight is nearly proportional to the lationship between fecundity and the square of the fish length, cube of the length for skipjack tuna. Consequently, tither and both he and Simmons (1969) fitted regression lines to the length cubed or weight may be used to describe the rela- the relationship between fecundity and the cube of the length. tionship between fecundity and fish size. The latter regressions had the higher coefficients of correla- Using Raju's (1964a) fecunditb-length cubed relationship, tion, although all four regressions were statistically significant the calculated fecundity estimate of skipjack tuna at mini- (P = 0.01). Joseph (1963) and Raju (1964a) fitted regression mum spawning size (40.0 cm) is 110,OOO ova. That Raju's lines to the relationship between fecundity and fish weight fecundity-length cubed relationship holds reasonably well for fish larger than about 69.0 mm is noted in Figure 22, which shows the extension of the curve and also the observed fecun- Idity of fish above this size by various authors. I In spite of the acceptable fecundity-length cubed relation- I I ship noted above, it would be most difficult to estimate the JOSEPH 1963 I I total annual egg production of the skipjack. tuna because of 0 RAJU 19640 on I I 1 ROTHSCHILD 1963 I* I) the extremely large variation in number of ova among 0 SIMMONS 1969 I I fish the same size, 2) the uncertainty in the number 1800 of of V BATTS 1972c I I times a fish spawns during the year (Section 3.16), 3) the A YOSHIDA 1966 I possibility of reduced fecundity at successive spawning in 4 1600 a the same year (Joseph 1963), and 4) incomplete knowledge LL concerning the size composition and total abundance of the 1400 n spawning stocks. 4 2 1200 (2) Frequency P- t :- 1000 The possibility of skipjack tuna spawning more than once n during a season has been discussed by several authors. Brock 3 ;800 (1954) was of the opinion that the multimodal distribution of ovum diameters during the spawning season and its absence at other times indicated that individual skipjack tuna taken 600 in Hawaiian waters spawn several times. As supporting evidence, he cited the absence of an overall trend in ovum 400 diameters during the spawning season (Fig. 23) and the absence of spawned-out fish until after the end of the spawning 200 season. Bukg (1956) determined multiple spawning by following the movement of ovum diameter modes through the various stages of development as indicated by ovum diameter frequency plots (Fig. 24). Raju (1964~)determined multiple spawning from the Indian Ocean by satisfying the four lines of evidence used by Clark (1934): I) The presence of multiple Figure ZZ.-Hegreaaion~ of fecundil? on length and iihrerred fecundit) erlimalea of skipjack luna aheve 690 mm. I) Jo5eph (IY63); 2) Haju (1964a); 3) fecundit). modes in diameter frequency polygons, 2) obtaining a high length', Haju (1964a); 4) Simmons 119691; and 5) Baltr (1972~). correlation in the progression of successive modes, 3) the

Table 7.--Comparison of fecundil~-lenplhand fecundi1)-weight relationships of skipjack luna from variou? sources.

/, 6.326 XR.613 213 2 713 28.6 0.00254 27 d 0.OOXXl342 24 7 67 01 22.5 3.23X - I.x54 c STAGE I

STAGE II

STAGE 111 Y

STAGE V

STAGE V-A

Figurr 23.-A1emye modal diamelrr of the Isryrst poup of o\a in Aipjack luna war) \ample\ rdlected from1949 to I951 in Hawaiian water\ (from Rrorh 19541.1

presence of ova remnants in maturing ovaries, and 4) the STAGE VI1 decrease in the numerical ratio of ova bet\\een maturing and mature group. % From the results of these studies, there seems to be little L doubt that skipjack tuna spawns more than once during a STAGE VII-A season. How many times it spawns is not yet known. but utilizing the reports by Brock (1954) and Bu%ag (1956), the 6 6 10 12 I4 16 I6 20 22 24 26 28 30 32 5 number of spawnings can be estimated, at leayt for fish in L Hawaiian waters. DIAMETER IN MICROMETER UNITS From Brock's 1949 and 1951 data in Figure 23, \\e note that in Hawaiian waters, fish \vith immature o\a (ova diam- Figure 2J.-Ora dinmrtrr frequrnr) pc,l)gon\ of \hipjack tuna with the eter 0.1 nim) occurred in February, and in 2 mo the o\a de- *laye* (ifma dr\rlopmrnt (trim HuZq IYShI. IEarh micromrtrr unit equals veloped into the mature stage (ova diameter 0.7 nim). If 0.0325 mm.1 development continues at this same pace, the ova should he in the ripe stage (Yabe 1954; Yoshida 1966; Batts 1972~)nith diameters from 0.8 to 1.2 mm in late April or early May. tempts to rear tunas in captivity. Collection of ripe ova from This is supported by the first captures of larval skipjack tuna females at sea has only resulted in sporadic success, probably in Hawaiian waters in late April and early May (Seckel 19723. due to the paucity of running ripe females in the commercial BuEag (1956), as well 2s others, had observed that after the catches and because attempts to hold adults as brood stock first hatch of ripe ova has been spawned, the ovaries revert has proven inefficient and costly. to the condition similar to that of ovaries in maturity \tape In June and July of 1980. female skipjack tuna (1.4-2.2 kg) 111 (Fig. 24), i.e., ova in the most advanced group are not confined at the Kewalo Research Facility of the U.S. National much larger than about 0.58 mm (18 micrometer units). OVP Marine Fisheries Senice in Honolulu ovulated ripe ova \sith- of this size would require about 6-7 wk to reach the ripe in 8 h after capture (Kaya et al. 1982). The rapid debclop- stage (based on Brock'c data), evclusibe of a probable resting ment of the o\a, followed by o\ulation and spawning, appar- period after the initial spawning. Hence, the earliest that a ently was induced by stresses experienced by the fish during skipjack tuna could spawn a \econd time after having capture and confinement. The ripe ova measured approxi- spawned once in early May would be in late July or early mately 1.0 mm as compared uith unobulated ova, 0.59-0.74 August. Since the spawning season in Hawaiian waters termi- mm. obtained from fish taken from the 5ame school and iced nates in September (Brock 1954), it \\auld be unlikely for immediately upon capture. Artificial fertilization of the ripe this specie\ to spawn a third time in the area. Thls does not ova resulted in successful embryonic developement and sub- mean that a third or even a fourth spa\\ning could not occur. sequent hatching of the larvae. Males brought live to the In fish with ovaries de\eloping more than two groups of ova. holding tanks did not re\pond in the same manner. Their migration to warmer waters in the fall and winter could allou testes \bere identical to those of fish iced immediately upon it to spawn a third or even a fourth time during a year. capture. Although all testes nere nqature, they failed to yield Another bit of information may be gleaned from Figure milt on moderate stripping pre\wre. Small amounts of thick 23. If the first spawning occurs as dacribed, then the dura- milt obtained from evcised testes, ho\\ever, were successfully tion of ova development from the immature to the ripe or used in fertilizing the ripe ova stripped from captive females. spawning stage can be estimated as being from 3 to 3.5 mo. The rapid maturation and ovulation procesws brought on by capture and confinement stre\ses are currently being ex- (3) Spawning in captivity ploited to routinely produce larval skipjack tuna5 for de- belopmental and gro\bth studies at the Kewalo Research Current interest in mariculture has resulted in many at- Facility.

25 (4) Areas and seasons eggs nere found to be in arrested stages of cleavage, whereas the buoyant eggs contained developing embryos. Gonadal stdie\ in the Pacific, Atlantic. and Indian Oceans indicate that skipjack tuna spann throughout the year in tropical water\ near the Equator and from spring to earl! fall 3.2 Preadult phase in subtropical saters, with the spauning period becoming shorter as distance from the Equator increases. Because sam- 3.21 Embryonic phase pling for gonads requires the capture of adults, these vudies have generally been restricted to \pecific areas where fishing Development of the skipjack tuna embryo has been studied has been done on a comrnerical basis or in area\ subjected to in detail by Ueyanagi et al. (1973, 1974) from artifically fertil- heavy experimental fishing. Such areas include uaters south ized eggs. They noted that embryonic development proceeded of Japan, Philippine\, hlarshall Islands, Ha\\aiian lilands, rapidly after fertilization (Fig. 25) and the larvae hatched in Ne\\ Caledonia, Marquesas-Tuamoto Archipelago, and off about I d. The incubational period noted by the former authors Central America in the Pacific Ocean (Kishinouye 1923; was 26 to 31 h in 23” to 25°C water. 21 to 32 h in 24.2” to Marr 1948; U’ade 1950; Brock 1954; Yabe 1954; Yao 1955; 27°C water, and 21 to 22 h in 26” to 29°C water; whereas, Schaefer and Orange 1956; Orange 1961; Ymhida 1966; the latter reported 22 to 27 h in 27°C aaier. Hence, there is Legand 1971; Naganuma 1979); uaters off Ghana, Ivory some indication that incubational period is related inversely Coast, Sierra Leone, Cape Verde Islands, Lesser Antilk\, to water temperature Cuba, and North Carolina in the Atlantic Ocean (RiLero and Fernandy 1954; Frade and Postel 1955; Gorbunova and 3.22 Larval phase Salabarria 1967; Simmons 1969; Zhudova 1969; Battc 1972~); and uaters around Madag r, Minicoy Ihnd. and through- Total length (TL) is used in discussing tuna larvae. It repre- out the tropical lone in the Indian Ocean (Raju 1964~;Mar- sents the distance from the snout to the end of the longest cille and Suiuki 1974; Stequert 1976). caudal ray before the caudal fin has forked. On larger larvae Lana1 captures, also indicative of spawning acti\ity, ha\e total length equals fork length. occurred not only in the arcac mentioned abo\e and in similar The newly hatched larva (Fig. 25) is about 2.6 mm TL months, hut also in intervening waters, e.%.. Pacific Ocean- (Ueyanagi et al. 1974). comparable with the size estimated by Matsumoto (1958). Stra$burg (1960), K1av.e (1963), Naka- Matsumoto (1958). According to Ueyanagi et al., the larvae mura and Matsumoto (lY67), Ueyanagi (1969. 1970); Atlantic absorbed their yolk sac within 2 d after hatching, but due to Ocean-Richards (1969), Richards and Simmons (1971 ), unsuccessful initial feeding, they died within 5 d. Ueyanagi (1971); Indian Ocean-Jones (1959), Gorbunova The development of the larvae is shown in Figures 25 and (1963, 1965a), Jones and Kumaran (:96?), Ueyanagi (1969). 26. Ueyanagi et al. (1974) described the earliest stages of the larvae thus: “Yellou pigment spots on the finfold were con- cpicuous in the prelarval stage. Small melanophores appeared on the dorsal edge of the trunk in the early prelarval stage 3.17 Spawn and moved toward the ventral edge [where they] tended to concerge toward the caudal peduncle.” The convergence of Ripe ovarian eggs are spherical, smooth, transparent, and these melanophores at the caudal peduncle leads to rhe even- usually contain a \ingle yellou oil droplet (Brock 1954; Yabe tual formation of a single, distinct black spot (Fig. 26a-d), 1954; Yoshida 1966). Eggs are 0.80 to 1.17 mill iii diameter, one of the principal identifying characters of the skipjack with mean diameters ranging from 0.96 to 1. I35 mm. The oil tuna larva. Other characters describing the Iarbae have been droplet caries greatly in six: Yabe (1954) reported a range of reported in Wade (19511, Yabe (1955), lshiyama and Okada 0.22 to 0.27 nim, Brock (1954) gave a range of 0.22 to 0.45 (1957), and Matsumoto (1958). These include a dispropor- nim, and Yoshida (1966) reported an average of 0.14 mm. tionately large head which is bent slightly downward in rela- That eggs of this six range are fully ripe and capable of tion to the body axis, the appearance of 2 or 3 melanophores being fertilized has been shown by Ueyanagi et al. (1973, over the forebrain area when the larvae are about 7 mm long 1974) and Kaya et al. (1982). (the number of melanophores increases to about 12 in larvae Eggs of other species of sconibrids that liace been fertil:zed about 14.5 mm in length), heavy pigmentation over the mid- artificially (frigate tuna, Auxis /hazard; bullet tuna, A. roche;; brain area throughout all siiec, and the appearance of the and yellowfin tuna) and reared through the hatching stage first dorsal fin spines in larvae about 7 mm long (the number are comparable in size and appearance with those of \kipjack of spines increases to about 13 in larvae 1 I mm TL). Pigmen- tuna (Harada et al. 1971; Harada, Murata, and Furutani tation on the first dorsal fin is limited to scattered melano- 1973; Harada, Murata, and Miyashita 1973; Ceqanagi et al. phores near the outer edge of the fin (Fig. 26d). The full 1973). Consequently, tuna eggs collected at sea in plankton complement of 16 spines and 15 rays in the first and second nets are extremely difficult to Identify to species. dorsal fins, respectively, and 15 rays in the anal fin are de- The spauned egg\ of tunas are buoyant in nature (Kikawa veloped by the time the larvae are about 12 mm long. At this 1953; Harada et al. 1971; Harada, Murata, and Furutani stage the young are considered as juveniles. 1973; Harada, Murata, and Miyashita 1973). During experi- The juvenile stage is characterized by a more fusiform ments in rearing art ially fertilized yellowfin tuna eggs, body and by a general increase in pigmentation over all parts Kikaua (1953) observed that most of the eggs uhich \\ere of the body. Juveniles up to 47 mm (Fig. 27d) are easily presumably dead turned opaque and sank to the bottom, bur identified by the concave outline of the first dorsal fin and its thocc still viable were transparent and buoyant. The opaque characteristic pigmentation, the moderately long snout, and

26 ye1 low

Figure 25.--lkvelopment of egg, and prelarlal stage of skipjack tuna. a) I2 h after fertilitation. 1.01 mm in diameter: b) IS h. 1.00 mm; c) 21 h, 0.97 mm; d) 13 h, 0.99 mm; e) just after hatching. IL 2.65 mm; f) 4 h. after hatching. TL 2.96 mm; g) 10 h. TL3.30mm; h) 19h,TL3.36mm;i)33h,TL3.57mm; j)43 h.TL3.70mm; k)84h.Tl.3.SSmm(fromUe)anagietal. 1974).

27 Figure ZS.--(b,iiinued. the number of vertebrae (20 precaudal and 21 caudal). The exponential curve to a set of size data and report the estimate first dorsal fin has scattered melanophores on the first three of Lm thus obtained as the maximum size of a fish. It should or four interspinal membranes and along the distal edge of be remembered that Lm is a parameter mathematically charac- the remaining membranes. The only other genus in which terizing the asymptotic phenomenon we call maximum size the juveniles are known to have similar-shaped first dorsal of a fish. Our estimate of it is a statistic whose accuracy is fins is Eurhynnus (Schaefer and Marr 1948; Wade 1950; dependent upon the representativeness of the sample used in Mead 1951). In Eurhynnus, however, the first dorsal fin is the calculation, and whose variance is, among other things, either completely or almost completely pigmented. Also, un- dependent upon the sample size. Thus if we need an estimate lihe Eurhynnus, juveniles of skipjack tuna do not develop of maximum size for other model building, e.g., estimating dark vertical bands over the dorsal half of the body. sustainable yield, then a statistic is what is needed. If we According to Godsil and Byers (1944) and GodGI (1954), want to describe the maximum size of a fish, then it may suf- adult skipjack tuna lack a swim bladder. Richards and Doke fice to report the largest fish recorded to date. In the follow- (1971), however, reported that all tuna larvae, including lar- ing paragraphs we will follow the latter procedure, while later vae of the skipjack tuna, develop shim bladders and gas in Section 3.43, we hill present estimates of Lm. glands at the smallest sizes studied (2.6 mm standard length), Miyake (1968) listed a skipjack tuna in the 106.5 to 108.4 but that the swim bladder degenerates in skipjack tuna be- cm size class taken on tuna longline. Although he made no fore the fish reaches a size of 20 mm. According to these reference to this fish, it could well be the largest skipjack tuna author$, degeneration of the swim bladder begin5 when the ever recorded. A fish of this size class, using the length-weight larvae reach a Size of 9.0 mm and the shim bladder is nearly relation developed for fish in the central North Pacific absent in specimens 24.0 mm long. Only the gas gland re- (Nakamura and Uchiyama 1966), would weigh between 32.5 mains in iuveniles above this size. and 34.5 kg (71.6 and 76.0 Ib). On the basis of growth parameters computed from data on modal progression and otolith readings (Table 8). such a fish would have a minimum age of 3.23 Adolescent phase 8-12 yr.

Juveniles below the size of first spawning (ca. 40 cm) have 3.32 Hardiness not been described and there is no information in the literature describing the initial appearance of the longitudinal As already discussed under Section 2.32, skipjack tuna can black stripes along the sides of the body below the lateral line. withstand a wide range of temperatures. At sea they have been found in water with temperatures as high as 30°C and 3.3 Adult phase as low as 14.7"C, which approaches the lower lethal ambient temperature of 13°C. as proposed by Stevens and Fry (1971). 3.31 Maximum size and longevity However in the short term and locally, skipjack tuna inhabit epipelagic waters characterized by narrow variations in ocean- It is comnion practice to fit a von Bertalanffy or negative ographic features. (Additional discussion in Section 3.6.)

28 Figure 26.-Skipjack tuna larvae. a) 3.1 mm TI ;h) 6.1 mm TI : c) 8.75 mm TI ; d) I0.Y mm 1 I (from Matwmoto 19581. ..

...

\' .._,. x

Figure 27.-Juvenile *hipjach luna. a) 14.5 mm TI : h) 21.0 mm n.: cl 27.0 mm TI.; d) 47.0 rnm TI. (from SEharfer and Marr 1948: Wade IY50; Marwrnolo 1958. 1961).

30 Table 8.--Sizr (fork length in centimeters) at axe and growth parameters of skipjack tuna from the Pacific. Indian. and Atlantic Oceans. Age in year5 Growth parameters

Source Area 012 3 4 5 6 7 io K L,(cm) hlethou

Pacific Ocean

Aikawa (1937) East ofJapan <26 26 34 43 54 ~ - ~ - - - Vertehrae Aikawa and Kalo (1938) Palau <27 21 37 46 55 M 12 80 - - - Vertehrae Chi and Yang (1973) Taiwan <21 27 47 62 73 81 - - -0 016 0.302 103 6 Vertcbrac Yokota et ai. (I 961) SouthofJapan- - 37 52 64 73 85 - - - - IG.0 hlodal analpis Sulu Sea Joceph and Calk,ns(lY69) East ofJapan 0.3 25 45 62 75 - - - - 0 19 141.8 hlodal anal!\i\: La\+a\aki'\ (1963)data Kawasaki (196%) South ot Japan - 15 45 63 73 71 - - - - - hlodal anal)\!\ and Hawaii Chi and Yang(1973J Taibran <36 36 60 75 - - - - -0.016 0.432 103.8 Modal analyw Yorhida (1971) Central Pacific - 35 - - - _-- - Uchiydmaand Struh5aker (1981) Hawan - 43 68 7Y x3 - - - - data Jo\eph andCalkinr(196Y) Eastern Paritic 0.3 30 50 62 70 - - - - 0.44 85.1 hlodal anal)\ii: SLhacter'5 (19hla)data Joseph and Calkins(196Y) Eactcrn Pacific 0.3 37 60 76 X7 - - - - 0.41 107.5 hlodal anal>ai\ Joseph and Calkin\ (1969) Hauaii 0.3 44 65 74 7X - - - - 0.77 82.3 Tagging. corrected data from Rothschild (lY67) Joseph and Callinr (1969) Hawaii 0.3 40 63 75 82 - - - - 0.59 W.6 lagging. uncorrectcd data from Rothschdd (1967) Skillman' Hawaii - 43 61 74 83 - - - - 0 39 101.1 Tagging; malesonly

Skillman Hawaii - 43 61 73 80 - - - - 0.41 92 4 Tagging; male\ and female, Josephand Calkins(lY69) tactern Pacific 0.3 31 51 M 72 - - - - 0.431 88. I Tagging; areraged data Josephand Calkin,(l969) Eastern Pacific 0.3 41 59 67 70 - - - - 0.829 72.9 Tagging; non-a>craged data Uchiyamaand Struhsaker (1981) Hawall - 44 68 83 91 - - - -0.02 0.55 102.0 Orolitti Indian Ocean Shabotiniets (1968) Indian Ocean - - - 40-45 40-60 ------First dorsal \pine Atlantic Ocean Battc (1972a) Western North - 41 49 57 64 - - - -4 329 0.195 79.6 Fir31 dorral\pinc Atlantic

'See text footnote io.

Under abnormal condition>, such as when fish are caught 3.35 Parasites, diseases, injuries, and abnormalities and handled for experimental purposes, skipjack tuna are not quite as hardy as other tunas and not nearly as hardy as Parasites found in skipjack tuna have been listed by Wal- some other marine or freshwater species commonly used in dron (1963), Silas (1967), and Silas and Ummerkutty (1967). laboratory experiments. Skipjack tuna can be used as an ex- The list by Waldron includes 26 trematodes, 4 cestodes, 2 perimental animal but laboratory procedures must be designed nematodes, 1 or more acanthocephalids, and IO copepods: with care. Mark-recapture experiments have been conducted that by Silas includes 33 trematodes and 1 cestode: and that successfully, but the animals must be handled quickly and by Silas and Ummerkutty includes 10 copepods. The last two with care. studies also provide information such as host, locality, location of infestation, and pertinent remarks on nomenclature 3.33 Competitors or occurrence. Chen and Yang (1973) listed one species each of trematode, cestode, and nematode, and two species of Fish that have been observed or taken with feeding aggre- acanthocephalids in skipjack tuna from waters off Taiwan. gations of skipjack tuna (Gudger 1941; Waldron 1963) have We have not seen the report by Love and Moser (1977). how- been considered as competitors of skipjack tuna. These fish ever, Forsbergh (1980) stated that these authors listed 36 include yellowfin tuna; albacore; kawakawa, Eurhynnus species of trematodes, 1 specie of cestode, 12 species of affinis; frigate tuna; dolphin, Coryphaena hippurus; rainbow copepods, and 6 species of nematodes and acanthocephalids. runner, Elagaiis bipinnulata; and whale shark, Rhineodon Cressy and Cressy (1980) presented a comprehensive account iypus. of copepods parasitic on tunas and tunalike fishes on a world- In addition, seabirds may be considered as competitors, wide basis. Because of the unreliability of most past litera- for both they and skipjack tuna feed on the same aggrega- ture, they attempted to clarify the taxonomic status of both tions of forage fishes at the sea surface. parasites and hosts. They resolved problems of synonymy of several species of copepods and listed five species parasitic on 3.34 Predators skipjack tuna which they had collected during the course of their study. Predators of either juvenile or adult skipjack tuna are The list of parasites (Table IO) was compiled from the listed in Table 9. papers examined above.

31 3.4 Nutrition arid grouth U’aldron and King (1963), E. Nakainura (1965), and Drago- vich (1971) determined that feedins peaks in [lie early morn- 3.41 Feeding ing from about 0800 to 1200, drops to a low betueen 1300 and 1600, and peaks again in the late afternoon, roughly (1) Tiine from about 1600 to cunset (Fig. 28). E. Nakamura (1965) as- sociaed this feeding pattern with the availability of food. He Feeding b\ skipjack tuna follous a more or le,s regular stated, “Zooplankter5 move do\bn\vard during the early day- pattern. From studies of stomach content\. Yuen (1959), light hours, presumably to reach a preferred level of illumi-

32 (A] STOMACH CONTENTS OF HAWAIIAN SKIPJACK TUNA I n i

(8)STOMACH CONTENTS OF HAWAIIAN ;; SKIPJACK TUNA I II r In W P 50 W G 25

0 ~ 0700 0% I100 0 1500 TIMEII OF DAY Figure 29.-Skipjack tuna catches bi time of day for wveral Hawaiian hait boats during Ihe 1956 and 1957 fishinz 5easnns 1(data from Yuen 1959).

(Fig. 29). If the fish were satiated near midday, then chumming with bait, which would involve more feeding, should not result in large catches; yet, the figure shows that the highest average catches occurred at about that time. Hence, E. Nakamura’s observation on the association of feeding with the availablility of food is preferable to the latter hypo- thesis based on volume of stomach content. Some seasonal variations in feeding are indicated in studies 0600 0800 1000 1200 1400 1600 1800 of stomach content volumes but for the most part, the vari- 0459 08159 Id59 1259 1459 1659 1059 ations reflect the seasonal changes in abundance of forage TIME OF DAY organisms. Waldron and King (1963) observed a noticeable decrease in the average volumes of food in stomachs collected Figure 28.-Diurnal variation in volumes of stomach contents of Hawaiian in Hawaiian waters during midsummer as compared with skipjack tuna (panels A and B) and diurnal variation in vnlumes (panel C) stomachs collected in late spring and early fall. The trend of and number of forage fish (panel d) in stomach5 of Marquesan skipjack the average volume followed closely that of the forage fish tuna (data from Waldrun and King 1963 (A); Yuen 1959 (6);and E. Naka- component. E. Nakamura (1965) observed that though the mura 1965 (C and D)). occurrence of forage did not vary from season to season in skipjack tuna stomachs from the central equatorial Pacific, nation. Since they serve as food for the forage organisms, the proportions of the three major food categories did $0. some of the latter, also seeking lower levels of illumination, Crustaceans were low in fall and highest in summer, and will tend to move downward and thus minimize their avail- molluscs were lowest in spring and highest in fall. In waters ability to the surface-dwelling skipjack. The minima occur around the Laccadive Islands, Raju (l964b) found that the around noon, the period when sunlight penetration is great- total average forage volume showed a peak in early spring est, when zooplankters are deepest, and when forage fish are and a lesser peak in the fall. The trend closely followed that least available to skipjack. During late daylight hours the of crustaceans, which dominated the food category in the zooplanters and forage fish begin their upward movement. areas sampled. Skipjack begin feeding heavily in the late afternoon hours before dark as food becomes more available.” He suggested (2) Food selectivity also that the diurnal variation in the volumes of stomach contents may also reflect the effects of satiation. He reasoned It is reasonable to expect that food requirements and the that “Skipjack, starting the day with their stomachs empty, capacity to satisfy the requirements, such as larger mouth feed actively during the early morning hours, and food con- and stomach, increase as the sire of fish increases. All studie\ sumption reaches a peak sometime before noon. A period of of this relationship (Yuen 1959; Alcerson 1963; Waldron and satiety occurs midday while dige5tive processes reduce the King 1963; Raju 1964b; E. Nakamura 1965) agree that the stomach contents. As the ctomach empties, skipjack forage average volume of food in skipjack tuna stomachs increa\e\ again, and the volume reaches a second peak prior to dark- with sire of fish. Differences in rhe diet have also been found ness.” That this may not always be the case is suggested in among the barious tizes of shipjack tuna. Generally, the the hourly catches of skipjack tuna in the Hawaiian fishery smaller skipjack tuna rely mainly on crustaceans for food;

33 the larger skipjack tuna. on juve~lileand small fishes. Yuen the volume of fishes, wliicli were the dominant food element. (1959) obsened that the percent either by iolunie or occur- Among the families of fish consumed, Scombridae, Mullidae, rence of fish in stomach\ of skipjack tuna collected near and Caraiisidne ucrc ~niportantnithin I6 hm: Scombridae Haizaii increased with an increase in rile. wtierear the per- was dominant betneen 40 and 80 km, followed by Carangidae, cent of tiioIIuscs and crustaceans decrea\ed. Similar obsena- Gempylidae, and Holoccntridae; and Scombridae, Gempyli- tiniis were noted generally for $hipjack tuna in tlie h’larqiiesa\ dae, and Euocoetidae \\ere important in offshore areas be- Islands (E. Nahaniura 1965). eastern Pacific Ocean (AIber- tiveen 161 and 322 kin. E. Nakamura(lY65) found no relarion- son 1963), cetitial Indian Ocean (Raju 1964h). and nestern ,hip between stomach content \olunies and distance from land Atlantic Ocean. off North Carolina, U.S.A. (Bat[\ 1972b). of skipjack tuna taken around the Marquesas Islands. He hlagnuson and Heit7 (1971), in their study of the gill raker noted, ho\ve\er, that food items categorized as reef-originat- apparatus among sconibridc and dolphins (Coryphaenidae), ing forms decreaxd \ignificantly from inshore to off5hore found that gill raher gap differed niarhedly among species along four 362 km (225 nii) \ur\ey tracks. The percentages of and lengths of fish. A 50 cm \Lipjack tuna. a 30 cm ycllo\\- reef-originating forms in the inner, middle, and outer 121 km fin tuna, and a 10 cni striped bonito, Sordu orrenra/r.r, all had (57 mi) sectors \\ere 61.5, 39.9, and 8.8, rcspecti\elq. an e\timated gill raker gap of I mni: and con\ersely, the gaps of a 50 cm fi\h of each species \\ere estimated to be ca. 1.0. 1.7, and 4.5 mm, respectively (Fig. .30). Comparing mean gill (4) Feeding hehabior raker gap with the \tomacli contents of fishes based on the literature, they \honed that the percent bolumes of crustaceans Only a fen studies have heen made of the feeding he1iaLior were inversely related to mean gill raker gaps and concluded of skipjack tuna both in the v,ild and in captivity, but thew that gill raker gap \\as related functionally \+itti the quantity have provided a wealth ol information. Nakaniura (I962), of smaller organisms in the stomachs. The presence of from his study of skipjack tuna in captivity, found that I) euphausids in stoniachs of skipjack tuna and their absence in when fed hourly until satiated, skipjack tuna exhibited an yelloufin tuna were cited as evidence for selection of organ- initial high feeding followed by feeding of small ainounts isms a$ determined by the magnitude of the gill raker gaps. throughout the day; 2) skipjack tuna had difficulty in seizing the food at night; 3) new fish introduced into tanhs learned to feed faster when evperienced fish Here already in the tanks; 4) food particles \\ere alnays taken at the surface or mid- depth, never off the bottom. and rwimming \vas often accel- erated prior to tahing the food; 5) they rejected \\hole shrimp or squid attcr ingesting a feu pieces, but when the rejected pieces were cut up into smaller pieces. the food was again accepted; and 6) capti\e skipjach tuna were never seen to prey upon small fish which \\ere present in the pool. Magnuwn (1969) studied other a\pects of feeding heha\ lor of skipjack tuna in capti\ity. In niie experiment, skipjach tuna were fed at intenals of I5 min throughout the da?. A period of intense feeding occurred berveen 0630 and 0830 (Fig. 31). During this period the fish did not fill their stomachs to capacity the first or elen the second or third time they \\ere offered food, but filled their stomachs slo~l!o\ei- the whole 2-11 period. The ma\iinurn capacity of the stomach \vas about 7u0 of the body ueight. but during the \\hole day the fish ate an equivalent of lSro of their body \\eight, and the stomachs were conipletel) empty by dawn. In another experiment, skipjack tuna that had been deprived of food for 24 h \rere fed at a uniform ratc for 42 min from 0900 to 50 100 I50 FORK LENGTH (cml 0945. The stomach contents approached a niauimum after about 30 min (Fig. 32.1). The proportion of food panicles attacked decreased a\ the stomach\ filled (Fig. 32-11), but very little change \+as noted until the contents exceeded 50mo of the stomach’\ capacity. Then the likelihood that a skipjack tuna \\odd attack a food particle decreased rapidly. indicating that satiation had occurred. The fi\h responded to (3) Distance from land food particles (i.e.. food particles re\ponded to but not attacked) even \\hen tlie stomach was full (Fig. 32-111). In examining feeding with respect to distance from land, Passage of food through the alimentary canal was esti- arbitrarily zoned at 16, 40, 80, 161, and 322 km (10, 25, 50, mated from 54 fish, 39 to 50 cm FL, that had been denied 100, 200, and over 200 mi), Waldron and King (1963) found food during the previous 24 h. The\e fish were fed a\ many the average volume of stomach contents increased with dis- thawed smelt as they would eat and their stoniaclis and 111- tance from shore up to 50 mi and varied irregularly at testines were examined at intervals over a 24-h period. The greater distances. The trend was due largely to \ariation in skipjack tuna ate the equivalent of about 8.6Oh of their body

34 TlME (MINUTES) ____- 0 25 5@ 75 I03 TIME OF MYI HOURS I FULLNESS OF STOMACH I%CAPACITY1

Figure 3l.-Diel changes in the feeding of skipjack tuna in capti\it). 1. Quantity Figure 32.-Changes in feeding behavior as skipjack tuna eats a meal. 1. &ti- of food eaten. 11. Cumulative weight of food eaten. 111. Estimated weight of mated weight of material in stomach. ll. Proportion of food panicles attacked. material in the slomach prior lo each meal. Food was offered 81 15-min intervals 111. Proportion of particles eliciting a response. Means and ranges shown in from WOO to 1845 (from Magnuson 1969). each plot. Proportion of stomach filled, shown along the time axis, was estimated from panel I (from Magnuson 1969). weight; about 10% of the initial quantity eaten had passed from the stomach each hour during the first 8 h; and the jack tuna exhibited such bars or bands, which disappeared stomachs were eTsentially empty within 12 h after a meal. when the fish were no longer interested in food. Magnuson (1969) noted also that the contents of the intestine Similar markings have been reported for Pacific bonito, increased rapidly during the first 3 h after the meal and the Sardu chiliensis (Magnuson and Prescott 1966), kawakawa intestine was essentially empty about 14 h after the meal. (Nakamura and Magnuson 1965), and dolphin (Strasburg Most waste material was evacuated from the intestine while and Marr 1961). the intestine was being filled from the emptying stomach. Defecation soon after eating was not surprising because of 3.42 Food the short intestine in skipjack tuna. Another aspect of feeding behavior is the appearance of Various authors have examined the food of skipjack tuna banded color patterns on the skipjack tuna. Strasburg and (Kishinouye 1923; Suyehiro 1938; Welsh 1949; Ronquillo Marr (1961) reported the appearance of such coloration on 1954; Hotta and Ogawa 1955; Postel 1955; Tester and Naka- skipjack tuna weighing from 1 to over 14 kg, but the bands mura 1957; Yuen 1959; Alverson 1963; Waldron and King or bars were not observed on all members of a school. As 1963; Raju 1964b; Thomas 1964; E. Nakamura 1965; Sund they explain it, the bands are formed when the dark horizon- and Richards 1967; Dragovich 1971; Batts 1972b; Roberts tal stripes are interrupted by light vertical bars. The transitory 1972). In addition, there are other reports with brief mention barred or banded appearance is likely under various condi- of the food of skipjack tuna. The most comprehensive studies tions and is produced presumably by the contraction of to date are those by Hotta and Ogawa (1955), Alverson melanophores. The vertical bars were noticed from a ship's (1963). Waldron and King (1963). and E. Nakamura (1965) subsurface viewing chamber during the chumming of fish in the Pacific Ocean; Dragovich (1971) and Batts (1972b) in schools. Nakamura (1962) confirmed the relation of the ap- the Atlantic Ocean; and Raju (1964b) in the Indian Ocean. pearance of the bars to feeding among skipjack tuna held in The major food items fall into three groups: fishes, crus- captivity. In his feeding experiments he noted that, in addi- taceans, and molluscs. Although fishes comprise the most tion to excited swimming behavior during feeding, the skip- important source of food for skipjack tuna in most of the

35 ocean\, variatinn\ in the order of importance (it thc major sented in the diet of the skipjach tuna. only tiw, Carangidae proirp\ 01 tood orpanisins are tound iii different areas and and Rali\tidac, \\ere common to all area\ o1'all oceans. Others \ca\on\ (Table 1 I). In the \re\terii and central Pacific and that were coninion to most of the areas \\ere Euocoetidae, \\e\tern Atlantic Ocean$. t'islw (49-950s of total \olurne) Slngnathidae, Holoccntridae, Bramidae, Chaetodontidae, c~nipri\cdtlie mo\t importair group, follo\red h) niollu\c\ Gempylidae, Sconibridae (iiicluding tlie tuna\), Ostraciidae, (4-5OO'u). and ci titracean\ (I -23"in) (Wcl\h 1949: Konqtiillo and Tetraodontidae. 1954; Maldrou wd Kiug 1963: I)rago\ich 1971: Halts 1972b). Tlic presence of \combrid\ in the \to~iiaclisof skipjack M'aldron arid King (1963) I-cported diftercnce\ in the I'ood tuna de.;erve\ special consideration, \ince this group of fish compo\ition of \kipiach tuna by i\land area\ in the central occasionally constilute a major portion of the \kipjack tuiia Pacific: "(I)Skipjack from the Hawaiian area depended on diet. Data from Waldron and Kiiig (1963) indicate that \coin- firlie\ to a grcater e\tciit than thobe froni tlic Plioeni\ or brids occurred in 10.6"h of 707 \hipjach tima stomaclls ex- 1 iiie I\lands; (2) \hipjach tioni the I'hoeni\ I\land area uti- amined and that this group comprised 25.O"i, of the total li& ~iioIIu\c\.cru~t;iccaiis. and fi\hcr cquall! a\ source\ of \olunie, the highe\t of all fish familie\ arid larger thaii the food; and (3) \hipjach from the 1 inc I\land\ xrea depended entire mullusc group. E. Nahamara (19653 reported the oc- on fishes to a le\\er degree rhau those troiri the other t\\o currence of juvenilc tuna in 24.8 to 4J.li1'u of 603 >tomactis area\ arid to a greater cxteiit on \quid\ arid cru\~act'ans." 111 e\arnined from fi\c cruise\ around tlie 3larquesas and Tua- the ea\terri side\ of [lie Pacitic and Atlantic Ocean\. cru\tit- nioiu Islands. This group ranhed the highest anicing all fish ceaiis \cere the iiiaiii wurcc ot food. The! compri\ed 50-6200 familie5 on four crui\e\ and fifth on one cruise. Dragovich of the tood. fish comprl\ed 33-37"o. and nlollu\c\, 4-13°'c~ (1971) also indicated high (25.OU'o) occurrence of tcombrids (Schaeter 1960: Al\ei-\on 1963: Drago\ich 1971). 111 the In- in 369 shipjach tuna stomach\ Iron1 the Caribbean Sea and dian Ocean around [lie Laccadi\e I\lands. crii\tacean\ \\ere adjacent uaters. Thi\ group rariked second only to the large the mo\t important food group. They made up 5gVn 01 the unidentified fish group. total \olurne, mollusc\ were 22"'u, arid h\li \\ere IOO'[I (Raju The wide variety of food organism\ in the stomach con- 1964b). At nearby Minicoy I\land fi\he\ tornied 4X"o of the tent\ and the \ariation\ in the importance of the major food food, crustaceans 47Oi1, and n~i\cellane~~~usitem\, rnoctl) groups have led to the conclu\ion that skipjack tuna are op- nioIIuscs, 5O;n (Thomas 1964). portunistic teeders and will prey upon any forage organisms The food of skipjach ttiiia in all thc major oceans includt.s that are aiailable to rhein. Cannibali\m among the skipjack a \vide \arict) of organi\nis. representing I I in\ertebrate tuna lend5 additional support to this concIu5ion. In the cen- orders and 80 or iiiore lisli tamilies (?able 12). Pa\t \ludic\ tral Pacific Ocean, E. Nakamura (1965) reported juvenile sliou that of the iri\errebratcs, t\\o group\ of arthiopods skipjack tuna in l2.4U:o of the skip.iach tuna stomachs con- (decapods and \tomatopods) and t\\o groups ot cephalopod\ taining food. He alto indicated that 7.80'0 ot 707 stomachs (octopods and squids) were found in \tomachi from nearl) all collected by U'aldron arid King (1963) contained juvenile localities. T~Kfith families represented in ~tomachcontent5 skipjack tuna. Conand and Argue (1980) reported that 3.3OIo vary considerably. with \ample\ taheri in the Pacific Ocean of 5,956 \tomachs of \kipjack tuna from the western Pacific ha\ing the greatest nurnber by tar. Hotta and 0ga.a (1955) Ocean (lat. 25"N-42"S, long. 134"E-I40'h') contained juve- li5tt.d 48 families, U'aldroii and King (1963) listed 42, and nile skipjach tuna. In the Atlantic Ocean, Suarer Caabro arid both Konquillo (1954) and t. Nahamtira (1965) li\ted 33. In Duarte-Bello (1961) and Drago\icIi (1971) al\o repoi-ted the the Atlantic Ocean. DragoLich (1970) listed 28 fi\h families in occurrence of ju~enileskipjach in \tomachr of skipjack tiiiia. the western and 21 in the eastern \ectors. Raju (1964b) listed only 10 fish families in the stomachs of skipjack tuna col- 3.43 Groirth rate lected from inshore \balers (about 8 hm) around Laccadive Islands and Thoma\ (1964) listed I I fish families from Alini- Various methods have been used to determine the grow111 coy Island in the Indian Ocean. Of the li,h lamilicc repre- of skipjack tuna and other tunas, including analyses of growth

36 37

I...... Table U.-< bnrinrred.

