MLML/ MBARIUBRARY 8272 MOSS LANDING RD. MOSS LANDING, Gil 95039 ASPECTS OF THE LIFE HISTORY OF THE BLUE SHARK, PRIONACE GLAUCA L., IN MONTEREY BAY, CALIFORNIA
A Thesis .Presented to the Faculty of the Department of Biology San Jose State University
(
In Partial Fulfillment of the Requirements for the Degree Masters of Arts
By James Thomas Harvey December, 1979 ABSTRACT.--Feeding habit, age structure, growth, morphology, and parasite data were collected on the seasonally abundant blue shark, Prionace glauca, in Monterey Bay, California from 1974 to 1977. Stomach content analysis of 150 blue sharks revealed a diet which was dominated by the northern anchovy
(Engraulis mordax), euphausiids (mainly ~anoessa spinifera), hake (Merluccius productus), and several species of cephalopods. The ingestion of l· spinifera marks the first record of preda tion upon euphausiids by this species. In general, the rna- jority of prey live an epipelagic life or become epipelagic nocturnally. The blue sharks ranged in total length from
98.5 to 204.5 em (x = 155.6! 3.9 em). Females were signifi cantly more numerous (124 females:24 males) and of greater age than males. Vertebral ring counts of 98 blue sharks showed the estimated age of sampled sharks to be 2 to 6 years. Length frequency data tends to support the assumption of an nular ring formation. Aging and length frequency data es timate growth rates of 12.2-28.2 cm/yr, the higher growth rates occurring at the younger ages. Only the linear mea- surements associated with the head region changed significantly when compared to the total length for the 115 sharks examined for allometric growth. Liver weights, gonad weights, and parasite relationships were also discussed.
l' i i i • I' i' TABLE OF CONTENTS
Page
ABSTRACT ... i i i
LIST OF TABLES vi
LIST OF FIGURES. v i i i
ACKNOWLEDGEMENTS X
I NT ROD UCT! ON . . 1
MATERIALS AND METHODS. 8 RESULTS. . 1 8
Length. 1 8
Allometric growth 21
Weights ••• 21
Reproduction. 24
Feeding habits. 26
Fish . . . . 33
Euphausiids. 40
Cepha 1opods. 41
Age and growth. 41
Parasites 45 DISCUSSION 50
Catches 50
Lengths 52
Weights 53
Reproduction. 54
Feeding habits. 55
i v Engraul is mo rd ax 59
Merluccius ~uctus 60
Euphaus i ids. 61
Cephalopods. 65
Age and growth. 67
LITERATURE CITED 7 1 APPENDIX . . 77
v LIST OF TABLES
Table Page 1. Allometric growth relationships for six linear
measurements on 115 blue sharks. 22
2. Prey items from 121 blue sharks collected between
1974 and 1977. Listed is the percent number
(% N), percent volume (% V), percent frequency of occurrence(% FO), and index of relative importance (IRI) for each prey item. The prey
are listed in decreasing order of importance, as determined by the IRI' s ...... 30
3. Prey items collected from 43 blue sharks in 1976.
Listed is the percent number (% N), percent volume (% V), percent frequency of occurrence (% FO), and index of relative importance (IRI) for each prey item. The prey are 1 is ted in decreasing order of importance determined by the I RI...... 35 4. Prey items from 58 blue sharks collected in 1977.
Listed is the percent number (% N), percent
val ume (% V), percent frequency of occurrence (% FO), and index of relative importance (IRI) for each prey item. Prey are listed in de- creasing order of importance as determined by
the I RI. 37 vi 5. Mean total length measurements for blue sharks with
assigned vertebral ring counts. Displayed are
the sample sizes, one standard deviation, and
95% confidence intervals around the mean total
lengths for females, males, and the total . . 44
vi i LIST OF FIGURES
Figure Page
1. Collection area for blue sharks in Nonterey Bay,
California . 9
2. External measurements recorded for 120 blue sharks
captured in Monterey Bay, California . 11
3. Example of measurements recorded for each blue
shark centrum. . . • ...... 15
4. Number of blue sharks caught per hour for weekly
intervals and the number of hours fished (effort)
for 1976 and 1977...... • . . 19
5. Frequency histograms for total lengths of blue
sharks caught in 1976, 1977, and all years
combined ... 20
6. Body weight-total length relationship for 134
blue sharks collected in Monterey Bay. 23
7. Liver weight-body weight relationship for 106
female and 19 male blue sharks collected in
Monterey Bay ... 25
8. Relation of cumulative prey items to randomly
pooled numbers of blue sharks sampled in:
(a) 1976, (b) 1977, and (c) all years combined 27
9. Feeding states of 121 blue sharks caught
between 0700 and 1300 hours, from all years
combined .. 29
vii i 10. Index of relative importance graph for the more
important prey items of 121 blue sharks, from
all years combined ... 32
11. Comparison of the major prey categories with regard
to percent number (% N), percent volume (% V),
percent frequency of occurrence(% FO), and
index of relative importance (IRI), in the years
sampled ..... 34
12. Index of relative importance graph for the more
important prey items of 34 blue sharks collected
in 1976 . . . • ...... 36
13. Index of relative importance graph for the more
important prey items of 58 blue sharks collected
in 1977 ...... 38
14. Ring radii measurements for blue sharks. 43
15. Growth curves for 16 rna le and 82 female b1 ue sharks
caught in Monterey Bay .... . • • 4 6
16. Comparison of growth curves from present study
and that of Stevens (1975)...... • 4 7
17. Comparison of the total 1 ength histograms with
lengths at a determined age for 98 blue
sharks. • • . • • 48
18. Locations of observed surface swarms of euphausiids. 64
ix
L ACKNOWLEDGMENTS
I am grateful to many persons who contributed, in many ways, to the successful completion of this project. In par ticular, many helpful friends at Moss Landing Marine Labora tories have donated their valuable time and suggestions. Dr. G. Victor Morejohn, my major professor, provided guidance and financial support. Dr. Gregor H. Caill iet served as my advisor and gave generously of his time and support. Dr. Robert Has sur also served on my committee and helped in editing the manuscript. I extend my thanks to Roger Helm, Sara Tanner, Kon Karpov, Jim Heberle, Jerry Kashiwada, Bob Cayce, Kon Cayce, and Robert Yoklavich, to name only a few who have aided in my field collections. Lynne 0. Krasnow was a constant source of help, information, and 1 aughs throughout the research. Mary M. Yoklavich gave much of her time in data gathering, moral support, editing, and final typing of this thesis, and to her I am extremely indebted. Finally, I would like to thank my parents, who were instru- mental in my education and career and who assisted in the completion of this project. This investigation was funded by a grant from NOAA, Office of Sea Grant, Department of Commerce, #04-6-158- 44021. A portion of the i 11 ustrations were prepared by Mike Mallon.