Arlantic Indian Pacific Ocean Ocean Ocean

38 marks on hard parts such as vertebrae (Aikawa 1937; Aikawa age, should the skipjack tuna pass through phases of no and Kato 1938; Yokota et ai. 1961; Chi and Yang 1973). first growth during the breeding period, and second, the uncer- dorsal spine (Shabotiniets 1968; Batts 1972a). and otoliths tainty in reading daily marks close to the nucleus (Lewis"). (Wild and Foreman 1980; Uchiyama and Struhsaker 1981); temporal progression of length-frequency modes (Brock 'I.euic, A. D. 1976. Tile relevance 01 data iolircted 111 P,ipun Ned, Giiinea to 1954; Kawasaki 1955a, b, 1963, 1965a; Schaefer 1961a; skipjack population \iudte\ in the uc\tern Pacihi. I)ocunicnt I066/76. S p IW partrnent of Primary Industry. I'apua Neu Guinea. blinj\ir! 01 Apricuitiirr. Yokota al. 1961; Joseph and Calkins 1969; Yoshida 1971; et Fore5ts. and Fishcrier. Fisheries Ui\i\ion. Su\a F ~JI Chi and Yang 1973); and data from tagged fish (Schaefer et al. 1961; Rothschild 1967; Joseph and Calkins 1969; Josse et al. 1979). Reviews of some of these studies were given by Shomura (1966a). Rothschild (1967), Joseph and Calkins (1969), Chi and Yang (1973). and Josse et al. (1979). A summary of the results of these studies is presented in Table 8 and representative growth curves are shown in Figures 33-35. Josse et al. (1979) reviewed the methods and results of most of the studies made to date and have concluded that counting seasonal growth marks on vertebrae, scales, and dorsal spines and following modal progressions of length frequencies were least reliable, that counting daily increments on otoliths was more reliable, and that measuring growth between tagging and recapture was the most reliable. Their low regard for counting growth marks and for following modal progressions stemmed from the failure of investigators to show irrefutably the periodicities in the appearance of growth rings and from the results of their ohn analysis of length-frequency data. They found that clear progressions of modes for more than a few months, other than in exceptional instances, were difficult to demonstrate and that the apparent Figure 34.-Gro*lh eslimales of cenlrdl Pacific skipjack luna. I) Lchijama and modal progression could give in a single region, in different 5lruhsaker (1981). otolith incremenls: 2) Skillman, lap. relurns. males onl? (see text foolnote IO): 3) Rothschild (1967). tag returns, uncorrected data; 4) Skillman. years, growths which were rapid, slow, nil, and even nega- tag relurnc. males and females (s?e lex1 footnote IO); 5) Brock (1954). modal tive. They pointed out, first, the inadequacy of determining progression; and 6) Rolhschild (1%7), lag relums. correcled data (from I:chi)ama growth from otolith increments to resolve the problem of and Slruhsaker 1981).

- 60 -E 50 0 W 40

r I "0 4 8 12 16 20 24 28 32 36 40 44 48

AGE IN MONTHS AGE IN MONTHS

Figure 33.-Growth estimates of weslern Pacific skipjack luna. I) Aikawa Figure 35.--Crowlh eslimales of easlern Pacifir skipjack luna. I) Joseph and Kato (1938). vertebral rings: 2) Kawasaki (1963), modal progression and Calkins (1969), tag relurns. averaged dala: 2) Joseph and Calkin, (Joseph and Calkins 1969; 3) Yokola el al. (1961). modal progression: 4) (1969). tag returns. nonaveraged dala; 3) Schaefer (1961a). modal progrer- Chi and Yang (1973). bertebrae; and 5) Chi and Yang (1973). modal sion; and 4) Joseph and Calkins (1%9). modal progression (from Joseph progression. and Calkins 1969).

39 While Josse et al. (1979) considered tagging data to be the (Joseph and Calkins 1969). most reliable, the pos5ibility of an interruption in gronth Uchiyarna and Struhsaker (1981) obtained growth estimates caused b! tagging itself has yet to be determined. \+'e cite as from otolith increments of skipjack tuna in Hawaiian waters. an example the nark by \Vild and Foreman (1980). \rho in- Their estimate5 varied some\\ ha1 from those obtained from ve\tigated the relation of otolith increment, and time for modal progressions iii tlie same area and in the eastern and tagged and recaptured skipjack and )ello\\fin tuna\ inarhcd \\estern Pacific (Joseph and Calkins 1969; Chi and Yang cline. The) observed that tlie number of incre- 1973). Although gro\rth \\as similar for fish increasing in age restimated time by appro\irnatel> 24oh during from 12 to 24 nio (24 cni), 11 \bas much higher for fish in- gro\\th from 42 to 64 cni o\er a period of up to 249 d. They creating in age from 24 to 36 mo (25 cm). further reported that the yo\\th ratc' of \hipjack tuna, esti- Gronth estimates derived from tagging she\+ little or no mated froni the Icngth at recapture and linear change in difference for fish in the central and eastern Pacific (Table 8). otolith dimension of tagged fish injected \\it11 tctrac\clinc Gro\\th of fish increasing in age from 12 to 24 mo and 24 to wa\ I. 15 cm/ino. The gronth rate \\as comparable \\it11 that 36 mo \\ere 18-23 and 9-13 cm, respectively, in Hawaiian obtained fiom earlier ragging studies by Iowph and Calkins \\aters (Joseph and Catkin, 1969, Skillman'") and 18-20 and (1969) in the ca\tern Pacific, but much le\\ tliiui that esti- 8-13 cni, respecti\el\. in the eastern Pacific (Joseph and mated from the latter's rt'\ults bawd on iiiodal progres\ion. Calhtn5 1969). The agrecment of the gronth rate\ I'rom otolith iiicr~iiieiitr Tagging studies in Papua Ne\+ Guinea by Kearney (1978) after tetracqcline treatment and froin ~ncrcnientalchange in ha\e indicated that 5kipjack tuna in that rcgion grew at an si7c indicate\ that both methods are cqtially good at niea\ur- alerage anntial rate of 7 cm. The estimate \vas derived from ing gro\rili rate of tagged fish but proiide no inforinatioii on fish betueen 2 and 6 hg (ca. 38.0-64.4 cm) uhich uere at the effect of tagsing itself. liberty for tip to 789 d. Kearriey stated "The available tagging The matter of reliability in the length of fish at relcase information . . . lea\es little doubt that the growth rate and sliould be considered also in tagging data. 111 iiio\t pa\[ Fludies ina~iniunisire of \kipjack in the we\rern subpopulation are the aicragc length of fish from the same amaand Struh- 5 cni. Onlq reccntl) in Papua Ne\\ Guinea (.lo\\e et al. 1979) saker 1981; Fig. 36) and tagging by JO~Xei al. (1979) and the Pacif~c(IA ITC") ha\e tagged fish been I4TTC (footnote 9) have confirmed this. Josse et al. (1979) elq at time of release, i.e., to tlic nearesi anal\zed published and unpuhlislied tagging data from the centimeter. Until similar data are obtained from other areas eastern Pacific, Ha\+aii. and Papua New Guinea and deter- and the adLerse effects of handling fish during tagging ha\e mined that the Io\rest gronth rates were observed in skipjack been clarified, the age and growth ol skipjack tuna nitist be tuna from Papua Ne\\ Guinea and the highest from Ha\baii. con5idered only at appro~imations. The IATTC (footnote 9) compared ne\\ tagging data (fish Gro\%th estimates of skipjack tuna in tlie \+estern North length ai release measured to nearest centimeter) from the Pacific have been determined only from ana1)sis of Lertcbrae eastern Pacific \+ith similar data from Papua New Guinea and modal progreuion. Aikawa (1937) and Aikaira and Kato (1938) made no serious attempl to \alidate growth rings as annual markh. Their lengths at age appear to be greatl) underestimated. Chi and Yang (1973). u\ing both methods, observed that two rings were formed annually on Lertebrae of skipjack tuna taken from waters around 'Taiwan and that growth estimates from modal progress~onwere higher than those obtained from growth marks on \ertebrae (Table 8; Fig. 33). The growth of skipjack tuna, based on modal progression, \%as24 cm from age 12 to 24 mo and 15 cm from age 24 to 36 mo. Growth estimates from modal analysis by Yokota et al. (1961) were lower than those obtained by Chi and Yang (1973) and comparable with the latter's estimates from vertebral analysis. Growth e\timates of skipjack tuna in the central and eastern Pacific have been obtained from modal progression, otolith increments, and tagging (Figs. 34, 35). Growth estimated from modal progresssion in both areas \vas comparable with that obtained by Chi and Yang (1973) in the western North Pacific and generally higher than that estimated from tagging. Growth between ages 12-24 and 24-36 rno were 25 and 1 I cm, respectively, in the central Pacific (Uchiyama and Struhsaker 1981) and 23 and 16 cm, respectibely, in the eastern Pacific

40 and found that skipjack tuna in the eastern Pacific grm at a In the central-eastern Pacific, Rothschild (1965), on the significantly faster rate than those in the Papua New Guinea basis of available evidence on lar\al distribution. gonad region. indices, size distributions, tag recoveries, catch predictions, Studies of skipjack tuna age and growth in the Indian and and immunogenetic studies, hypothesired that a laree portion Atlantic Oceans have been minimal. Shabotiniets (1968) of the skipjack tuna taken in the eastern Pacific Ocean orig- determined the size at age of skipjack tuna in the Indian inate in the equatorial PaciTic; that a large component of pre- Ocean from growth marks in the first spine of the first dorsal recruits (<35 cm) moves eactward and is \plit into a northern fin (Table 8). Since he did not validate these marks as annuli, group that enters the Baja California fishery area and a the size at age he obtained thus appears questionable. Batts southern group that enter5 the Central and South American (1972a) also made a study of the growth and age of skipjack fishery areas; and that the skipjack tuna remain in the east- tuna from growth marks in the first dorsal spine of fish ern Pacific for several month\ before they move offshore from the western Atlantic Ocean. He, too, failed to show into equatorial waters to spawn (Fig. 37). that the growth marks were annuli. His sires at ages 1 through A tagging study by Fink and Bayliff (1970) showed detailed 4 essentially represent a straight line and differ greatly from movements of skipjack tuna in the eastern Pacific fi\heries that obtained by others using data on modal progression or (Fie. 38). They reported that there appear to he Inn maiii tag returns (Table 8).

3.5 Behavior

See Section 3.41(4) for feeding behabior; Section 3.13 for reproductive behavior. CENTRAL AND 3.51 Migrations and local movement5

Migrations of skipjack tuna have been determined for certain areas and hypothesized for others through various methods, such as following the movement through a fishery of fish groups identified by size or age, from tagging, population genetic studier, and from tuna longline catch data. The most direct evidence has been from tagging data, but there is one weakness in this method-it only gives the net movement Figure 37.-H)pothe\ired origin and migration of skipjack tuna between the from point of release to point of recapture and does not central equatorial Pacific and the northern (Mexican) and wuthern (Crntrdl and show the actual path taken by the fish in the interim. South Ameriral fisheries of the eastern Pacific Ocean (from Rothachild 196s).

Figure %.--Inshore migration of skipjack tuna of the A) northern fisher) group nnd 8)southern fisher! group based on tagging data; numbem refer to months (from Fink and Ba)liff 1970).

41 groups of skipjack tuna in the eastern Pacific; that recruits to with the western limit some distance west of long. 130"W; the northern fishery first enter the fishery in the Revillagigedo and that fish of the southern group move eastward in the Islands in April, migrate north along the Baja California NECC and return to the central Pacific in the South Equa- coast during spring and summer, return south in the fall, and torial Current. then migrate to the central Pacific; and that recruits to the Recoveries in Hawaii of skipjack tuna tagged in the eastern southern fishery enter the fishing area in or near the Panama Pacific showed the capability of the skipjack tuna to negoti- Bight and migrate both northwest to Central America and ate long migrations. Seckel (1972) developed a numerical south to the Gulf of Guayaquil. Although a few fish tagged drift simulation model based on geostrophic and wind-driven off Ecuador in the Gulf of Guayaquil were recovered off currents as a potential mode of skipjack tuna migration from Baja California, they reported little interchange of skipjack the eastern Pacific northern fishery into Hawaiian waters. He tuna between the northern and southern fisheries. determined that fish could drift from an area between lat. Williams (1972) has extended Rothschild's hypotheses by 10' and 20"N at long. 120"W to an area between lat. 19" proposing three migration models for the recruitment of and 22"N at long. 155"W in 21 to 23 mo (Fig. 40). Although skipjack tuna into the eastern Pacific fisheries: An active the time intervals are within the range of values for skipjack migration model (Fig. 39A), where the fish migrate eastward tuna tagged in the eastern Pacific and recaptured in Hawaii, actively along zonal productivity bands at the northern and they are, by far, longer than most (Table 13). southern edges of the North Equatorial Countercurrent In the northwestern Pacific for fish caught in the Japanese (NECC); a passive migration model (Fig. 39B), where the coastal fisheries, lmamura (1949) noted that skipjack tuna fish are passively carried eastward in the equatorial counter- migrated annually from the southern seas northward in the currents; and a gyral migration model (Fig. 39C), which in- warm Kuroshio in the spring and summer and returned south volves both active and passive migration. In the last model as the cold Oyashio became stronger in the fall. Kawasaki Williams proposed that the fish of the northern group move (1955a, b) proposed that there are two groups of skipjack counterclockwise around a zonally narrow' equatorial gyre tuna in the southwestern Japanese waters which migrate consisting of the NECC and the North Equatorial Current, north from the Ryukyu Islands to southern Japan and back,

Figure 39A.-Active migration model: A) routes of )oung skipjack tuna into the southern fisher) and B) routes of young skipjack tuna into the northern fisher). NEC = Norlh Fquatorial Current: \ECC = Norlh Equatorial Countercurrent: SEC = South F4uatorial Current; SECC = South Equatorial Countercurrent. (From Williams 1972.)

-r-r---- r -7 , , , ,

i,/.h' 'j

t ".

Figure 39B.-Passive migration model: A) routes of )oung skipjack tuna into the southern fisher) and B) route3 of >omg%kipjack tuna into the nonhern fisher). See Figure 39A for abbreviations. (From Williams 1972.)

42 , .. A ., "..I.*\.,". I.. I.. ...1". ".,

- ,...~, . . >- -. * -* ". .. , .I ,.. ~ %_.Id. I. .I/. .e. .I , . .. L__ .~ .

."/. ,. .O, ... .. _d

Figurr U).--lacation\ of drifting ohjrctr in June of Ihr third modd year that wrrc introduced in each of the pre\iour 30 mo a1 long. 120-\\. I>d*hrd linr, indirsle mort wrrlrrl) location rrachrd h? object\ introduced wrr? quarlrr (frnm Srckrl 1972).

43 long I I?45 '\\ I dl II 5"\, long. I5Y-l:'t la1 21 lh'h, limp Ill 01 w

1 a.25 45 I\. lonp. 112'47 '\\ LJI 21 I6 N. long III'IW \\ tat 2PI17'h. long. I I I 'I6 '\% la1 Zl-lh". lonp. I I I '04 'M la ?I"lh N. Ion$. I I I =w'H

tuna in the Pacific. a \\c\tern and an ea\tern central sub- Marshall Islands; and fish tagged off Volcano Island were re- population, arid t\\o groups of skipjack tuna \\ithin the \\est- covered in Kiribati (South Pacific Commission 1981, Fig. 6). ern Pacific uubpopulation. an A group, deriicd from spawn- R'hile straight lines connecting tag release ard recovery ing in the northern winter, and a B group, derited from points do not necessarily reprewnt the actual paths of the \pa\\ninS in the northern \unimer. The migrator! paths of fish, the net movement <,f fish from the south equatorial Ihese group\ (Fig. 5) are clearly restricted to the \\ectern Pacific to the North Pacific and vice versa is significant. Pacific west of long. 170"E and the migratory paths in Japa- hligrations of hhipjack tuna ha\e been examined on a iicse coa\tal waters agree w~ththe path\ proposed by Ka\\a- wider scope in the Pacific. Knsahara (1968) cited Naganurna," ,ahi (1955a. b). who postulated teberal migratory routes of skipjack tuna In the western equatorial Pacific intenri\e tagging of skip- (Fig. 41), based on the catch as well as monthly length fre- jach tuna has been carried out in recent years by [lie Tohoku KIKL (Japan), the Department of Agriculture, Stock and I.isheries (Papua Ne\\ Guinea), and the Far Seas Fisheries Research Laboratory (Japan). Preliminary analkses of tag ie- coveries have revealed considerable pole\rat d niigration of shipjack tuna wtrhin the boundaries of long. 130' and 160'E \\ith none being captured farther east than long. 173"E (Kearney 1975). F;or the Paptta Ne\\ Guinea area, Lewi\ (19x0) reported that the c\\ential feartire\ of migration \\ere the interchange of shipjack tuna betueen the Bismarck and Solomon Sea\ during Nobember-April and [lie northerly nio\ement from the Biwiarck Sea in the Iuly-October period. Long-term reco\erie\ (fish 60-390 d at large) in other routh- ern and \\e\tern Pacific area\ indicate straight-line migrations in ewes\ ot 1,000 mi (South Pacific Conimt\\ion 1981). Fish ragged off Ne\\ South \'ale\, Australia, \\ere reco\eretl in the Solomon, Samoa. and Society Islands, Kiribati, arid northern Ne\\ Zealand; fish tagged off northern Ne\\ Zea- land \\ere recovered in West Samoa, Losalt), and Society Island\; fish tagged off Tu\alu \\ere recovered in the north-

\\?stern Haaaiian I\land\ and near Palmyra Island; fish tag- kigore Il.-Origin and migration route, of \kipjab tuna po\lulatrd from luna ged north of Ne\\ Ireland were recovered in Kiribati and the longline data (from Kmaharn 1Y6X). quencies of skipjack tuna iahen in the titila lonpline fi\her\. \ho\vn a\ \traipht-line nio\enicnt\ bct\\cen tapping and ICCIII>- Matsunloto (1974, 1975). on the basis of tuna longline catch tiire sites, and do not necessaril! reflect the actual pit[lis data for four siiccessive years (1964-67), proposed that there taken by the fish in mi gratin^ from one point to another, nor are a number of semi-independent stocks of skipjack tuna in the time required to negtiate the distance\. Neiertheless. the Pacific Ocean and that the\e Ftockc mipate in roughl! mo5t of the midoceanic mo\ernents reflect the routes prw circular paths (Fig. 42). The migrator! pathr \\ere siio\\n to pohed b) Ivlatcunioto (1975). follow a clockwise direction in the central and nertern North Local mo\emcnrs of skipjach tuna Iiri\t. been \ttidietl b! Pacific, and counterclockwise in the eactern North Pacific tracking fish tapped nith ultrasonic transmitters. A small and in the Southern Hemisphere, corresponding \\it11 the skipjack tuna (44 cni) trached for X d in Ha\\aiinn \\aters h! flow of surface currents of the major nater masses. By fol- Yuen (1970), made niphtl) journey\ of 25-106 kni a\\ay Iron1 lowing the movement of high catch rate cells by quarter\ mer a bank and, nith one exception. returned to the bnnh each several successive years, Matsumoto (1975, Fig. 12) has \ho\\n morning (Fig. 44A, B. C). On the one exceptton. the ti\h \\a\ the probable routes by uhich fish can rnobe from one area to 9 km short of the bank; ho\\ecer. it remained there all day the next and from the eastern to the v.e

Figure 42.--Mo~emenl of the \ahus geographic \lock* of shipjack tuna in the d: Pncific Ocean. The numeral) along lhe migrator? roule, represenl quarlm and Iocitlions of high catch-per-effort cell\ of skipjack luna taken h) Ihe Japanese longline fishery. 1964-67. Slock de4gnalions are shown in parenlhece\ (from Malsumoto 1974).

4 16W, B 160.1.

16C01. ID I ~- I . -DAY TRACKING , t_ NIGHT TRACKING . I HOUR INTERVALS .6J KbULA BANK 4 21'. ' 'S 3.5 2 sell 00 I I11g

46 Uda (1933) stated that skipjack tuna congregate around whale sharks (Rhinodontidae) in fear of spearfish. Tominaga (1957) also reported that skipjack tuna associate with basking sharks (Cetorhinidae) for protection from marlin. The latter's observations of this relationship indicate that the shark is the likely leader and the skipjack tuna the follo\\ers, and that the attachment of the skipjack tuna to the shark is quite strong. The skipjack tuna "swim in front, behind, to the sides, above, and below the shark. When attacked by a spearfish, the skipjack close in toward any part of the shark'r body. Upon chumming such a school, the skipjack will come toward the bait, but if the shark moves auay from the ship, - the skipjack will proceed after the shark immediately." tipurr45.1Ratiir of delerlicin of sch~wIswith bird\ (Hb),school, wilh- Association of skipjack tuna with whales may also be for out birds (Rg).and schools wiih sharks (Es)lo total schools in each IO-d protection, but is not as close as that with sharks (Tominaga period (from Kimura 1954). 1957). According to Tominaga, the association usually occurs with one or two whales, seldom with a herd. When attacked birds were abundant in hlay and June but \\ere rclatively by marlin, the skipjack tuna merely comes in the vicinity of scarce during the peak of the seawn, July to September. the whale. In this association, the skipjack tuna always pre- Schools associated with sharks first appeared in early June, cede the whale and may abandon the whale while the school were predominant in July, and dimppeared in October. is being fished. Schools unaccompanied by birds \\ere abundant in August Skipjack tuna are found associated also with anchored and September and predominant in October. floating objects. Fishing for tunas around such objects (bam- In more southern areas west of the Bonin Islands (lat. 19"- boo rafts) has been done for many years in the Philippines, 24"N, long. 136"-147"E), schools associated with whale where tuna were caught by hook and line (Murdy 1980). The sharks have been reported in October and schools associated introduction of purse seiners in the early 1960's (Aprieto with logs in February (Tohoku Regional Fisheries Re\earch 1981) and the rapid development of techniques for purse Laboratory undated a). Further south, in the area ]at. 2 "-SON, seining around the rafts have resulted in a highly successful long. 134"-150"E, schools associared uith logs and bird commercial fishery for tunas (Matsumoto"). Recent experi- flocks regularly occurred from December through February. ments with fish aggregating devices constructed of two 55-gal Lastly, in waters south of the Equator, around Papua Ne% steel drums and moored in depths of 400-2,200 m in waters Guinea and the Solomon Islands, schools were generally asaround the Hawaiian Islands have been successful in attrac- sociated with bird flocks, with few instances of association ting skipjack tuna and other tuna schools in sufficient quan- with sharks or logs (Tohoku Regional Fisheries Research tities for commercial pole-and-line fishing (Matsumoto et al. Laboratory undated b, d). Living Marine Resources (1977), 1981). Similar experiments are being conducted by several however, reported that numerous logs of all sizes from tuigs island states in the S 11th Pacific and in the Indian Ocean. to entire trees were sighted and fished by three U.S. purse seiners in August-October 1976 in the area northeast of (3) Distribution of types of schools Papua ,New Guinea (lat. 3ON-45, long. 138°-154"E) in the South Equatorial Current. More specifically, T. K. Kazama'l The distribution of the various types of schools differ by reported few log sighting in the area lat. 8"-3"N, long. area and time. In the northwestern Pacific Ocean, off north- 147"E, but that sighting, increased conyiderably to the south eastern Japan, Uda (1933) reported that skipjack tuna schools (lat. 2"-4"S, long. 138"-147"E), numbering several hundred associated with birds, whales, or logs generally appeared in per day with the greatest single concentration of logs extend- greatest number in the main Kuroshio system, while schools ing over an area approximately 15.5 m (SO ft) Nide and 1.8 associated with sharks appeared for the most part in warm km (I mi) long. water cells where the Kuroshio and Oyashio impinged upon A vastly different situation prevails in the central Pacific each other. He also noted that schools associated with whales Ocean, where almost all of the fish schools sighted are ac- were seldom found in the southern portion of the Kuroshio. companied by birds. Murphy and lkehara (1955) obserbed Kimura (1954), in a more extensive study off northeastern that about 85Vo of all fish school> \ighted in water5 around Japan, obtained additional details: I) Schools unaccompanied and between the Ha\\aiian, he,arid Phoenix I4and5 were by birds were more often found at the boundaries of the accompanied by birds. Like\\i\e, for tho scouting cruises Kuroshio and Oyashio, 2) schools associated ~ithsharks also around the Hawaiian Island\ during the \pring of 1953, occurred in warmer waters slightly south of the two current Royce and Otsu (IY55) reported that every one of 253 fish boundaries, and 3) schools associated with birds were seldom schools sighted \\as accompanied by bird$. Undoubtedly, this seen in offshore waters (ca. 800 km). He further determined dependence on bird flocks for finding tuna \chciol\ in Ihe the percent occurrence of the various types of schools and central Pacific Ocean ari\e\ from ilie proalrncc of bird\ in plotted the average occurrence of the three mmt common the area and partly from llie proailin$ \ea \1atc, \\hicIi I\ types of schools in the area (Fig. 45). Schools associated \\ith

47 terlderic! to aggregate h! \pccie\ 111 adtl~tion. Broadhead and Orange (1960) ob\er\ecl tliiit the frequency distribution\ of the lenyrli\ of \hipiach tiiiia 111 purr arid mixed specie5 school\ \\ere \itiiiI:tr, \\heres\ tho\c of !ello\\ fir1 tuna differed noticeablq (Fig. 37). Kairasaki (1963) compared length-frequency distributions of skipjack tuna taken from \ariciui type, of schools in Japa- ne\e \raters and noted that the \ariatioris in length within each school type increased in tlie following order: pure school (~irhout birds), bird-associated school, whale-ascociared schoot, shark- or drift\rood-associared \chool. Although Ka\\asaki's classification of pure- and bird-associated schools is confu\iiig, a pattern is discernible here, i.e., the less mobile the object of aswciation, the greater the size range of fish associated \%it11 it. This observation is, thus, consistent with Brock's (1954) hlpothesia, since schooling under slow moving objects does not require uniform maximum suimming ability. Catches of tunas from under stationary floaing objects further support BI-ock's hypothesi\. h,latsunioto (footnote 12) obsened that piit re heine catches brneath anchored bamboo raft\ in tlie Philippine\ included tuna\ (skipjack, yelloibfin, and bige)c tiilia>, kanakawa, and frigate and bullet tunas) ranging vidcly in 5izes from 23 to 63 an. One or t\ro large yeIlo\\fiii tuna or- bigeye tuna, 30 to 70 kg or more. were also

BIRD FLOCKS SKlPJ4CK SCHOOLS TOTIL FISH SCHOOLS tahcn occa~ionallv.

H4WAll4N ISL4NDS ~ ~~ I i

Eigure 46.--hrdrilnPI %ariationin rdle of bird flock. *kipjack luna whoolr. and PURE IKCJACKIISJII I.+1CWOOLI total fish whaol \ighting* for three major island group\ (from Waldron 1964). I 1 I 1 I I i I 1 0400 100 '00 700 *w s00 ,ow ,100 ItW (4) Length distribution of \chool\ LIYTH D# -TU.

Brock (1954) noted a comparaticely mall range of lengths Figure 47.-Erequenc? dialributicins uf lengths of jellow fin luna and skipjack within iiidi\idual xhools in the Hai%aiian fisher), in contra51 luna from school, of pure and mi\ed-,prcie\ compusilinn sampled from bait to rhe range of lengths in the landings a\ a \\hole. The nieaii 'escl cMches (from Broadhead and Orange 1960). range of lengths for single school sample\ \%a\11.3 cni, nith 5 and 21 cm being the least and greatest, whereas the range for the wasonal landing \+as 47 cni. He thus concluded that (5) Sire of school the skipjack tuna school \+as highly \i/e-sclecii\e and h)po- theaized that tlie segregation by \iLe \\a\ likel? due IO the Estimation of school size has been attempted in the eastern niauiinuni \\\iniming speed attainahle by fi\h of the \ame ,ize. Pacific Ocean by Orange et al. (1957), based on the catch- Bawd 011 obsercations from the eatern Pacific tiiiia fisher^, per-set by purse seine vessels, and by Broadhead and Orange Schaefer (1948) suggested that the tendenc! of tuna\ IO ag- (1960), based on the catch-per-school by bait boats. Esti- gregate by \ire might, in \ome ca\es, be \tronger than the mates bated on purse seine catches were considered more re-

48 liable than those based on bait boat catches because it is studied was 13.5 tons, with a range of 1 to 130 tons (from assumed a greater percentage of a school is taken by seining their table 2). Along the northeastern coast of Japan, the than by baitfishing. However, actual school sizes would still average catches-per-successful set of one-boat and two-boat be greatly underestimated, since entire schools are not always purse seine vessels were 6.3 and 8.6 tons, respectively (Inoue caught by the purse seine (Orange et al. 1957). 1959). Either the schools in the eastern Pacific were larger The frequency distribution of catch-pcr-succersful set by than those in waters off Japan, or the fishing environment species composition categories plotted by Orange et al. (1957) and technique were inore conducive to greater catches from showed that the distributions of pure skipjack tuna schools similar-sized schools in the eastern Pacific. It is also possible were skewed very strongly toward small catches (Fig. 48). that seiners in the eastern Pacific are less apt to set on small with more than 50% of the sets falling in the two smallest schools than seiner5 off Japan. On the basis of Figure 48, size classes, i.e., 0.25-4.9 and 5.0-9.9 tons. (Note: Orange et one can say that the occurrence of small schools (<20 short al. used short tom.) The average catch-per-ret of pure skip- tons) was the rule and that large schools over 50 diort tons jack tuna schools in the eastern Pacific for the 4-yr period occurred less frequently.

1955 916 SETS PURE YELLOWFIN 245 SETS PURE SKIPJACK 129 SETS MIXED

1954 463 SETS PURE YELLOWFIN 299 SET9 PURE SKIPJACK 172 SETS MIXED s0" 30b\20

1953 605 SETS PURE YELLOWFIN 142 SETS PURE SKIPJACK 191 SETS MIXED

1952 563 SETS PURE YELLOWFIN 208 SETS PURE SKIPJACK 216 SETS MIXED

TONS OF CATCH PER SINGLE SET

Figure 48.-Prrrrnfage frequenr? dictrihutinnp of ratch-per-srl in the eiehl principal fishing area* of Ihe ea\Iern Pacific tuna fkher?. fur each ?ear 1952 through 1955. hr ~prcie+rornpohilion calrporir\. Open circle5 repre\enl catrhr* of pure )ellow fin tuna. Solid circle\ reprebent calche, of pure Ekipjark luna. Trianglrr reprewnl ratrhr* of mixed aprrir, (from Orange et al. 1957).

49 The frequency distribution of catch-per-school from pole- school of skipjack tuna was often visible at the position of and-line fishing (Broadhead and Orange 1960). was similarly the tagged fish. On several occasions, both day and night, skewed strongly toward the small catches (Fig. 49). The ma- switching the sonar to the active mode disclosed many fish jority of the catches (about 65%) from pure schools fell into targets in the vicinity of the tagged fish. the two smallest size categories, 0.5 and 1.5 tons (note: Broad- head and Orange used short tons), and the mean catch for all (7) Activity of schools schools was 2.8 tons. The difference in the mean catches by bait boats (2.8 tons) as compared with that of purse seine That schooling occurs at depths in excess of 100 m was vessels (13.5 tons) probably reflects lower efficiency of pole- shown by Kimura et al. (1952) and lwasaki and Suzuki (1972). and-line fishing and the likelihood that the purse seine vessels From vessels equipped with echo sounders, Kimura et al. may shun small schools more often than pole-and-line boats. (1952) located fish schools between depths of 20 and 150 m. Broadhead and Orange (1960) compared the sizes of schools They identified them as skipjack tuna by tracking them on fished in the eastern Pacific and Hawaiian fisheries by plot- the echo sounder and fishing them as they reached the sur- ting the distribution of catches from the two areas. Data face. In some instances chumming with baitfish caused the from the Hawaiian bait boat catches yielded a J-shaped schools to rise to the surface from depths as great as 100 m curve similar to that of the eastern Pacific catches but the within 45 sec, a speed of 2.2 m/s (4.3 kn). points fell well below that of the latter. The mean catch-per- Underwater observations of skipjack tuna schools by Stras- school was about 1 ton compared with 2.8 tons from schools burg and Yuen (1960), Strasburg (1961), and Yuen (1970) fished in the eastern Pacific Ocean. On the basis of this com- provide further insight into the behavior of skipjack tuna parison, they stated, “It appears that the skipjack tuna ichools schools. Strasburg and Yuen (1960) observed that the activity fished in the Eastern Tropical Pacific area are, on the average, of schools varied with fish size. First, small skipjack tuna Tomewhat larger than those fished in the vicinity of the (ca. 20 cm) schooled in large numbers (in the thousands), Hawaiian Islands (assuming that the bait vessels capture the and in spite of their size, the schools seemed to respond in- same percentage, on the average, of each school encountered stantaneously to stimuli. The fish were closely spaced and in the tu’o regions).” Such a comparison, houever, is dubious maneuvered with precision. Even during feeding, these schools since their assumption is incorrect. Both ves5el size and num- never entirely lost their integrity. Second, in schools of me- ber of men fishing per boat differ greatly betueen the two dium-+ed fish (45-65 cm), feeding activity was frenzied and fisheries, thus resulting in disproportionate catches. most semblance of schooling uas lost. The fish made rapid dashes to the surface at speeds of about 12.9 m/s (25 kn), either singly or in pods of half a dozen or so; hence, their snimming uas seldom horizontal but oscillated vertically in patterns resembling a series of sine curves. Third, schools of large skipjack tuna (70-80 cm) appeared lethargic in comparison with schools of smaller fish. There were no signs of schooling during feeding, and the individual fish never appeared to swim faster than about 5.1 m/s (10 kn). More often the fish cruised at 1.0 to 2.1 m/s (2 to 4 kn), swimming nearly horizontally, with surface dashes being relatively un- hurried. Strasburg and Yuen (1960) also noted that I) water sprayed on the surface while chumming increased feeding frenzy, resulting in increased catches, 2) fast chumming (twice normal) resulted in decreased catches, 3) slow chumming or insufficient bait caused the fish to scatter and reform into

TONS PER SCHOOL schools away from the vessel, resulting in decreased catches, and 4) neither sound, blood, or skin extracts appeared to have much effect on actively feeding schools. Figure 49.-Perceniage frcquenc) distrihulions of catch-per-school (Ions) b) One other school activity was observed by Strasburg (1961). hail vessels, h) calegor) of school. 1956-58 (from Broadhead and Orange 1960). During experimental fishing in Hawaiian waters, he noted that a school being fished would abruptly dive vertically and (6) Schooling at night vanish from view. Examination of stomach contents of fish from such schools showed that they had consumed postlarval Some evidence for skipjack tuna schooling at night is Synodus variegaius and juvenile Holocentrus lacteoguitatus, available in the literature. Nakamura (1962) observed that both reef-type fishes, and that the occurrence of these fishes skipjack tuna in captivity swam slowly about the perimeter in the stomachs was significantly related to diving frequency. of the pool, often with their bodies normal to the light rays Observations on the number of diving schools indicated that from the floodlight. Fish were observed once at night with- diving was the rule rather than the exception. The number of out the floodlight. On this occasion (moonlight was suffi- dives per school ranged from 0 to 8 (Fig. 50) with a mean of cient to allow the fish to be seen), the fish remained in a 2.7. The schools were away from the surface as briefly as 3 s school and swam slowly around the pool. Other evidence of or as long as 28 min. In a later study (Strasburg et al. 1968) schooling at night comes from Yuen (1970). While tracking reef-type fishes, such as those found in the stomachs above, skipjack tuna fitted with ultrasonic tags, he observed that a were observed from a small submarine at depths of 107 to

50 88(c) Condition of gonads Brock (1954) commented on the rarity of skipjack tuna with fully ripe gonads and the lack of spawned-out ovaries within the spawning season in his extensive sampling of fish in the Hawaiian skipjack tuna fishery. He suggested that fish with ova larger than 0.7 mm in diameter become progressively less available to the fishery. This suggests that female skipjack tuna may abstain from feeding, immediately prior to and during the spawning period. Yuen (1959) found that maturation of the ovary did not appear to affect biting response, except in fish with ripe eggs. That skipjack tuna likely undergo a period of fasting is borne out by fishermen’s remarks (see Section 3.41(4)) concerning the futility of fishing such schools.

(d) Distance from land

:1 NUMBER OF DIVES PER SCHOOL Suyehiro (1938) measured biting quality by catch rate (number of fish per man per 100 min), designating a catch of 16 or less fish as poor biting and 17 or more fish as good Figure 50.-Frequency of diving in Hawaiian skipjack luna schools (from biting. Applying this criteria to schools fished in Japanese Sfrasburg 1961). waters by 17 vessels, he found that skipjack tuna schools around islands bit poorly, whereas schools in the open sea 192 m, suggesting that skipjack tuna schools may have de- generally bit well. Yuen (1959) reported a similar relation- scended to these depths to feed. ship; however, this was true only for large (>60 cm) fish.

(8) Biting response of schools (e) Time of day

The factors influencing the biting response of skipjack Uda (1940) reported that there is a relation between time tuna schools have been studied by a number of scientists. (hour of catch) and total catch, as well as between time and These factors include (a) state of hunger, (b) behavior of catch-per-school. He observed that catches peaked three prey, (c) condition of gonads, (d) distance from land, (e) times during the day, a primary peak between 0500 and 0900, time of day, and (f) weather. a secondary peak between 1200 and 1300, and a tertiary peak between 1600 and 1800; and that about half of the day’s catch was made between 0500 and 0900, and about two- (a) State of hunger, as determined by the thirds of the day’s catch prior to noon. He explained the pat- amount of food in the stomachs tern of catch thusly: “The fish school and feed most actively in the early morning, and once their stomachs are filled their Uda (1933), Suyehiro (1938), and Hotta et al. (1959) noted appetites decline, but around noon, for reasons connected that skipjack tuna responded to bait well when their stomachs with the time required for digestion, their appetites again in- were empty, and poorly when full. Uda (1933) further ob- crease and they become slightly active.” He believed that the served that skipjack tuna with stomachs between the extremes decrease and increase in appetite occurred again in the eve- of fullness and emptiness tended to respond more poorly ning just before sunset. While his explanation above agrees than when their stomachs were emptier. This statement, how- with the results obtained by Magnuson (1969) from feeding ever, is contrary to Yuen’s (1959) observation that skipjack experiments conducted on skipjack tuna in captivity (see Sec- tuna schools responded to bait longer when the major food tion 3.41(4)), similar peaks were not reflected in the catch items in the stomachs were in the earlier stages of digestion rates shown in 2 of the 4 yr he examined. and that the response became greater as the stomachs emptied. A similar study was done in the central Pacific by Uchida Similarly Uda’s (1933) statement is contrary to Magnuson’s and Sumida (1971), but rather than using catch and catch (1969) observation that attacks by captive skipjack tuna on rates as the variables, they used number of schools sighted food particles decreased rapidly only after the stomach con- and number of schools fished successfully. These variables tents exceeded 50% of the stomach’s capacity. plotted against time of day (Fig. 51) resulted in curves not unlike that obtained by Uda (1940); however, their interpre- (b) Behavior of prey tation of the curves differed. Fishing success (i.e., schools yielding catches) increased rapidly from daybreak to a peak Skipjack tuna feeding on fast-swimming fishes such as at 0901-1OO0, dipped slightly at 1001-1100, and was followed tunas, carangids, and gempylids, exhibit a more favorable by two peaks at 1201-1300 and 1401-1500. The authors at- biting behavior than skipjack tuna feeding on slower swim- tributed the dip at 1001-1100 to reduced scouting effort due ming chaetodontids, scorpaenids, molids, and acanthurids to time taken for lunch. They suggested that the time taken (Yuen 1959). for breakfast and dinner also may have partly affected the

51 15 I (g) Other aspects of biting behavior SCHOOCS SIGHTED 10 In the western Pacific Ocean, IJda (1940) indicated that in - most of the schools fished, catches generally occurred be- $5 tween 10 and 40 min of fishing, that the catch rate (catch- a0 per-school) increased in direct proportion to the increase in LO fishing time up to 80 min, and that when fishing time exceeded 80 min, neither the total catch nor the catch rate SCHOOLS WITH CATCHES showed any increase. Similarly, in the central Pacific Ocean, z IO fishing duration of most schools was between 5 and 40 min (Yuen 1959; Uchida and Sumida 1971) and the catch-per-

5 school increased proportionally with fishing duration (Fig. 52). Yuen (1959) also measured other factors that seemed to influence catch. Of these, I) fishing duration, 2) peak catch '0501 0701 0901 1101 I301 1501 1701 rate, 3) postpeak duration, 4) rate of increase of prepeak 0600 0800 1000 1200 1400 1600 I800 catch rates, and 5) mean number of hooks per minute were TIME OF SIGHTING OR FISHING all found to be related significantly to total catch (Table 15). Of these, 2) and 3) were subsequently used as measures of skipjack tuna response, on the premise that peak catch rate Figure Sl.-Frcquencie\ of xhool \ighting\ and \choolc wilh calche\. b) would measure the degree of interest or intensity in feeding lime of day far seven Hawaiian \kipjack tuna fi3hing \ei\el*. June-4ugu\t 1961 (from t chide and bumida 19711. and postpeak duration would measure the duration of interest.

reduced sightings and catcher near wnrise and sunset. Addi- tionally, unlike the .lapanere fishery, \\here most of the day's catches were made prior to noon, most of the day's catch in NUMBER CAUGHT PER SCHOOL ... the Hawaiian fishery occurred after midday (Table 14). ..

4. Tshle I4.-Perccnlagr of the dab', total cnlrh ahoard the \e\\cI\ in the fin1 lh) 0900). wcond (0901-12WI, WEIGHT CAUGHT PER SCHOOL third (I20I-lS~H)).and fourth (after 1501) quarter, of Ihe fkhing daj for seven Hawaiian \kipjach tuna fishing .. \es%h, June-Augusl 1967 (from I'rhida and bumida .. 1971).

Vec5ris birct Second Third Fourth

A 3 3 31.5 42 4 22.8 B I5 5 15.3 35 4 33.8 17 0 20.2 23.7 39.1 0 9.2 24.9 35.2 30.7 10 7.1 41.6 28.5 22.8 7.2 40.9 33.3 IR.6 16.4 10.3 21.0 52.3 10.8 26 4 31.4 31 4 10.8 37 2 68.6 100.6 0 I 10- AVERAGE SIZE .. (f) Weather

To what degree weather affects the biting behavior of skipjack tuna schools has not been clearly determined. Suyehiro (1938) reported that in the western Pacific Ocean biting K seemed to be better in cloudy than in clear weather, and that i+ z biting appeared equally good in rain and fog as in clear weather. He noted, however, that the reliability of the latter I 6 II 16 21 26 31 3: 4, 46 51 %>bo /I# I, ,I, was questionable due to few data. He also reported that wind 5 10 15 20 25 30 35 40 45 50 55 60 velocity was not related to biting quality. In the central Pa- FISHING DURATON (MINUTES) cific Ocean, Yuen (1959) observed that weather conditions were predominantly uniform and biting behavior did not change by much. On a few days darker than usual, the ueather Figure SZ.-RelaIion between fihhing duration and arerage balues of rdlch per school. amount of bait wed per rchool. numher of men fishing per affected fishing only in decreasing the chances of sighting school. and size of fish per school. June-August 1967 (from Uchida and schools. Sumida 1971).

52 3.6 Physiology

3.61 Energ) transfer (metabolism)

Rapid and efficient energy turnover, more than any other single biological factor, characterizes the skipjack tuna’s physiological ecology. Life in the warm and relatively unpro- ductive tropical waters necessitates elaborate adaptations for locating and efficiently utilizing the patchily distributed food resources. Studies of these adaptations and estimates of energetic rate processes have provided information arid insights for modeling of important management parameters (Sharp and Francis 1976). The detailed understanding of the skipjack tuna’s energy budget has had its genesis in basic biological information obtained from experiments \bit11 captive Yao (1962) examined the biting qualities as judged and re- specimens at the Kewalo Research Facility of the National corded on fishing reports by Japanese fishermen. In these Marine Fisheries Service in Honolulu. Indeed, this research reports biting qualities were judged as good when: facility is the source of much of what is known about the basic biology of tropical tunas.

I) Fish were attracted in large numbers immediately upon (I) Energy budget chumming and there was a sudden initial increase in catch, 2) the number of fish increased beyond the fishermen’s ca- In all animals, energy transfer in and out of the animal is pacity to catch them, quantified in the energy budget or mass balance equation 3) the duration of fishing above a minimum catch rate was (Ricker 1968): long, 4) catch per school was large, and C=R+U+f+G+B 5) maximum catch was attained quickly. where C = rate of food consumption Yao calculated the biting qualitia of schools, employing Yo- R = rate of metabolism shihara’s (1960) theory on the mechanisrn of skipjack tuna U = rate of excretion fishing, by the equation F = rate of egestion G = rate of gamete production

W=N (I - (I ~ Ar)e-Al) B = rate of growtli. where W is the number of fish caught, I is fishing duration. For our purposes the units in the analysis of this rclation- N is number of fish in \cliool, and 1 is the biting coefficient ship will be given in caloric units (kcal). Skipjack tuna, for expressed as the reciprocal of the length of time until the instance, contain an average of 1.46 kcal/g of live weight catch rate reached a nlaximum. Yao’s calculations indicate (Kitchell et al. 1977), and the mean caloric value of skipjack that I) through 4) tend to be judged higher as school \ize tuna forage is assumed to be 1.1 kcal/g wet weight (Kitchell et increases, even when the degree of biting was the same. lg- al. 1978). noring school size, he found no statistical differences in the The rate of metabolism (R) is lumped by Kitchell et al. mean biting coefficient among schools judged as good, aver- (1978) into two component\: I) The energy, or specific dy- age, and poor by the fishermen. namic action (SDA), required to process the forage, and 2) Yao (1962) also observed that the mean biting coefficient, the remainder of the metabolic work (M). Table 16 present5 0.135, for small schools (c1,OOO fish) was extremely high, as the energy budget values of a 1 kg skipjack tuna under six compared with the mean coefficient, 0.085, of large school, input-output levels (Kitchell et al. 1978). Values for SDA, U, (>2,000 fish). He suggested that the high mean coefficient and Fare assumed from work on other fish to be IS, 5. and for small schools was due to selective fishing of only good 15% of ingested calories. Thus, the energy available for M biting schools, whereas fishing was done on both good and and storage as growth or gonadal development is 0.65 of the slow biting schools \\hen the schools were large. calories eaten. Input of calories in the table range from star- Summarizing the above, it Teems that fish respond well to vation, maintenance calories (no growth) of 5.9% of body chum when their stomachs are less than half filled and when weight per day, ingestion of necessary calories to produce they are feeding on fast-swjimming prey; that schools in off- “normal” growth (0.7% of body weight per day, Uchiyama shore areas respond better than those inshore; that fish, and Struhsaker 1981) at three arbitrary multiples of activity, particularly females, respond poorly during spawning; that and maximum ingestion of 30% of body weight per day. The the response reaches a peak in the early morning between maximum ingestion rate was determined in laboratory studies. 0800 and 1000; that there may be more than one feeding Growth under these input conditions varied from - 3.6% peak during the day; that the response generally lasts from 5 under starvation conditions to a maximum growth rate of to 40 min, depending on school size and state of hunger; 6.9% of body weight per day when fish were feeding at maxi- and that weather may not be a factor in influencing feeding mum rations (30% of body weight per day while maintaining behavior. levels of activity nearly three times those at minimum sus-

53 tainable cruising speeds). If activity levels include metabolic tuna, the fixed costs decline rlightly (an economy of scale) as costs to five times that at minimum cruising speed, growth size increases, allowing it to become larger before the con- rates would be only 0.7%/d at maximum rations. Kitchell et vergence of costs and profits occur. Obviously, any differ- al. (1978) reasoned that these levels of activity were unrealis- ences between real income (foad availability) and maximum tically high and, therefore, the observed growth rates of income potential will cause the zero-profit level to develop at 0.7%/d indicated limited food availability rather than high a smaller size. levels of activity. In skipjack tuna, unlike most other animals, the routine (2) Respiration metabolic rate per unit of weight does not decrease as size increases (Brill 1979; Gooding et al. 1981). Large fish have Intermediary metabolism is the process wjhereby energy is approximately the same metabolic rate per unit of mass as made available for biological pofier, the fixed costs referenced small fish. The reasons for this phenomenon are obscure. in the preceding section. Intermediary metabolism, some- However, in skipjack tuna, as in most other animals, the times called internal respiration, is measured in units of oxy- relative capacity for feeding does decrease as size increases. gen consumed, calories transferred, carbon dioxide liberated, In absolute terms, large fish can eat more than small fish but or power in watts. All are stoichiometrically relatcd. External in relative units, the maximum ration per unit of w,eight de- respiration is defined as the mechanism which delivers 0, creases as size increases. Ability to acquire energy and the and expels CO,. energy costs of metabolism thus converge as skipjack tuna Since skipjack tuna cannot use buccal or opercular pump- size increases. This interesting relationship can be used to ing to force water over their gills, they must continually swim predict the limits of growth. It has been thown that to pursue or they \rrill suffocate. They are “ram ventilators.” A 44 cm and capture prey takes a metabolic rate approximately tmo skipjack tuna swimming at a basal speed of 66 cm/s, has a times the rate required to just swjim at minimum speed (speed gill resistance equal to 7% of its total swimming resistance required to maintain hydrostatic equilibrium, Magnuson (Brown and Muir 1970). The cost of this extra resistance is 1973). Then the maximum ability to provide surplus energy approximately 1 to 3% of its total metabolitm when swim- for growth (0.65 of maximum ration) is equivalent to the ming at basal speeds. minimum activity necessary for feeding by skipjack tuna Within the gills, O2is extracted from and CO, delivered to weighing 25-30 kg. the Hater. Here, as in other structures dealing with energy For yellowfin tuna, unlike skipjack tuna, the metabolic transfer in the tuna, there exist modifications for rapid ex- rate per unit weight declines as size increases. The maximum change. Within the secondary lamellae of the gills, blood feeding rate also declines but at a slightly more rapid rate flows obliquely to the long axis rather than with it as in other than metabolirm. As in skipjack tuna, both raies converge teleosts (Muir and Brown 1971). This oblique pathway allows but at levels that predict maximum yellowfin tuna sizes of a greatly shortened length of the absorbing vessel, reducing 150.200 kg. The maximuiii predicted \izes of the tno turns the total blood pressure drop across the skipjack tuna’s gill can be compared xith maximum sizes in Section 3.31 for by 16 times. The short path length allows for small diameter skipjack tuna (22-25 kg) and the largest known yellowfin absorbing vezsels as well as thinner, more efficient lamellae. tuna (180-200 kg). The latter reduces resistance to water flou. Large gill areas An economic analogy may help make these concepts more result from the increase in total number of lamellae and their understandable. If: I) feeding rate is taken as income; 2) length. These adaptations result in a gill, which, while deli- egestion, excretion, and SDA rates as taxes (proportional !o cately constructed and fine grained, has an area of from 4 to income); and 3) metabolic rate as fixed co~ts,then growth 30 times larger than other teleosts. (somatic and/or gonadal) can be considered net profit. Small Thus with this large gill surface area, the tuna gill’s effec- animals have the potential for large profits because their tiveness in removing oxygen from the water is higher than fixed costs are low and their income potential is high. As size other teleosts’. Stevens (1972) has estimated that skipjack iicreases, so too do fixed costs and taxes, but potential profit tuna can extract up to 90% of the oxygen in the water that margin narrows due to a less rapid increase in income poten- enters the mouth. Other fish can extract from 10 to 30%. tial. Eventually they converge at a point that dictates the Four techniques have been employed to estimate oxygen maximum size. In yellowfin tuna, in contrast to skipjack uptake: 1) Whole animal, in which one or more tuna are con-

54 fined within a sealed tank and the drop in dissolved oxygen muscles averaged 2 mg O,/g per h, for white muscle, 0.4 mg is measured as the tunas respire; 2) starvation experiments, O,/g per h. Tuna muscle is obviously a fast respiring muscle where energy consumption is measured by loss of weight and comparable with rat thigh muscle at its physiological temper- caloric density; 3) in vitro experiments that measure oxygen ature (Gordon 1968). Another interesting aspect of this work uptake of various tissue samples; and 4) restrained experi- is the lack of much of a temperature effect upon respiration; ments, where oxygen consumption is measured from a per- a Q,oof virtually 1 is observed. Dizon et al. (1977) also ob- fused, paralyzed fish. served this temperature compensation of swimming speeds. Of these four techniques, the measurements of oxygen Perhaps this rapid temperature compensation, something ob- consumption from fish swimming in enclosed chambers is the served in other animals whose habitats have rapid tempera- most common. Gooding et al. (1981) found that skipjack ture changes, is an adaptation for their behavior of fast, con- tuna’s “standard” metabolic rate (SMR) was two to five tinuous, vertical movements from the thermocline to the times that of similar-sized, active non-tuna species. However, surface. the true SMR for tunas is oxygen consumption rate at zero One difficulty in determining respiration of tunas is to ar- activity. This true rate must be extrapolated from rates col- rive at a common level of activity which produces a re\pira- lected from fish swimming at various voluntary speeds. The tion rate which can be compared with other fish. Utually regression relating consumption rate to size and swim speed this value is the SMR, which is defined as the energy require- is as follows: ments of a postabsorptive animal completely at rest. Tunas cannot stop swimming so this activity level is meaningless. log VO: = - 1.20 + 0.19 log W + 0.21 S Gooding et al. (1981) referred to the routine respiration rate, that is, the energy requirement of a tuna swimming at itr where VO, = oxygen uptake (mg OJg per h) “characteristic” speed. A standard rate can be determined W = fish weight (g) from the routine measurement by extrapolating the swim- S = swim speed (body lengths/s). ming speed to respiration rate relation back to zero activity. Another approach is a direct measurement of respiration on Of note is the weight exponent of near 0.2 compared with a paralyzed, restrained fish (Brill 1979). -0.2 of typical fish. Because the swim speed of routinely The SMR of 33 restrained fish ranging in size from 0.3 to active skipjack tuna is inversely related to weight, routine 4.7 kg was: metabolic rate is virtually independent of fish weight.

Lacking any caloric input, skipjack tuna lose mass and log VO, 0.8987 ~ 0.437 log W caloric density from their tissues from metabolic demand. The oxycalorific equivalent relates oxygen uptake values to where V02 = SMR (mg OJg per h) those of calories transferred, 3.4 cal/mg 0,. A tuna swim- W = fish weight (8). ming at its weight-dependent characteristic swimming speed (about 1.4 body lengthsls) has an energy demand (from How do these values compare for other fish and for other Gooding et al. 1981) of log VOi = -0.54 + 0.08 log N,’. methods of determining tuna respiration? Again the weight Thus, a 1,500 g skipjack tuna, swimming at its characteristic exponent is different. Other teleosts range from 0 to about respirometer tank speed would consume 64 kcalld. In a fast- -0.350 (quoted in Brill 1979). The value of -0.437 indi- ing fish, the energy comes from mobilization of body tissues; cates that as body size increases, the SMR decreases relatively Kitchell et al. (1978), citing other sources, estimated that faster than for other teleosts which contradicts Gooding et 20% overhead must be obtained from the tissues; the over- al. (1981). However, the values predicted for the SMR by head pays for the deamination of proteins (IS’%) and the Brill’s method compares favorably with the extrapolations of excretion of nitrogenous waste (Solo). This will add an addi- speed to zero of Gooding et al.’s regression. Compare 0.253 tional requirement of 16 kcalld: 80 -- (80 x 0.2) = 64. mg OJg per h determined by extrapolation of the regression The energy content for a whole skipjack tuna is approxi- to 0 and 0.324 mg OJg per h determined by Brill (1979). mately 1.46 kcallg, which for our 1,500 g example is 2,190 Brill reported that SMR’s for tunas by either method exceed kcal. Thus, a skipjack tuna swimming at 1.4 body lengthsls those reported for other teleosts by 5 to 10 times. should lose about 3.7% of its total energy per day. A logical next step is to inquire if high respiration rates How does this compare with a real, fasting fish? Work at correspond to a sensitivity to low dissolved oxygen (DO) the Kewalo Research Facility demonstrated that starving levels in the habitat. Work reported in Dizon (1977) and skipjack tuna lose weight at 1.8Vold. But weight loss is not Gooding et ai. (1981) indicate that this is so. Skipjack tuna the complete story. Fish utilize fat and hydrate as they starve, show definite signs of stress when DO levels fall below 3.5 so weight loss underestimates energy loss (Kitchell et al. 1977). mg OJI. Both investigations report dramatic increases in They estimate that skipjack tuna lose about 1.8% of energy swim speed around 4.0 mg OJI. Dizon (1977) failed to ob- content per unit weight per day. This change of caloric den- serve any increased swim speed responses in yellowfin tuna sity is added to the absolute weight change to yield an inde- at oxygen levels as low as 2.5 mg OJI. The swim speed re- pendent estimate of energy loss of 3.6%, which compares sponse seems to be an adaptation to remove the animal from favorably with the 3.7% figure estimated from respiration stressful habitats. An alternate explanation, increased ram jet measurements. ventilation, is not indicated since metabolic O2 demands rise Gordon (1968) estimated metabolism from still another faster than the 0,delivery to the gills as swim speed increases. approach. Metabolic rates of unstimulated, minced muscle Although these data indicate a great sensitivity to low 0, from skipjack and bigeye tunas were measured. Both red and environments, skipjack tuna can probably be conditioned to white muscle preparations were employed. Values for red penetrate waters below 2 mg O,/I for a reward, as was done with kawakaua (Chang and Diron“). Hence the correlatioll (3) Locomotion of purse 5eining success uith a shallow, O:-deficient thermocline (Green 1967) is probably contradicted by the tunai’ For many years, the biochemiitry of the skipjack tunas’ willingness to penetrate toxic habitats for short periods. unique intermediary metabolism har been researched by P. Hochachka and his students. The following is from Hocha- chka et al.’s (1978) excellent summary of the skipjack tunas’ unique “pouer plant and furnace.” Skipjack tuna, as other tunas, have an unusually large and distinct red muscle mass (8%) (Magnuson 1973), which is distinct and separable from the white (Fig. 53). This fact makes the tuna an excellent

co cv

r do PCV I I

K peloms

T.albacores

Figure 53.-Transverse section\ of four luna species \ho*ing the positions of Ihe red muscle (shaded areas), Ihe central and lateral rete mirabile (r). and the major blond vesscIs suppl>ing Ihr Telia; dorsal aorta (da). posterior cardinal vein (pvc). cutaneous arleries (ca), and veins (01. Note (hat Ihe position nfculsneous artcrieI and \pin) In tuihw?tru\ linmru~is reversed compared with that in other specie, and that onl) an epaxial pair is present. Alw. Ih~iiii~ii~rhi~iinrn dnr, not hate 3 p#nIeriorcardinal bein lfmm Graham 1975).

56 subject for muscle biochemistry studies. Previous data on Yuen (1966) has recorded swimming speeds from skipjack teleosts supported separation of function for the two types of tuna using cine techniques from a ship’s observation cham- muscle: red is aerobic and is thus used for basal level swim- bers at sea. Speeds ranged from 0.5 to 14.4 body lengthsls. ming; white is anaerobic and is used for high speed and burst Dizon et al. (1978). employing ultrasonic tracking methods. swimming. Recent workers suggest that there might be more recorded swimming speeds that clustered around 2 body overlap of function than heretofore suspected (sources cited lengthd-not exceptionally fast, but they observed that in Hochachka et al. 1978 and in Brill and Dizon 1979). In sometimes the tuna would maintain speeds above 6 body general, the red muscle is highly vascularized and contains lengthsls for over 30 min, and over 3 body lengthsls for significant amounts of fat and glycogen, high amounts of over 240 min. Trout, in contrast, can only maintain 5 body enzymes of aerobic metabolism, and tremendous numbers of lengthsls for < 5 min (Brett 1973). But we doubt that tunas mitochondria. Red muscle thus appears totally aerobic, burn- are the fastest fish; Fierstine and Walters (1968) compared ing either carbohydrate, fat, or both. This is the typical tele- acceleration times of wahoo and yellowfin tuna and found ost pattern. White muscle is, however, unusual. It contains that wahoo could accelerate around six time\ faster. b’hilc high amounts of glycogen and concomitantly high glycolytic this is not surprining in a “lurking” predator like the \\ahno, enzyme activities. But the enzymes for aerobic metabolism it provides insight into tuna design criteria. The impres5ion also occur in large quantities. Mitochondria exist in far that emerges is that the skipjack tuna should be viened as a greater numbers than in typical teleost white muscle, and fat sustained performer, continually swimming at \peed\ con- droplets also occur. While white muscle contributes to burst siderably above most other teleosts’, but perhaps not capable swimming, supported by the “most intense anaerobic sly- of the high speed bursts of the lurking predators. colysis thus far known in nature” (Hochachka et al. 1978: 154). most white muscle functioning is aerobic-based. This Small tuna species (at least as adults) are totally lacking in fact will be important when we later discuss thermoregulation. a swim bladder and are, as a result, negatively buoyant (Magnuson 1973). Perhaps this is an adaptation to allow The biochemical and physiological adaptations of the skip- them to rapidly forage throughout the water column without jack tuna characterize a high performance animal. This is ob- danger of embolism. The ultrasonic studies reported by vious to anyone familiar with the morphology of the tunas. Dizon et al. (1978) showed continuous vertical movement Strong selection pressures have operated to create body and that ranged between the surface and 273 m; these were some- fin configurations, swimming movements, and musculature times completed in less than a minute. to minimize drag and maximize thrust production per unit of Because the fish are negatively buoyant. lift must be pro- input energy. Adaptations for reducing drag are more exten- vided to maintain hydrostatic equilibrium. The pectoral fins sive in the tunas than perhaps in any other group. The skip- provide most of this lift (Magnuson 1973). Since lift is gener- jack tuna has an almost perfect body shape for longitudinal ated from the forward motion of the fish, the necesity of streamlining (Magnuson 1978). Drag reaches a minimum maintaining hydrostatic equilibrium imposes a minimum when maximum body thickness is 22% of length (Webb swim speed on the skipjack tuna. If speeds fall below, this 1975). In contrast, the wahoo has a ratio of 12% (Magnuson minimum, insufficient lift is generated and the flsh either 1973). sinks or must resort to tail-down-head-up swimming behavior or a kind of flapping of the pectoral fins. The minimum Turbulence is reduced by the presence of longitudinal, swimming speed of skipjack tuna (Fig. 54) falls as size in- horizontal keels on the caudal peduncle (Webb 1975; Magnu- creases, from above 3 body lengthsls for a I2 cm animal to son 1978). Similarly, the midline finlets across the dorsal below 1.5 for a I00 cm one (Magnuson 1973). Incidentally. and ventral portions of the posterior quarter of the body Magnuson (1973) reported that the minimum speeds pre- direct the water in a smooth flow as the tail beats in rapid, dicted for skipjack tuna are identical to those predicted by but low amplitude oscillations. The avoidance of turbulent Shuleikin (cited in Magnuson 1973) as most efficient for flow around the fish results in lower drag. The oval peduncle, migration by aquatic species. faired with the lateral bony keels, slips back and forth through the water with a minimum of resistance and yet provides a Measurements of drag by the various body and fin com- strong link with the high aspect, lunate tail. Drag producing ponents can be used to estimate power consumption. Magnu- structures are absent or reduced or can be removed from the son (1978) and Magnuson and Weininger (1978) probided water stream. No scales are present, save at the corselet, so accurate estimates of body dimensions and drag estimates the body is smooth. The eyes, nares, and mouth structures for the various tunas. Iliron and Brill (1979) and Gooding are almost perfectly faired into the body surface. The dorsal et al. (1981) have used these to determine power required and and pelvic fins are used only during turns so in straight-line heat generated at various swim speed\. An estimate for the swimming, the dorsal fin is slotted into the back and the 1,500 g example skipjack tuna’s theoretical power uptake pelvics are appressed into grooves. The pectoral fins provide can be calculated by the following. lift to the negatively buoyant body and must remain in the water stream. However, when the skipjack tuna turns, the 1) Total input power to swim is the sum of the power re- outer fin is appressed into a lateral groove on the body sur- quired for caudal thrust divided by the muscle efficiency of face and its body pivots. Magnuson (1978) stated that during the propulsion system (20‘70) (Webb 1975) and added to the burst swimming, both pectoral fins are appressed into their power required for nonswimming processes (Brill 1979; respective body depressions, thus presenting a smooth body SMR, see Section 3.61(2)). surface. Tuna fins have high aspect ratios; the length is long 2) Thrust power must be equal to drag force multiplied by with respect to the width. Induced drag is relatively smaller velocity (power equals force times velocity) and is estimated for this fin shape (Magnuson 1978). by: Using Brill’s (1979) SMR relationship (0.35), the total required power should be 0.49 nig 02/gper h. which compare \\ell with Gooding et al.’s (1981) measured value of 0.498 mg O:/s per ti.

3.62 Therrnoregulaticin

Stevens and Neil1 (1978) characterire the life history strategy of the tunas as energy speculators. Tunas gamble relatively large amounts of energy to quickly move through their forage-poor enbironment and anticipate correspondingly large energy returns. Adaptations for energy speculation have produced many of the unique specializations that we have so far described for fast suimming and rapid energy overturn. It has also presumably brought them to the verge of homeo- thermy. Tunas, and some pelagic sharks, maintain their body temperature above that of the surrounding water. As indicated in earlier sections, tunas, particularly skipjack tuna, have exceptionally high metabolic rates. Because the propulsion system is only 20% efficient, 800’0 of the input power to the system is available to heat the tissues. In most teleosts this excess heat is carried from the trunk muscles by the venous system to the gills, where the heat is lost to the water. Thermal equilibrium occurs at a much faster rate than the mass transport of 0: and C0:. so the heated venous blood thermally equilibrates uith the seawater. As a result, excess tipre 54.--F~iimated minimum swimming qpeeds else\en rromhroid fi\hr\ temperatures of most teleosts never exceed a feb tenths of a for mainlahing hldroslalir equilihrium in (a) rm/wr and (h) hod? Imglhs/\rc (from Mapnuson 1978). degree. The thernioconserving mechanism taxonomically distin- guishe the 13 species of true tunas from the rest of the scombrid family (Klaue 1977; Collette 1978). Heat is transferred P=(O.~XQXSXVxCdx 10 ’)x Vx253 from the venous to the arterial sides of the circulatory system in a system of countercurrent parallel arterioles and venules where P = required thrust power (mg O,/h) in close contact (Fig. 53). These are the rete mirabile (“won- e = water density (1.0234) derful nets”). Tunas have four different types: S = surface area (0.4 L’, where L = fork length) V = velocity (centimeters/s) Cd = coefficient of drag (dimensionless number I)Cutaneous retia ser\ed by cutaneous arteries and veins relating surface area and velocity to dras force) which are unique among teleosts. This system is very large in 253 = a multiplier that converts matts to nig O,/h, bluefin tuna and provides all of the muscle blood tlow. In assuming an oxycalorific equivalent of the skipjack tuna, however, it is small and of preturnably 3.4 cal/mg 0,. minor importance (Stevens and Neil1 1978). 2) Visceral retia are found within the bluefin tuna, alba- 3) The coefficients of drag and body surface area have been core, and bigeye tuna but are absent in the skipjack tuna. calculated for skipjack tuna and others by %lagnuson and Weininger (1978). For the purpose\ of this treatment, a 3) Eye and braii? retia are found in the bluefin tuna and simple 0.4 L’ a<\umption is sufficient for bod! \urface and albacore but unknoun in the skipjack tuna, although they an estimate of’ drag coefficient of: exhibit elevated hrain temperatures. 4) Central rete are well developed in the skipjack tuna and other small tunas. It is located directly beneath the vertebral column. Steven5 et al. (1974) has described the retia in great detail (Fig. 55). where p = uater \isco\ity (0.0096).