X INTRODUCTION
The pelagic, marine ecosystem has become a current topic in scientific research, due to man's increasing interest and activity in the open ocean. Man's impact upon this system will be most apparent at the higher trophic levels. Pelagic sharks represent top carnivores in this complex and unex plored region of the ocean. They have also become a target in the development of elasmobranch fisheries (Holden, 1973; Ron s i v a 11 i , 1 97 8) . Un t i l r e c en t 1 y , the r o 1 e sharks p 1 ay in the pelagic environment and questions regarding their basic biology have not been explored. Information pertaining to the biology of these higher trophic level organisms may help to understand the intricate ecosystem to which they belong and the effects of man's activities on this system. The blue shark, Prionace glauca Linnaeus, is considered common in the warm temperate, tropical, and subtropical oceans of the world. Strasburg (1958) reported the blue shark to be the most abundant of the pelagic sharks in the central Pacific between 20°5 and 50°N latitude and 105°E and l85°W longitude. He found that the greatest abundance occurred north of 20°N latitude in the eastern part of the Pacific. Neave and Han avan (1950) found an extension of the distribution in the north Pacific to 57°N latitude in the Gulf of Alaska. Miller and Lea (1972) considered this species common in the eastern Pacific, from Chile to the Gulf of Alaska, but uncommon in the tropics. Blue sharks have been sighted from 0°N to 40°N latitude in the western Pacific (Suda, 1953). Bigelow and
1
L -----·------2
Schroeder (1948) described the blue shark as the most plenti ful large oceanic shark in the Atlantic and Mediterranean Oceans. It is distributed from Africa to southern Norway in the eastern Atlantic and from Cuba to Newfoundland in the western Atlantic. In the Indian Ocean it is found from Africa to Australia, Indonesia and the Nicobar Islands between 17°N and 37°5 latitude (Gubanov and Grigor'yev, 1975). The migration of the blue shark into colder subpolar and temperate waters usually occurs during the hemispherical sum mer and early fall, when surface water temperatures increase. The studies of Neave and Hanavan (1960), in the Gulf of Alas ka, found blue sharks distributed only to 45°N during May and June, when the surface water temperature ranged from 5° C to 10° C. In August and September, however, they had increased their range to 57°N latitude, when the water warmed to approx • imately 15° C. They found that blue sharks were present in i water with temperatures ranging from 11 to 17° C. In the Pacific, Strasburg {1958) postulated a north-south seasonal migration which corresponded to the movement of a temperature transition zone. Like the albacore, blue sharks apparently move north with isotherms having temperatures from 13.3° C to 23.3° C. Gubanov and Grigor'yev (1975) have recorded a temperature range of 11° C to 27.6° C for sharks caught in 80 to 200 m of water. The seasonal migratory habits of the blue sharks are described by Beckett (1970) and Stevens (1976). Beckett
L 3 tagged 1,176 blue sharks in the north Atlantic and described a counter-clockwise pattern of movement. Eleven tagged ani- mals were recovered; one traveled 424 miles in 48 days. An- imals tended to move northeast in summer and south in late fall, with movements offshore in winter. Stevens marked over 2,000 blue sharks southwest of England and thirty of these were recovered. The locations of recovered tagged blue sharks indicated a latitudinal migration of large females into the England area, followed by smaller males and females. As in many fish stories, the size and growth of animals can be greatly exaggerated. To date, the largest documented blue shark was 3,830 mm in total length (TL) (Bigelow and Schroeder, 1948). Published accounts by Bigelow and Schroe der (1948) and McKenzie and Tibbs (1964) describe blue sharks measuring up to 3,350 mm and 3,290 mm in total length, respec- tively. In areas where a large number of sharks were caught, some size difference due to sexual dimorphism was shown. Me- Kenzie and Tibbs (1964) collected data in the north Atlantic on 306 blue sharks. The average length for males was 2,310 mm; females averaged 1,820 mm. Tricas (1977), working in southern California, found the largest male to be 2,050 mm and the largest female to be 2,000 mm. (TL). Relatively few growth estimates for blue sharks are available in the literature. Bane (1968), from a tagging program around the Channel Islands, suggested a growth of 456 to 600 mm/year (sexes and age classes were not 4 distinguished). Stevens (1975) used a vertebral aging technique, along with tagging, to derive a growth estimate of approximately 300 mm/year for young animals. Elasmobranch aging has been difficult due to a lack of seasonal hard tissue deposition. Teleost fishes have been successfully aged by examining hard tissues such as otoliths, scales, and opercular bones (Williams and Bedford, 1974). These structures are either unavailable or inadequate for age determination in el asmobranchs. Researchers, therefore, have turned to spines, tooth replacement rates, calcified verte- brae, length-frequency analysis, and tagging efforts for ag ing (Daiber, 1960; Holden and Meadows, 1962; Holden, 1972; Moss , 1 97 2 ) . Lately the emphasis on elasmobranch aging has centered on vertebral ring deposition. Paraffin and xylene impregna- tion methods have been used to enhance the decalcified rings (Oaiber, 1960). Alizarin Red S staining of vertebral ring calcium deposits has been attempted with some success (La Marca, 1966). Stevens (1975), working with blue sharks, modified an older technique of silver nitrate staining of calcified areas. Finally, X-ray spectrometry has been shown to yield comparable results to other aging techniques, al though it is time consuming and expensive (Jones and Geen, 1 977). To date, the feeding habits of the larger pelagic sharks have received the greatest amount of attention. A number 5