The 1,500 g (43 cm) example skipjack tuna s\+imming at 1.4 Because of the countercurrent rete, metabolic heat is body lengthsls should theoretically have a coefficient of drag trapped within the muscle mass of the body with excess tem- of about 0.02, require 0.028 mg O,/g per h of thrust and peratures ranging from Ioto 21 above the Furrounding thus five times as much input power to the propulsion system water (Barrett and Hester 1964; Carey et al. 1971; Stevens to “pay” for the 20% efficiency of the system (80rn is lost as and Fry 1971; Graham 1975; Dizon et al. 1978; Stevens and heat, some of which warms the body). Input required is thus Neil1 1978). 0.14 mg O,/g per h, which must be added to the pouer re- Tunas have several thermoregulatory options (Dizon and quired for nonsuimming functions such as osmoregulation. Brill 1979):

58 needs and alter the effectiveness of thermoconserving ctruc- tures. It is difficult to use field data as evidence for phy5iological thermoregulation. Barrett and Hester (1964) determined a regression between sea surface temperature (Tu)and body temperature (Tb): Tb = 0.58 Tu + 16.39. Pre\umably, if Tb was constant over a great range of Tu’s, one could assume a thermoregulatory ability. In skipjack tuna, the slope is different from unity implying some thermoregulatory proceLs. However, other workers (Carey and Teal 1969; Stevens and Fry 1971) observed muscle temperatures quite different from Barrett and Hester’s (1964), although the fish were taken in waters of the same temperature. Still, Stevens and Fry (1971) concluded that skipjack tuna could maintain a fixed Tb in waters ranging from 25“ to 34°C; that is, that they do regu- late. Conclusions drawn from such field evidence, however. are not justified because the thermal histories of the fish prior to capture were unknown. Very cool water is available to the fish within less than a minute before the time it is Figure 55.-Schemalic drawing illustrating the major features of the vaxular caught, boated, and measured. Consequently, sea-surface heal exchanger of skipjack tuna. DA. dorsal aorta: K. kidne): M. muwle: temperature does not necessarily represent the real habitat PCV. posteardinal vein: V, vertebra. Left inset shows pattern of arterial blood temperature, Moreo.uer, thermal inertia causes 73 to lag be- flow; right inset shows patterns of venous blood flow: mall arrows indicate hind apparent changes in Tu, and activity of the fish is a heat tlsnsfer from venules to arlerioles in the exchanger (From Stevens et 81. 1974). critical determinant of heat production and presumably Tb. All these affect the thermal history of the fish before they are captured. 1) Behavorial thermoregulation To differentiate between thermoregulatory options, experiments must be conducted that measure Tb and activity at Since tunas are mobile and live in a heterothermal environ- specified, constant Tu’s. Dizon et al. (1978) and Dizon and ment, they can behaviorally select optimal thermal habitats. Brill (1979) investigated thermoregulator:. performance in Except for bluefin tuna, the distribution of the others is narrowly circumscribed by temperature (Sund et al. 1981). skipjack and yellowfin tunas,.where Tu could be fixed and Tb measured by ultrasonic telemetry. Swim speed in an And because they “store” heat, they can behaviorally regu- annular tank was constantly monitored with photocells. late activity to alter heat production: less activity means less Under these conditions a simple Tb versus Tu regression heat produced. reveals little temperature adjustment. Body temperature is clearly dependent upon Tu: Tb = 3.14 0.97 Tu. Dizon et 2) Passive thermoregulation + al. (1978) estimated heat production (H,,) using the same techniques outlined in the previous section for determining Any process that stabilizes body temperature without re- total power input. Heat production is the input power, minus quiring nervous system intervention can be (haracterized as the output power dissipated as thrust, plus the SMR. Use of passive thermoregulation. these relationships allows comparisons to be made between Water temperature- and swim velocity-related heat pro- fish of different sizes swimming at different speeds. An index duction have been suggested as affecting body temperature. of whole-body thermal conductance can be developed, Water temperature affects water viscosity and density and thus influences drag forces which, in turn, alter the energetic

H, k(Tb ~ TU) requirements of swimming. Thermal inertia might explain much of what was considered where HL = steady state heat loss physiological thermoregulation in the past (Carey et al. 1971; Neil1 and Stevens 1974; Neil1 et al. 1976; Dizon and Brill 1979). Because of the retia, heat is exchanged with the en- Since the fish is assumed to be in steady state, that is, Tb is vironment at a much more reduced rate in tunas than in constant, then H, must equal H,,. In contrast to yellowfin similar-sized teleosts; body temperature changes in tunas tuna, skipjack tuna were found to exhibit a great deal of thus can significantly lag behind environmental changes. variability in the whole-body thermal conductance over the As swim velocity increases, the surface heat dissipation temperature range from 20” to 30°C. (If regulation were oc- rate is increased. However, it does not appear that this pro- curring, increases in Tu should be accompanied by increases cess is sufficient for stabilizing body temperatures in response in H, so that Tx would get smaller where Tx = Tb - Tu.) to increased heat production as tuna swim faster (Dizon and Nevertheless, even though H,, is tightly linked to swim speed, Brill 1979). changes in swim speed were not accompanied by changes in body temperature. Clearly, some mechanism existed in skip- 3) Physiological thermoregulation jack tuna to alter either the pattern of H,. heat loss, or both. Dizon and Brill (1979) extended the above experiment by Activity-independent thermoregulation requires that the forcing tunas to swim at high speeds in water temperatures nervous system has the ability to recognize thermoregulatory approaching their upper lethal limit. Under these conditions,

59 if physiological regulation was possible, the tuna would Q,oof 2, a twentyfold change in metabolic rate can be con- demonstrate it. Swim speed was increased by force feeding verted to a fortyfold change, if the change is accompanied plastic-coated weights to 23 fish. Only three survived the by a IO” rise in temperature. Perhaps the retia temperature treatment long enough to collect data. Two of the fish were function is only secondary; its main one may be to retard able to significantly increase whole-body thermal conductance mass transfer of lactic acid, the byproduct of anaerobic and one with no decrease in swim speed. Dizon and Brill glycolysis. Then lactate from the white muscle would pass to (1979) consider this true physiological thermoregulation. the red muscle, where it would be metabolized by that tissue’s There are two situations in tunas which require some ther- liverlike enzymes (Stevens and Neil1 1978). But much of the moregulatory adjustments: I) Tx should be increased or de- white muscle circulation bypasses the rete mirabile entirely. creased when ambient temperatures approach lethal limits, There also might be benefits occurring simply from stability and 2) extremely rapid increases in heat production accom- of the body temperature. Neil1 and Stevens (1974) and Neil1 panying increases in swim speed must be dissipated to prevent et al. (1976) suggested also that because of the thermal inertia, muscle overheating. The tuna could meet these two exigencies perception of very weak horizontal gradients could be ac- with I) some physiological process that would alter the effec- complished. But because of the skipjack tuna’s habit of tiveness of the heat exchanger, and 2) changes in the relative constantly making vertical migrations (Dizon et al. 1978), we contribution of the red and white muscle fibers to swimming. wonder if the horizontal gradients have much meaning to the Prevention of overheating presents no problem. There has tuna. been much in the literature on the overheating of large, active tunas in warm water, notably Barkley et al. (1978) and Sharp 3.63 Hypothetical habitat of skipjack tuna (1978), to define inhabitable regions in the ocean. However, there is no physiological data indicaticg that tunas can over- Barkley (1969) has hypothesized that the habitat of the heat under free-swimming normal conditions. If the notion adult skipjack tuna coincides with the area where a shallow that the white muscles are only used for high speed swimming salinity maximum occurs seasonally or permanently, whereas is discarded, a way out of the overheating conundrum is that of larval skipjack tuna coincides with the area having a apparent. In the section on energetics, the argument was permanent shallow salinity maximum. Thus, a hypothesized made that white muscle fibers are graded into contributing to maximum depth and distribution can be mapped (Fig. 56). swimming propulsion at a relatively low swim speed (Hocha- Temperature and oxygen data can also be utilized to delimit chka et al. 1978; Brill and Dizon 1979). White muscle fibers distributions based upon size (Figs. 57-59). Barkley et al. are vascularized by pathways which bypass the vascular heat (1978), based upon information from Neil1 et al. (1976). con- exchanger (Kishinouye 1923; Godsil and Byers 1944) so the sidered three environmental conditions that would be likely heat or a portion of it is lost at the gills, like other nonther- to operate to determine distribution of skipjack tuna. These moconserving fish. are: 1) A lower temperature limit around 18°C. 2) a lower Control of the relative contribution of the two fiber types dissolved Oi level around 3.5 p/m, and 3) a speculative upper to swimming might also serve to adjust Tb in response to the temperature limit, ranging from 33°C for the smallest skip- first exigency. At high environmental temperatures, the tuna jack tuna caught in the fishery to 20°C or less for the largest. might rely more on the white muscles, which add to the body According to the analysis, skipjack tuna larger than 11 kg heat burden to a lesser extent than rhe red. In addition, should find relatively few habitable regions within the eastern there might well be some regulation of the effectiveness of tropical Pacific Ocean (Fig. 60). While this agrees with fishery the heat exchanger itself. data, the third condition does not seem to hold (see Section In summary, tunas have relatively large numbers of processes 3.62). The authors arrived at this condition by extrapolating to deal with thermal challenges. They obviously can employ from data obtained from restrained fish and by predicting behavioral responses seeking new habitat reducing of or or temperatures for a fish swimming with red muscle only. increasing swim speed. Thermal inertia helps stabilize body These conditions could then result in thermal runaway; that temperatures during periods of rapidly changing environ- is, a positive feedback system could be generated with muscle mental temperatures. Physiological mechanisms exist as seen temperature increases causing faster swimming, causing in- in the observation that heat production and body temperature creasing muscle temperatures. But as indicated in the pre- are not always linked. vious section, tunas do not overheat even though they are As to the question, “Why be warm in the first place?’ very active in warm water. Some process intercedes to reduce many ideas have been suggested, but no real answers have temperature excess (Dizon and Brill 1979). emerged. Because of the fast swimming, energy speculative nature of the tuna, most suggestions have centered on swimming. The original assumption (Carey et al. 1971) is that 3.64 Responses to stimuli higher temperatures increase muscle power. However, Walters and Fierstine (1964) found that a yellowfin tuna, whose body (I) Vision temperature was twice that of a wahoo, exhibited speeds only slightly greater and acceleration times considerably less. Nakamura (1968) studied the visual acuity of skipjack tuna Neil1 and Stevens (1974) suggested that recovery time from and kawakawa using conditioning techniques. Tunas were anaerobic activity might be lessened because of the increased taught to respond to targets bearing either vertical or hori- temperature. Perhaps energetic efficiency is enhanced, or zontal stripes in order to receive food and avoid electric there are biochemical advantages to the thermoconserving shock. At lower light levels, visual acuity of the two species structures. Hochachka et al. (1978) felt that the tuna has was similar but at higher levels, the skipjack tuna did better greater control over its highly charged metabolsim. Give. il (Fig. 61).

60 UNITED STATES

Figure %.-Depth in meters of the shallow salinity maximum in the Pacific Ocean, based on all available oceanographic station data, averaged within areas of 2" of longitude by 2"of latitude. Regions where a shallow maximum is present during one or more quarlers but not all year are indicated by hatching. A region analogous to the halched area in Ihe North Pacific must also be present in the South Pacific but cannol be shown due lo sparsily of data (from Barkley 1969).

Figure 57.-H)pothetical maximum depth (meters) of the skipjack tuna habilat Figure 58.-HypotheIical minimum deplh of the skipjach tuna habitat in the in the eastern Pacific Ocean, a$ determined by the deplh of the 18°C isotherm Pacific Ocean east of the 180°meridian, fur fish Neighing about 6.5 kg (I4 Ib) (hatched area) or the 3.5 ml/l(5 p/m) isoplelh of dissolved oxygen (crosshalched which are limited lo water cooler than 24°C. Contours show the depth. in meters, area). Contour interval is 50 m except for a few areas near the coast. where a 25 of the 24OCisotherm (from Barkle) et al. 1978). rn contour interval is used (from Barkle) el al. 1911).

The role of visual acuity in the life of pelagic fishes may conditions as that in the experimental tank. He also deter- involve, in addition to the detection of prey and predators, mined (hat the skipjack tuna could prey on object5 as sinall the recognition of transient body marks, such as the vertical as 0.9 mm, based on the minimum sire of food particle that bars exhibited by the skipjack tuna duriiig feeding (Strasburg could be retained by the gill rakers, and that it would be and Marr 1961; Nakaniura 1962; Nakamura and Magnuson able to resolve prey of this size at a maximum diytance of 1965) or during courtship (Iversen et al. 1970). as well as 54 cm. The transient vertical bars on the flanks of skipjack other permanent body markings. Nakamiira (1968) calculated tuna, being about 2 cm wide, would he resolved at a maxi- the distances of resolution of prey or body marks a\ 36 m, if mum distance of 12.4 m, whereas the permanent black longi- the skipjack tuna were in waters having [he same visibility tudinal stripes on the belly, being 0.5 cm wide, would be re-

61 Figure 59.-lhickness ef Ihe h\polhelical habitat la!er (meters), for 6.5 kg skip- Figure 60.-Water temperalure al thorc depths where Ihe concentration of dis- jack luna in Ihe eastern and cenlral Pacific Ocean. Contour, were obtained b? 5ohed oxtgcn is 3.5 mlbl. Ikeper water is cooler and lower in oxkgen, shallower rubtracting depths of Ihe upper habitat limit (Fig. 571 from Ihe lower one (Fig. water is warmer and has more oxjgcn. Skipjack tuna weighing more lhan 11 kg 561. In the crosshatched areas off Mexico and Peru. there should be no habitat require well-oqgenated water cooler than ZIT; they should find all the shaded wilable for fi5h of lhis or larger sizes. In Ihe hatched ares. water warmer lhan area5 stressful. Similarl). 4 Lg skipjack tuna should find Ihe area enclosed b) the 24°C i5 present above the habilat lajcr. Immedislcl) be)ond this area. Ihc 26'C conlour either loo warm or loo poor in dissolved oxygen. Smaller skipjack habitat (dashed depth conloursl extends to the sea surface. Out5ide of the 18°C tuna would seldom enco~nlerthermal sire% in the easlern lropical Pacific, and surface isotherm, Ihe Haler is probably too cold for %kipjacktuna (from Barkle) can inhabit all area5 b? ,la?ing in the shallower. o\)ecn-rich la)m (from Barkley CI al. 1978). et al. 1978).

solved at maximum distances of 3.1 m, again in waters having the same visibility conditions as those in the experimental tank. These conditions would be met in pelagic waters typical of the tropical ocean with an unobstructed sun at an altitude of 65 '. The presence of color vision improves perception, but tunas are color blind. Work by Tamura et al. (1972) and Kawamura et al. (1981) failed to find chromaticity-type S- potentials. This is a technique where electrical potentials are measured from the isolated or in situ retina. The chromaticity S-potential is considered by visual physiologists as a defini- tive test for color vision. The latter authors looked for but failed to find these potentials in yellowfin tuna: bigeye tuna; albacore; striped marlin, Terruprurus audax: blue marlin, Mukaira nigricans: and black marlin, M. indica. Tamura et al. (1972) recorded S-potentials from skipjack tuna, kawakawa, and frigate tuna and failed to find the chromaticity type. That these fish are color blind is consistent with the findings by Tester (1959) that tunas exhibited no color pre- ference in behavior tests. Also, most wavelengths of light are rapidly attenuated with depth, so that the principal habitat of the pelagic fish is a monochromatic one. Munr and McFar- land (1977) found only a single visual pigment in retinal extracts of wahoo, yellowfin luna, kawakawa, black marlin, and blue marlin. This is also a strong indicator of the lack of color vision. LOG OF LUMINANCE OF WHITE STRIPES (FOOT-LAMBERTS 1 (2) Temperature

Figure 61.--\isual acuity curbe, of skipjack luna and kawakawa. turhvlnrn Skipjack tuna have thermal receptors and can make be- ntth7ir. at adaptive illumination of 170 luxes (from Xaknrnura 1968). havioral decisions based on Zemperature stimuli. Dizon et al.

62 (1974, 1976), using heart-rate conditioning techniques, dem- Senegalese purse seiners fishing in the Gulf of Guinea. Chur onstrated temperature perception in skipjack tuna. Steffel et et al. (1980) likewise reported that the sex ratio of fish cap- al. (1976) demonstrated that free-swimming, captive kana- tured by purse seiners in the eastern tropical Atlantic from kawa could discriminate temperature thresholds of 0. IO” to 1969 to 1977 did not differ from I:l. 0.15”C. We suspect that skipjack tuna can do as well because Fur the Indian Ocean, Raju (1964a) found males predomi- this degree of sensitivity has been demonstrated in other tele- nating in most months, especially for older age groups in osr species. Even though this seems like a high degree of samples collected in the Minicoy Islands. Marcille and Ste- sensitivity, horizontal gradients in the ocean are never likely quert (1976) and Stequert (1976) presented monthly data on to exceed O.OOOIo to 0.001 “C/m. This fact, and the tunas’ the sex ratio of fish collected from Japanese bait boats fish- habit of making continuous vertical movements through ing off the northwest coast of Madagascar from February gradients of several degrees, makes it unlikely that they use 1974 to March 1975. There was no apparent trend in the the weak horizontal temperature changes as orienting cues. monthly data and all but one of the values fabored females. For the entire period, the sex ratio uas 0.83:l and ranged (3) Mechanical from 1.01:1 to 0.72:l. For the Pacific Ocean, Schaefer and Orange (1956) found Sound does not seem to affect the behavior of skipjack that more females (0.73:l) occurred in the samples from the tuna at sea (Strasburg and Yuen 1960). Noise produced by young fish taken in the eastern tropical Pacific fishery; how- hammering on the hull failed to alter the behavior of the ever, sex could not be determined for a large proportion of tuna being fished. HowJever, it is doubtful that skipjack tuna the samples. Yoshida (1960) reported that the sex ratio was are deaf. lversen (1969) determined threshold curves (thresh- 1.05:l for samples collected in the central South Pacific. In olds versus frequency) for kawakawa and yellowfin tuna. Hawaii, Brock (1954) showed that males predominated in the Thresholds were not remarkable when compared with other catches during most time periods (1.16:l overall) and differed teleosts. significantly from 1:l in the September-December period in York (1974), on the other hand, found that sudden or ir- 1949 and 1950 (1.64:l and 1.32:1, respectively). .4lso, catches regular noise, as caused by worn bearings, a bent propeller from experimental trolling in inshore Hawaiian waters shaft, a slack rudder, or changes in throttle with a “high (Tester and Nakamura 1957) showed a predominance of revving” engine, caused schools of skipjack tuna as well as males (1.57:l). For the northern Marshall Islands area (Marr yellowfin tuna and albacore to sound. In addition, York re- 1948). males again predominated (1.60:l). For fish taken off ported some success in attracting skipjack tuna schools by Taiwan, Hu and Yang (1972) reported a preponderance of playing back recordings of anchovies “breezing” and gannets males (1.31:l) in the 50-59 cm FL interval, while the ratio diving. was 1:l in the adjacent IO cm FL intervals. Monthly data showed considerable variability, for example, from 3.01: 1 to (4) Chemical 0.64:1, but there was no apparent trend. Off Japan, the ratio was reported to be 1.09:l (Waldron 1963). Wade (1950) re- Tests at sea to attract skipjack tuna using extracts from ported that females dominated in the Philippine catch with a skipjack tuna, yellowfin tuna, and anchovy were either nega- ratio of 0.86:l. Likewise in New Zealand, females are re- tive or inconclusive (Tester et al. 1954). Other substances, ported to dominate the catch, with the ratio being 0.76:l such as skipjack tuna blood sprayed in the water or skipjack for fish caught by purse seine over the period December tuna blood and body slime allowed to drain from the scuppers 1976-March 1978 (Habib 1978). into the water failed to affect the behavior of the skipjack These statistics suggest that those fisheries known to de- tuna (Strasburg and Yuen 1960). pend on young, immature fish have sex ratios favoring females Mhile those fisheries harvesting predominately older, 4 POPULATION spawning age fish exhibit sex ratios favoring males.

4.1 Structure 4.12 Age composition

4.1 1 Sex ratio Few, tables of age composition have been presented in the literature because of the inherent difficulties in aging skip- Most of the sex ratios reported in the literature are by- jack tuna as pointed out in a previous section. For the most products of studies on maturation and fecundity. No real use part, age composition has been determined from tables of was made of the sex ratio information including attempts to sire composition using various growth equations. Until skip- relate changes in hex ratio with maturation, size of fish, jack tuna can be aged with certainty and with greater ease spawning season, or changer of availability or migration than is currently possible using otoliths or other hard parts, associated with attainment of maturity. The discussion below little use is likely to be made of tables of age composition. will proceed by ocean and all ratios are presented as number of males to number of females. 4.13 Size composition For the Atlantic Ocean, Batts (1972~)presemed data obtained from recreational catches off tw~locations in North Since all fisheries capture skipjack tuna over a restricted Carolina, U.S.A., in 1964-66. Over all years and both areas, sire (age) range and most over a limited geographical range, the sex ratio favored females in all but one case and ranged the size-frequency distributions and other measures of size from 1.06:l to 0.58:1, averaging 0.86:l. Cayre (1979) found composition given below are in all likelihood not representa- a ratio of 0.95:l for a small sample collected in Dakar from tive of any complete stock or population. Length-frequency

63 distributions have been published most commonly to simply the Hawaiian fishery, modal groups are found at approxi- describe the sire composition of the catch and document mately 35, 50, and 75 cm, while in the summer months they seasonal changes in a fishery. They have been used less fre- are found at approximately 45 and 70 cm. Whereas Brock quently to study recruitment, relationships among areas or (1954) found progression of modal groups and based a growth fisheries, growth, and gear selectivity. From another per- model on them, Rothschild (1965) found the progression to spective, Sharp (1976, 1978, 1979) and Barkley et al. (1978) be irregular with instances of regression. proposed that the temperature and oxygen structure of the oceans in interaction with the physiological properties of skipjack tuna limits the distribution of larger individuals. Iat QUARTER 2d OUARTER 3d OUARTER 4th QUARTER 5, t This subject is discussed more fully in Section 3.63. 0 GULF OF CALIFORNIA

(I) Length composition 5

0 D All length measurements are fork length unless otherwise stated. Modes were determined by visually inspecting the distributions in all but one case. 0 5 10 1 (a) Pacific Ocean E5

sYO

For the eastern tropical Pacific Ocean, Broadhead and 3 ID REVILLAGIGEW ISLANDS

Barrett (1964) presented quarterly length-frequency distribu- 5 tions for four northern areas of the fishery in 1954-60. While 0 there was considerable variability among years, the distribu- 1 A BAJA CALIFORNIA tions for 1956 (Fig. 62) show that the four areas generally 151 had a single mode, though of different size. The Baja Cali- fornia area tended to have consistently smaller fish (40-50 cm), while the Gulf of California, the Mexican coast, and the Revillagigedo Islands tended to have more fish between 60 LENGTH tmm) and 70 cm. Data presented for more recent periods, for example. 1967-79 for the entire Commission’s Yellowfin Regu- Figure 62.-Length distribution of skipjack luna For 1956 by quarter of the year latory Area (IATTC 1980), likewise show considerable varia- for the Gulf of California, Mexican waters, the Hevillagigedo Islands, and coastal bility among years and, probably because several areas were areas of Kaja California (modified from Broadhead and Barretr 1964). combined, the distributions tended to show multiple modes. Diaz” showed that the length-frequency distribution from I purse seine catches frequently shows more large fish than do I 1960 those for bait boats. His data also indicated that fish off 15 Ecuador were mostly between 50 and 60 cm. While the skipjack tuna taken in the northern area of the fishery are generally considered to comprise a single stock, the variability shown here as well as the morphometric and genetic findings of Sharp (footnote 4) suggest that a considerable amount of heterogeneity may exist. For Hawaiian waters, Rothschild (1965) compared the third quarter length-frequency distributions for Baja Califor- nia (taken from Broadhead and Barrett 1964) with those from Hawaii (Fig. 63) and found a remarkable similarity for the small modal group in 1954 and 1960. In 1959, however, the two distributions differed considerably. Rothschild (1965) inferred from this figure and other evidence that the small fish in the Hawaiian and eastern Pacific (at least Baja Cali- fornia) fisheries have a common origin and that the origin is in the central equatorial Pacific Ocean. Houever, from Fig- ure 63 and other evidence, it is apparent that there are differences in size distributions between the eastern tropical Pacific and Hawaiian fisheries. The Hawaii size frequency is bimodal or trimodal, including small fish as in the east but large fish in addition. Summarizing over years for the winter months in

LENGTH [MM 1

“U\ai. E. L. 1’166. Growth ot \kiplack tuna. liarslrunnlrcprlalll/r. in theraii- ern Pacilic Ocean. Inter-Am. Trop Tuna C‘omm , lnlernal Rep. 2. 18 p. Inter- Figure 63.-Length-frequenc) distributions for skipjack tuna taken during the Amcncan Tropical Tuna Conirnirilon. c/o Scrlpps In\iliuimn of Oceanopapli), third quarter of the )ear from fiaheries off Kaja California and the Hawaiian La Jolla. CA 92037. Islands (from Rothrchild 1965).

64 For the equatorial region in the central Pacific Ocean, ex- (Legand 1971); whereas exploratory bait boat catches in De- perimental longline catches showed the presence of fish from cember 1977-January 1978 showed a range of 38-74 cm, with 47 to 84 cm (Shomura and Murphy 1955). While most of the modes around 43, 50, and possibly 55 cm (Kearney and Hallier fish were between 70 and 80 cm, longline catches are com- 1978a). In New Hebrides data from exploratory bait boat monly believed to be biased toward larger individuals. catches in December 1977-January 1978 indicated a size For the South Pacific, most data have resulted from ex- range of 41-78 cm with modes near 45 and 51 cm (Kearney ploratory fishing rather than from commercial or subsistence Lewis, and Hallier 1978). In Papua New Guinea, exploratory fisheries. Rothschild and Uchida (1968) found that experi- bait boat catches showed a range of 36-66 cm with a mode at mental catches in the Marquesas Islands showed a trimodal 56 cm (Kearney and Hallier 1979). whereas the size range for distribution with mode\ at 47 (dominant), 67, and 75 cm. commercial bait boat catches was 46-69 cm (Wankohski Bayliff and Hunt'h prewnted data assembled from various 1980). For the Japanese purse Feine fishery to the northeayt sources for the Marquesas and Tuamotu Islands by various of Papua New Guinea, Honma and Suzuki (1978) presented months from 1957 to 1959 and 1977 to 1980. In most cases, data showing catches ranging from 29-30 to 73-74 cm in there were one or two size modes with the major one at ap- 1970-74 with a single mode ranging from 44 to 53 cm. There proximately 50 cm and a lesser mode sometimes occurring was no indication of a progression of modes with time. For around 70 cm. For the Society Islands, Bayliff and Hunt Indonesia, Simpson (1979) presented information on the size (footnote 16) again presented data assembled from various composition of the bait boat fishery in Ambon, Bitung, sources by various months from 1973 to 1978. Some of these Sorong, and Ternate. In February 1977 and January-May data were collected from the subsistence fishery in Tahiti. 1978, the size range was 30-72 cm with a single mode at There appeared to be three modes, which in many cases fell around 50 cm. A more ambitious sampling project is no& roughly in the 40-50, 60-70, and 80-90 cm intervals; the total being conducted by Indonesia (and Philippines) in coopera- range was 32-91 cm. They also found some evidence of pro- tion with the U.N. South China Sea Fisheries Development gression of modes which they felt indicated growth, but Josse and Coordinating Programme and a report on the first year'\ et al. (1979) concluded otherwise. Moving slightly to the east, sampling (1979-80) will be available shortly. a single mode was found at 45-50 cm for samples taken at For the northwestern Pacific, we will first discuss the Trust Pitcairn and Gambier Islands in 1980. For American Samoa, Territory of the Pacific Islands, then Philippines, Taiwan, Kearney and Hallier (1978~)presented data for May-June and Japan. Within the Trust Territory for exploratory Japa- 1978 showing a range of 39-64 cm with modes at about 45 nese longline operations south of lat. 10"N in 1950-51, the and 60 cm. The sizes of fish collected in West Samoa in July size range was from 47 to 82 cm with a single mode at 57 cm 1978 were somewhat smaller, 36-58 cm, and showed only one (Murphy and Otsu 1954). For exploratory bait boat catches mode around 49 cm (Kearney and Hallier 197%). Moving along a cruise track from the northern Mariana Islands slightly westward into Tuvalu, the length frequency of fish through Truk and Ponape to Kosrae in November 1979, the collected in June-July 1978 had a range of 35-66 cm and size range was 27-60 cm with modes at 30 and 52 cm (Kear- exhibited three modes at around 38, 52, and 61 cm (Kearney, ney and Hallier 1980b). For the northern Marshall Islands, Hallier, and Kleiber 1978). Slightly to the north in the Gilbert experimental trolling catches had a size range of 34-74 cm Islands (Kiribati), the range of fish taken by exploratory bait with modes at 45, 55, and 65 cm (Marr 1948). The size com- boat in July 1978 was 38-62 cm, with modes around 40 and position of the catches made by the Japanese distant water 47 cm (Kearney and Gillett 1978). In Fiji the FA0 bait boat bait boat fleet in an area encompassing the northern Mariana development project obtained fish ranging in size from 29 to Islands and Palau Islands during June 1964-April 1966 shoned 84 cm in 1972, 1973, 1974 (FA0 1974a). Two modes were a range of 35-75 cm (Kasahara and Tanaka 1968). The distri- apparent at approximately 46 and 54 cm. Length-frequency butions were multimodal in most months with modes falling distributions from the developing purse seine fishery in New in the 40-50, 50-60, and 60-70 cm intervals. Progression of Zealand (Vooren 1976; Habib 1978; Habib et al. 1980a, b, c) the smallest mode was quite apparent. Data collected during indicated a size range of 30-70 cm, but generally there was 1965 from the bait boat fishery based in Palau Islands indi- only one strong mode at 45-50 cm with minor modes around cated a range of 30-74 cm, and a prominent mode at 50 cm 35 and 55-60 cm appearing in some month/area strata. At in June and 58 cm in October (Higgins 1966); whereas data Norfolk Island, exploratory bait boat catches in March 1980 collected in 1967 and 1968 showed evidence of at least two showed a size range of 42-68 cm and a mode at around 64 cm modes, one between 45 and 50 cm, and the other around 60 (Kearney and Hallier 1980a). cm (Uchida 1970). Since 1964 the Tohoku RFRL, Japan, has For the southwestern Pacific, Kearney and Gillett (1979) been issuing reports on the Japanese southern uater fishery reported that off Queensland, Australia, the size range of (Tanaka undated a, b, c, 1978, 1979, 1980; Tohoku Regional fish taken by exploratory bait boats was 35-70 crn with Fisheries Research Laboratory undated a, b, c, d), which uas modes at 48 and 62 cm; off New South Wales, the range was initially limited to the area within the Equator and lat. 24"N. 39-66 cm with modes at 46, 51, and 60 cm. In New Caledonia, and long. 125" and 15O"E. Initially, the data were obtained data from experimental trolling in 1956-60 showed a range of only from bait boats: the season usually started in June and 40-75 cm standard length (SL) uith a strong mode at 50 cm was over by April of the following year, and the area firhed SL and possibly minor modes at 54, 60, 65, and 72 cm SL was from the northern Mariana Islands to Palau Islands. Now, purse seiners have entered the fishery and the fishing area has expanded to well belou the Equator and east to long. 150"W. A few generalizations can be gleaned from these reports. First, it is apparent that catches from shoal- a\sociated school1 generail! had a \ingle niodc around 3 cni.

65 uhercas open ocean catches were multimodal. Second, purse associated with floating debris, sharks, or whales had a range seine catches generally exhibited only two modes around 40 of 4-18 cm with modes at 45, 62, and 70 cm. and 50 cm whereas bait boat catches exhibited several modes. Third, there were great variations in the frequency distribu- (b) Indian Ocean tions among months, years, and areas as well as variations in the amount of fishing effort expended in these timelarea Just as the fisheries are relatively underdeveloped in this strata that make interpretations difficult. ocean compared uith the Pacific and Atlantic Oceans, there For the Philippines, length-frequency distributions appear- is likewise less information available on the length composi- ing in the literature have been derived primarily from experi- tion of the stocks. Marcille and Suzuki (1974) summarized mental fishing operations. The troll-caught fish from October length statistics obtained from Japanese longline operations 1947 to November 1948 had a range of 34-65 cm with a single during the period 1967-71. The size range and modes for mode at 50 cm (Wade 1950). Chikuni (1978) presented length- each area in the Indian Ocean were as follows: South of frequency distributions for fish caught by exploratory purse Indonesia, 36-86 cm with a single mode at about 50 cm or seine fishing primarily at night in assxiation with rafts less; eastern central area, 36-88 cm with two modes at 55 and (‘‘payao” or “payaw”) from November 1974 to June 1977. 64 cm; western central area, 44-78 cm with a mode at 50 cm In Mor0 Gulf, nearly all of the fish taken were between 40 in the first and second quarters and at 60 cm in the fourth and 55 cm from January through July. Small fish, 25-35 cm, quarter; Bay of Bengal area, 38-84 cm with a single mode entered the fishery in May and became more prominent in generally above 60 cm; and northwestern area, 42-84 cm also October and December. In the Sulu Sea, the size range &as with a single, but strong mode usually above 60 cm. Gener- 30-70 cm in July and a broad mode was centered at 52 cm. ally there was no indication of a progression of modes with The size range was much smaller in May and September, time. With the data combined over all areas, two modes at with modes at 62 and 52 cm, respectively. Evans et al.’7 55 and 68 cm were apparent. reported length-frequency distributions for both small-scale For the waters of Sri Lanka, Sivasubramaniam (1965) pre- and commercial fisheries based on Camiguin Island in the sented figures showing the size composition by coastal area Bohol Sea. For handline and various sustenance gear, the and gear type. For the west coast, troll-caught fish had a size range in March-November 1977 was 37-84 cm TL, with range of 20 to 70 cm, with a single mode centered at the 50- possibly two modes at 66 and 72 cm TL. For commercial ring 55 cm size class. On the east coast, catches by bait boats and net boats during the same period, the size range was 18-63 trollers had a range of 16 to 70 cm, while for gill net catches, cm TL, but the sample size was too small to determine modes. the range was 26 to 70 cm. A single mode occurred in the For Taiwan, Hu and Yang (1972) collected samples in 51-55 cm interval for all gear types. On the south coast, which fresh fish markets from skipjack tuna caught by trolling off is the primary tuna fishing area, the size range was 21 to 80 the southwest coast between August 1970 and November cm for all gear types, and a single broad mode generally 1971. The samples ranged from 23 to 71 cm and exhibited occurred in the 41-45 to 46-50 cm interval. For fish taken in modes at 30 and 49 cm. several areas and by various gear types, Sivasubramaniam For Japan, Kawasaki (1952, 1955~1,b, 1964, 1965b) used (1972) found five modal groups at 34-36, 42-44, 52-55, 62-64, length-frequency distributions for skipjack tuna from various and 72-74 cm intervals by using the probability paper method areas in the coastal fishery to separate hypothesized non- of Harding (1949) and Cassie (1954). For experimental Japa- migratory and migratory stocks. The distribution varied con- nese bait boat fishing, the size range was 28 to 72 cm with siderably among months and areas with respect to both the modes occurring at 32-34, 44-46, and 58-60 cm intervals size range and the number of modes. The total range was (Sivasubramaniam 1975). from 25 to nearly 80 cm and a distinct mode appeared in For the Indian fishery in the Laccadive lslands from 1958 every IO cm interval in at least one time or area stratum. to 1961, Jones and Silas (1963) reported a size range of 32-72 Modes within the 40-60 cm range occurred commonly and cm. During the December-April period, two modes at about often showed a monthly progression in average size. Iwasaki 48 and 60 cm were observed, while during other months, (1976, 1980) determined that the size of fish varied with the only the 48 cm mode was apparent. The authors stated that means of capture and whether the school was associated with the samples indicate size specific recruitment to the fishery. banks, floating debris, birds, and sharks or whales. For fish For the waters off Madagascar, samples collected during caught in Japanese waters by bait boats, schools associated August 1973-March 1975 had a size range of 32-71 cm and a with birds had a size range of 20-80 cm with modes at 32, single prominent mode at 49 cm, as well as a less well-defined 45, 58, 67, and 75, cm; those associated with banks had a mode in the 50-55 cm range in some months (Marcille and range of 42-62 cm and a single mode at 49 cm; those associ- Stequert 1976). The authors noted that the smaller mode pro- ated with floating debris had a range of 25-61 cm and modes gressed from < 45 cm to just over 50 cm from September at 34 and 52 cm; and those with sharks and whales had a 1973 to May 1974, but no progression of modes was evident range of 33-61 crn and a mode at 50 and possibly 40 cm. For in the remainder of the time period. purse seine-caught fish, schools associated with birds had a range of 41-54 cm and a single mode at 45 cm while those (c) Atlantic Ocean

With the ICCAT emphasizing the description of tuna fisheries and the assessment of the tuna stocks in the Atlantic, a number of papers are now available describing size composition of skipjack tuna. For catches by U.S. purse seiners in the eastern tropical Atlantic during 1968-74, the size range

66 was 25-70 cm (Sakagawa et al. 1976), and a single mode Coast-Senegalese purse seine, and Japanese purse seine fleets. usually occurred at 45-50 cm, though at times two modes at In 1969-71, the distributions for all of these fleets were uni- 45 and 50 cm were indicated. For catches by Korean bait modal with a peak at about 50 cm. In 1972-73, each individ- boats in the same area in 1975, Choo (1977) presented data ual distribution was still unimodal, but the fleets were fishing showing the ranges of 33-65, 32-62, 31-75, and 36-54 cm in different sized fish, thus giving the overall distribution a bi- each of the four quarters, or 31-75 cm overall. Quarterly modal character with modes at approximately 40 and 55 cm. average sizes were stated as 49.8, 48.5, 45.6, and 44.1, or Length-frequency distributions for specific fleets may be 47.6 cm overall. The size ranges of fish taken by Japanese found in Pianet (1974). Bour (1976). Sakagawa et al. (1976). longline boats in the Northern and Southern Hemispheres and Ansa-Emmim (1977). For the northwestern Atlantic, were 44-84 and 48-86 cm, respectively, while the only obvious Batts (1972a) reported a size range of 26-76 cm for fish taken mode occurred at 72 cm in both hemispheres (Kume 1977). by charter sportfishing boats off North Carolina, U.S.A., in For Japanese bait b.oat catches in the Gulf of Guinea during the summers of 1964 and 1965. He presented length frequen- 1974 and 1975, the size range was found to be 37-62 cm, and cies by age groups (up to five) based on examination of few fish below 40 cm were captured (Kikawa and Higashi growth rings in the dorsal fin spines, a method generally 1979). Then for Japanese purse seiner catches in the same considered least reliable by recent investigators (see Section area during 1967-74, the size range was greater, 22-75 cm, 3.43). and fish below 40 cm were well represented. The authors indicated that recruitment of 30 cm fish occurred continu- (2) Size at first capture ously throughout the year. Modal groups w'ere not clearly defined nor was any modal progression apparent. Experi- The size at first capture of fish amounting to significant mental U.S.S.R. purse seine catches in the eastern Atlantic numbers in most years in most fisheries, is about 40 cm. Re- from 1969 to 1977 consisted of fish with a sire range of 28- cruitment into the fishable stocks generally takes place at a 63 cm and modes occurring in the intervals 36-37, 44-45, and smaller size, around 30 or even 25 cm for many fisheries 52-53 cm (Chur et al. 1980). In waters off Brazil, Zavala (Kawasaki 195Sa, 1964; Sivasubramaniam 1965, 1972; Hu Camin (1978) reported a size range of 54-78 cm with a mode and Yang 1972; Iwasaki 1976, 1980; Marcille and Stequert at about 66 cm for fish taken on tuna longline gear in May- 1976; Sakagawa et al. 1976; Choo 1977; Habib 1978; Honma August 1977. and Suzuki 1978; Kikawa and Higashi 1979; Habib et al. Coan (1976) constructed composite length-frequency distri- 1980a. b, c; Tanaka undated a, b, c, 1978, 1979, 1980; butions for fish caught by longline and surface fleets of the Tohoku Regional Fisheries Research Laboratory undated a, participating states over the period 1968-73 (Fig. 64). These b, c, d). For the ring net and purse seine fisheries in the distributions were all unimodal with a peak at approximately Philippines, the size at first capture is around 25 cm and the 50 cm. Sakagawa and Murphy (1976) produced length-fre- size at recruitment is around 15 cm (Evans et al. footnote 17; quency distributions comparing the United States purse Choo'n). seine, French-Ivory Coast-Senegalese bait boat, French-Ivory (3) Size at maturity 6001 , 6001 1 See Section 3.12.

(4) Length-weight relationships

Length-weight relationships have now been published for all oceans (Table 17), but they are not available for all fisheries. Neither have the papers cited below included studies of sexual, seasonal, or long-term variations. z 4001 1969 400 1972 All of the studies cited in Table 17 fitted the allometric growth equation W = 6L" where W is weight in grams, kilo- grams, or pounds, L is usually fork length in centimeters or millimeters, a is the coefficient of allometry, and 6 is another constant. In all but one of the cited studies, the log-linear transformation of the equation,

log,W = log)^ + a logrL

was used to estimate the parameters using predictive (linear) regression analysis. Today it is generally believed that the 11 I I 1 length-weight relationship is intrinsically nonlinear, meaning

OL 30 (40 50 60 ' FORK LENGTH(cm)

Figure 64.-Length compoaition of the skipjack tuna catch from the caslern Atlantic Ocean (fmm Coan 1976).

67 lahk 17.--1 rngth-uciaht relatinnrhip\of $kipjack tuna.

Calculated ho ’we Coeilicleni \reteht of of range Con~iant 01 allometr) Viephi Length 55 em iish S<,Llrcc 1 (ICBIIt\ tIIh (en11 h a unit unit (kp) C omnienti

3.67 e cm Ft~ 149 9 Column, 4and Y ?\timated Sroni Lda’\ Tip. 6. Kzgression ~tatt\iuw\pv:t. 20 10.60 11.01 I3 3.16 p cm FL 3.57 Bajt hoat catrhei. 2hR 3’)-x3 I.X7X* IO 3.2164 Ib em PL 3 31 Sue ranprcalculaied.

YZJ iy-71 i ~S:X in’ 3.403 lb mm FI. 3.50 Bait boat and purse seine catche\ 1.282 19-71 3 763 x IO ’ 3 265 Ib mm FL 3.58 Includes data from Chatuin 11959) 1x9 34-66 3.267 x IO 3.0569 Ih cm TL. 3.40 Malesonl) Data from Ronquillo‘5 fig. 25 and regrewon equations 2 96482 Ib em TL 3.33 Female\ onl?. Data from Ronquillo’s he. 25 and regrexsnn equations. I.2YX 33-xx 4 546X 10~’ 3.36836 Ih mm FL 3.50 Bait hoat catches.

M4 16-76 2 5mx 10.” 3 3533 kg mm FL 3.33 Troll carchec 2.554 36-64 5 hlI x 10‘ 3.31497 ke em FL 3.30 Lop linear reeresion anal)\,? 520 411-73 J I IS x io 3 409 kg em FL 3.35 Linear reerewon analy\ts. x4x 41-62 1 lil x 10 3.15X ke cm FL 3.54 Ban boat catcher.

lix) 3s-SJ 6 ?Oh x 10.’ 3.19 e mm FL 3.35 Punt wne catchec 200 JX-X’ 5.‘00, 10 a 2 20 kg cm TL 3.71 Handlinecalche5.

4.1 17~62 3 727x 10 I 70 kg CIII TL 3.39 Artisanal tichine sears I20 38-71 3 475X 10.” 3.29 e mm Ft 3.60 Pune seine carche,.

that parameters estimated from a log-linearized relationship are biased. Corrective procedures are available, but none were employed in the papers cited. In addition, Ricker (1973) has pointed out that the predictive regression method (uhich asumes a dependent-independent variable situation) tends to produce inflated estimates of a, especially when the sample range truncates that of the tru: population; a geometric mean functional (reduced major axis) regression (which does not assume a dependent-independent variable situation) producer less biased results. Pianet (1974) used the latter procedure but performed it on log-transformed data. A summary of these studies is presented in Table 17, and a T typical curve descrihinx the relationship is given in Figure 65. The table is an updated venion of a similar table presented by Nakamura and Uchiyama (1966), and the figure, based on data from the central Pacific containing the largest sample tize and widest size range of all studies cited, was taken from 5 the same reference. The calculated weights of fish of a com- FORK LENQTI IYY ) mon size, based on the regession staristics of the various authors, show close agreement except for that obtained by

Uda (1941). The estimates of the coefficients of allometry Figure 65.-I,ength-~eight relation of skipjack tuna: lug Heieht = ~ 8.34241 + are amazingly similar, except for those published by Ebans et 3.36836 log length lparameters not corrected for tran\formation bia3): number of observations. 1.298: size range. 327-877 mm: data collection period F-ebruar) al. (footnote 17), and no effect of ocean or gear type is 1948-December 1960 irom filer of Southwest kirheries Center lfmm Vakamura apparent. and Cchi)aina 1966).

68 4.2 Abundance and density (of population) Since some fishing effort directed primarily at yello\vfin tuna is included in the calculation, this index is biased. Several (I) Pacific Ocean attempts have been made to improve the index. Calkins (IY61) and then Joseph and Calkins (1969) calculated relati\e density Forsbergh (1980) has recently reviewed the history of the after eliminating those areas of low skipjack tuna catch \\here measurement of apparent abundance of skipjack tuna in the the fishing effort was directed primarily at yelloufin luna. eastern tropical Pacific. Shimada and Schaefer (1956) pro- The resultant index of relative abundance again did not shoa duced the first measure of relative density by comparing the a long-term trend over the 1951-65 period. RelatiLe density daily catch rates of bait boats standardized by vessel class. was highest in the third quarter, and there appeared to be no They concluded from the trends shown in Figure 66 that the relationship between the indices in the areas north and south fishery was having no measurable effect on the stock. Since of lat. 15"N. Subsequently, Pella and Psaropulos (1975) ad- purse seine vessels have almost entirely replaced bait boats in justed the fishing effort statistics by simulating the effect of the fishery, the measure used today is reported catch divided the following factors on the fishing power of vessels: Vessel by reported fishing effort standardized to class 3 purse seine speed, probability of capturing sighted tuna schoolz, time vessels (101-200 short tons or 94-181 t of carrying capacity). spent in a set, and portions of schools retained that are set For a later period, 1960-79 (Fig. 67), the index in terms of upon succestfully. Using a new standardized fithing effort purse seine units shows considerable annual variation but statistic based on their simulation, they found a different his- again no discernible trend. tory of relative stock abundance over the years of the fishery (Fig. 68). There seems to be some indication of a decrease in abundance of skipjack tuna in the northern grounds and a definite decrease in the southern grounds. It is not knoun at this time which index of abundance is the better descriptor of the stock(s). Later, the IATTC computed relative abundance

using only those 5' latitude by 5 O longitude areas and 3-mo I periods where 200 short tons (181 t) or more of skipjack tuna were caught and 100 or more standardized fishing days were expended. This procedure retained 89% of the catch and eliminated 43% of the purse seine fishing effort in 1961-79. The resulting indices of fish density for the years 1951-79 (Fig. 69) show no clear trend in the areas north of lat. 15"N and between lat. 15" and 5"N, whereas south of lat. 5"N the trend has a convex shape (Forsbergh 1980). For the bait boat fishery in Hawaii, a number of estimates of relative abundance have been made. These indices, measured in catch per trip or per effective trip (as in Fig. 70), are highly correlated with catch and show no long-term trend (Yamashita 1958; Shippen 1961; Uchida 1967, 1976). A

Figure 66.-Catch per standardized-da? fished, total catch. and calculated relative fishing intensit) For skipjack tuna in the ea9tern Pacific Ocean, 1934-54 (from Shimada and Schaefer 1956). 04biL CLASSES INCLUDED NORTHERN AREA CLASS 3 OMlTTED CLbSSES 384 OMITTED

y 005

oca

015 , , , , , , , , , , , , , , SOUTHERN AREA 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 0-0 ALL CL1SSES INCLUDED I I \ ... CLASS 3 OUlTTED 010- ', - CLASSES 3 a+ OMITTED - '1t it6

19TC 1971 1972 1973 1974 1975 1976 1977 1978 1979

Figure 67.-Monthl) and annual catch per standard da)'a fishing (CPSDE) for Figure 68.-Annual hiomn\\ indices of Aipjarh tuna in the Irlditional fi4iinu skipjack tuna. in class 3 purse seine units, in the eastern tropical Pacific during arw\ oP the eastern Pacific Orran wing different ramhinationr nt PI da*w*. 1W-79 (from Forsbergh 1980). 1960-72 (from Pella and Pvaropaln\ 1975).

69 In the Japanese southern water fishery (routh of lat. 24"N R and from long. 125"E to 150"W), catch per vessel increased both for the 1958-68 period in the Bonin-northern Mariana Irlands area (Iwasaki 1970) and for 1964-75 over the entire fishery (Kasahara 1977). Hornever, this trend probably reflects the evolution to larger boats in the tleet rather than changes in relative population density. While catch per day for some areas in the southern water bait boat fishery (Fig. 71) has shown a declining trend (Kasahara 1971), a similar index derived from Japanere purse seine operations in tropical waters shows no such trend (Honma and Suzuki 1978). For the bait boat fishery off the northeast coast of Japan in 1951-62 (Kawasaki 1964) and off the south and southwest coast in 1957-69 (Kasahara 1971), no trend in relative abundance was evident. The same was true for the purse seine fishery in coastal waters from 1971 to 1974 (Honma and Suruki 1978). However, Kasahara (1975) showed that the relative density has declined with increasing fishing effort in the Japanese coastal fishery during the period 1958-72. There Figure 69.-Indice\ 01 abundance of *kipjack tuna (in ton, per da)', fkhing is a regular seasonal cycle in relative abundance with the standardized lo class 4 hail hoats and c1a11 3 purw \einer\l for lhree area5 nf the highest values occurring in June-August (Anraku and Kawa- eastern Paritic Orean (from Eor\hcrgh 198111. . Lastly, lshida (1975) showed that there was no

-- 7- ~ VI L1 15'-24'N - TOTAL CATCH IE 0, 147'-155'E CATCH/STANDARD DAY FISHED 28 N \ '0 '0 12 5"s- IO"N \ 14 1350-1550E \ 26 0 \ LL z v) C6 24 4 W 2 z L" 122 141'-147'E -z m5 t i2 120 2 (1: + a r I I8 -I 5 Y 3 16 - I 011963 1964 I965 1966 1967 1968 1969 0. 1950 1955 1960 1965 1970 YEAR

Figure 71.-Indices of relative abundance for the fishing 5eason Ma)- Figure 7O.--Total calch. calrh per slandard da! fished. and Ihe relative October of skipjack luna in the Japanese southern water fisher). 1963-69 fishing inlensits of skipjack luna laken in Ihe Hawaiian fisher?. 1948-70 (from Kasahara 1971). (from Uchida 19761. marked seasonal trend is quite apparent with the highest values occurring in May-September (Shippen 1961). For the purse seine fishery in New Zealand, relative abundance in terms of catch per set, catch per effective set, catch per day, and catch per season-day shows no long-term trend over the 1975-76 through 1979-80 seasons (Habib 1976, 1978; Habib et al. 1980a, b, c). As in Hawaii, there is a marked seasonal trend, but with the highest density occurring in the 0.2 I January-February period. In Papua New Guinea for the locally based bait boat fishery, Wankowski (1980) presented relative abundance indices showing the highest values occurring in May-September and the lowest values occurring in December-February. No long- Figure 72.--Catrh per da! for Japanese bait hoah of various size classes in the term trend for the period 1970-79 was apparent. weCtern Pacific (from lshida 1975).

70 trend in the catch per day of Japanese bait boats from 1957 has been voiced about recruitment into the population(s), but to 1973, apparently over all western Pacific fishery grounds little actual research has been reported in the literature. Re- (Fig. 72). cently Forsbergh (1980) described work carried out on this subject by the IATTC in the eastern tropical Pacific. An (2) Atlantic Ocean index of relative abundance of young skipjack tuna in the fishery was tested against three factors: Sea surface tempera- A number of estimates of relative abundance have been ture in an hypothesized spawning area in the central tropical determined using data from the surface fishery in the eastern Pacific (long. 130°W-180") approximately 1.5 yr earlier, tropical Atlantic. As is the case with the eastern tropical barometric pressure differences at stations in the Indian and Pacific fishery, this is a two-species fishery and similar prob- Pacific Oceans, and a mixing index in the spanning area. lems exist in separating fishing effort directed at skipjack and While a significant relationship was found between relative yellowfin tunas. For the local bait boat fishery in Angola, de abundance of skipjack tuna in the fishery and temperature Campos Rosado (1971) presented data showjing a steady in the central tropical Pacific (IATTC 1972, 1973), no obvi- index of relative abundance for both species combined, while ous biological explanation for this relationship was apparent. the index for yellowfin tuna has declined proportionally to Subsequently it was found that the temperature variations in the increase in the index for skipjack tuna. The relative den- the spawning area were correlated with the southern oscilla- sity derived from purse seine fishing showed an increase in tion index. This index, which is defined as the difference the last half of the year for both United States and Japa- between sea-level atmospheric pressure at sites located in the nese vessels (Sakagawa 1974; Kikawa and Higashi 1979). Indonesian equatorial low region and those in the South However, no consistent seasonality in the catch per day sta- Pacific subtropical high region, has been used to study large- tistics for Japanese bait boats was apparent (Kume 1978; scale variations in meteorological and oceanographic condi- Kikawa and Higashi 1979). None of these studies, nor Fon- tions occurring over the equatorial Pacific, including the El teneau and Cayre's (1980) study on the French-Ivory Coast- Nix0 phenomenon off the northwest coast of South America Senegalese purse seine fleets, found a long-term trend in rela- (Quinn 1976, 1977). In turn, the southern oscillation index tive abundance. However, a study by Pianet (1980) utilizing has been found to be related to wind conditions in the cen- data from French-Ivory Coast-Senegalese, United States, and tral equatorial Pacific. During the same period Lasker (1975, Japanese bait boat and purse seine fleets did find a slight de- 1978, 1981) showed that the survival of anchovy larvae in the cline in relative density over the 1969-78 period (Fig. 73). California Current was dependent in part on the availability of sufficiently concentrated food and that this occurred with stable structuring of the upper mixed layer of inshore waters. During periods of high wind or strong upwelling, this stable structuring is destroyed and food organisms are dispersed i6 throughout the upper mixed layer resulting in too low a concentration for survival of anchovy larvae. Hypothesizing a similar phenomenon with respect to the survival of skipjack tuna larvae in the central equatorial Pacific spawning area, a significant correlation was found between the index of abundance of fish between 12 and 24 mo of age in the eastern t- tropical Pacific fishery and an index of mixing (the curl or I cube of the wind speed) in the central Pacific approximately 8 60 9 1.5 yr earlier. While the relationship is statistically significant, -. it accounts for only 47% of the variation and is thus a poor IU predictor of catch. % 40- 12

4.4 Mortality and morbidity 7" t Most estimates of mortality coefficients appearing in the literature have been calculated for the stock in the eastern tropical Pacific. Using tagging data from 1957, Fink (1965) -:io0 10 20 30 40 50 60 70 estimated the total mortality coefficient Z to be 6.98, the STANDARDIZED EFFORT I 10" fishing mortality coefficient F to be 2.10, and, using a value of 1.06 for mortality due to tagging from work on yellowfin Figure 73.-Relation between ratch and CPUE \ersus standardized effort in the eastern Atlantic (m = 2. K = 1) (from Pianet 1980). tuna, the coefficient of natural mortality M to be 3.82, all on an annual basis. Joseph and Calkins (1969). using tagging 4.3 Natality and recruitment data from a later period, estimated M on an annual basis as 1.68. Again utilizing more tagging data for the eastern tropi- variousfactors relating to natality were discussed in set- cal Pacific, Bayliff" estimated 2 to be 0.58, F to be 0.35, tion 3.1. Reproduction, and more specifically fecundity, was covered in Section 3.15. Recruitment into a fishery, in terms of migration, was discussed in Section 3.51. "Baylilt. W. H 1977. Estimair\ 01 ihs raic~(>I nmialii~(11 *hipi.wh lu11~1111 the eastern Pacific Ocean denled from iaepiiig s\prrinirni*. InIcI--\Ill rinp Since recruitment into the established and major fisheries T~~~ ~omm..lnlernai R~~.IO. 59 Inter-Anwrtcari T~O~IC'IITU~M < WWWWW. around the world is extremely variable, much speculation C/O Scrippc Insitrution olOceaii<,raph!, I ii lolla. C')t 92017

71 and M to be 0.23, but in this case, on a monthly basis. Using data resulted in an estimate for maximum sustainable yield of a completely different approach, Sillirnan (1966) simulated a 92,500 t for the eastern tropical Atlantic. catch history for the eastern tropical Pacific fishery by allowing M to vary from 0.2 to 0.7 and holding Z constant at 0.8. (2) Pacific Ocean The best fit was obtained with M at 0.3, but this method does not provide a unique solution. Most authors indicated In the eastern tropical Pacific, Joseph and Calkins (1969) that their estimates should be considered as preliminary and estimated yield per recruit, using the Ricker (1958) model, acknowledged that the estimates of M included emigration for both the northern and southern skipjack tuna fisheries and losses due to tagging. Considering the lifespan of skip- (Fig. 74). Their model assumed that all individuals in the jack tuna to be about 5 yr, Murphy and Sakagawa (1977) stock make two passes through the fisheries, and it included stated that the published estimates of M were either too ION von Bertalanffy growth parameters and mortality estimates (0.3) or too high (1.68 and 3.82). derived in the same paper. From Figure 74, it can be seen Using tagging data for 1973-74 in Papua New Guinea. that the yield per recruit for the northern fishery could be Lewis (1980) estimated 2 on a monthly basis as being equal increased only slightly by a doubling of the fishing effort (a to 0.257 overall and 1.285 when the stock was exposed to the multiplier equal to 1.0 represents the level of fishing mortality fishery. Lewis also pointed out that the estimates of 2 in- in 1963), while that for the southern fishery could be included emigration. creased 1 to 1.5 times by increasing fishing effort 2 to 2.5 times. 4.5 Dynamics of poQulation (as a whole) Rothschild (1966) and Silliman (1966) both estimated the potential yield for the combined eastern Pacific stocks if Assessments of the state of the stocks are currently avail- they were harvested beyond the range of the existing fishery. able for the Atlantic and the eastern Pacific, while estimates Using the Beverton and Holt (1957) yield per recruit model of potential production are available for the western Pacific and lengths of time exposed to the existing coastal fishery of and the Indian Oceans. Most of the results must be viewed as 2 and 6 mo (Fig. 75). Rothschild estimated the yield could be preliminary because of the highly variable relationship be- increased between 2 and 17 times the then existing catch. tween catch per unit effort and effort, as well as the low re- Silliman (1966) estimated the potential yield using a popula- liability of estimates of population parameters. tion simulation model which held the total mortality coeffi-

(I) Atlantic Ocean

Two estimates of the potential yield are available. First, Shomura (1966b) argued that since the Atlantic Ocean is half the size of the Pacific Ocean, the potential yield for the At- lantic should be half that for the more well-developed fisheries in the Pacific Ocean. Using a catch of 234,100 t in 1962 for the Pacific, he estimated the potential yield for the Atlan- tic to be 117,000 t, whereas using the largest reported catch for the Pacific, 662,000 t in 1978 (FA0 1980), results in an estimate of 331,000 t for the Atlantic. The harvest reported for the entire Atlantic Ocean was 87,714 t in 1979 (FA0 1980). [Japan.] Fisheries Agencyzoestimated a total production of 100,000 t for the North Atlantic and 100,000-150,000 t for the South Atlantic. The method was based on the abundance of skipjack tuna larvae compared with that for other commercial tuna species. A yield-per-recruit analysis of the eastern tropical Atlantic fishery by Hayasi (1974) indicated an optimum size at first capture of 0.6-1.3 kg (about 33-40 cm). Hayasi concluded that there was no evidence that skipjack tuna in the Atlantic Ocean was fully exploited. Sakagawa and Murphy (1976) examined the relationship between total catch and normalized catch per unit effort for several gear types in the eastern tropical Atlantic. They concluded also that the stocks were not being fully exploited since there was no consistent trend in the data. Recently, Pianet (1980) found a slight but apparently significant decline in catch per unit effort versus effort for standardized French-lvory Coast-Senegalese, United States, and Japanese bait boat and purse seiner data from 1969 to 1978 (Fig. 73). A production model fitted to these Figure 74.-Yield per recruit of skipjack luna at age of entry into the northern fishery (lop) and southern fi$her) (bottom). eastern Pacific Ocean, using yon :"[Japan.]Fisheries Asency. 1%8. On the powbiticy 01 developing rnarlnr fish- Benalanff) growth parameters from ungrouped data (VBCF 1) and grouped er) resources. Information, cited in Kawasaki 1972. data (VBGF 2) (from Joseph and Calkins 1969).

72 Suda (1972) elaborated on the above procedure by saying that since about twice the number of skipjack tuna larvae were taken in plankton tows as larvae of all other commercial tunas, the spawning stock of skipjack tuna was also roughly two times that of other commercial tunas. Therefore, the potential production of skipjack tuna should be at least two times more than that of all other commercial tunas. Both Kawasaki (1972) and Matsumoto (1974) noted that Suda's projections of adult skipjack tuna catch from larval abundance was oversimplified. By citing differences in fecundity and average body sizes between skipjack tuna and other tunas, Matsumoto showed that the conversion ratio of 2:l in favor of the skipjack tuna was not logical. One other irnpor- tant factor not taken into account by Suda was the difference z in the efficiency of the different types of fishing gear used in taking the various species of tunas and the effect this would have on the conversion ratio. Figure 75.--Values of R, (ratio of yields under nhole-life exploitation to lield under limited-life exploitation) for skipjack tuna. as a functinn of X belween I and 2. lpper curve is for assumed sojourn time of 2 mo, lower curve for 6 mo 4.6 The population in the community and the ecosystem (from Rolhschild 1966). 4.61 Physical features of the biotope cient Z constant at 0.8 and allowed the natural mortality of the community coefficient M to vary from 0.2 to 0.7. Maximum sustainable yield was estimated as 225,000 t with M equal to 0.3 (Table Skipjack tuna inhabit the epipelagic zone of the worlcfs 18). If Rothschild's (1966) estimate of maximum length of major oceans and apparently only make forages into deeper skipjack tuna is conservative and if the escapement stock zones. As such, they generally live in the upper mixed layer from the eastern Pacific fishery is only a segment of the total where temperature and salinity variations are small and fish available in the central Pacific, both of which are likely, where oxygen is at or near saturation. Latitudinal and longi- then both Rothschild and Silliman underestimated the poten- tudinal variations in temperature and depth of the mixed tial yield from the central Pacific. While the results from layer determine to a great extent the distribution of the several both these authors suggest that yield could be increased by races of skipjack tuna. The greatest concentrations of fishery harvesting the escapement stock from the coastal fishery, vulnerable skipjack tuna are limited to the temperature range Joseph and Calkins (1969) observed that yield per recruit 17"-28"C. The major water masses and their associated cur- could be increased by harvesting fish younger than were then rents also influence the distribution of the species, not only available to the fleet in the eastern tropical Pacific. through drift of the larvae and possibly the adults as well, but also through the availability of food associated with current boundaries and areas of upwelling. Except for these latter areas of higher productivity, the epipelagic zone is Table IX.--Ealimale~ of sustainable yield for the ea\tern-central characterized by low productivity. Pacific stock of skipjack tuna at 11of0.03 and al selected \aluc5of F(from Silliman 1966).

~~ ~ Effort 4.62 Species composition of the community 1,ooO hoat- Akerage days from The most important or obvious members of the community sustainable yield = F (1.wOt) 4 Tonc/boar-day are the permanent members of the nekton that feed and re- produce in the epipelagic zone. These include some sharks, 0.5 180 33 5.5 glaucus, maxi- 0.6 200 40 5.0 Lamna nasus, L. ditropis, Isurus Cetorhinus 0.8 220 53 4.2 mus, Prionace glauca, Pterolamiops longitnanrts, and others: 0.9 220 60 3.: many flying fishes, Exocoetus volirans, E. obtusirostris, E. I .O 225 67 3.4 monocirrhus, Hirundichthys speculiger, H. ronde!etii, H. 1.1 215 73 2.9 albimaculatus, Prognichthys gibbifrons, P. sealei, and others;

t4 = 0.01501 from F=0.5 and,/ = 33.3. for 1952-56. all the Scomberesocidae; several Scombridae, Casterochisma melampus, Allothunnus fallai, Thunnus alalunpa, T. albacares, 7.obesus; marlins, Tetraplurus audax, T. albidus, T.

[Japan.] Fisheries Agency (footnote 20) estimated potential angustirostris, Makaira ~i~qricans;swordfish ~ Xiphias gladius; yields for various oceans and subareas based on the abun- the dolphin, Coryphaena eyuiselis; opah, Larnpris regius; all dance of skipjack tuna larvae and juveniles and their occur- the Bramidae; many Nomeidae and Centrolophidae, Nomeus rence in the stomachs of predators. These estimates are: albula; species of genera Psenes, Cubiceps, Schedophiliis, Centrolophus, and Ichichthys; Molidae; and some others. A Japanese coastal area Increase of 200,000-400,ooO t second group of nekton includes those fish that spend their Entire Pacific Ocean lncrease to 800,000-1,~.ooOt adult stages in the epipelagic zone but whose egg and juvenile Indian Ocean 200,000-300,OOO t. stages are found elsewhere. These include the whale shark,

73 Rhincodon typus; the dolphin; bluefin tuna, Thunnus thyn- the Pacific and off both coasts of Africa, and by the United nus; some halfbeaks (Family Hemiramphidae) of the genus States, Ecuadorian, Maldivian, Korean, and Indonesian Euleptorhamphus; needlefishes (Family Belonidae) of the fishermen, to namc only the most obvious instances. Gener- genera Platybelone and Ablennes; and flyingfishes (Exocoe- ally, the gear consists of a bamboo pole varying from 3 to 6 tidae) of the genera Cypselurus and Cheilopogon. A third m although fiberglass is sometimes used now. The length of group includes the eggs, larvae, and juvenile stages of fishes the line varies depending on the distance of the fishing loca- that inhabit the neritic (pelagic and littoral zones) and the tion from the sea surface. Generally, a barbless, artificial lure abyssal zones. Among these are some Atherinidae, Scombridae, is used which is designed to imitate either a baitfish or a Carangidae, Gonorhynchidae, Synodontidae, Holocentridae, squid. The design of the bait boats varies considerably de- Stichaeidae, Mullidae, Scorpaenidae, Hexagrammidae, Cot- pending on the nationality and much effort has been ex- tidae (Hcmilepidotinae), Nototheniidae, Chaenichthyidae, pended in recent years, particularly by the Japanese, in Acanthuridae, Bothidae, Cynoglossidae, Pleuronectidae, modernizing the boats. Cleaver and Shimada (1950) and Gonostomidae (Cyclothone, Vinciguerria), anglerfishes Yoshida (1966) provided descriptions of the boats that were (Ceratioidei), and apparently some lanternfishes (Myctophi- in use a number of years ago in Japan and the United States. dae). Also present are some mesopelagic species that migrate Descriptions of 200 and 250 gross tons (GT) Japanese bait into the epipelagic zone during the night. These include the boats appear in Kearney and Hallier (1980b). More modern sharks, Euprotomicrus bispinatus and probably Isistius bait boats are equipped with baitwells with recirculating or brasiliensis; the snake mackerel, Gempylus serpens; subsur- even refrigerated water, automatic fishing poles, and fish face lanternfishes of the genera Myctophurn, Symbolophorus, finders. Centrobranchus, Gonichthys, Tarletonbeania, Hygophum, Because the Japanese style bait boat carries more fisher- Loweina; a few members of Families Melanostomiatidae men than other types (over 35 compared with as few as 6) (Photonectes, Echiostoma); and Astronesthidae (Astro- and, thus, experiences problems in obtaining enough qualified nestha); and others (Parin 1968). fishermen, the Japanese have been experimenting with automatic gear, such as a continuous circulating mainline with 4.63 Interrelations of the population of the hooks on short droppers (Inoue 1966; Igeta et al. 1978) and species in the community and ecosystem mechanical pole machines (Iwjashita et al. 1967; Suzuki Tekkojo Kabushiki Kaisha"). The automatic pole machines Waldron (1963) has adequately described the position of are now used on 80% of the Japanese bait boats larger than the skipjack tuna as follows: "Within the marine community 200 GT, but not on the narrow but highly productive bow the skipjack may be listed both as prey and predator, although area (Maruyama 1980). These machines have also been tried as a large adult it may be only one step removed from a in Australia, as well as in Hawaii and the west coast of the climax predator. In its larval and juvenile stages it serves as United States. food for larger fish, including adult skipjack. As an adult it As the name implies, bait boat fishing includes the chum- serves as food for larger tunas and spearfishes, and at the ming of live bait to attract and hold tuna schools close to the same time preys upon small to moderate-sized pelagic crus- vessel. Thus, bait boat fishing is essentially a double fishery, taceans, molluscs, and fish. Skipjack compete for food with where suitable baitfish resources must be found, captured, tunas and other fish of similar size and habits. They might hardened for future use, and transported to the fishing even be considered as competing with sea birds, for the food grounds in baitwells of the fishing boats. In addition to these organisms are often apparently driven to the surface of the technical aspects of baitfishing, the ability of baitfish stocks water, where they are preyed upon by both skipjack and to withstand harvesting pressure has been investigated by various sea birds." Bayliff (1967) for the eastern tropical Pacific, Wetherall (1977) for Hawaii, and Dalzell and Wankowski (1980) for 4.64 Hypothetical habitat of skipjack tuna Papua New Guinea. Because of the limited availability of natural baitfish supplies in small island areas, some interest Metabolic and physiological properties of skipjack tuna in has been shown in raising or culturing baitfish (Baldwin relation to the environment have been discussed in Section 1975, 1977; Gopalakrishnan 1979). A workshop on baitfish 3.63. has covered many of these subjects (Shomura 1977). Advantages of bait boat fishing are the relatively small 5 EXPLOITATION capital investment involved, ability to harvest small schools of fish, ability to operate out of small ports with a minimum 5.1 Fishing equipment of technical support, and ability to utilize unskilled labor, The major disadvantage is that it is a double fishery. Other The two most productive means of catching skipjack tuna disadvantages include the size of the fishing crew, depen- on a wjorldwide basis have been pole-and-line and purse dence on the biting behavior of the tuna schools, and depen- seine fishing. Other methods include gill netting, trolling, dence on good weather conditions to find and fish tuna trap fishing, harpooning, and beach seining. Recently the im- schools. portance of flotsam or man-made aggregation devices has increased greatly. Likewise, aerial spotting has become com- "Suruki Tekkojo Kabushiki Kaisha. 1970. Report on the development of an mon in some fisheries, and the application of remote sensing automatic Tkipjack fishing machine. From a mimeographed report by the Suruki is being investigated. Tekkojo Kabushiki Kaisha (Suzuki Ironworks Co.. Ltd.). Ishinomaki, Miyagi, The pole-and-line, bait boat, or live bait fishing method is Japan, Sept. 30, 1970. [Engl transl. by T. Otsu. 1970. Southwest Fnh. Cent. Honolulu Lab., Natl. Mar. Fish. Sew, NOAA. P.0 Box 3830, Honolulu. HI or has been employed by Japanese fishermen throughout 968 12.1

74 Purse seine fishing for tunas began in the eastern tropical dent on this association. Most purte 5eine sets take place Pacific in the 1950’s when many of the bait boat clippers either at dusk or dawn. Also, anchored rafts are now em- began converting to purse seine gear (McNeely 1961). The ployed on a commercial scale in the Philippines (Aprieto development of the Puretic power block. which lifts the net 1980, 1981; Matsumoto footnote 12) and in Hawaii (Matsu- with its float line and purse rings, thus enabling the net to be mot0 et al. 1981), and they are being deployed experimentally stacked on the deck for the next set, made this possible. throughout the South Pacific, e.g., in American Samoa, Technical aspects of the purse seine are described in McNeely West Samoa, northern Marianas, Guam, Palau Ihnds, (1961) and Green et al. (1971). Newer developments include Cook Island, and Tonga (Matsumoto footnote 12): in the lighter fabrication of the net to allow for greater length and eastern Pacific (Guillen and Bratten”); and in the Indian depth and other modifications to increase the survival of Ocean, for example, in the Maldives: and probably in other porpoise (Coe and Vergne 1977). The purse seine net is basi- areas as well. In the Philippines, small scouting boats or cally a long net that is set around a school. The ends are canoes are used to determine whether tuna have been at- brought together and the purse line is drawn until the bottom tracted to the rafts. If so, a light skiff ties up to the raft (or of the net is pursed or closed. While the first U.S. purse payao) to concentrate the fish for seining. The lights used seiners in the eastern tropical Pacific were as small as 130 GT, vary from gasoline lanterns to powerful electrical lights, they now are much larger, commonly around 1,ooO GT and either submerged or above the surface, depending on the (ize as large as 2,000 GT. Modern purse seiners carry a full com- of the operation. When it is determined that the fish are plement of electronic gear including fish finders and satellite sufficiently concentrated around the light boat and the raft, navigation equipment. Similar vessels are now being built in the light boat is allowed to slowly drift away until there is several American countries (e.g., United States, Mexico, and room to set the purse seine around the light boat without Peru), Spain, France, Poland, and Japan. Fishing operations becoming entangled in the raft. A given purse seiner, which have expanded from the eastern tropical Pacific to the west- can be anything from a converted tuna longliner to a 2,000 ern Pacific including off Japan, Trust Territory of the Pacific GT purse seiner, will use 15 or more rafts, setting up to 3 Islands, Philippines, Papua New, Guinea, and New Zealand. times a night and averaging a little over I set per night. Tuna The more successful boats in the open ocean or small island are caught on over 90% of the sets. areas of the western Pacific tend to be smaller, averaging Advantages of purse seine fishing are independence from around 500 GT, than in the eastern tropical Pacific. A sub- baitfish resources, lower requirements for shipboard man- stantial purse seine fishery takes place in the eastern tropical power, and highly efficient catch rate per man per vessel. Atlantic, and the principal countries in the fishery are France, Disadvantages include the size of the capital investment, in- Spain, United States, Japan, and U.S.S.R. Exploratory fish- ability to fish in rough waters, inability (currently) to fish ing has taken place in the Indian Ocean. during the day in waters with a deep thermocline, the re- Both bait boats and purse seine operations have rradition- quirement for sophisticated unloading and support facilities, ally depended on the spotting of free-swimming, bird-associ- and large fuel consumption except when using anchored rafts. ated, or flotsam-associated tuna schools from the bridge or Gill nets are the primary gear used to catch tuna in Sri Crow’s nest of the fishing boats. Many large purse seine boats Lanka and Somalia. The gear used in Sri Lanka is described now carry helicopters to search for fish schools, and land- in de Bruin (1970) and Pajot (1978). Skipjack tuna are quite based airplanes are commonly used in some fisheries, e.g., in commonly caught in traps and drive-in nets in the Philippines New Zealand (Bell 1976; Habib”). Attempts are now’ under- ([Philippines.] Bureau of Fisheries and Aquatic Resources way to use remote sensing of sea surface temperature gradi- 1980). ents from satellites or aircraft as an indication of likely fishing areas (Evans 1977: Stevenson and Miller 1977; Eggleston 5.2 Fishing areas and Paul 1978; Noel 1978; Petit”,”; Petit et al. ”). While the association of skipjack tuna schools with tlot- The major fisheries have developed adjacent to continents sam (including whales and large sharks) has been known for or large islands where upwelling or other oceanographic fea- some time (Inoue et a!. 1963, 196% b; Greenblatt 1979) and tures lead to a concentration of skipjack tuna near the sur- exploited by both bait boats and purse seiners, the new purse face (Fig. IO). The shaded areas around various islands have seine fishery in the equatorial western Pacific is very depen- been exaggerated while subsistence fisheries in the South Pacific Ocean and the small but developing fishery off Aus- tralia have not been indicated. Generally, the surface fisheries %. Habib, Forum Fnheries Agenc). P.O. Box 627. Honiara. Solomon Island\, extend from the neritic-pelagic environment into the adjacent, pers. commun. 26 June 1981. oceanic-pelagic environment. Reports of skipjack tuna being “Petit, M 1979. Compte-rendu \uccinct des trdvaux accomplis lor, de la pre- miere, periode de l’operation radiometrie arrienene et prospection thoniere (06 taken in estuarine environments (river plumes primarily) have fevrier 1979-11 avril 1979). Ref. Article 3 - paragraphe 3-2 du contract No. 1 been received from the southwestern Pacific Ocean. Open DOM-TOM-ORSTOM.O.R.S.T.O.M.,CentiedeNoumea,[email protected] T.O.M., oceanic surface catches are generally associated with upwell- B. P. AS, Noumea-Cedex, Neu Caledonia. ing zones between opposing currents, such as along the equa- “Petit. M. 1979. Compte-rendu des travau~accomplis lors de la deuxieme periode de l’operation radiometrie aerienne et prospection thoniere (16 juin 1979- torial currents, the Kuroshio, and the North Pacific subtropi- 14 juillet 1979). Ref. Article 3-2 du contract No. 1. DObl-TOM-ORSTOM cal countercurrent. O.R.S.T.O.M..CentredeNoumea,nopag.O.R.S.T.O.M..B. P. A5, Noumea- Cedex. New Caledonia. ”Petit. M., J. Muyard. and F. Marsac. 1980. Compte-rendu des tra\auh accomplis lors de la troisierne periode de l’operation radiometrie aerienne et “Guillen. R.. and D. A. Braiten. 1981 Anchored raft experiment 10 aggregate prospection thoniere (25 septemhre 1979-11 fehvier 1980). Ref. Article 3-2 du tunar in the eastern Pacific Ocean. Inter-Am. Trop. Tuna Comm , Internal Rep. contract No. I. DOM-TOM-ORSTOM. O.R.S.T.O.M.. Centre de Nouniea, 17 14, 10 p. Inter-American Tropical Tuna Commission, c/o Scripps lnititutinn of p. O.R.S.T.O.M., B. P. AS, Noumea-Cedex, New Caledonia. Oceanography, La Jolla, CA 92037.