( of papers, dealing exclusively with this subject, have been published on the blue shark. Typical variations due to re- gional differences have been described, but in general the blue sharks feed on the available pelagic organisms with which they co-occur. Small schooling fishes, such as herring, sardine, saury, and mackerel, were found to be the predominant prey items; cephalopods represented the second most important prey group ingested (Bigelow and Schroeder, 1948; Strasburg, 1958; - Le Brasseur, 1964; Stevens, 1973). Many of the cephalopods were characterized as being deep-water species, and a great diversity was found in this group (Stevens, 1973; Tricas, 1979). Blue sharks were also found to be preying upon an occasional non-schooling fish, bottomfish, shrimps, salps, crabs, bivalves, and inorganic material. Diel activity patterns of the blue shark have been ex amined by Tricas (1977) and Sciarrotta and Nelson (1977). Both of these groups worked near the Channel Islands off California. Tricas described movements of blue sharks at night, which were found to be associated with the availability of shoals of the squid, Loligo opalescens. Sciarrotta and Nelson, following telemetered sharks, found increased activ ity in the evening and night. Movement in the twilight hours was primarily directed toward shore and was probably a result of food availability. l j! .!l 6 The reproductive biology of the blue shark has not been
throughly documented. A1 though it appears that sexual segre- gation occurs during the summer,' the mating season has been described by Suda {1953) to be June through August off Japan. Gubanov and Grigor'yev (1975) propose that mating may contin ue all year long. Embryos have been found throughout the year in female sharks from the Indian and Pacific Oceans (Strasburg, 1958; Gubanov and Grigor'yev, 1975}. This data tends to substantiate the concept of year-round breeding. - Fecundity estimates vary considerably, with data indicating from 28 to 100 young per adult female (Bigelow and Schroeder, 1948; Strasburg, 1958; Gubanov and Grigor'yev, 1975). The most often quoted range appears to be about 25 to 40 young per female (Suda, 1953; Hart, 1973). The young may develop differentially after internal fertilization (Gubanov and Grigor'yev, 1975). Development is viviparous with the embryo being nourished by a well developed yolk-sac placenta attached to the uterine wall (Bigelow and Schroeder, 1948). At birth the young range from 300 to 530 mm (TL) (Hart, 1973). Bigelow and Schroeder (1948} report the smallest free-living blue shark to measure 530 mm (TL). The females of this species appear to give birth at lengths as small as 1,500 mm (TL), although the majority start to reproduce at approxi- mately 2,000 mm (TL} (Bigelow and Schroeder, 1948; Suda, 1953; Gubanov and Grigor'yev, 1975). The blue shark in the eastern Pacific, and particularly ; i l nearshore, has received limited attention. Answers to
L --·····------7
( questions regarding its basic biology along the California coast are incomplete or lacking. With this in mind, a study was begun to investigate the feeding habits, age distribution, growth, morphology, parasites, and migrational patterns of the blue shark population in Monterey Bay. Particular atten- tion was given to the predation of blue sharks on local fish ery stocks, such as the northern anchovy (Engraulis mordax) and the market squid (Loligo opalescens), which are presently being harvested in Monterey Bay. MATERIALS AND ~1ETHODS Collections and observations of blue sharks were accom plished in Monterey Bay, California (ca. 36°SO'N, l21°SO'W) (Fig. l ). Monterey Bay is approximately 53,600 hectares in area and is bisected by a deep submarine canyon (up to 1,000 fathoms within the bay). The canyon provides water of depths up to lDO fathoms within five miles of the coast. The large expansive sand flats, which flank the canyon to the north and south, range up from about 50 fathoms deep at the canyon's edge towards the coastline. The surface water temperature in the middle of the bay ranges from l0.5°C in April to 16. 5°C in September (Abbott and Albee, 1967). Collection attempts were made throughout the bay, but were most frequent in an area no greater than 19,000 hectares, five kilometers west of Moss Landing (Fig. 1). The primary collection area was located in the middle of the bay, over the Monterey submarine canyon, in approximately lOD fathoms of water. Blue sharks were collected on a weekly basis, when- ever possible, from September 1974 through October 1977 in the summer and early fall months (June to October), with more concentrated fishing effort occurring during 1976 and 1977. The time of collection was ordinarily between 0800 and 1400 hours, although three attempts were made to collect sharks at night. Collections were made from the R/V ORCA (a thirty- one-foot cabin cruiser) and a sixteen-foot Boston whaler. Blue sharks were captured in three ways: l) longline, 2) hook and line off the boat, and 3) hook and line with rod
8 ... 9
122° w 50' 43' 3 7" - • •• Cop.•t.olo t ...... •••
Wciconvil!e
...... -··~~--"·-..-~ .. __ .-· ··-
il ll'. )» ~
rU)! ,....
~;a G)! I ::::: > I·, ll\ \. :·:. ~· · r- .... !>' ill' 0' ::- • Morino lll / ! !',; ;' ·40' ,/ "'ll' / I ..... ~ . ... ,\ .1 I .· .. "·~ ··---J _/./.,,._~_··. ---"MONTEREY \ BAY
NAUTICAL p,jiLE.S 0 l 2 4 5 Depth in fathoms
Figure 1.--{ollection area for blue sharks in Monterey Bay, California All capture attempts were made wi thin the lined area. 1 0
and reel off the boat. The longl ine consisted of quarter
inch braided nylon rope (75 meters in length) to which one
two-meter stainless steel leader and a #2 baited hook were
attached every five meters. The hooks were baited with
either anchovy (Engraulis mordax) or squid (Loligo opales
cens). The longline was suspended from the surface by four
meter lines attached to orange surface buoys. A one-gallon,
perforated, plastic bottle, filled with macerated anchovies (f. mordax), served as chum and was attached to each 1 ongl i ne. - After numerous balls of tangled line and small catches, a
more efficient means of capture was initiated. The method
simply involved hanging the chum bottle and 2-3 baited lines
three meters below the surface around the sides of the boat.
This method allowed quick recovery, close observations of
feeding behavior, and possibly better catch rates. On sev-
eral occasions sharks were caught with rod and reel with a
single baited hook lowered to approximately 20 to 30 meters.
The location, weather, sea state, and presence of other
organisms was noted at each collection site.
After being transported back to the laboratory, usually
within an hour, the sharks were weighed (within 0.5 kilo-
grams) and eight linear measurements were recorded along
with an estimate of girth (to the nearest millimeter) {Fig.
2). Each shark was then sexed, the liver and gonads weighed
on a triple beam balance to the nearest gram, and wounds and
external and internal parasites were noted. The stomach
- 11
r14------TL ------i'i ~ SD ·I ~~--ED
SE -i1 ll'. SJ )>. .~ ~ SA g) ,_(I)< TL: TOTAL LENGTH § s SD: SNOUT - DORSAL FIN C) !!::: > :lll ED: EYE DIAMETER *I' r- SN: SNOUT - NARES > Ill'o- !Ill SE: SNOUT- EYE !:; 0 SJ: SNOUT - JAW i SA: SNOUT- ANUS G : GIRTH
Figure 2.-External measurements recorded for 120 blue sharks captured in Monterey Bay, California.