75 5.3 tisliing \eason\ southern water fishery, the number of sets by single-boat seiners increased from 60 in 1968 to 428 in 1974. Gerierally. fisheries exi\ting in the equatorial, tropical area5 do not sliow much 5easonal variation except possibly a tlight 5.42 Selectivity increase in catches during both the northern and southern summers. Fisheries situated more poleward in the subtropics Pole-and-line gear (as used on bait boats) tends to take or bordering on the temperate zone \how more seasonality smaller and fewer Size classes of skipjack tuna than does with tlie peak catctie5 occurring in the summer months for purse seine gear. The selectivity of pole-and-line gear can be the respective hemisphere\. modified by changing hook size, weight of the pole, or bait Specific details on seasonality in various fi\heries for the size, but most significantly by merely selecting for size of fish w'estern Pacific and the Indian Oceans may be found in in a school. Likewise, the size selectivity of purse seine gear Uctiida (1975), for Neu Zealand in Habib (1976, 1978) and can be varied by selecting schools and by adjusting mesh size Habib et al. (1980a, b. c), for Papua Neu Guinea in Wan- to retain fish only of the desired size or larger. Longline gear, kowski (1980), for the eastern tropical Atlantic Ocean in which catches skipjack tuna only incidentally, is known to Sakagawa and Murphy (1976). and for French Polynesia and take mostly large individuals as discussed in Sectinn 4.13. the eastern tropical Pacific in Forsbergli (1980). 5.43 Catches 5.4 Fishing operations and re\ul[\ (I) Total annual catches 5.41 Ettort and intensitv From 1961 through 1979, the nominal catches of skipjack Various means of measuring fishing effort directed at skip- tuna from all oceans have more than tripled, reaching 698.5 t jack tuna were discussed in Section 4.2. Changes in the effi- in 1979 (Table 19). While the catch of all tunas has increased ciency of the gear were discussed in Section 5. I. varying amounts over this period, that for skipjack tuna has In tlie eastern tropical Pacific. reported effort is 22 to 26% increased more rapidly than the other principal market species less than the total effort; however, there is no apparent trend of tunas (yellowfin tuna, albacore, bigeye tuna, and bluefin in the rate of reporting (Forsbergh 1980). The amount of tuna). More specifically, the proportion of skipjack tuna fishing effort increased from I934 to the 1950's. remained catches has increased steadily from 24.5% in 1961 to around fairly constant during the 1960'5, and then increased again 40% in the late 1970's (Fig. 76). Catches of skipjack tuna through most of the 1970's. first surpassed those of the traditionally dominant yellowfin In Hawaii, estimates of relative fi5liing intensity (Fig. 70) tuna in 1965, fell below in 1968 and 1969, and then remained fluctuated substantially Irom year to year and were at a above after 1970. Clearly the Pacific Ocean is the most im- somewhat higher level during the 1948-56 period than in sub- portant area for skipjack tuna fishing with catches there sequent years (Ucliida 1976). accounting for 80 to 90% of the world catch. Also, the fish- In the Papua New Guinea bait boat fishery. the amount of eries of the western Pacific alone accounted for 67.1% of the fishing effort has increased from some 500 d iii 1970 to 8,000- world skipjack tuna catch in 1979 (Fig. 77). The developing 9.000 d by 1979 (Wankowki 1980). In the New Zealand fisheries in the Atlantic and the Indian Oceans accounted for purse seine fishery, about 400 d of effort have been expended 12.5 and 4.7% of the world skipjack tuna catch in 1979. in each fishing season starting in 1976-77 (Habib 1976, 1978; Habib et al. 1980a. b). (2) Total annual yields from different For the Japanese bait boat fishery, there has been a slight fishing grounds increase in the number of trips from around 7,000 in 1970 to 10,000 in 1976 by all size classes of boals in the coastal fish- A more detailed breakdown of catches is provided in Table ery (norrti of lat. 15"N). while for boats between 50 and 100 20 for selected countries in the most productive skipjack gross metric tons (GMT). the number of trips increased from tuna fishing areas. In the eastern central Atlantic Ocean, about 1,400 to 8,000 (Bour and Galenon 1979). For the Spain and France have traditionally been the major producers southern water fishery, Kasahara (1977) showed that the but Japan, and more recently Korea, have become significant total number of fishing days for all size classes of bait boats participants in the fishery. In the Indian Ocean, the produc- increased from nearly 9,000 in 1970 to over 21.000 in 1975, tion of the two major fishing countries, Maldives and Sri while the increase for 250 GMT boats was from around Lanka, has declined. In the northwestern Pacific Ocean, 2,600 to nearly 20,000 d during tlie same period. Honma and Japan is essentially the only producer, and their fishery reached Suzuki (1978). in their preliminary description of the Japanese a maximum of some 107,000 t in 1973. In the central western purse seine fishery, showed that the number of single-boat Pacific Ocean, the Japanese distant water fishery is the major purse seiners increased from 16 in 1969 to 52 in 1974, whereas producer and has shown a large increase from around 35,000 the number of double-boat purse seiners declined from 55 to t in 1966 to 198,000 t in 1978. Production by the Philippines, I2 over the same period. The number of trips for the single- Indonesia, Papua New Guinea, and the Solomons has also boat purse seiners varied from some 390 to 940 and for the shown marked increases in the 1970's. In the eastern central double-boat purse seiners from 1.500 to about 340 over the Pacific Ocean, the United States has been the leading fishing same period. In the period 1971-74 the number of sets for nation, producing up to around 100,OOO t. Ecuador has been single-boat seiners in the coastal fishery tluctuared between the second largest producer, with a maximum of around 1.000 and 2,000 sets, whereas for double-boat seiners the 17,000 I. Mexico has recently been adding significantly to its number of sets declined from around 1.300 to 400. In the purse seiner carrying capacity and should be expected to con-

16 Table 19.-Annual landings (in 1,OOO 1) of skipjack tuna from the major oceans by FA0 statistical areas (FA0 1968, 1971, 3971, 1976, 1977, 1978, 1979. 1980). Year Area 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 AtlanticOcean' 0.3 0.3 2. 14.3 17.9 25.7 22.7 36.2 32.0 51.6 67.9 73.1 71.8 119.0 67.8 73.5 97.6 95.6 87.6 Northwest 21 0.5 0.0 0.0 0.0 1.8 0.4 - 0.4 0.0 0.1 - 0.0 0.2 0.0 0.4 0.3 Northeast 27 ______2.6 Western 1.1 1.0 1.1 1.2 1.8 1.3 1.6 1.7 1.6 2.1 4.1 2.9 4.7 6.0 1.9 2.1 central 31 No breakdown by Eastern area 10.8 16.4 24.0 20.0 31.8 29.9 49.5 61.9 70.4 67.0 101.1 63.1 66.5 86.9 88.3 77.5 central 34 Southwest 41 0.4 0.5 0.6 1.5 0.8 0.4 0.4 0.8 1.0 0.6 0.5 1.1 0.6 0.6 1.4 1.4 Southeast 47 1.5 0.0 0.0 0.0 0.0 0.0 0.1 0.1 0.1 2.0 13.3 0.7 1.5 4.1 3.6 3.7 lndianOcean - - - 0 13.2 16.0 18.1 16.6 18.7 29.7 31.4 20.1 24.2 41.3 36.2 38.4 30.3 30.4 32.6 Western 51 [No bre;&:aown by ] 13.2 16.0 18.1 16.5 18.6 27.4 29.0 16.3 20.1 36.7 31.7 32.4 26.2 25.3 27.0 Eastern 57 0.0 0.0 0.0 0.1 0.1 2.3 2.4 3.8 4.1 4.6 4.5 6.0 4.1 5.1 5.6 PacificOcean 219.0 252.4 200.8 252.4 235.9 308.6 335.9 273.6 269.6 304.0 328.2 330.1 434.3 510.0 436.3 554.3 504.8 665.8 578.3 Northwest 61 187.2 145.8 208.4 176.0 147.6 163.1 166.2 119.8 157.1 202.6 127.2 135.5 151.1 130.0 157.3 143.0 Northeast 67 - 0.2 - 0.1 - 0.1 0.2 0.3 0.0 0.1 0.5 0.1 6.7 0.4 5.8 0.5 - - 35.7 35.2 42.5 41.5 70.0 114.8 119.9 173.0 303.0 205.4 252.9 272.5 359.7 316.9 w:?:::a171 w:?:::a171 Nobre;;;yby Eastern [ ] 53.4 76.3 54.2 106.9 74.5 51.5 58.9 87.4 50.1 52.0 75.3 84.5 134.2 91.4 130.0 107.7 central 77 Southwest 81 1.5 0.0 0.0 0.2 0.1 0.0 0.0 0.2 0.5 1.8 1.7 6.4 6.3 64 9.8 8.5 Southeast 87 10.3 13.6 10.3 17.5 8.9 13.4 8.7 5.7 2.5 4.8 2.3 4.4 3.1 4.1 3.2 1.7 Total 219.3 252.7 203.0 266.7 267.0 350.3 376.7 326.4 320.3 385.3 427.3 423.3 530.3 670.3 340.3 662.2 632.7 791.8 698.5

'Landings occur in the Mediterranean but in very small amounts.

Figure 76.-Annual nominal catches of the principal market species of tunas from all oceans (FA0 1968. 1973, 1975. 1979, 1980) and catches of skipjack tuna as a percent of the total.

PKIFIC OCEAN ITOTALI

ATLANTIC OCEAN

Figure 77.-Percent of skipjack tuna catches by ocean areas. 89% ' iesa r&o ' 8972 I&+ ' I& #&e '

1977. A retie\\ on the use 01 he haittiche\ to capture ikipjack tuna. BI OCH, M. F., and J. G. SCHNEIDER. tiotcu~ontrsprlonttr.111 the tropical Pacific Ocean uith empha\i\ on their 1x01 . Skstema ictith)ologiac icoriibur L\ illii\traturii l3crolini. 584 p. hehakior. sur\i\al. and a\ailahtlit). In R. 5 Shomura (editor). Collection BONNATERRE. 1. P. 01 tuna haitfi\h paper\. p. 8-35. ti.S. Dep. Commer.. NOAA Tech. 1788. Tableau encyclopidlque et m\ethodique de? trot\ &ne5 de la naturc. Rep. NMFS Circ. 408. lchthyologieh. 215 p. BARKLEY. R.A. BOUR, W. 1969. Salinity nidmnia arid the 5hipjach tima, ~unu~~~~~ti~c~~~Iuirtt~Bull 1976. Croi\wicc du liitao (hurwwinuy ~1~4u~~ticlF\t-Atlantiqur trop~'A. Jpn. Soc. ti\h. Oceanoer.. Spec. No. (Prof Uda'\ Coniniemorau\e Note prhliminaire. 1111 Fr.. Fnpl. ahI.. Jr BARNARD, K. H. 1929. Field booh of marine liilie\ 01 the Atlantic coiiit 1rom I ahrxhi to 1925. A nionoeraphnf thc marine li\hei 01 Sonth Alrica. Ann. S. Aft. Texas. G P. Putnam'\ Son,. N L . 332 p. hlus. 21, 1065 p BREUtK. <'. >I.. Jr ,and t HAI PtKN. BARNHART. P. S. 1946. Innate and acquired beha\ior .illect~iigthe dpgre~ldiioii (,I l~\hc\. 1936. Marine h\hec (11 wuthern California Uni,. Calif he\\, Brrlele!, Ph)wd Zool. 19:154-190. 209 p. BRFTT. J. R. BARRETT. I.,and F. J. HESTER. 1973. Energ\ e\prnditure 01 rockc\c ~~lmon,Oncortrwz~/itt\ mvho. dur~ 196.1. Bod? teinpcrature of~ello\\linand shipjack tuiiar ti1 relation to \ea ing rustatnrd pertormanee. .I ti\h Re\. Board Can 10~17YY-lXOY. wrface temperature. Nature (L.und.)203:Y6-97 BR1GGS.J C. BARRETr. I.,and H. TSUYUKI. 1YfL. Fiihss of uorlduidc (circumtropicall iliitributioti. ( opela IYhO. 1967 Serum tran\terrtn polymorphism m \om? \conihroid li\he\. Copsia 171-180 1967.551-?57 BRI1.L. R. \\ BATTS. B. S. 1979. The elfect of body weon the \taiidard nietaholtc rate 01 \hipinch 1972a. Age and grouth ot the skiplack tuna. har~uiiunusp~Iui~ir\(Linnae- tuna, Kotruu~ontr~pria,,ir~.ti4i. Bull.. L S 77:494-4YX. its), In North Carolina water\. Che\aprake Sci. 13 237-24. BRlt I , R \\.,and A F DIZON. 1972h. Food habits of the \kipjack tuna. harwwonm [wIutnt5, in North 19iY. Eflect of temperature oil ~wtonictuitcli 01 uliile iiiii\cle .ind pre- Carolina uaters. Cherapeahe Sci. 13: 193-200. dicted maximum \uimmmg \peed\ of \kiplael\ tuna. hatwunnr,\ /xlo,ti,,. 1972~. Sexual maturity, fecundity. and \e\ ratio\ ot tlie \kiplael tuna. Enbiron. BIOI.Fishes 4:IYY~ZO5. Xursuwonuspelomrc (Linnaeu\l. in North Carolina uater\. Tram. Am. BKOADHE..\D, G. C., and I. BARRtrT. Fish. Soc. 101:626-637. 196.1. Some factorr altcctin$ tlie dirtrihution and app'iretit ahundnncc 01 BA'r Llft, M'. H )ellnutiti and skipjack lund 111 lh tern Pacilic Ocean (In Fngl and 1967 GroHth. mortalit). and e\ploitatm~01 the E-ngraulldae. nith \pecldl Span ] Inter-Am Trop. TunaConim. Bull. X 411)-473 reference to the anchineta, Crlmi.rouir\- vt~~rtceru5,arid tlic colorado. BROAI)H[.4D. Ci. ('., and< I OKANGl Anrhoo nmo. In the eastern Pacific Ocean. [In Engl. and Span I Inter- 1960. Specie\ and \lie relatioiirhtp wtliiii \cIi(iiil\ <)I )ello\+liti and \hi[>- Am. Trop. Tuna Comm Bull. 12.367-432, tach tuna, a\ ~ndiiatedb) idtilie\ 111 the ea\terii t~op~ciilI',ILI~IC 0'c.i~. BELL,<; R. [In Fngl. and Span I Inter~Anilrop. runa Conitii. Hull 1.44Y-4Y? 1976 Aerial \potting tor pelagic lidie\, [Ne% Lealand I \lini\t. Agric BROCK, V. E. Fish.. Fish. Re\ UI\ , Occa\. Puhl II:17-JX 194') A preltniinar\ report on furur/ii~niiu~wlx in Hau'iiiaii natcv .ind a BELLOC. G. kc! to the tuna, arid titna-like lirhe\ ot Hanail. Pac. SLY. 3~271-277 1955. Le\ thons de la hlc'diterrane'e. Deii\i~mcnote: thonine ut honite. 1954. Some a\pect\ 01 thc hiolog) of the .iku. hormno,>i,~/Wlwii,\, ln the Proc. Tech Pap. Gen Fish. Counc. >lterr.,FA0 3(?2):471-JXh. Hauaiiati I\lands. Pac. 41.1. X:94-I(W. BERG, l~.S. 1959. The tuna remurce in relation to nccanoyaphic li.dlitie*. Itr Tuna 1940. Classification of tidies. hoth rccrni and lo,\il [In Ru\\. and tngl I indurtr) conference paper,. \lay IYSY. p. 1-1 I. I1.S. Fi\h \\,Id1 Sen , J. W. Eduardr Co., Ann Arbor. Mch.. p. 87-517. Ctrc. 65 BEVERTON, R. J. H., and 5 I HO1.T. BROCK, \. E.,and R. H. KICCEhBURGH. I.

19 'Tunicata. Vertebrata. Koch. Stuitgart. 854 p. Sci. Rep. Fish. 183. 14p. CASSIE. R M. CUVIER, G. 1954. Some use\ of probability paper in the analksi5 of 5ize irequenc) 1829. Le r&ne animal. Nouvelle ed. tom. II. Deter\ille. Paris. 406 p. diriribution\ Aust. J. hlar. Freshuater Re,. 5:513-522. CUVIER, G.. and A. VALENCIENNES CAYRE, P 1831. Histoire naturelle des poisons, Vol. 8. F. G. Levrault. Paris, 375 p, 1979. Determination de I'age de listao, hurctrnoniir pelunrir. dcbarquer a DAI.ZELL. P. J.. and J. W. J WANKOWSKI. Dakar; Note prCliminaire. [In Fr., Engl. sumnt I Collect Vn Sci 1980. The biology, population dynamics, and fisheries dynamics of ex- Pap , In1 Comm Consen Ail. Tuna, (SCRS-1978)8.196-200. ploited stocks of three bait fish species. Srolephorus hererolobus. S. CHAT\\lN, B. XI. devisi. and Sprorellordec srucrlrs. in Yrabel Passage, Neu Ireland Province, 1959 The relatmn\hip5 heiur.cn length and ueight of )ello\\iin tuna Papua Nen Guinea. [Papua Neu Guinea.] Res. Bull. 22, 124p. (.Lrorhunnus,,ru~ro~lrrrrrr)and \kiplack tuna (Kurrunonuc pelutiti5l from DAY. F. the eastern tropical Pacilic Ocean. [In Fngl. and Span I Inter-Am. 1878. The fishes of India; bemg a natural histoi) 01 the fishes knoun to Trop. Tuna Conim. Bull. 3:307-352. inhabit the seas and frerh uaterr of India. Burma, and Ceklon. Vol. I. CH6Y.C.-J..and R -T. YANCi. 778 p. Dauson and Sons, Lond. (Lithograph reproduction 1958 ) 1973. Parasite5 of yello\\tin tuna In the uater\ wuthuesi ofi Taiuan de BEAUFORT, L. F., and u'. M.CHAPIIAN. Acta Occanogr. Taiuan 3: 1x1-198. 1951. The fishes of the Indo-Australian Archipelago. IX. Percomorphi CHEN. S.-C .,and T.-H TAN. (concluded), Blennoidea. E. J. Brill. Leiden, 484p. 1973. A prelimman report on occurrence of luna lanae In %aten adlacent de BRUIN, G. H. P. to Taiaaii and South China Sea. Rep. Inrt. Fish. Bin1 Zlini\t Fcon 1970. Drift-net fishing in Ceylon uaters. Bull. Fish. Res. Sin. Ceylon All. Nail. Taiuan Unib. 3:158-171. 21: 17-31. CHI. K.-S.,and R -T. YANG de BUEN. F 1973. Age and groutii of skipjack tuna in the udters drnund the xnthern 192h. Caiilogo tcttol~gicodel h.lediterr&eo EspaTol y Marruecos. Result. part olTaiuan. Acta Oceanopr. Taiwan. 3:199-221 Camp. Acuer;. Int., Madrid 2, p. 150. 159, 167. CHIKUNI. S 1930. lctiologia espahla. I. Scomhnformes y Thunniformes. Bol. 1978. Part I. Report on fishing tor tuna in Philippine !\aten dnd biological Oceanogr. Pesca, Madrid 15(162):34-53. features 01 the re\ource$. In FAO. 1978. Test tirhinp for tuna and small 1935. Fauna mol&ica Cathogo de Ins peces ibirtcos, de la planicie pelagic species Reports on tlie operation of FA0 chartered purw \?mer\ continental, aguas dukes. pel&icoc y de Ins abismos pr6ximos. Segunda in Philippine and South China Sea \+aten, 1974-1977. FAO. SCSIDEV, parte Noias y reshenes. Inst. Esp. Oceanogr., Ser. 2,89:91-149. 78/18,44p. 1958. Peces del suborden Scombroidei en aguas de Chile. Rev. Biol. Mar., CHOO, U. 1. Valparaiso 7:3-38. [Engl. trand. In files of Southuest Fish. Cent., Nail. 1977. Report on the Korean baitboat Iishen ~n tlie Atlantic Ocean. 1975. hlar. Fish. Ser!., NOAA. Honolulu, H196812.I [In Engl.. Fi and Span. sunini I ('ollect \ol Sci. Pap.. Int. Comm. de CAMPOS ROSADO. J. hl ConserL. Ail. Tunas (SCRS-IY7h)6:h9-71 1971. Long-term changer in abundance of )ellnufin and skipjack off the CHUR. V N., \' B. GRUDININ, and V. 1 ZHARO\. coast of Angola. J. Cons. Cons. Int Explor. Mer 34:65-75. 1980. Data on length-age cnmpo\ition and gonad maturity stager 01 \kip- de MIRANDA RIBEIRO. A. jack (Korruronus pelumo) of the eastern tropical Atlantic. Collect. 1915. Fauna Bradiense. Peires. Pari V. Ph)soclisti. Arch. Mus. Nac.. Vol. Sci. Pap., In[. Comm. Con\er\. At1 Tuna, (SCRS-1979) 9:245-254 Rio de Janeiro 17. 600 p. [Page, not continuously numbered.] C1.ARK.F N. DER.4NIYAGAL.A. P. E. P. 1934. hlaturit) 111 the California sardine (Surdinu \h Oame. Firh Bull. 5:79-1 I I. 42.4') p. DIZON, A. E. CLEAVkR. t.C., and B. M. SHIMAD.2 1977. El iect of dirsolbed oxygen concentration and salinity on summmg 1950. Japanese \kipjack ~hurruwonuspeloi~iicl tishing method\. Commer. speed of tun species of tunas. Fish. Bull., U.S. 75:&(9-653 Fish Re\. l2(ll):l-27. DIZON. A. E., and R. u'. BRILL. CLEAIENS. W. A,. and G V. MI1 BY 1979. Thermoregulation in tunas. Am. Zool. 19:249-265. 1946. Fnhe\ of the Pacific coact 01 Canada. Fish. Re5 Board Can , DIZON. A. E., R. W. BRILL, and H. S. H. YUEN. Bull. 68, 368 p. 1978. Correlations betueen environment. physiology. and activity and the COAN. A. L. effects on thermoregulation in skipjack tuna. In G D. Sharp and A. E. 1976. lxngrh and age conipo\ition 01 \kipjack tuna rrom the 4tlantic Dtzon (editors), The ph)\iological ecolog) of tunas. p. 233-259. Acad. Ocean. 19hR-73. C.ollect. \<>I.Sci. Pap , Int Comm. ConserL. All. Press, N Y. Tunas (SCRS-1975) 5:133-141 DIZON, A. E., T. C. BYLES, and E. D. STEVENS. COE. J. hl..and P. J. VERGNE. 1976. Perception of abrupt temperature decrease by restrained skipjack 1977. Modified tuna purse seine net achietes record Iou porpoise kill rate. tuna. Korsuwonuspeloma. J. Therm. Bml. 1:185-187. Mar. Fi5h Rev. 39(6):1-4. DIZON. A. E.. W. H. NEILL,and J. J. MAGNUSON. COLLETTE, B. B. 1977. Rapid temperature compensation of volitional swimming speeds 1978. Adaptations and systematic, oi the mackerel, and tunas. In G. D. and lethal temperatures in tropical tunas (Scomhrtdae). Environ. Biol. Sharp and A. E. Dizon (editors). The physiological ecolog) o1 tunas. Fishes 2:83-92. p. 7-39. Acad. Pres. N Y. DIZON, A E., E. D. STEVENS, &. H. NEILL, and J. J. MAGNUSON. COLLETTE, B. B., and L N. CHAO. 1974. Sensiririry of restrained sk!pjack tuna (Kursuwonuspelumis)to ahrup! 1975. Syitematics and morphology of the bonitos (Surdu) and their rela- increases in temperature. Comp. Biochem. Physiol. 49A-291-299. tives (Scombridae. Sardim). ti*h. Bull , b.S 73:516-625. DONGUY, J. R , H'. BOUR. P. GALENON. and J. A. GUERERDRAT. COLLETTE. B. B.. and R. H. GIBBS. Jr. 1978. Lec conditions oceanographiquei et la ppche de la honite (Kursuwonus 1963. A preliniinar) rebieu of the fiche, of the iamll) Scomhridae. FA0 pelumn)dans le Pacifique occidental. Cah. O.R.S.T.O.M., S&. Ocekn- Fish. Rep 6(ll:23-32. ogr. 16(3-4):309-3 I7 CONAND. F.. and A H ARGUE DRAGOVICH. A. 1980. Prelimmar) ob\srration\ nn ju~enile\kipiack irom the \tomacha of 1970 The food of skipjack and )ellnufin tunas in the Ailantic Ocean. adult skipjack caught by pole-and-line sear South Pau. Comm.. Reg. Fish. Bull , U.S. 68:445-460. Tech Meet. tiih. 12, 21 p. 1971. Food of skipjack tuna in the Caribbean Sea and adjacenr oceanic CRESSEY. R., and H. B. CRFSSEY. water\. In Sympovum on In\e\tigations and Recource5 of the Caribbean 1980. Paraiitic copepods oi imackrrel- and tund-like Ii\he\ (Yconihridael Sea and Adjacent Regions. FA0 Fish. Rep. 71.2.27-40. oftheworld. Smithson. Contrib. Zool. 311, l8dp DRESSLAR. F B.. and B. FESLER. CUNNINGH.ALI. J T. 1889 4 rebieu of the mackerels (Scombrinae) of America and Europe. 1910 On the marine f~\he\and ~n\ertehr:ite\01 Si. Helena. Proc. Zoo1 Bull. LS Fish Comm. 7(1887):429-446. Soc. Lond.p.86-131. ECKLES, H. H. CUSHING. J t , Jr 1949. Obser\ations on juvenile oceanic skipjack (Korsuwonus pelomrs) 1956. Ohrer\aiionr on seralog) of tuna. U.S. Fish Mildl Serb , Spec from Hawaiian balers and sierra mackerel (Scomberomorus sierra) from

80 the eastern Pacific. U.S. Fish Wildl. Serb., Fish Bull. 51:245-250. Acad. Nat. Sci. Phila. Monogr. 2, 349p. EGGLESTON, D., and L. S. PAUL. 1945. Los peces del Peru. [In Span.] Mus. Hisr. Nat. "JaLier Prado," 1978. Satellites. sea temperature?. and skipjack. In G. V. Hahib and P. E. Lima. 289 p. Roberts (compilorc). Proceedings of the Pelagic Fiqheries Conference, 1949. The fishes oi Oceanla-Supplement 3. Mem. Bernice P. Blchop July 1977, p. 75-84. [New Zealand.1 hltnlsi. Agric. Fish., Flch. Res. Mus. 12:37-186. Di*..Occas. Publ. 15. FRADE. F.. and F. de BUEN. EHRENBAUbl, E. 1932. PoicFonS Scombrlformes (evcepre' la Famtlle Sronlhrrdae). Clef de 1936. Naturgecchichte und nirtxhaftliche hedeutung der scefische Nord- classification principalement d'aprgs la morphoingle interne. Comm. europas. In H. Luhbert and t Ehrenhaum (editors). Handbuch der Int. Explor. Sci. Mer Me'diterr.. Monaco. Rapp. P.-V. R&n. 7:69-70. seefischerei Nordeuropac. Band Sturrgari 2, 337 p. FRADE. F.. and E. POSTEL. EIGENMANN. C. H., and R. S. EIGENSIANN. 1955. Contribution k I'&ude de la reproductton des mmhnd& et ihonld;r 1891. Addition? io the tauna of San Diego. Proc. Calit. Acad. Sci. Ser de I'Atlantique tropical. Rapp. P:V. R&n. Con\ Int. Explor. Mer 2,3:1-24. 137:33-35. EVANS, R. H. FRASER-BRUNNER, A. 1977. Remote sensing: Wiih applicauons to the evploiiation and manape- 1950. The fisher of the famlly Scombridae. Ann. hlag. Nai. Hist., Ser. men1 of Atlantic tuna stocks. [In Engl.. Fr. and Span. resume.] Collrci 12. 3:131-163. Vol. Sci. Pap., Int. Comm. Conserb. Atl. Tunas (SCRS-1976) 6:11-49. FUJINO, K. EVERMANN, B. W.. and A. SEALE. 1967. Revieu of suhpopulai~onstudies on skipjack tuna. Proc 47 Annu. 1907. Fishes of the Philippine Islands. Bull. U.S Bur. Fish. 26(1906): Conf. West. Assoc. State Game Fish Comm.. Honolulu. Hawaii, July 16-20, 1967, p. 349-371. 49-110. FAO. 1969. Atlantic skipjack tuna genetically distinct from Pacific \pccimms. 1968. Yearbook of fnhery statistics, catches and landings. 1967. FA0 Copeia 1969:626-629. Yearh. Fish. Stat. 24:c46-c48. 1970a. Immunological and biochemical genetlcs cf iuna5. Tian\. Am 1971. Yearbook of fishery statistics, catches and landings. 1970 FA0 Fish. Soc. 99:152-178. 1970b. Yearb. Fish. Stat. 30:331-332. Skipjack tuna subpopulation identified h) generic characteristic5 In 1973. Yearbook of fishery statistics. catches and landings. 1972. FA0 the w'estern Pacific. In J. C. Marr (editor). The Kurorhio. A symposium Yearb. Fish. Stat. 34:384-406. on the Japan Current, p. 385-393. East-West Center Press, Honolulu. 1971. 1974a. Local tuna fishery, Suva, Fij,. LIvehait pole-and-line fishing for Genetic markers in skipjack tuna from rhe Pacific and Atlaniic tuna (based on work of R. E. K. D Lee). FAO, Rome, FI:DP/FIJ/70/504. Oceanr. Rapp. P.-V. R&. Conr. In[. Explor. Mer 161:I5-IR. Tech.Rep. 1,89p. 1972. Range of the skqqack tuna suhpopulation in the western Pacific Ocean. In K. Sueawara (editor). Proceedings of the Second Symposium 1974b. Yearbook of fishery staiistics. catches and landings, 1973. FA0 Yearb. Fish. Stat. 36:412-434. on the Results of the Cooperative Study of the Kuroshio and Adjacent 1975. Yearbook of fishery statisiics. catche\ and landing?. 1974. FA0 Regions. The Kurorhlo II. Tokyo. Japan, September 28-Ocioher I. 1970, Yearb. Fish. Stat. 38:130-131. p. 373-384. Saikon Publ. Co., Lid., Tokyo. 1976. Yearbook of fishery statistic?. catches and landings. 1975. FA0 1976. Suhpopulatlon identification oi skipjack tuna specimens froni the l'earh. Fish. Stat 40:131-132. southnestern Pacific Ocean. [In Engl.1 Bull Spn Soc. Sci. Fbsh. 1977. Yearbook of fishery statistics, catches and landings, 1976 FA0 42: 1229- 1235. Yearb. Fish. Stat. 42:94-95. 1980. Genetic isolation of sklpjack tuna in the wextern Pacific Ocean. In 1978. Yearbook of fishery starisirs, catches and landings, 1977 F.AO Symposium for the Co-operailbe Study of the Kuroshlo and Adjacent Yearh. Fish. Stat. 44:102-103. Regions. Proceedings of the Symposium for the Co-operative Study of 1979. Yearbook of fishery statistics. catche5 and landings, 1978. FA0 the Kuroshio and Adjacent Reglonr. The Kuro\hlo IV. Tokyo. 14-17 Yearb. Fish. Stat 46:120-I2I. February 1979. p. 732-742. Salkon Publ. Co.. Tokyo. 1980. Yearbook of fishery stati\tics, catches and landings, 1979 FA0 FUSINO, K., and T. KANG Yearb. Fish. Stat.48:155-156. 1968a. Serum esterase groups of Pacific and Atlantic tunas. Copeia FIERSTINE, H. L.. and V. WALTERS. 1968:56-63. 1968b. Genetlcs 59:79-91 1968. Studies in locomotion and anatoniv of ccombroid iiihes. Men1 Transferrin groupr of tunas. FUSINO, K., and T. K. KAZAMA. South. Calif. Acad. Sci. 6. 31 p. FINK, B. D. 1968. The Y system of skipjack tuna blood groups. Vox Sang. 14:383-395. 1965. Estimations, lrom tagging experiment,, of mortality rates and other GIBES. R. H.. Jr.. and B. B. COLLETTE. parameters respecting yellowfin and skipjack tuna. [In Engl. and Span.] 1967. Comparative anatomy and sysiematics of the tunas, genus Thunnus. Inter-Am. Trop. Tuna Comm. Bull. 10:l-82. U.S. Fish Wiidl. Sew., Fish. Bull. 66:65-130 FINK, B. D.. and W. H. BAYLIFF. GMELIN, S. F. 1970. Migration? of yellowfin and \kipjack tuna in the eastern Pacific Ocean 1788. Pisces. In C. Linne. Systema naturae per regna iria naturae. xcunduiii as determined hy tagging experinlent\, 1952-1964 [In Engl. and Span.] classes, ordines, genera. species. cum characterihus, dlfferenrris. synony- Inter-Am. Trop. Tuna Comm. Bull. 15:l-227. ms. locls 1(3):1126-1516. FONTENEAU. A,, and P. CAYRE. GODSIL. H. C. 1980. Analyse de I'Aat de\ stocks d'alhacore (Thunnus alhacarec) et de 1938. The high sea? tuna fishery of California Calif Div. Fi\h Game, listao (Karsuwonus pelamis) de I'Atlantiqiie e\t au 30 septemhre 1979. Firh Bull. 51, 41 p. (Analysis of the status of yellowfin and skiplack ,locks (Thunnus alba- 1954. A descriptive study of certain tuna-like fisher. Calif. Dep. Fish Game, Firh Bull. 97. 185 p. cam and Katsi,wonu.cprlamrs) in the eastern Atlantic In September 1979.) [In Fr., Engl. summ.] Colleci. Vol. Sci. Pap.. Int. Comm. Conseri GODSIL, H. C., and R. D. EYERS. All. Tunas (SCRS-19791 9:230-244. 1944. A qystematlc study of the Pacific tunas. Calif. Diu. Fish Game, FORSBERGH, E. D. Fish Bull. 60, 131 p 1969 On the climatology, oceanography and firheries of the Panama GOODE, G. B. (editor) Bight. [In Engl. and Span.] Inter-Am. Trop Tuna C-omm. Bull. 1884 The fisheriv and fishery industries of the United StaieT. Sect I. 14:49-385. Natural histor) of useful aquatic animals. Part 3: The food fiche? of the 1980. Synopsis of biological data on the skipjack tuna. Kamwonucpelamir United States. p. 163-682. U S. Gob. Print. Off.. Wash.. D.C. (Linnaeus, 17581, In the Pacific Ocean. In W.H Bayliff(editor). Synop- GOODE, G. B.. and T. H. BEAN. 1879. sis of biological data on eight species of scomhrids, p. 295-360. Inter- The oceanic bonito on the coast of the Unlted Slates. Proc. U.S. Am. Trop. Tuna Comm.. Spec. Rep. 2 Natl. Mus. 1:24-26. FOURMANOIR. P. GOODING, R. M ,and S J. MAGNUSON. 1957. Poissons teleosteens des eaui malgaches du Canal de Mozambique 1967. Ecological significance of a drifting object to pelagic fishes. Pac. M&. Inst. Rech. Sci. Madagascar, Ser F. Oceanogr. 1:1-316. sci. 21:486-497. FOWLER. H. W. GOODING. R. M., W. H. NEILL. and A. E. DIZON. 1928. Fishes of Oceania. Mem. Bernice P. Bishop Mus IO. 540p. 1981. Respiration rates and lowoxygen rolerance limits in \kipjack tuna, 193R. The fishes of the George Vanderhilt South Pacific Expedition, 1937 Kotsu won us pelamis. Fish. Bull., U.S. 79:3 I -48.

81 GOPALAKRISHNAN, V. HARADA.T.. 0. MURATA, and H. FtiRUTANI. 1979. Status and problems of culture of baitfish for the skipjack fishery 1973. On the artificial fertilization and rearing of larvae in marusoda. in the Pacific region. In T. V. R. Pillay and W. A. Dill (editor$). Adrances Auxrs raprinosoma. [In Jpn.. Engl. synop.] Mem. Fac. Agric. Kinkt m aquaculture, p. 58-62. FA0 Technical Conference on Aquaculture, tint\. 6:113-116. Kyoto. Japan, 26 May-2 June 1976. Fish. Neuc (Book,). Farnham. HARADA. T.. 0. MURATA, and S. MIYASHITA. Engl. 1973. On the artificial fertilization and reartngof lar\ae in hirasoda. Auxis GOKBUNOVA, N. N. rhazord. [In Jpn.. Engl. s)nop 1 Mem. Fac. Agrr Ktrki Univ. 6:109-112. 1%3. Larvae of scombroid fiihes (Pisces. Scombriformes) from the Indian HARDENBERG. J. D. F. Ocean. [In Russ., Engl. summ.] Tr In,[ Okeanol. Akad. Nauk SSSR 1950 Developmeni of pelagic fisheries Proc. Indo-Pac. Fish. Counc. 62168.95. [Engl. transl. available, U.S. Dep Commer., Off. Tech Ser\.. I949 138- 143. Wash., D.C.] HARDING. J. P. 1965a. On the distribution of scombroid lar\ae (Pwes. Scombroldet) in 1949 The use of probahiltt\ paper for the graphical analycir of polymodal theeastern part of the Indian Ocean. [In Rusc , Enel summ ] Tr. Inst. frequenc) dtitrihution$. J. hlar. Bioi. Avoc. U.K. 28:141-153. Okeanol. Akad. Nauk SSSR 80:32-35. HAYASI, S. 1965b. Seasons and conditions of spawning of the wmbroid Tishe, (Pirces. 1974. A comment on the skipjack siock in the Atlaniic Ocean. Collect. Scombroidei) [In Russ., Engl. cumm.] Tr. Inst. Okeanol. Akad Nauk Vol Sci. Pap.. In[. Comm. Conserv. Ail. Tunas (SCRS-1973) 2:134-140. SSSR 80:36-61. [Engl. Iran4 abailable. U.S. Dep. Commer.. Off HENNEMUTH. R. C. Tech. Serv., Wash., D.C.1 1959. Additional information on the length-weight relationship of skipjack tuna from the eastern tropical Pacific Ocean. [In Enpl. and Span.] Inter- GORBUNOVA, and 0. SALABARRIA. N.N.. Am. Trop. Tuna Comm. Bull. 4:25-37. 1967. Reproduccion de Ins peces del suborden Scombroidei (Pisces. Scom- HERRE, A. W. broldei) en las regmnes occidentales del Atlantxo. [In Kuss.. Span. 1932. A check li\t of fishes recorded from Tahiti .IPan-Pac. Res. Inst. .iumm.] (Reproduction of scombroids (Pisces, Scombroidel) in uestern 7(1):2-6. region, of the Atlantlc ) In Sower-Cuban tnh In\e\t., VNIRO. 1933. A check list of fishes from Dumaguete. Oriental Negros, P. 1.. and bloscou 2:120-131. [Engl iransl. by U' 1.. Klaue. 1968. 24p.; Iiiicr-Am its immediate vicintt). J. Pan-Pac. Res. Inst. 8(4):6-1 I. Trop. Tuna Comm.. La Jolla. Cali1 ] 1953. Check list of Philippine fishes. U.S. Fish Wildl. Serv.. Res. Rep. GORDON, M. S. 20,977 p 1Y68. Oxygen consumption of red and uhte muscle\ from tuna fishes. HERRE. A W' ,and A. F. UMALI. Science (Waih.. D.C.) ISY:87-'M. 1948. English and local common name5 of Philippine fishes. U.S. Fish GOSLINE. W. A,, and E. BROCK. V. Wildl. Serv.. Circ. 14. 128 p 1960. Handbook of Haw'aiian fi\he\. liniv. Hauaii Prers, Honolulu. HIGGINS, B. E. 372 p. 1966. Sizes of albacore and bigeye. yellowfin. and rkipjack tunas in the GRAHAM, J. B. major fkhertes of the Pacific Ocean. In T. A. hlanar (editor). Proceedings 1975. Heat exchange in the yellouttn tuna. Thunnuy olhocurec. and \kip- of the Governor's Conference on Central Pacific Fi5hery Resources. p. jack tuna, Korsuwonu, prloifris. and ihe adaptibr significancc ofelebatcd 169.195. Stateof Hawaii. Honolulu. body temperaiurec in scombrid ti+\. Fish. Bull , U.S. 73:219-229 1967. The dtstnhutton of juveniles of lour species ol tunas m the Pacific GREEN. R. E. Ocean. Proc. Indo-Pac. Fish. Counc. IZ(Sect. 2):79-99. Relation5hip the thermocltiie to \iicce\\ 01 purv seining tor 1967. of 1970. JuLenile tunas sollecied by mtduater trawling In Hawaiian waters, tuna. rrans. Am. Fkh. Soc. 9h:I26-130. July-September 1967 Trans. Am. Fish. Soc. 99:hO-69. GREEN, R. t.. W. F PERRIN, and B P PtTKIC H HILDEBRAND, S. F. 1971. lhe American tuna puns \cine ii\hcr\. In H. Krl\tjonsion (edltorl. 1946. A descripti\e catalog of the shore ishe, of Peru. b.S. Natl. Mus. Xlodcrn fi\hmg gear 01 the aorld 3. p 1x2-194 Fi\h Nea\ (Boi~k\I. Bull. 189, 530p. I ond HOCHACHKA. P.\V., M'. C.HCLBERT. and M.GUPPY. GKttNBI ATT. P. R. 1978. The tuna power plant and furnace. In G. D. Sharp and A. E. Diron 1979. Associations of iiina uith flnicani in the ea\terii tropical Paciiic (editors). The physlologtcal ecology of tunas, p. 153-174. Acad. Press, Firh Bull.. U.S. 77:147-155 N.Y. GUDGEK. E W. H0EK.P.P C. 1941. The food and feeding tiabii, of the wlidle \hark. Xhitroodon Ivpu\. IW. Catalogue des poissonr du nord de I'Europe. a\ec les noms vulgaires J. Elisha Ilitchell Sci. Soc. 57:57-72. don1 on se sen dans le%langues de ceite region Cons. Explor. Mer, CIZNTHER. A Publ. Circum. 12:l-76. I86O. Caialogur ,>ithe acanthnpiei)g~an tishe\ in the collectinn oi the HONMA. M., and Z. SUZUKI. Brttt\h hlurcum. Vol 2. 54Xp. Taylor and Franc(\. Lond. 1978. Japanese tuna purse seine fishery in the western Pacific. [In Jpn.. 1876. Die Fiicheder S;;d\ee .I,\lui Godeffro! ?(Ill,257 p. Engl. cumm I Far Seas Fish. Res. Lab., S Ser. IO. 66 p. HABIB. G. HORNELL, J. 1Y76 The 1975-76 purse seine \kiplack fnhcr). In Procredinp\ of the Sktp- 1935. Report on the fisherlec of Palestine. Croun Agents Colonm. L.ond., lack luna C.onterence. Jul! 1976. p. 40-46 [Nru Zealand I \lintsi. 106 p. Agric. FI~,Fi$h. Res. Dib.. Occas. I'uhl. I I HOTTA. H. 1978. Skipi.ick biology and the 1976-77 pur\e-wne fi\hrr) In G V. 1953. On the distribution oivoung of \kipjack. Koisuwonusprlarnr~in the Hahkh and P. E Rohcrii (cornpilor\). Proceedings 01 the Pelagic f.c\herie\ wthern sea5of Kyushu. [In Jpn.. Engl. abrtr.] Bull. Tohoku Reg Fish Res. Lab. 2.19.21. Conference. Jul) 1977, p. 17-26, [New Lealand.] Ilin!\r. Agric. ti511 . Fi\h Rc5. Dtb., Occa\ Publ. 15 HOTTA. H., T. KARIYA. and T. OGAWA. 1959. A stud) On the "biting" of skipjack in the lire-bait fishery. Part I. HABIB. C;., I 1.CI EhltNT, and K A. FISHEK. Relation between the "hiring" and the alimental canal in ihe Tohoku Sea 1980a. .The 1977-78 purse-seine \kipjack fi\her) in Neu Zealand uaier,. area. [In Jpn., Engl. summ I Bull. Tohoku Reg Fi5h. Res. I.ab. [Neu Zealand.] hlini\t. Apt. hTh.. Fish Re, DI,.. Occa\ Publ. 25. 13:6@78. 42 p. HOTTA. H..andT.OGAMA 19ROb. The 1978-79 purse seine rkiplack li\her) In hew Zealand mater5 1955. [New Lealand.] hlm~t.Agric. ti\h , tiih Res. DIL..Occa5. Pub1 26. On the rtomach contents of the skipjack. Karsuw~onusprlornrs. [In Jpn.. Engl. summ.] Bull. Tohoku Reg Fish. Res. Lab. 4:62-R2. 39 p. HU. F.. and R -T. YANG. 1980~. Tlic IY7Y-80 pur$e-rcine \kipjack firher) In Neu Zealand water\. 1972. A preliminary study nn sexual maturlt! and fecundity of skipjack [New Zealand.] hlini\t. Agric Fi\li., t$\li.Re\ DI\ , Occa\. Pub1 29. tuna. [In Engl ,Chin. abstr.] J Fish Soc. Taiuan 1:88-98. 42 p. HUNTER, J. R.. andC. T. MITCHELL. HAKADA. T.. K. \lIZUNO, 0 MURATA, S. \1IYASHIT4, and H. 1967. Association 01 fishes with flot3am In the offshore waters of Central HURUTANI. Amer~ca USFl$h Wildl. Sen , Fish Bull. 66:13-29. 1971. On theariifictal teriiliiation and rcarlng 01 lanae In \ellow fin tuna. IGETA, Y.. K. YOSHIDA, K AMANO. >I. IWASHITA, and C. MIYAZAKI. [In Jpn., Engl. synop.] Mem. Fac. Agric. Kinki Univ. 4:145-151. 1978. Manufactured and angling test of auiomattc circularing angling

82 machine for skipjack. [In Jpn.. Engl. sunim.] Bull. Jpn Soc. Sci Fish. IWASHITA, M., M. INOUE. Y. ICETA, K. YOSHIDA. R. AMANO, and K. M:331-340. KODAMA. IMAMURA, Y. 1967. Mechanifaiion nipole-aiid-line 114iiii~lor \hiptach-I. fahricat~in 1949 The skipjack fishery. [In Jpn.] In Sui5aii K&a, The iexi ofihe Iishery and tesiiiig 01 ihe StM No. I. [In Jpii.. Lnpl. 5uniiii I .I kaciih! Zldr Jpn. Fish. Assoc. Vol. 6, Fishing Section. p. 17-94. [Engl. transl. b> W. Sci.Technol..Tokai Linib. 2 211-2IY. C.Van Campen. 1951. The Japane\e shipjack fisher). In U.S. Fish Wildl. [JAPAN.] tlSHERIES AGENCY Ot, RLSLARCH DI\.ISION. Serv.. Spec. Sci. Rep. Fish. 49.67 p.] 1967a. Annual report o1 eiinri 2nd caich mti\i~\hy area on Japanere iunalonpline fishery, 1964. ti41 Apenc) Jpii., Re\. DI\.,379 p. INOUE. M. 1967b. Annual report 01 ellnri and caicli \iaii\iicf h) area nn Japane\e 1959. On the relation of behabiours of ,ktpjack and tuna shoal) io (heir iunalongline fishery. 1965, €t\Ii. Apenc! Jpn.. Re,. 1)n , 375 p. catch inierred from the data for wne lisher). (In. Jpn., Engl. \umm.] 1968. Annual report 01 ettort and iatcll \iaii,iic\ h) area nii .lapane\e iiiiid Bull. Jpn. Soc. Sci. Fish. 25:I2-l6. longline fi\hery. 1966. Fnh Ageiicb Jpn.. Re\. DIL..299p. 1966. Automation of skipjack and luna fnhing by the use ofttie lift \)stem. 1969. Annual report o1 efinrt and caich \taii\tic\ hy area on Japanex iiina [In Jpn.] Tuna Fishing 51:24-25. [Engl. rransl. by J. ha, 1966, 4 p.: U.S. longline fishery, 1967. Fish. Agency Jpn., Res. Dib,, 293 p Civil Admin., Ryukyu I,..for Bur. Commer. Fish. Bid Lab., Honolulu.] 1971. Annual report of eitiiri and catch ,iatiriics by area on Japane\e luna INOUE, M., R. AMANO, and Y. IWASAKI. longline fishery. 1969. ti\h. Agency Jpn.. Res. Di,., 29Y p. 1963. Studies on en\ironments alluring skipjack and other tunas-I. On 1972. Annual report of effori and catch siati)iic\ by area on Japanese iuna the oceanographical condition of Japan adjacent uaiers and the drifting longline fishery, 1970. Fish Agency Jpn.. Res. DI~..326 p. substances accompanied by skipjack and other tunas. [In Jpn., Engl. 1973. Annual report of effort and catch \iatistic~by area on Japanae tuna summ.] Rep. Fish. Res. Lab.,Tokai Uni\. 1:12-23. longlineiishery, 1971. Fish. Agency Jpn., Res. Div.. 319 p. INOUE, M.. R. AMANO, Y. IWASAKI. and M. YAMAUTI. 1979a. Annual repori of elinri and caich \iausiica.by area on Japanw iuna 1968a. Studies on environments alluring skipjack and other tunas-Il. On longline fishery. 1977. Fish. Agenc) Jp?.. Res. VI\.. 235 p the driftuoodsaccompanied by skipjack and tunas. Bull. Jpn. Soc. Scl. 1979b. Annual report of effort and catch siatisiics by area. Japanex skip- Fish. 34:283-287. jack baitboat fishery. 1977 Fish. Agenc) Jpn.. Re\. Div.. 333p. 1968b. Studies on environments alluring skipjack and other tunas-Ill. 198Oa. Annual report of etfori and catch staiistics by area on Japanex iuna Tagging experiments on the experimental driftuoods as part of ecological longlinefishery, 1978. Fish. Agency Jpn.. Re,. Div.. 241 p. study of tunas. Bull. Jpn. Soc. Sci. Fish. 34:288-294. 1980b. Annual report ofeffori and catch stati\ti~sby area. Japanese skipjack baitboat fisher), 1978. Fish. Agency Jpn.. Res. Dib., 287 p. INTER-AMERICAN TROPICAL TUNA COMMISSION. 1981. Annual report of effort and caich siaiistics h\ area on Japanex tima 1972. Bi-Monthly report. May-June 1972. Inter-Am. Trop. Tuna Comm.. longline fisher), 1979. Fish. Agency Jpn., Res. Div.. 243 p. La Jolla. Calif., 16p. JENKINS, 0.P. 1973. Bi-Monthly report, January-February 1973. Inter-Am. Trop. Tuna 1904 Report on colleciinns of Cishe\ made in the Hawaiian I\lands, uiih Comm., La Jolla, Calif., 22p. descriptions of new species. Bull U.S. Fish Comiii. 22l1902):417-51 I. 1980. Annual report of the Inter-Amertcan Tropical Tuna Commission JONES, S. 1979. [In Engl. and Span.] Inter-Am. Trop. Tuna Comm., La Jolla, 1959. Note5 on eggs. larvae and jubeniles 01 firhes from Indian Waterr. 111. Calif., 227 p. Katsuwonus pelanns (Linnaeus) and IV. Neolhunnus macropIer~is(Tem- ISHIDA, R. minck and Schlegel). Indian J. Fish. 6:360-373. 1975. Skipjack tuna fishery and fishing grounds (Katsuo gyogy6 to Pyoj?;). JONES, S.,and M. KUMARAN. From Reports pertaining to effects of ocean disposal of sohd radioactive 1963 Distribution of larval iuna collecred by ihe Csrlsberg Foundaiion’s wastes on living marine resources (Hbshasei kotai haiki butsu no kaiy6 Dana Expedition (1928-30) from the Indian Ocean. [In Engl.. Fr. rkume‘.] shobun ni tomonau kaisan seibuisu tb ni kansuru chosa hokokusho). [In FAOFish. Rep. 6(3):1753-1774. Jpn.] Jpn. Fish. Agency, Tokai Reg. Fish. Res. Lab., Tohoku Reg. Fish. JONES, S.,and E. C.SILAS. Res. Lab., and Far Seas Fish. Res. Lab., p. 88-92. [Engl. transl. by T. 1960. Indian tunas-A preliminarv review, uiih a key for their identifica- Otsu, 1975. 10 p., transl. no. 12: Southu,est Fish. Cent.. Narl. Mar. tion. Indian J. Fish. 7:369-393. Fish. Serv., NOAA. Honolulu, HI 96812.1 1963. Synopsis of biological data on skipjack Karsuwniis pelanrir ILin- ISHIYAMA, R.. and K. OKADA naeus) 1758 (Indian Ocean). FA0 Fish. Rep. 6(2):663-694. 1957. Postlarval form of the skipjack (Kouuwonus pelamis) from the 1964. A systematic review of the scombroid fishes of India. In Proceedings Phoenix Islands. [In Jpn.. Engl. summ.] J. Shimonoseki Coll. Fish. of the Symposium on Scombroid Fishes, p. 1-105. Mar. Biol. Acsoc. 7:141-146. India. Symp. Ser. I I\’ERSEN. E. S., and H. 0.YOSHIDA. JORDAN, D. S. Am. Nat. Ser. Gp. Holi and N 789 p., 18 pl\ , 1957. Notes on the biology of ihe *ahno in the Line Islands. Pac. Sci. 1907. Fishes. I. To., Y.. l1:370-379. 673 illus. JORDAN, D. S ,and B. W EVERMANN IVERSEN. R. 7. E. 1898. The fishes of north and middle America. Bull. U.S Nail. hlu\. 1969. Auditory ihresholds of the scomhrid fish Eurhvnnus affinrs. uiih 47:2183-3136. comments oil the use of sound in tuna fishing. FA0 Fish. Rep. 6213): JORDAN. D. S.. E. W. EVERMANN. and H. M. CLARK. 849-859. 1930. Check list of the fishes and fishlike Lertebrates ot north and middle IVERSEN. R. T. E., E. L. NAKAMURA. and R. M. GOODING. America north of the northern boiindar! of Veneiiirla and Colombia 1970. Courting beharior in rkipjack luna, Karsunonus pelanrrs. Trans. Rep. U.S. Comm. Fish. 2(1928),670p. Am. Fish. SOC.99:93. JORDAN. D. S., and C. H. GILBERT. IWASAKI, Y. 1882. Synopsis o1 the ti\he\ of Norili America. Bull. U S. Nail. >lu\ 1970. Recent status of pole-and-line fishing in southern Waters. From 16. 1018p. abstract ll-(l),p. 8-12oia paper presented at Synip. I. Japan Tuna Fish- JORDAN, D. S..and C. L. HUBHS. ery Research Conference. February 1970, compiled hy the Far Sear Fish. 1925. Record of fishes obiained b) Dabid Siarr Jwdan in .Idpan, 1922 Res. Lab.. Shimiru. [Engl. tran4. by T. Otsu, 1970,8 p.; Souihuesr Fish. Mem. Carnegie Mu\. 10393-346 Cent., Nail. hlar Fish Ser\., NOAA, Honolulu. HI 96812.1 JORDAN. D. S., and E. K JOKDAh. 1976. Study on the shoals of skbpjack by body wecompmitmns. [In Jpn.. 1922. A Ii*f of the fi\he\ of Hauaii. uiih noi~.\and de\cription\ 01 neu Engl. summ.] Bull. Jpn. Soc. Sci. F.ish. 423543-548. \peiie,. hlem Carneeic \I,,\. IO 1-92, 1980. A stud) on [he body si7e composition of yellnufin tuna and skipjack JOSEPH. J. shoals caught by pune seine,. [In Jpn.. Engl. rumrn.1 Bull Jpii. Soc. 1963. Fecundity 01 yellowlin tima (TIirm,iu, nlhawrr,) and \Liptach (hurw Sci. F3sh. 46:lY-25. won~i~~eluni~~)irom ilie Pacttic Ocean. [In Fngl and Span.] Inter-Am. IWASAKI. Y., and T. SUZLKI. Trop Tuna Comm Bull. 7:251-2Y2. 1972. On the di5iribuiion of skipjack shoal, Lieaed lrom firhing ws\el re- JOSEPH.J.,andT. P.C.41 KINS ports and echo-sounder record5 and diurnal change of swimming layer of 1969. Population dknaniicr 01 the \hiplack iuna Ihoriri*oni~cprl“,Irrc)01 ~kipjadin the uestern tropical Pacific Ocean [In Jpn.. Engl ab\ir.l J the rasiern Pacilic Ocean [In Enpl. and Span.] Inier-Am. Trop. Tuna Faculty Mar. Sci. Technol., Tokai Univ. 6:YS-IW. Comm. Bull. 13:l-273.

83 . R. htAKNtY. A. I 11\15, A SkIITH. I kI.ARLC. Pacific In Studies on \kipjack ~n rhe Pacilic. p. 89-69. FA0 Firh. Tech. and P. h. IORII INSON. Pap. 144 1Y79. Lrouih 01 \klptack k~ut111';ic. < onin.. Occ'i\ Pap I I, 83 p 1978. Some li!poilicw\ on \hiptack. lhot\inwnrrc peIomi0 in the Pacillc JOLHII\. I , ~IKIr. I e IIAWIS Ocean. Souih Pac (omr . Occa.. Pap. 7. 23 p. 1Y24 ('araln~.uc~llu~rrc! der dniiiiaut indrin\ cnme\rible\ de\ $IC\ de lY-/Y. An o!er\leu (11 recciii change\ in ihe tiiherhe\ lor highl) mlgraiory et de\ mer\ IiniitiopIie\ d\ec leur, nnm, cninmunl ti,mL,i~\ ct firs \pecie\ ~n ilie ue\iern Paulic Ocean and projection\ lor futurc de\rlop- , hl&n 011 \ci. ICCII. PKII ~~arji,,S& spk.. PI I, 2x1p mentr South Pac. Bur. Ecnn. Cw7p ,SPEC (7Y)17, YY p. JI AKI-7. I1 KtARNt1. K. E., atid K I).611 I ET r IY74. Lldiidr de\e\a el ~IUI~~hlar I'exa 106-44-47, 1978 liiterm report 01 the acrk\ii!e\ 01 the Shlplaih 5unc) and A\\e\\- hAZ.1OHAKA. I m~ntProgramme In ilw udicn 01 rlie Ciilhert I4andr (5 - 25 Jul! IY7X) lY4l. Sconihroidei (e\cIume 01 Cazdnp~lorme\l [In Spii I tci(kiic%hip- South PdL. ro111m . SAlpl'lck \Ur\ 4 Progr'l,,,"le. prel,,,,. C,,unlr) ponica IS-Z(?), I25 p IO? lip. Kep 11, Ilp

KASAHARA. h 19%. lnterini rrpori (11 the dci~\~tic\(It the Skipjack Sur\c) and ,\\w,. 11, IPhX. A look ai rlie \kiplack ld~er)and Ii1iure [In Ipn I Bull Ipn. inen1 Programme in ihtl uater\ 01 Au\irdlid (I April ~ 13 >la\ 1979). Sot. 11\11. Oceanopr I3:127-132. [I-ngl. rrdnd b! T. Oiru. 1969. 9 p , South Pac. Conim , Shiptach 'iun 4\w\\. Programme. Pielliil < ouniry Snuil~e\th\h ('mi , Nail. Xldr ti4l 5eri.. NOAA, Honolulu. HI Rep. 17. I5 p 968 I 2.1 KEARNFY. R. E., and J.-P HA1.L IFK 1971. Skipjack luna rewurcc and It41~ngground\. Suiian Sekal ?O( 101. 1978a. Inierinl repori ofthc d~i~\iimof ihc Sklpjdch Sune) and A\\e\\- 30-37. [Engl. iran\l. byT Ot\u. 1972, 20p.; Siluthue\t Fish. Cent , Nail. ment Programme in ilie uarer, 01 Neu Caledonm (13 December 1977-19 Mar. Fish. Serv., NOAA, Honolulu. HI96812.1 January 197XI. South Pac. Comm.. Skipjack SunA5\nr. Programme, 1975. Nanpo katsuo gyogyo-sono shtgen to gljitsu. [Extsttng \late and Prelim. Country Rep 3, 20p. trend of skipjack resources in the exploited areas.] [In Jpn.1 In Spn. Soc. 1978b. Interim report ofthe acti\~t~esof the Skipjack Surbe! and Assess- Sci. Fish. (compiler), Skipjack fishery in the southern fishmg ground. Its ment Programme In the uaten of Western Samoa (6 - 14 June 1978). resourcesand technique. Fish. Sa. Ser ,Tokyo 11:7-29. South Pac. Comm., Skipjack Sur\. Asses\ Programme, Prelim Country 1977. The trends in the southern water sktpjack tuna fishery (Nanpo katsuo Rep. 8, lop. gyogy6 no d6ko). [In Jpn.] Sui\an Sekai 26(3):28-33. [Engl iransl by 1978~. Interim report of rhe act~vitiesof ihe Skipjack Surrey and Assesc- T. Otsu. 1977. I5 p.. [rand no. 24; Southwest Fbrh. Cent.. Nail. Mar. men1 Programme In the watery o1 Amerlcan Samoa (3 I May - 5 June, 15 - Flsh. Serv.. NOAA. Honolulu. HI96812.3 21 June 1978). South Pac. Comm.. Skipjack Surv. Assess. Programme, KASAHARA. K ,and T. TANAKA. Prelim. Country Rep. 9. 9 p. 1968. On the fishing and the catches of skipjack tuna (Karsunonus pelorno) 1979. Second interim report of the actik~tiesof the Skipjack Survey and In the souihern uaters. [In Jpn.. Engl summ.] Bull. Tohoku Reg. Fish Assessment Programme in the Haters of Papua New Culnea (14 May - 2 Res. Lab. 28:117-136. July 1979). South Pac. Comm., Sklpjack Surv. Assess. Programme, KAWAMURA. G.. W.NISHIMURA, S. UEDA. and T. NISHI. Prelim. Country Rep. 18. 14p. 1981. Color vision and spectral senwibiiy In tuna\ and marlins. Bull. 1980a. Interim report of the actIvLties ot the Skiplack Survey and Assecs- Jpn. Soc. Sci. Fish. 47:481-485. men1 Programme in the waters of Norfolk Island (26 - 30 March 1980). South Pac. Comm.. Skipjack Sur\. Asses Programme. Prelim. Country KAWASAK1.T. 1952. On the populaiions of ihe \kipjack. Karsuwonus pelamis (Ltnnaeus). Rep. 24, 9 p. 1980b. migraring to the north-easiern \ea area along the Pacific coast of Japan. Second interim report of the act~\itiesof the Skipjack Survey and [In Jpn.. Engl. summ.1 Bull Tohoku Reg. Fish. Res. Lab 1:1-14. Assessment Programme in the waters of the Trust Territory of the Paciflc 1955a. On the migration and the grouih of the \kipjack, Kai.suwonus Islands (2-21 November 1979). South Pac Comm., Skipjach Surv. Assess Programme. Prelim. Country Rep. 19, 14p. pelamis (Linnaeus). in the \outh-ue*tern sea area of Japan. [In Jpn.. Engl. KEARNEY, R. E., J:P. HALLIER,and P. KL-EIBER siinim.] Bull. Tohoku Reg. Fish. Re?. Lab. 4:83-100. 1978. 1955b. On the migration and the grouth of the skipjack. Karsuwonus Interim report of the aciiwties of the Skipjack Survey and Awss- pelanits (Linnaeus). in the ILUand Bonin Sea areas and the north-eastern men1 Programme in the uaieri of Tuhalu (25 June - 4 July 1978). South Pac. Comm., Skipjack Sur\ Asses\. Programme, Prelim. Country Rep. sea area along the Pacific coast of Japan. [In Jpn.. Engl summ.] Bull. Tohoku Reg. Fish. Res. Lab.4:101-119. 10.911 KEARNEY, R. E.. A. D. LEWIS. and J:P. HAL1 IER. 1958. On the lluctuation of the fisheries condttlon\ in the livebait fishery 1978. Rapport interimaire \ur les activ~tiecau titre du programme d'etude of skipjack m water? adjacent 10 Japan. 11. [In Jpn , Engl. summ.) Bull. et d'evaluation des stockr de bonites dam les eauk des Nouvelles-Hebrldes Tohoku Reg. Fi\h. Re\. Lab. 11.65-81. 1959. On the qructure of "fish $chool" of tunas. [In Jpn.. Engl. abstr.) (5-13 dicembre 1977 - 20-23 janrler 1978) [In Fr.] Souih Pac. Comm.. Skipjack Surv. Assess. Programme. Prelim. Country Rep. 4. 18 p. Jpn. J. Ecol. 952-54. KIKAWA. S. 1963. The grnuth of skipjack on the northeastern Sea of Japan [In Jpn.. 1953. Obser\ations on the spauning the big-eyed tuna (Purathunnur Engl. summ.] Bull. Tohoku Reg. F!*h Res. Lab. 23:44-M) of mebachr Kishlnouye) near ihe iouthern Marshall Islands. [In Jpn.. Engl 1964 Population structure and dynamlcs 01 sklpiack in ihe North Paclfic summ.] Conirib. Nankai Reg. Ftsh. Re5. Lab. l(24). lop. and 11, adjacenl water\ [In Jpn., Enel. summ.1 Bull. Tohoku Reg. Ftsh. KIKAWA. S.. and N. HIGASHI. Res. Lab. 24:28-47. 1979. Distrtbuiion, apparent relative abundance and compowton 1965a. Ecology and dynamics of the \kipjack populat~on.1 Clasrtfication. size of skipjack iuna in ihe Gulf of Gulnea uaters from Japanese surface data. distributton and ecology. [In Jpn.1 Jpn. Fish. Resour Prot. Assoc., Stud. Ser. 8:l-48. [Engl. transl. b) hl P. hliyake. 1967. 54 p.: Inter-Am. Collect. Vol. Sci. Pap., Ini. Comm. Conrerv. Ail. Tunar (SCRS-1978) 8: 189-195. Trop. Tuna Comm.. La Jolta. Calif.] KIMURA, K. 1Y65b. Ecology and dynamic, ot the \kipjack population. II. Resources 1954. and firinngcond,nons. [In Jpn.] Jpii. Fish. Resour. Pmt. Assoc., Stud. Analysis of skipjach (Kursuwonus prlarnn) Thoah hn the mater of "Tohoku Kaiku" by 115 associaiinn u~thother anmals and objects based Ser. 8:49-108. [Engl. tranrl. 1967. 7Yp.: b.S. Joint Publ. Re\ Sen.] on the records by fishing boats. [In Jpn.. Engl. summ I 1972. The cklpjack tuna remurce (har\uo no shlgen ni tiuliel. [In Jpn.] Bull. Tohoku Reg. Fish. Re<. Lab. 3. 87 p. Suisan Shuho (The Fnhmg and Fond Indwtry Meekl!) 660:32-38. July 15. 1972. [Engl. tran\l 1973. In U.S. Dep. Commer.. Mar. tish. Re\. KIMURA, K.. M. IWASHITA. and T HATTORI. 35(5-6):1-7 1 1952. lmagrnfrklpjack and tuna recorded on echo soundtng machine. [In Jpn.. Engl. 5umm.l Bull. Tohoku Rep. Fi\h Res. Lah l:l5-lY. KAYA. C. hl., A. E. DIZON. S. L). HtNDKIX. T K. KAZAXlA. and \I.K. K. Qti E E: NTH KING. J E., and I. I.IhtHARA 1982. Rapid and spontdneou, maturation. ovulat~on.and *pauninguf ma 1956. Comparati\e \iud! of food nf hlgeye and yelloufiri tuna in the hy newly captured \kipjack tuna, Katsuwonus pelamis. Flsh. Bull., U.S. cenlral Pacific L' S. Fish Mildl. Scr,., Fish. Bull 57.61-85. 80:393-396. KISHINOUYE. K. KEARNEY. R. E. 1915. A stud} of the macherels. cybuds. and tunas. Sutsan Gakkai Hi, 1975. The stock rtructure of rhipiack rewurces and the posslhle Implwa- l(l):l-24. [Engl. transl. by W.