- 12 contents were sieved through a #60 (250 micrometer) screen, fixed in 10% formalin, and in two to three days were trans- ferred to 40% isopropyl alcohol and stored for later analysis. For age determination, a section of the vertebral column was removed just anterior to the first dorsal fin. Each section, usually consisting of 8 to 12 vertebrae, was stored in 50%
isopropyl alcohol until it was analyzed one to two months 1 ater. The stomach contents of each shark were subjectively scored according to a scale of state of digestion and fullness - described by Dewitt and Caill iet (1972). Stomachs were rated a four when 75-100% full, three when 50-75% full, two when 25- 50% full, one when 1-25% full, and zero when the stomachs were empty. The state of digestion was similarly scored. The gen- eral state of the stomach contents was rated four when the ma- jority of prey did not appear to have been digested. A score of three to one corresponded to decreasing levels of digestion, and zero signified an empty stomach. Stomach contents were sorted and each prey item identi- fied to the lowest possible taxon. Cephalopod beaks were identified utili zing a key by Clarke (1962), a pictorial guide by Pinkas, 01 iphant, and Iverson (1971 ), and a refer- ence collection of cephalopod beaks at the Moss Landing Marine Laboratories. For each blue shark the prey items were enumerated, measured, and subjectively rated as a per- centage of the total volume of prey. When either otoliths or beaks represented prey species, the number of prey was 1 3 determined by the largest number of right or left otoliths, or greatest number of upper or lower beaks. Special care was taken to record ingestion of anchovy or squid that was used as bait. The bait was marked with distinctive cuts to help facilitate identification. To determine the size of Loligo opalescens ingested, three measurements were taken on both the upper and lower beaks. The size of the squid could then be estimated from a linear regression of the beak mea surements on dorsal mantle length, as reported by Kashiwada, - Recksiek, and Karpov (in press). The importance of each prey species was calculated uti lizing the index of relative importance (IRI) which was for mula d by Pinkas, 01 iphant, and Iverson (1971 ). An IRI value was calculated for prey items from each year and all years combined, thus providing a way of ranking each prey category according to its significance in the blue shark diet. The index of relative importance was calculated by summing percent number and percent volume of each prey item per stomach and multiplying by percent frequency of occurrence. The Spearman rank correlation test was used to test changes in dietary rankings for different years (1976 and 1977) and for all years combined. The adequacy of the number of sam ples for stomach analyses was verified by a plat of the cumu lative number of prey categories against the randomly pooled number of fish samples (Hurtubia, 1973; Cailliet, 1976). 1 4
The technique used in aging was a slightly modified v e r s ion of the one used by Stevens ( 1 9 7 5 ) . Us ua 1 1y two vert e- brae were separated from the preserved vertebral section and the haemal arch, lateral processes, and connective tissue were removed to expose all surfaces of the centra. They were then washed in distilled water for five to ten minutes before their placement in 1% silver nitrate. The centra were allowed to soak in silver nitrate for five to ten minutes; they were then exposed to ultraviolet 1 ight for six to eight minutes. The centra were next washed briefly with distilled water and - fixed with 5% sodium thiosulfate for three to four minutes. After a final washing in distilled water they were stored in 50% isopropyl alcohol. The number of rings visible was counted before and after the silver nitrate process. The rings were counted independently by two persons. Discrepancies in counts were discussed until a concensus was obtained. Each ring was measured along the 1 ateral intermedi alia radius at the 90°-270° axis using an ocular micrometer (Fig. 3). The ring radii were measured from the center of the centrum to the beginning of the dark region of the ring. In addition to ring counts and radii measurements, the centrum radius was measured from the center to a point at 90° on the centrum edge. Utilization of this method, along with other parameters, facilitated the establishment of two estimates of total body length at a given age. First, the number of distinguishable rings from the centrum's center to its perimeter gave an estimate of age. Second, a measure of the centrum radius and total l 5
,..._-C--t>~
-'jj1 lll'. ~
';;J ~11)1 ,;;l i'1
rf 1 6
body length of each shark provided a formula that predicted a total length for a known centrum radius. Measuring ring radii, and applying this to the equation, predicted a total length at each ring count. This information was then com- pared to the aging data to substantiate length distribution and possible age classes. A best fit logarithmic equation was used to establish a growth curve for aged sharks. This line was then compared to the von Bertalanffy growth curve of Stevens (1976). Growth -jjl curves were generated for males, females, and all sharks com ,....:o; i! :Jl!\ bined. At-test was used to compare slopes of regression .<; ' M if __ lines after the data had been logarithmically transformed (!)o r- (Zar, 1975). The difference in the proportion of males to :a~ females within age classes was tested by the use of a 2 x 4 G)< il:: >- contingency table (Sakal and Rohlf, 1969). :DI ~· Length frequency histograms of sharks collected in 1976 r- )>- Ill' and 1977 were compared between themselves and with the total ,..0< !<; by a Chi-square goodness of fit test (Sokal and Rohlf, 1969). 0< :l1' iiil Length-weight relationships for male and female sharks fhl were derived from a power equation and were compared by the use of at-test. The Chi-square test was utilized to eval- uate the number of females caught in comparison to males. Liver weight data were analyzed as the ratio of liver weight to body weight. Ratios were transformed utilizing an arcsine transformation. After transformation, means and confidence intervals were calculated and comparisons were
------~------~·····--·----· ~~ ''I 'I l 7 made between males and females. An analysis of variance test was performed to determine if the regression of liver weight/ body weight on body weight was significantly different from zero (Zar, 1975).
... " i '.~.,·.'' RESULTS A total of 120 blue sharks was caught in the summer I months of 1976 and 1977, when 54 and 66 animals were col- lected, respectively. An additional 30 sharks were examined for feeding habit analyses, sex, and length determination.
These thirty sharks were call ected in 1974 and 1975 in a preliminary study of potential squid predators. Blue sharks were caught as early as 25 June and as 1 ate as 17 October, although occasional sightings of blue sharks occurred through- out the year. A total of 52 collection attempts was made - with a combined effort of approximatley 82 hours of fishing
(see Appendix A). The number of animals caught per fishing hour (catch per unit effort = CPUE) varied dramatically from day to day and month to month. The highest CPUE occurred on
10 August 1977 when a total of 11 sharks was caught in two hours. When data from all years were combined, the highest catch occurred in August (Fig. 4). Eighty-eight sharks were captured in August as compared to 41 in July, 10 in September,
10 in October, and one in June.