84 1917. A new order ofthe Teleostomi. Suisan Gakkai HZ 2(2):1-4. [Engl LEGAND, M. transl. by W. G. Van Campen. 1951. In U.S. Fish Wildl. Serb.. Spec. SCI. 1971. Donnbes sur la bonite a ventre ray: dans le sud-ouest Pacifique. Rep. Fish. SO:I-3.1 [In Fr., Engl. abstr.] Cah. O.R.S.T.O.M.. S;r. Oceanogr. 9:403-409. 1923. Contributions to the comparative study of the so-called scombroid LENARZ, W. H. fishes. J. Coll. Agric.. Imp. Univ.. Tokyo 8:293-475. 1974. Length-weight relations for fibe ea\tern tropical Atlantic rcombrids. 1926. An outline of studies of the Plecostei (tuna and skipjack) in 1925. Fish. Bull., U.S. 723848.851 Suisan Gakkai Ha 4(3):125-137. [Engl. transl. by W. G. Van Campen. LESSON, R. P. 1950.In U.S. Fish Wildl. Serb., Spec. Sci. Rep. Fish. 19:l-8 I 1828. Description du nouveau genre Irhrhyoph,%et de plusieun especes KITCHELI.. J. F., J. J. MAGNUSON, and W. H. NEILL. inidires ou peu connues de poissons. . . . recueillis dans le voyage autour 1977. Estimation of caloric content for fish biomass Environ. Biol. du monde de “La Coquille.” M&. Soc. Hist. Nat. Paris 4:397-412. Fishes 2:185-188. 1830. Les poissons. In L. 1. Duperry (editor), Voyage autour du monde KITCHELL, J. F.. W. H. NEILL, A. E. DIZON,and J. J. MAGNUSON. exe‘cute wr la corvette ”La Coquille.” pendant le5 ann& 1822.25, 1978. Bioenergetic spectra of skipjack and yellowfin tunas In G. D. Sharp chapter IO. vol. 2:66-238 and A. E. Dizon (editors), The physiological ecology of tunas. p. 357-368. LEWIS, A. D. Acad. Press, N.Y. 1980. Tagging of skipjack tuna (Karsuwonus pelamrs) ~n Papua New KLAWE, W. L. Guinea waters. 1973-1974 Papua New Guinea. Dep. Prim. Ind. Re?. 1960. Larval tunas from the Florida Current. Bull Mar. Sci. Gulf Bull. 26,31 p. t 3 append. Caribb. 10227-233. LINNAEUS. C. 1963. Observations on the spawning of four specier of tuna (Neorhunnus 1758. Systema naturae per regna tria naturae, secundum clas\e\, ordines. marropferus, Kalsu wnnus pelamis, Auxis fhazard and Euthynnus linearus) genera, Tpecies, cum characteribus. differentiii. synonymii. loc~\.Tom. I in the eastern Pacific Oceap. based on the distribution of their larvae and (Regnum animale), 10th ed. Holmiae. Lithoprinted. 1956. Br. Mu*. Nat. juveniles. [In Engl. and Span.] Inter-Am. Trop. Tuna Comm. Bull Hist.. 824p. 6:449-540. LIVING MARINE RESOURCES. 1977. Whatisatuna? Mar. Fish. Rev. 39(lI):l.S. 1977. Pacific Tuna Development Foundation final report Tuna purse- KOGA, S. seine charter to the western Pacific. July-Nobember 1976. Living Marine 1958. On the difference of the stomach contents of tuna and black marlin Resources (San Diego). 14 p. + 17 tables. in the south equatorial PacificOcean. [In Jpn.. Engl. summ.1 Bull Fac. LOVE, C. M. (editor). Fish. Nagasaki Univ. 7:31-39. [Engl. transl. by G. Y. Beard, 1964. I2 p.; 1970. EASTROPAC Atlas, Vol. 4. U.S. Dep. Commer., Natl. Mar. Southwest Fish. Cent.. Natl. Mar Fish. Serv., NOAA, Honolulu, HI Fish. Serv , Circ. 330, viii + I2 p. + figs. 968 12.1 1971. EASTROPAC Atlas. Vol. 2. U.S. Dep. Commer., Natl. Mar. KOJIMA, S. Fish. Serv., Circ. 330. vi, + figs. 1956. Fishing for dolphins m the western part of the Japan Sea-11. Why 1972 EASTROPAC Atlas, Vol. 6. U.S Dep. Commer.. Nail Mar. do the fish take shelter under floating materials? [In Jpn., Engl. summ 1 Fish. Serv., Circ. 330, vi t figs. Bull. Jpn. Soc. Sci Fish. 21:1049-1052. [Engl. transl. by W. Ci. Van 1974. EASTROPAC Atlas, Vol. 8. U.S. Dep. Commer.. Natl. Mar. Campen. 1962. 7 p.; Southwest Fish. Cent., Natl. Mar. Fish. Serv.. Fish. Serv.. Circ. 330. vi! + figs. NOAA, Honolulu. HI 96812.1 LOVE, M. S., and M. MOSER. IW. Fishing for dolphins in the western part of ihe Japan Sea-V. Species 1977. Parasites of California. Oregon. and Wa*hington marine and of fishes attracted to bamboo rafts [In Jpn.. Engl. summ.] Bull. Jpn. estuarine fishes. Univ. Calif. Santa Barbara. Mar Sci. In~t..530p. Soc. Sci. Fish. 26:379-382. [Engl. transl. by W. G. Van Campen, 1962. L~TKEN.c. 4 p.; Southwest Fish. Cent.. Natl. Mar. Fish Serv.. NOAA, Honolulu. 1880 Spolia Atlanttca. Bidrag til kundskab om formforandringer lios HI 96812.1 fiske under deres vaext og udwklmg, saerligt hos nogle af Atlanterhaveis KUME. S. Hflsefiske. K. Dansk. Vid. Selsk. Skrift.. Kjobenhavn, Ser. 12:40’-613. 1977. Some biological information on skipjack caught by Japanese longline MACLEAY, W. fishery in the Atlantic Ocean. Collect. Vol. Sci. Pap., Int. Comm. 1881. Descriptive catalogue of Australian fishes. Svdney 1:191-192. Conserv. All. Tunas (SCRS-1976) 6.75-78. MAGNUSON, J. J. 1978. Change in catch per unit of effort for skipjack and yelloufin tuna 1969. Digestion and food consumption by skipjack tuna (Kar.ruu,onur caught by Japanese pole-and-line fishery in Gulf of Guinea, 1969.1976. pelamis). Trans. Am. Fish. Soc. 98:379-392. Collect. Vol. Sci. Pap., Int. Comni. ConserL. All. Tunas (SCRS-1977) 1973. Comparative study of adaptations for continuous swimming and 712 1-23. hydrostatic equilibrium of rcombroid and xiphoid fishe,. Fish. Bull., KURODA, R. U.S. 71:337-356. 1955. On the water temperature in the fishing grounds of the skipjack, 1978. Locomotion by scombrid fishes: Hydromechanics. morpholog), and Kalsuwonu.spelamis(Lmnaeus), caught in the north-eastern sea area along beha\ior. In W. S. Hoar and D. J. Randall (editors). Fish phywdogy. the Pacific coast of Japan. [In Jpn., Engl. summ.] Bull. Tohoku Reg. Vol. 7, p. 239-313. Acad. Press. N Y. Fish. Res. Lab. 4:47-61. MAGNUSON. J. J., and J. G. HEITZ. LACCPZDE, B. G. E. 1971. Gill raker apparatur and food selectivity among mackereli. tunas. 1802. Histoire naturelle des poisons. Paris, Plarsan 3, 558 p. and dolphins. Fish. Bull , U.S. 69:361-370. LAEVASTU, T., and H. ROSA, Jr MAGNUSON, J. J.. and J. H. PRESCOTT. 1963. Distribution and relat~abundance of tunas In relation to their 1966. Court?hip. locomotion. feeding. and nii\cellanenu\ behabiour of environment. FA0 Fish. Rep. 6(3):1835-1851. Pacific bonito (Sorda chilrensis). Anim. Behav. 14:54-67. La MONTE, F. MAGNUSON, J. J., and D. WEININGER. 1945. North American game firhe5. Doubleday, Doran and Co.. Garden 1978. Estimation of minimum 5urtained \peed and associated hody drag City,N.Y..202p. of scombrids. In G. D. Sharp and A. E. Diron (editors). The phy\iological LASKER, R ecologyoftunas,~.293-311. Acad. I’m\, N.Y. 1975. Field criteria for survibal of anchovy larvae The relation hetueen MARCILLE, J.. and B. STEQUFRT inshore chlorophyll mawmom layers and wccersful fin1 feedme. Flsh. 1976. Etude prilimmaire de la cro!\\ancc du li\tao (hoicuwonu~pdanirc) Bull., U.S. 73:453-462. dans I’ouesi de I’Ocian Indirn tropical. (First re\iilts of ihc \tud) of listan 1978. The relation betueen oceanographic condition? and larbal anchov) (Korsuwonuspela,nrs) in the tropical uestern Indian Ocean.) [In Fr , Fn91 food tn the California Current: ldentificaiion of tactors contributing 10 summ.] Cah O.R.S.T.O.M.. Se‘r Oc:anogr l4(2).139-I5l recruitment failure. Rapp. P:V. Rgun Con,. Int. Explor. Mer 173: MARCIL1.E. J.,and 2. SUZUKI. 212-230. 1974. Distribution of skipjack caught by Japane\e tuna 101 1981. Factors contributing 10 banable recrui!ment of ihe northern ancho,?’ the Indian Ocean [In Jpn., Ingl. 5umm I tlull. Tar (Enp,aulis mnrdu) In the Calitornm Current: Contrasting yearc. 1975 Lab. (Shimiru) 10.87-107. through 1978. Rapp P.-V. Rgun. Coni. Int. Eplor Mer 178:375-388. MARR, J. C. Le GALL, J. 1948. Observation5 on the spauninp of oceanic skiplach (Kurwb)wiii> 1934. Karruwonusprlamrr. J. Cons. (‘on, Perm, In1 Explor. Mer. In pelantic) and )ellow fin tuna (.lrorhunnt~~nuxroprrru~) 1n t tic norihc.rn Faun. Ichthyol. Atl. Nord. 15. Marshall Islands. U S. Fi5h Wildl. Serb.. Fich Bull 51:201-206.

85 MAKLYAhlA. T XlORRO\\, J E. I980 Report on the wuthern water \kipjack tuna fi\her) (Nanp6 kai\uo I954 tishe5 from ta?t Africa. niih neu records and de\cripiion\ of iwo e)og!.< ni kanwru repnin) Iln Jpn.] Ini. \lanap?. AWL. Tol!o. neu species. Ann. hlag. Nat. Hi\t., Ser. 12. ?.?97-X20. ,Aiicii\l 211. IYSII. I2 p Iimnimhcrcdl II "$1 twm h\ 1 Otw. Y p 1957. Shore and pelagic fixhe\ from Peru, with neu record\ and ihe descrip- iran4. no. 4Y: \ouihue~t Fnh Ccni.. Nail. Mar. F$+. Scri , hOAA. tion ill a neu ipecies of Sphoeroider. Bull. Bingham Oceanoer Colleci. tlcuiolulu. HI YhXI2 I Yale UniL. 16(2):5-55. MAI\I I. K. %ltiIR. B. S.. and C. E BROM N. 1942. The gonad, of \kipjack lroni Pal.io water,. [In Jpn.] Souiti Sea 1971. Effect, of blood path\\ay on the blood-pre\\ure drop in fi\h gill\,

S~I5:117-122. [Lnpl iran4 b) \V (8 Van Campen. 1950. It?L.S. Firli with special reference io tuna\ J. Fi9. Re,. Board Can 28:947-955 Wild1 Sen , Spec. So. Rep. II\h. 20. h p.] bll:NRO, I. S. R. \IAT\UhIOTO. M.21. 1955. The marine and fresh uaier fi\he\ of Cevlon Dep. €XI. Aff , IY5X. I>e\cripiion and ili\irLhution of I.ir\ae of four \pecie\ 01 tuna in (en- Canberra, 351 p. iral ~ac111c~aier,. U.S FI~I\wciI. ~cr\, FI\~ BUII. 5x:31-72. 1958. The fishes of'she Ne\\ Guinea region. A check-list of the fishes of 1961 (~olleci~onand dc\cripiion\ of luiciiilc luna\ from ihe central Neb Guinea Incorporaiing records of species collected bv the Fisherie5 Pacific. Deep-sea Re\. X:279-286. Surve) Vessel "Fairwind" during the years 1948 to 1950. Papua Neu 1Y74 111s.\kipjack tuna. hutriinoni,c pelumi%,an undcruiiliicd re\o~~rce tiuinea Agrr J. 10(4):97-369 hlar. Fish Re\ 3618) 26-33 MbNZ. F. \\ ,and H'. N McFARLAND 1975. Di\irihution. rcIat~\cabundance. aiid mo\cmcni 01 \h>p\acktuna. 1977. E\olutionary adapiationi of firhe?io the photic environment. In F horcr!*.orrucprloinrs, in the Pacific Ocean hased on .Japanese tuna long- Crercitelli (editor), The kirual system In \ertehrates, p. 193-274. Handh. line carche%. 19M-67. U S. Dep. Commcr.. hOAA Tech. Rep. NhlFS Sen\. Physiol 7(5) Springer-Verlag. N.Y. SSRF-695. 30p. ZltiRDY. E. 0. 'LIAISUhIOTO. M M , T. K. KAJAhlA. aiid 1) C AASTFD. 1980. The commercial har\estin_e of tuna-attracting payaos: A poiclhle 19x1. Anchored Ii\h aggregatiny de\)cc\ in Iiauaiian \\aien. hlar. Fi\h. boon for small-wale fishermen. Ini. Cent. L.i\ing Aquat. Re\aur. Re\. 43(9).1-13 Manage Neuscl. 311): 10.13. IIArSllhlOTO. M. hl.. I- H. rAl HOT. 13, I3 COL 1 LTTt. .ind K S iHO- hllJRPHY, G 1.. and I. 1. IKFHARA. \IlIRA. 1955 A summary of sighung, of fi\h school\ and bird flock\ and of irolling 1969. Pacific honiio (Sorb chii,mwl and \Lipiacl tuna lharruunnit\ in the central Pacihc. U.S. Fi\h Wildl. Ser\.. Spec. Sci Rep. Fish. ploirm) wiihoui 5riipc\. ('npeia 196Y:i97-3YX. 154. IYp. hlc(AHt, hl. bl.. and D hl. [)LAN SIURPHY. G. I ,and T. OTSU. 1970. Fcierase p<,l\morpli~\m\~II ilic ilipiac!. tuna. hot\ut+oniic jwloifiic 1954 Analysis of catcher of nine Japanese tuna longline expedition\ to Comp. Biochem. Phy\iol S4 h71~hSI the western Pacific. U.S. Fish Mddl. Serb.. Spec. Sei. Rep. Firh. 128. 46 p. hlcCAHF. 21 hl.. 1) I\I DkAN. and C. S 01SON. hlURPHY. T. C.. and G. T. SAKAGAWA. 1970. hluliiplr formy 01 h~ph~irphopluconair.deh\drogena\c and alpha- 1977 A rekieu and eLaluailon of e\iimaie\ of natural mortalit) rare5 of cerophmphate deh!drogenaw 111 ilie \Lipiach tuna. harcrinfini~~ tuna?. [In Fngl.. Fr. and Span. r;sume'] Colleci. Voi. Scl. Pap.. Int. ianiis Comp. Biochem. Ph>\iol.34:755-757. Conim. Consen. Ail. Tiinas(SCRS-1976)6:117-123. hlcNFLl Y. R. I hIAGANUMA, A. 1961 Pune seine reiolutim 111 tuna fi\hing. f'ac Fnherman 59(7).27-58. 1979. On Tpawnmg actiwt!e\ of skiplack tuna in the besiern Pacific Ocean. MFAII, C;. \V [In .Ipn , Engl. summ.] Bull. Tohoku Reg. Firh. Res. Lab 40:l-13. IY5I. Po\ilar\al .Vvrolhunnii\ ,iiam)ptwi,c, Aut15 thu:ard. and titthrnnrrs NAKAMURA. E. L. lrnrutuc from the Pacific cna\t of Central ,America. U.S. Firti hildl. 1962. Obserharlons on ilie hchabior of rkipjack tuna. Eirrhvnnuspeloiriis. Serb,, Fi\h. Bull 52:121-127. in captivity. Copeia 1962.499-505 hlEtK. S. F.. and S E. HI1 DtBRAND. 1965. Food and feeding hahit\ of skipjacl tuna (Karsun,onrrcpelamrr) from 1923. The marine li\he\ of Panama Field Slu\. Nat. His1 , Puhl. 215. the Marquesas and Tuamoiu Islands. Trans. Am. Fish. Soc. 94236-242. Zoo1 Ser. I5.Pari 1.330~ 1968 Visual acuity of two tunas, Karsuujonus pelomi, and Euthwnus MENUIS. A. S. qurnrs. Copeia 1968:41-49. 1954. Fishes of Ceylon. (:A catalopue, kc\ B bihliographi.) Bull. Fl\h. NAKAMURA, E. L., and J J MAGNUSON Re\. Stn. Ceylon 2. 222 p. 1965. Coloration of the scomhrid fish Eurhvnnus aJfino (Cantor). Copeia MIYAKE,hl P 1965:234-235. 1968. Di\irihuiion of \kipiach in the Pacific Ocean. hased on records of NAKAMURA, E. L., and, W. M. %lATSUhIOTO. incidenial caichei h) ilie lapanex longline luna ti\her). [In tngl. and 1967 Distribution of larval tuna5 in MarqueTan aaters. U.S. Fi\h Wild1 Span.] Inter-Am. Trop. Tuna Comm. Bull. 12.509-608. Serv.. Fish Bull. 66:l-12. NAKAMURA, L.. and J. H. UCHIYAMA. hllYAKC. 51.. and S. HAYASI. E. 1966. Length-weight relations of Pacific tunai. In T. A. Manar (editor). 1972. Ficld manual lor \iati\ii~~and 5aniplinp of Atlantic tunas and tuna- Proceedings of the GoL'ernor's Conference on Central Pacific Fichery like fi\lie\ lni. C omm. of ihe NAKA"rURA. I. ycllo\\fm tuna (Thunni,s uihocarer) 111 the adiaceni \ea of ihe Paciiic ma\i 1965. Relationships of fishe, referable to the whfamily Thunnmae on ihe of Japan [In Jpn.. Engl. \)nap ] Bull. tarSea5 ti\h Re\. Lah. (Shmiiu) hasis of ihe anal 5keleton. Bull. Misaki Mar. Biol lnst , K)oto Univ. 3 215-228. 8.7-38. 1972. Geographical di\irihution and relaiibe apparent abundance of \me NEILL, W. H., R. K. C CHANG. and A. E. DIZON. ccomhroid fiihe, bawd on the oc~'urrc11cc~in ihe \iomach\ of ape\ 1976. Magnirude and ecological implications of tlicrnial inertia in Tkipjack predator\ caught on tuna longline-I. Ju\enile and younp of ikipjack luna tuna. Korsiru,onurpela,nis (Lmnaeus). Enbiron. Biol Fiihes I .61-80. (horcuu,onu~prlo,,r,~).[In Jpn , tngl ah\ir.] Bull. tar Sea\ FiTh. Re\ NEILL. W. H.. and E. D. STEVENS. I ah. (Shimiiu)h.lll-I57 1974. Thermal inertia versuT ihermoregularion on "warm" iurtles and tuna. Science (Lb'ach.. D.C.) 184:IOOR-IOIO. hlORI. K.. S. IJFYAN4Cil. and Y. NISHIKAHA. NICHOLS, J. T., and R. C. MURPHY. lY7l. The debclopmciit of ariificialli fertiliied and reared lar\ar of the 1944. A collection of fiyhec from the Panama Biglit. Pacific Ocean Bull ?ellowfin tuna. Tliiinnvr alhocores. [In Jpn.. tnpl. 5hnop.J Bull. Far Am. Mu$.Nai. Hist. 83:221-260. Sea\ Fi\h. Re'. I ah. (Shunvu) 5:219-212. NISHIKAWA. Y.. S. KIKAWA. M. HONMA. and S. UEYANAGI. k1ORICC. J. 1978. Disirihution atlas of larbal tunas. billfishe, and related cpecm - 1951. IJn ca;aci:re systehatique pou\anr w\ir \a sgparer le\ e\p&e\ de Results of lanal suney, b) R/V Shumo Mom and Sho.vo Mom (1956- rhunnidae Ailantique\. Re\. Trai. Inti Sci Tech P&hei Marit. 1975). [In Jpn., Engl. summ.] Far Seas Fish. Res. Lab. (Shimizu). 1t~s-74 SSer.9.99~.

86 NOBRE, A. POTTHOFF. T., and W. J. RICHARDS. 1935. Fauna marinha de Portugal. Pari I-Vertebrados (hlamlferos, Keptir 1970. Juvenile bluefin tuna, Thunnrir rhwnus (Linnaeust. and other e Peixes). Unib. Porto, Portugal. 574p. scornbrids taken by terns in ihe Dr) Tnrtuea5. Florida Hull. Slai SCI NOEL, J 20:389-413. 1978. Utihsation des donnes thermiques de tke'dJtection pour I'aide a la POWLES. H. pahe (U$eof remote sensing thermal data for helping fisheries.) [In Fr 1 1977. Island mass effectr on the diirrihution of Ianae of two pelapic li\h In Utilisation pour I'oc~ano!ogie des satellites d'obrerbation de la terre, species off Barbados. FA0 Fish. Rep. 2003333-346. p. 63-65. Centre Nat. d'Etudes Spatiales, Lannion (France): Publ. QUINN. W. H. CNEXO. Paris, Actes Colloq.. No. 5. 1976. Use of southern o~cillationindices to asses the physical en\ironment OKADA. Y. of certain tropical Pacific fisheries. In Proceedings NMFSIEDS Work\hop 1955. Fishes of Japan. Illustrations and descriptions of fishes of Japan on Climate and Fisheries. April 26-29. 1916. p. 50-70. Cent. Climatic and Maruzen Co., Ltd.. Tokyo, 462 p. Environ Ascess.. Columbia. Mo U.S. Dep. Commer.. NOAA. OKADA, Y., and K. MATSUBARA. NMFWEDS, Wash., D.C. 1938. Keys to the fishes and fish-like animals of Japan. [In Jpn.] Sanseido 1977. Use of southern owllation inde.: anomalies for predicting El Nik Co.. Tokyo, 584p. type activity. [In Engl., Span. r&ume'.l Cienc. Mar. 4:40-66. ORANGE, C. J. RADOVICH. J. 1961. Spauning of yello\rhn tuna and skipjack in the eactern tropical 1963. Effects of water temperarure on the di\tribution of mne scuinhrid Pacific, as inferred from studies of gonad development. [In Engl. and fishes along the Pacific coast of North America. [In Engl., Fr. and Span. Span.] Inter-Am. Trop. Tuna Comm. Bull. 5.459-526. re'sum;.] FA0 Fish. Rep. 6(3):1459-1475. ORANGE, C. J., M. B. SCHAEFER. and F. M. LARMIE. RAFINESQUE. C. S. 1957. Schooling habits of yellomfin tuna (Neolhunnus macroprerus) and 1810. lndice d'ittiologia siciliana: ossia catalogn rnetodico del nnmi launi. skipjack (Karsuwonuspelamrs) in the eastern Pacific Ocean, as indicated italiana, e siciliani dei pesci, che si rinvengono in Sicilia: disposti cecondo by purse seine catch records. 1946-1955. [In Engl. and Span.] Inter-Am. un rnetodo naturale e seguiro da un'appendice che contiene la dercrinone Trop. Tuna Comm. Bull. 2:83-126. di alcuni nuovi pesci siciliana. Messina. 70 p. OSBECK, P. RAJU, G. 1765. Reise nach Ostindien und Chma. , . . AUS dern Schaedischen 1960. A case of hermaphroditism and some other gonadal abnorrnalirier Sbersetzt von J. G. Ceorgi. Johann Christian Koppe, Rostock. xxvi In the skipjack Karsuwonus pelanrrs (Linnaeusi. J. Mar. Biol. Arsoc. + 552p. India 2:95-102. PAJOT, G. 1964a. Fecundity of the oceanic skipjack Karsuwonus pelamrs (Linnaeu\) 1978. Fishing gear and methods for off-chore fishing in Sri Lanka. Bull. of Minicoy In Proceedings of the Sympos)um on Scombroid Fi*he\, p. Fish. Res. Stn.. Sri Lanka28:59-69. 725-732. Mar, Biol. Assoc. India, Symp. Ser. I. PALMA. F. 1964b. Observations on the food and feeding habits of the oceanic skip- 1941. Nombres de peces cubanos y floridlanos. Carbonell, Habana, 82 p. jack, Katsrrwonus pelamrs (Linnaeus) of the Laccadive Sea during the PARIN. N. V. years 1958-59. In Proceedings of the Symposium of Scombroid Fisher. p. 1968. Ichthyofauna of the epipelagic zone. Academy of Sciences of the 607-625. Mar. Biol. Assoc. India, Symp. Ser. I. U.S.S.R. [In Russ.] Institute of Oceanology, Izdatel'stw "Nauka." 1964~. Studies on the spawning of the oceanic ckipjack Karsuwnur Moskva 1%8. [Transl. by M. Raveh. edited by H. Mills, 1970, 206 p.; Israel pelamrs (Linnaeus) in Minicoy waters. In Proceedings of the Symposium Prog. Sci. Transl., available U.S. Dep. Commer.. Natl. Tech. Inf. Serv.. on Scombroid Fishes, p. 744.768. Mar. Biol. Assoc. India, Symp. Ser. I Springheld, Va. as TT 69-59020.) REGAN, C. T. PARONA. C. 1909. XI.-On the anatomy and classification of the scombroid fishe5. 1919. II tonno e la sua pesca. [In Ital.] Xlem. R. Com Talassogr. Iral. Ann. Mag. Nat. Hist., Ser. 8, 3:66-75. Veneria68,255 p. REINTJES, J. W.,and J. E. KING. PELLA, J. J.. and C. T. PSAROPULOS. 1953. Food of yellowfin tuna in thc central Pacific U.S. Fi5h Wildl. 1975. Measures of tuna abundance from purse-seine operations in the east- Serv., Fish. Bull. 54:91-110. ern Pacific Ocean, adjusted for fleet-wide evolution of increased fishing RICHARD, J. power, 1960-1971, [In Engl. and Span.] Inter-Am. Trop. Tuna Comm. 1905. Campagne scientifique du yacht "Princesse-Alice" en 19M. Bull. Bull. 16:283-400. Mus. Oceanogr. Monaco 41,30 p. [PHILIPPINES.] BUREAU OF FISHERIES AND AQUATIC RESOURCES. RICHARDS, W. J. 1980. 1978 Fisheries statistics of the Philippines. Philipp., Minist. Nat. 1%9. Distribution and relative apparent abundance of larval tunas collected Resour.. Bur. Fish. Aquatic Res., VoI. XXVIII, 374p. in the tropical Atlantic during EQUALANT surveys I and 2. In Proceed- PIANET. R. ings of the Symposium of the Oceanography and Fisherie5 Resoiircr~of 1974. Relations pads-longueur des listaos (Karsuwonus pelamrs) aches theTropical Atlantic, p. 289-315. UNESCO. Paris. dans le secteur de Pointe-Noire. [In Fr., Engl. summ.1 Collect. Vol. Sci. RICHARDS, W. J.. and G. R. DOVE. Pap., Int. Comm. Conserv. Atl. Tunas(SCKS-1973)2:126-133. 1971. Internal development of young tunas of the genera Ka/sunsonuJ. 1980. La pecherie de listaos (Kalsuwonus pelamrs) dans I'Atlantique Eulhynnus. Auxrs, and Thunnur (Pisce% Scombridae). Copeia 1971: tropical est &at des stocks au 31 dgcembre 1978. [In Fr., Engl. summ.1 72-78. Collect. Vol. Sci. Pap., Int. Comm. Conserv. All. Tunas (SCKS-1979) RICHARDS, W. J.. and D. C.SIMMONS. 9:275-281. 1971. 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87 KI\AS. I R ofgrouth. age. and \chooling habits. LS Fish Wildl. SKW. Fish, Bull. 1949. (heck Ii\t (11 the Florida game and commercial marine fishes. ~n~ 51:19?-2oO. cluding thow 01 tlie Gull 01 Mexico and the Wesi Indx\, w~ihapprohed 1960. Reporl on the Inieuigarion5 of the InterAmerican Tropical Tuna coninion name\. Utii~.\hami Mar Lab.. Fla Stair Board CO~W, Commi\\ion for the )ear 1959. [In tngl. and Span.] Inter-Am. Trop. Educ Ser. 4, 39 p. Tuna Comm., Annu. Rep. 19?9. p. 39~156. 1951. A prelimmar) rebieu of the hesiern North Atlantic li\hes of the 1961a. Appendix A. Report on the intestigation\ of the Inter-American fanill) Scombridae. Bull. iylar. Sct GulfCarihb. 1:209~230. Tropical Tuna Commisrion for tlie year IW. [In Engl. and Span.] Inter- KIVCRO. L H., and hl J. FERNANDEZ Am.Trop. TunaComm , Annu. Rep. 1960.40-183. 1954. Estadw lar\ale\ ju\eniles del bonito (harsuwonur pelum,s). 1961h. Tuna oceanograph) programs in the tropical central and ea\iern Torreia 22, 14 p. 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Studies of the sexual de\elopment and \pawnitig of yellowfin tuna n,onurpelomrs L.. in eastern Aurtralian uaters, and 11s relation to surface (.Veorhunnus mucruprerus) and skipjack (Kursuwonus pelamis) in three temperature. Aust. J. Mar. Freshuater Res. 3:lOl-1 IO. areas of the eastern Pacific Ocean. b) examination of gonads. [In Engl. RONQUILLO, 1. A. and Span.] Inter-Am. Trop. Tuna Comm. Bull. 1:283-349. 1953. Food habits of tunas and dolphins based upon the examination of SCHULTZ. L. P. their stomach contents. Phillpp. J. Fish 1954, 2:71-83. 1960 Suborder Scombrina. Family Scombndac. Tunas. In I.. P. Schultr 1963. A contribution to the biology of Philippine tunas. FA0 Fish Rep. and collaborators: W. M. Chapman, E. A. Lachner, and L. P. Woods, 613): 1683-1752. Fishe\ofthe Marrhall and hlarianas Islands, p. 410-417 Bull. U.S Natl. ROSA, H., Jr. Mus. 202(2). 1950. Scientific and common name5 applied to tunas. mackerel<. and \pear SCHULTL. L. P., and E. >I.STEARN. fishes of the world uith notes on their geographic distribution. FAO. 1948. The aa)sof fisher. Van Nmtrand (‘0.. N.Y.. 264 p. Wash., D.C., 235 p SEAL€. A. ROTHSCHILD. B. J. 1940. Report on fishes from Allan Hancock exprditions in the California 1963. Skipjack ecology In W. G. Van Campen (editor), Progres\ In 1961- Academy of Sciences. Allan Hancock Found. Pac Exped. 9:l-46. 62. p. 13-17 U S. Fish Wildl. Sen , Circ. 163. SECKtL. G. R. 1965 Hypotheses on the origin of exploited \kipjack tuna (horsuwanirs 1972. Hawaiian-caught \kipjack tuna and their physical enblrnnment pelomis) in the eaitern and central Pacific Ocean. U.S. Fish Mildl Fish. Bull., U S. 70:763-787. Serv , Spec. Sci. Rep. Fish. 512, 20p. SENTA. T. 1966. Preliminary assessment of the yield potentlal ofthe skipjack tuna In 1966. Experimental studm on the significance of drifting seaweeds for the central Pacific Ocean. In T. A Manar (editor). Proceeding\ of the juvenile hrhe\-lll. 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R&mh des connai*\ance\ actuellcs vir halYuuonw peluml~(Llnn;). of Indian Ocean tuna\) [In Ru,\ ] Tr. VNlRO 64, Tr. ArcherNlRO [In Fr.1 Bull. In*[. PZche5 Marit. hlaroc 7:33-53. 28.374-376. (Engl. tranil. b) W. L. Klaue. 1968, 5 p.: Inter-Am. Trop. ROYCt. W. F Tuna Comm.. La Jolla. Calif.] 1957 Obwr\ation5 on the spearfi\hes (11 the central Pacific. U S. Fish SHARP.(; D Wildl. Serb , Flsh. Bull 57:497-554. 1969. Electrophoretic study of tuna henioglobtn5. Comp. Blochem. ROYCE, \\ F., and T OTSU Ph)\iol. 31-749-755. 1955. Obrer\ation of skipjack xhools in Hauaiian uaters in 1953. U.S. 1973 An electrophoretic study of hemoglobin* of wme scombroid fishes Fish Hildl. Serv.. Spec. Sci. Rep. tish 147. 31 p. and related forms Comp. Blochem. Phywd. 448:381-388. SAKACAWA. G.T. 1976. Vulnerablltt) of tunas as a function of en\lionmental profiles. [In 1974. Participation by Panamanian and U S seiners in 1972 tuna fisher) Engl. and Jpn.] In Maguro Gyogy? KyGikai Gijiroku. 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Bull. ?8:335-361 SNODGRESS. R. E.. and E. HELLER. 1960. Estimate\ of laryal tuna ahundance in the central Pacttic I' S h\h. 1905. Shore fishes of the Re\illagigedo, Clipperton. Cococ and Galapagos Wildl. Serb., Fi\h. Bull 60:23I-255. Idands. Proc. Wach. Acad. Sci. 6:333-427. 1961. DiLing helia\iour 01 Hauaiian \kiptach iiina J Con\ Con\. Int. SOEMARTO. Explor. Mer 26:223-229. 1960. Fish behaviour with special reference to pelagic shoaling species: STRASBURG. D M ., E. C JONFS. and R. 1. B. IVERSLN Lajang (Decaprrrus 'pp.). Proc. Indo-Pac. Fi\h. Counc. 8(Sect.3) RY-93. 1968. Uie o1 a small submarine lor hiolopical and oceani~gaph~cierearch. SOKAL.. R. R.. and F. J. ROHLF. 1. Cons. ('on,. Int. F\plor. \ler 31:410-426,. 1969 Biometry. The principles and practice of \tatistics in hioloeical re- STRASBCRC;. D M' .and .I. C, CIkRR. *earth. W.H Freemail, San Franc , 776 p. 1961. Banded color phii\c\ iit iuo pelagic t141e\. f'onphuenu I!!pp!tru~and SOLDATOV, V. K., and G. J. LINDBERG. 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“canma ” [In Jpn.. Engl summ.] Bull. Jpn. Soc. SCI. Flsh. 9:231-236. IEngl. transl. by W. G. Van Campen, 1951. In U.S. Flsh Wlldl. Serv.. Spec.Sc1. Rep. Fxh 51.18-24.) 1957. A con\ideration on the long year\ trend of the flsheries fluctuatton in relation to \ea conditions. Bull. Jpn. Soc. Sci. Fish. 23:368-372. 1961 Frqhenec oceanograph) in Japan. especially on the principle< of fish di\trihution. concentration. dispersal and fluctuation. Calif. Coop. Oceanic Fish. In\est. Rep. 8:25-31.

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Distribution and relatne abundance of lanai skipjack tuna (Kotsu- Bull.. U S. 70:741-762. u,oniispelamis) in the uestern Pacific Ocean. In J. C. Marr (editor). The YABE. H. Kuroshio. A symposium on the Japan Current, p. 395-398. Eact-\Veet 1954. A study on spanning of chipjack m the Saisunan Sea area. hi Center Ptess, Honolulu. General \leu offisher! science. Tok)o [In Jpn.] Jpn. Accoc ,Ad\. Sci. 1971. Larval distribution of tunas and billfishes in ihe Atlantic Ocean. In 182-199. [Engl. transl. by G. Y Beard, 1959. 9 p.; in tiles ol Southncit Symposium on Investigationc and Resources of the Caribbean Sea and Fish. Ceni., Natl. Mar. Fish. Serv.. NOAA. Honolulu. HI 96812.1 Adjacent Regions. FA0 Fish. Rep. 71.2:297-305. 1955. Studies on the firh larvae in the ue\tern Paciftc Ocean I. The poet- UEYANAGI, S.,K. MORI, Y, NISHIKAWA. and A. SLDA. IarLae of Korsuwsonus pelamis. [In Jpn.. Engl. summ.] Bull. Jpn. SOC. 1973. Report on experiments on the development of tuna culturing tech- Sci. Fish. 20:1054-1059. [Engl. transl. b) G. Y. Beard, 1958, 2 p.; in hie* niques (April. 1970-March, 1973). [In Jpn.. Engl. summ 1 Far Sear Fish. of Southuest Fish. Cent., Natl. Mar. Fnh. Serv.. NOAA, Honolulu. HI Res. Lab., S Ser. 8, 165 p. 968 12.1 UEYANAGI, S., Y. NISHIKAU‘A, and T. MATSUOKA. YABE, H., and T. MORI. 1974. Artificial fertilization and larval development of skipjack tuna, 1950. An observation on the habit of bonito, Karsun,onus vopans. and yel- Korsuwonuspelamis. [In Jpn., Engl. summ.1 Bull. Far Seas Fish. Res lowfin, Neorhunnus macrupcerus, cchool under the drifting timber on the Lab. (Shimizu) 10179-188. surface of ocean. [In Jpn., Engl. abstr.] Bull. Jpn. Soc Sci. Fish. VALENCIENNES, A. 16:35-39. [Engl. transl. by W. G. Van Campen, 19.54, I2 p.; Southwesi 1836. Les poissons. In G. Cukier, Le &ne animal. Fortin, Masson et Fish. Cent.. Natl. Mar. Fish. Serv., NOAA. Honolulu, HI 96812.1 Cie, Paris, 392 p. YABE, H., Y. YABUTA, and S. UEYANACI. VAN PEL, H. 1963. 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91 iiilcking uiih iilira\iinicde\xc\ J tLdi. Krr Board Can 27:2071-2079. Fkh. Oceanngr.. Vopros? Ikhimiogbl 43:2W-223. [Engl. iran4. by A. R. 7AVAI A CAMIN, 1 . A Ciocllne. 196R. 22 p.; in ides of Souihueq Fish. Cent.. Nail. Mar. Fnh. 1978 Anoidcione\ wbre la prcwncia del hiado en el %ideve \iir del Brazil. Serv., NdAA, Honolulu, HI 96812.1 [In Span., tnel. and Fr. summ.] Colleci. VdScj. Pap.. 1nt Comm. ZHUDOVA. A%. Conwn Ail. Tuna, (SC RS-1977) 7:X2~83. 1969 Larbae of scombroid fnha (Scombroldel, Perrifnrme,) o1 ihe central /HAROV. V. 1 porlion of the Ailantlc Ocean. [In Rusr.1 Tr. AtlantNlRO 25:100-108. 1967. Cla\rilicaiion 01 the \iombroid I'irhe\ (Suborder Scombrodei, Order IEngl. irand by W. 1.. Klaae. 1910, I1 p.; Inter-Am. Trop. Tuna Comm.. Percilorme\). [In Ku\r.J AilanilulRO. Kalingrad obl.-All. Rec. Inst. I a Jolla. Calif.]