Lengths
Overall, blue sharks ranged in total length from 958 mm to 2,045 mm, with a mean of 1,557! 39 mm (! 95% confidence interval) (Fig. 5). In 1976, they ranged from 1,234 to
2,045 mm (x = 1,584! 55 mm) and were not significantly dif ferent in mean tota 1 length from those collected in 1977
(x = 1,536 ! 58 mm) or all years combined. Likewise, there was no significant difference in size distributions when
18 0::: 9 :::) 0 0 0 4 \ I • 8 -W ,...o I \ \C.P.U.E ..-' I (f) 0 I e / 7 ' / I LL 1- / I 3 \ 0 I \ . 6 (f) (.9 o .. I ' I :::) ... I 0::: EFFORT--,/ ' \ :::) 'o 0 I 5 <{ I \ o, I 0 u \ I I 2 0 ' / I G 4 I ' '/ I (f) e I 0 LL. ~ I e I 0 .... ,o. 3 0::: ... I I' \ ,...o' ...... I' <{ \, ' I 0::: 0 " 'o--o • 2 I ""'· \ / w (f) CD ~ 0 :::) z \ z 0 \L) r-- r-- tO tO tO tO tO r-- r-- r-- r-- r--·"Ir-- r-- r-- r-- r-- -· r-- r-- r-- r-- r-- r-- 1'-: r-- r-- r-- r-- r-- r-- r-- r-- r-- r-- r-- r-- r-- C) C) 1- 1- 1- ...1 C) C) 0.. z z ...1 ...1 ...1 ...1 C) C) C) C) 0.. 0.. 1- ::::> ::::> ::::> ::::> ::::> w ::::> ::::> ::::> ::::> ::::> ::::> ::::> ::::> ::::> ::::> w w (.) ""';) -:> ""';) -:> ""';) ""';)
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ...... ~ ...... 10 D FEMALES 1976 (54) ~ MALES 5 1000 1200 1400 1600 1800 2000 10 1977 (66) sn :Qtl, 5 ""~ u>- z w ,.~ ::> 0 0 l>j w 1000 1200 1400 1600 1800 2000 Z, 0:: ::0 lL. B :1>' s::: 20 ~- )J~ , ;L'I' 1974-1977 nii (149) , ,.-· I ll'~ 15 ! :J~ ' :OI : )>• ,:J> ·"', :O' ~ ;;1, 10 :Jl.il< 5 0 1000 1200 1400 1600 1800 2000 TOTAL LENGTH (mm) Figure 5.-Frequency histograms for total lengths of blue sharks caught in 1976, 1977, and all years combined. The hatched area represents the number of males; the bars are additive. (Sample sizes are in parentheses.) 21 comparing 1976 and 1977 and all years combined. The 124 female specimens averaged 1,591 + 40 mm (range: 1,010- 2,045 mm) as compared to a mean of 1,384 + 104 mm (range: 958- 1,835 mm) for the 24 male sharks. Allometric growth Three linear measurements changed significantly in pro- portion to total length (snout-eye, snout-nares, and head length) (Table 1 ). All three of these head measurements ,_ decreased proportionately with the total length, while the other four measurements (snout-anus, snout-dorsal, eye di- a'lleter, and tail span) remained constant. Weights 81 u e s h a r k s co 1 1 e c ted i n Monterey 8 ay ranged i n tot a 1 body weight from 3.6 to 38.1 kg (ii = 15.7 ~ 1.4 kg). Blue shark body weight (vi) to total length (TL) relationship for males and females can be described by the equations: males(n=l9), \v=l.20 x 10- 7 TL 2 · 51 (r=0.65, P There was no significant difference between the slopes for males and females (P<0.05). Therefore, all the sharks were combined.and the weight-length relationship was expressed by the equation: body weight=2.57 x 10-9 TL 3 · 05 (r=0.72, P Livers v1ere excised from 124 blue sharks (105 females, 19 males) and weighed. Fifty-one livers had the left and 22 TABLE 1.-Allometric growth relationships for six linear measurements on 115 blue sharks. Regression Carrel at ion equation coefficient Me as u rem en t (TL = total length) ( r) Head length ( HL ) HL = 26.7 0.001900 TL 0.32000* Snout-nares ( S- N) S-N = l 5 . 3 0.001750 TL 0.11000* Snout-eye ( S- E) S- E = l 8. 9 0.001600 TL 0.11000* Snout-dorsal (S-O) S-0 = 3 9. l 0. 000400 TL 0.01400 Snout-anus (S-A) S-A = 46.2 + 0.000420 TL 0.01000 Tail span (TS) TS = 29.4 + 0.000021 TL 0.00021 * signifies significance at 95% level. 43.0 ,-.---,----,--~--r--.,----,----,---...,.--,.--- 38.0 0 0 BW =2.6 x Jo-9 TL 3.05 33.0 0 0 -01 0 .X: 28.0 0 0 ~ 0 00 1- 0 0 0 0 0 I 0 0 0 0 (!) 23.0 w ~ ! 8.0 >- 0 0 0 m 13.0 8.0 3.0 ° 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 N f<) <:t l() tO 1'-- co Ol 0 N N N w TOTAL LENGTH (mm) Figure 6.-Body weight-total length relationship for 115 female (o) and 19 male (o) blue sharks. The line is formed from the above equation. -·· -· --- "' "---·- V~1~"1~Y~~'3'f l '11~9.'ffl V~'U\UU l 'i~~'!~~ t 24 and right lobes weighed separately. The mean liver weight for blue sharks was 1,185.9 ~ 143.1 g (range: 205-4,400 g). The liver weight (LW) to body weight (BW) relationship for males and females was expressed as: males(n 19), LW(g)=-0.01+0.06B\·I(kg),{r=0.7l,P Rep rod uc t ion A significantly greater number of females (n=l24) were co11ected than males (n=24) (:X. 2=67.6, P 0 4100 -- LW • -0.03 + 0.10 BW ( ~) 3600 ---- L W • - 0.0 I + 0.06 BW ( d') 0 0 ~ 3100 0 0 0 0 ~ 2600 0 (!) 0 w 0 0 0 3: 2100 a:: w 0 > 1600 _J 0 1100 0 0 0 600 0 0 0 0 0 0 0 0 r 40 A 30 --·---·-· ./" 20 / 1976 en / (n=54) w (" 0:: 10 • 0 <.9w f- - _...... / .---·-·-· w 30 • 0:: ,..,..--·-·./ n... ;· l.J... 20 . 1977 0 ._...-.--"' (n= 66) 0:: 10 ( w • m ~ :::> 0 z 10 20 30 40 50 60 70 ..,., 50 I' w c I'.. > __...... )<" f- 40 -· --·-· nI' 30 ~ /" :::> • TOTAL 0 20 ( (n=l50) 10 . 0 I 25 50" 75 100 125 150 J POOLED NUMBER OF FISH '!} Figure B.--Relation of cumulative prey items to randomly pooled numbers of blue sharks sampled in: (a) 1976, (b) 1977, and (c) all years combined. 28 were intact or retained their flesh. Fish appeared in a variety of states of digestion from whole, freshly ingested animals to the remnants being only the otolith. Euphausiids were normally found freshly ingested, although occasionally eyes and carapaces were the only distinguishable remains. The prey were generally well digested and infrequent in the blue sharks collected (Fig. 9). Based upon the state of digestion and fullness of the stomach most of the sharks collected from 0700 to 1300 were not full nor had fed recently. ~~ ' llti. The second most frequent category was a condition of recent '" I r~ ! '" but not full. :1 ,. i The dominant i terns in the stomachs ~1ere undetermined ·~ I .::1 I fish parts, fish and cephalopod eye lenses, and digested ma ,, "·-" :.< .II terial (Table 2). With all years combined, the most impor- ""o# '" r'i tant discernible prey items, based upon the indices of rela ;';'.\' iii tive importance, were I· mordax, euphausiids (especially ,, Thysanoessa spinifera), pacific hake (Merluccius productus), '11 ,.\1 and Octopus spp. Together with cephalopod parts, spiny dog ,. i'i fish (Squalus acanthias), and four species of cephalopods, il' the above constitutes the rna in diet of blue sharks in Monte rey Bay (Fig. 10). Euphausiids were the most numerous items in the stomachs, followed by f. mordax, Octopus spp., and cephalopod parts. The northern anchovy comprised the most volumetrically important portion of the diet, followed by ~· acanthias, _li. productus, and I· spinifera. Octopus spp. I! appeared more frequently in blue shark stomachs than did the !' FULLNESS 2 3 4 z w 80 0 A u I- (/o)Hf z (f)w NOT FULL : FULL BUT : w OR RECENT NOT RECENT 0:: g 2 0:: :::J lL u 0 u 60 w 3 0 I- (f)~ ~ 4 >- uz w 40 :::J w0 0:: LL 1-z 20 w u 0:: w a_ 0 A 8 c D A 8 c D A B c D 1976 1977 TOTAL FEEDING STATES FOR SHARK CAUGHT BETWEEN 0700-1300 N Figure 9.--Feeding states of 121 blue sharks caught between 0700 and 1300 hours, <.D from all years combined. I I 30 TABLE 2.-Prey items from 121 blue sharks collected between 1974 and 1977. lis ted is the percent number (% N), percent volume (% V), percent frequency of occurrence (% FO), and index of relative importance (IRI) for each prey item. The prey are listed in decreasing order of importance, as deter mined by the IRI's. Prey Species % N % v % FO IRI Fish parts 11 . 7 2 7. 1 51 . 2 1 9 85.2 Lenses 26.6 5.8 45.5 14 71. 8 Digested tissue 5 . 3 7.3 30.6 383.6 - Engraulis mordax 6 . 9 1 0. 4 1 7. 4 300.8 Euphausiacea 1 0. 2 3.2 1 4. 9 1 9 7. 9 Th,)lsanoessa spinifera 8.7 5.4 12.4 1 7 3. 6 ;l i•lerl ucci us 2.!::_0 ductus 2.9 5.6 1 9. 8 1 69. 3 ,, Oc tot~ us spp. 3.2 1.8 24.8 124.4 " Cephalopod parts 3.0 3.7 15 . 7 1 05. 9 ~ I Sgualus acanthi as 2.3 8.0 9. 9 1 01 . 8 " Gonatus s pp. 2 . 5 2.4 14.9 73.5 ~ I [o 1 i go ~ oealescens l . 4 1 . 3 1 5 . 7 41.7 • I Histioteuthis heteropsis 1 . 2 1 . 1 l 2. 4 2 8. 4 • Oc to~o teu this deletron l . 3 1.3 9. l 24.1 "' Terrestrial plant fragments 1 . 1 1.2 6.6 15 . 2 •3 C1ueea harengus ~alasii 1 . 1 2 . 2 3.3 10.9 • A1 g ae 0.4 l . 7 5 . 0 l 0. 4 .- VamJ;J):'roteuthis infernal is 0.8 0.5 7.4 9.4 ,, On,)!cho teuthi s boreal i-jaeonicus 1.3 0.4 4. 1 7 . 1 ' II it I Cithari chth,)!S sordidus 1 . 3 l . 4 2.5 6.5 I, l'inoe lot:oma fimbria 0.9 l . 2 1.7 3.4 I;. Porichthrs notatus D.3 1.0 2.5 3. 1 •' Sebastes paucispinus 0.3 0.9 2.5 2.9 • El asmobranchi a 0.3 0.8 2.5 2.8 • Sebastes goodei 0.2 1.3 1 . 7 2.5 :;' Inorganic material 0.4 0.7 1.7 1.9 • Genjlonemus 1ineatus 0. 5 0. 5 1 . 7 1.5 · Myctophi dae 0.4 0.5 1.7 1 . 5 Stenobrachius leucoesarus 0.8 0.8 0.8 1 . 4 EuJ;Jhausia eacifica 0.6 0. 1 1 . 7 1 . 0 Feathers 0 . 1 0.2 3.3 0.9 Detritus 0.7 0.2 0.8 0.7 Argonauta eacifica 0.2 0. 1 2.5 0.5 Sjlngnathus californiensis 0. 1 0. 5 0.8 0.5 Isopoda 0.3 0 . 2 0.8 0.4 Pleuronectiformes 0.2 0.2 0.8 0.3 Sco rpaeni dae 0.2 0.2 0.8 0.3 Terre s t i a 1 insect 0.2 0.1 1 . 0 0.3 ~·i Ph,i:l1 oseadix s p. 0. 1 0. 1 1.0 0.2 lj!Oj:lSetta exilis D. l 0.2 0.8 0.2 I 31 TABLE 2.--Continued. Prey Species % N % v % FO I R I Chi lara ta.):'lori 0. l 0. l 0. 8 0.2 Sebas tes s p. 0 . l 0. l 0.5 0. l Pandal us jordani 0 . l 0. l 0.5 0. l Sebas tes jordani 0 . l 0 . l 0.5 0. l Prionace glauca tooth 0. l 0 . l 0.4 0. l Do s i d i c us gigas 0. l 0 . l 0.4 0. l Gonatus ~ 0. l 0. l 0. 4 0. l Lam~etra tridentata 0. l 0. l 0.3 0. l •r '• ' i ••Cj Prionace qlauca 1974 - 1977 0::: w CD :::::!: :::>z 20 ~ w N 40 Figure 10.--Index of relative importance graph for the more important prey items of 121 blue sharks, from all years combined. 33 proceeding abundant prey: t~. productus, E. mordax, and cephalopod parts. In general, euphaus ii ds were the most numerous prey item, with fish occupying the greatest volume and occurring the most frequently. The relationships among the major prey groupings as represented by number, volume, and frequency of occurrence remained fairly constant throughout the years of sampling (Fig. 11). Prey rankings, however, were signifi- 2 cantly different between 1976 and 1977 (r =215, P <0.5) and 2 1977 and all years combined (r =0.79, P More detailed results of predation on the ten most important prey items (represented by three prey categories) are presented below. Fish.--The northern anchovy, I· mordax, was present in 23 (17%) of the 121 blue shark stomachs which contained some material. When present, the number of anchovies varied from 34 TOTAL (~=121) 1974-1975 (n• 20) 1976 (nc 43) 1977 (nc 58) %N %N °/oN %N Ul 0 Ul 0 Ul 0 Ul 1'i oi--,--'or-.,.---io or--.,.-...:;o;:-_,_-...:;o o;-_,_-...:;o;:-_,_-..:;o o,__,..._.:;:o'---.-_;;6 f.IISC. %V 0/oV 0/oV %V ()\ cs ()\ a ()1 o ()\ a or-_,.-..:;o~-.-..:;o or-.,.-~or-_,_-..:;o or-.,.-~or-.,.-~o o~-,.--~o~,__,o ' I• " lr' MSC. I 1: %FO %FO %FO %FO I 0 Ul 0 0 Ul Ul 0 I 0 0 0 0 g; 0 0 0 0 0 0 0 I.'· I! FISH I I, CEPH. I. IRI IRI IRI g g g g g g g g or-.,.--'io'--,--'lo or-_,_-..:;o;:-_,_-..:;o or-.,.-..:;o;:-_,.-..:;o o;:-_,...-o:;:-.,.-..:;o Figure 11.--Comparison of the major prey categories with regard to percent number (%N), percent volume (%V), percent frequency of occurrence (%FO), and index of relative impor tance (IRI), in the years sampled. 35 TABLE 3.-Prey items collected from 43 blue sharks in 1976. Listed is the percent number (%N), percent volume (%V), per cent frequency of occurrence (%FO), and index of relative importance (IRI) for each prey item. The prey are listed in decreasing order of importance determined by the IRI. Prey Species % N % V % FO I RI Lenses 29.0 7.5 41 . 9 1 52 7. 4 Thysanoessa spinifera 21. 4 1 2 . 5 30.2 1 02 6. 5 Fish parts 5. 3 20.3 3 9. 5 1 01 0. 4 Eng r au 1 is rna r d ax 7.8 11 . 6 27.9 542.6 Sgualus acanthias 3.8 1 5 . 5 1 6 . 3 31 3. 1 Octopus spp. 5 . 2 3. 1 30.2 2 51 . 0 Digested tissue 2.7 6.4 20.9 1 91 . 8 Loligo opalescens 2.4 3.4 23.3 134.7 Merluccius productus 2. 5 0.6 1 6. 3 50.0 Clupea harengus palassii 0.7 4. 0 7 • 0 32.5 Algae 0.7 2 . 5 9. 3 2 9. 9 Citharichthys sordidus 3.2 2.8 4.7 27.9 ~I Terrestrial plant fragments 2.3 0.6 9. 3 2 7. 0 I Go nat us s p p . 2 . 1 0.2 9.3 21 . 2 Euph a us i ace a 2. 1 0.2 7.0 1 6. 6 Cephalopod parts 1.4 0. 7 7.0 1 4. 6 El asmobranch 0.8 2.2 4.7 1 3. 7 Stenobrachius leucopsarus 2.3 2 . 3 2.3 1 0. 8 Histioteuthis heteropsis 0. 7 0. 1 7.0 5. 7 Sebastes goodei 0. 1 1.6 2.3 4. 1 Pleuronectiformes 0.6 0.5 2.3 2.4 Lyopsetta exil is 0. 3 0.6 2. 3 2 . 1 Porichthys notatus 0.3 0.6 2.3 2. 1 Vampyroteuthis infernal is 0.3 0 . 1 4.7 2.0 Onychoteuthis boreali-japonicus 0. 1 0.3 4.7 1 • 8 Octopoteuthis deletron 0.3 0. 1 4.7 1 . 6 Myctophi dae 0.6 0. 1 2.3 1.5 Chilara taylori 0. 3 0.2 2. 3 1.2 Sebastes jordani 0 . 1 0. 1 2.4 0.4 Phyllospadix spp. 0. 1 0. 1 1 . 6 0.3 Terrestrial insect 0. 1 0. 1 1.6 0.3 Prionace glauca tooth 0. 1 0. 1 1.0 0.2 Prlonoce glauco 1976 TOTAL 40 0:: IJJ ID ~ 20 z ~0 40 Figure 12.-Index of relative importance graph for the more important prey items of 34 blue sharks collected in 1976. 37 TABLE 4.--Prey items from 58 blue sharks collected in 1977. Listed is the percent number(% N), percent volume(% V), percent frequency of occurrence (% FO), and index of relative importance (IRI) for each prey item. Prey are listed in de- creasing order of importance as determined by the IRI. Prey Species % N % v % FO I R I F i s h Parts 1 2 . 2 31.1 63.8 2766.2 Lenses 30.6 5.6 56.9 2059. 1 Digested tissue 7.8 5 . 2 43. 1 5 61 . 1 fvJe r 1 u c c i u s productus 4. 1 9.8 29.3 407.3 Euphausiacea 1 3. 8 2.6 19. 0 31 2. 3 Eng raul is mo rda x 5 . 5 9. 7 1 5. 5 236.0 Cephalopod parts 3 . 2 5.4 22.4 192.8 Gonatus spp. 3.4 4.2 22.4 1 71. 2 Histioteuthis heteropsis 1 . 9 2. 3 20.7 86.3 Octopus s p p • 1 . 9 1 • 2 27.6 84. 7 Octopoteu this del etron 2.5 2.7 1 5 . 5 81. 9 Sgualus acanthi as 2.0 5 . 1 8.6 61.1 ,, Vamp~roteuthis infernal is 1 . 4 0.9 1 2 . 1 2 8.1 L o 1 i go opalescens 1 . 2 0.3 1 5 . 5 21. 9 Terrestrial plant fragment 0.6 2.0 6 . 9 1 8. 2 Sebastes [!aucispinus 0.6 1.9 6.9 1 7. 0 Anoplopoma fimbria 1 . 9 2.4 3. 5 1 4 . 7 Thtsanoessa spinifera 2. 2 1.9 3.5 14.2 Algae 0.3 1.7 3. 5 6.9 Gentonemus lineatus 1 . 0 1 . 0 3.5 6. 5 Detritus 1 . 5 0.4 3.5 6.4 Euphausia pacifica 1 . 2 0. 1 3.5 4.4 Feather 0.2 0.4 6.9 3 . 7 Sebastes goodei 0.2 1 . 6 1.7 3.2 Inorganic material 0. 1 1 . 4 1 . 7 2.4 Myctoph i dae 0. 3 1 . 0 1 . 7 2.4 Argonauta pacifica 0.4 0. 1 5.2 2.3 S,)"ngnathus californiensis 0. 1 0.9 1 . 7 1 . 7 Porichthts notatus 0 . 1 0.9 1 . 7 1 . 7 Scorpaenidae 0.4 0.3 1 . 7 1.3 Sebastes spp. 0.2 0. 1 5. 2 1 . 3 Terrestrial insect 0.2 0. 1 1 . 6 0.5 Phtllos[!adix spp. 0. 1 0. 1 1 . 7 0.3 El asmobranch 0. 1 0.1 1 . 7 0.3 Do s i d i c us gigas 0. 1 0. 1 1 . 0 0.2 Gona tus ~ 0. 1 0. 1 1 . 0 0.2 Lampetra tri dentata 0. 1 0.1 1 . 0 0.2 Pr/onace glauco 1977 TOTAL 40 w <6., f':-<; ~ ,...,~ :J ...J 0 > 20 0~ a::: w Q) ~ 2 20 ~0 w ro 40 Figure 13.--Index of relative importance for blue sharks collected in 1977. 39 1 to 46 with a mean of 7.3 ~ 5.6 per shark (~ 95% confidence interval). Ingested anchovies ranged in standard length from 75 mm to 150 mm with a mean of 10.46 + 3.2 mm. In 1976, 12 (27.9%) of the blue sharks had consumed anchovies with the average being 9.4 + 8.4 anchovies per shark. The standard length of ingested anchovies averaged 102.7 + 2.8 mm for this year. In 1977, only 8 sharks (13.6%) preyed upon anchovies, averaging 3.3 + 4.3 fish per shark with a mean anchovy stan dard length of 132 ! 12 mm. The sampled blue sharks fed upon anchovies mainly in the months of July and August. Only two sharks, one caught in September and the other in October, contained this fish. Although anchovies were not the most numerous prey ingested, they did constitute the greatest volume. When fed upon, anchovies comprised more than 50% by volume of the prey in 14 (60.9%) of the sharks. The pacific hake, ~· productus, was consumed by 23 blue sharks (20%). Most of the hake were represented only by otoliths. Usually only one ~- productus was ingested, except on three occasions, when two were present. The largest estimated Merluccius, based upon otolith lengths, was 400 mm in standard length while the range was from 94 to 400 mm. These are probably conservative estimates of standard length due to otolith erosion as it passes through the digestive system. The spiny dogfish, acanthias, was present in 12 (10%) of the sharks which had something in their stomachs. Only 40 one blue shark fed upon more than one dogfish, in that instance taking four. The total length of dogfish ingested ranged from approximately 200 mm to BOO mm in total length. In about half of the cases, the dogfish were either partially digested or in multiple pieces; rarely was the dogfish com pletely intact. Euphausiids.-Thirty-five (28.9%) of the blue sharks contained euphausiid remains. Only two species of euphausiids could be identified as prey, I· spinifera and Euphausia pacifica. I· spinifera occurred in 15 (12.4%) of the sharks 1-1hile !_. pacifica was present in only twa (1.7%). Uniden tified euphausiids and I· spinifera were ranked two and three when all data were combined. In 1976, I· spinifera was determined to be the most important prey item. On 26 July 1976, 12 sharks were captured, 9 of which contained I· ~inifera. The numbers of l· spinifera present in the stomachs of this sample ranged from l to 2.179 (val ume = 180 cm 3 ). Six of the sharks on that day contained more than 600 euphausiids. I· spinifera was present on only three other days of sampling in 1976. This represented a total of five sharks. In 1977, I· spinifera was found to be of little importance in the diet of blue sharks. g. pacifica was identified in only two blue sharks, collected on ll and 15 July 1977, when six and seven euphau siids were present in the stomachs, respectively. Unidenti fied euphausiids, largely represented by paired eyes or 41 carapaces, were present in 18 (15.0%) of the samples. l~hen present, one to 500 animals were observed, sometimes repre senting 100% of the stomach contents. Euphausiids were present in sampled blue sharks only in July and August. Observations of swarms of euphausiids at the ocean's surface coincided with shark predation (see ap pendix B). Cephalopods.--Nine genera of cephalopods were identified from blue shark stomachs. Other than Lol igo opal escens, the majority of cephalopods were represented only by beaks. Oc topus spp. appeared in 29 (24%) of the 121 blue sharks with identifiable prey items. Gonatus spp., !:_. opalescens, Histio teuthis heteropsis, Octopoteuthis deletron, and Vampyroteuthis infernalis occurred in decreasing abundance. The market squid,!:_ . .£.P_alescens, appeared in 20 (16%) of the blue sharks containing prey items. The dorsa 1 mantle length of ingested~- opalescens ranged from 28 to 134 mm (x = 95.7 + 10.3 mm). The greatest number of Loligo ingested at one time was seven. L. .£.P_alescens was the fourth most important identifiable prey species for blue sharks in 1976, and was ranked tenth in 1977. Over all years, Loligo was the eighth most important prey item consumed. Age and growth Ninety-eight blue shark vertebrae were analyzed for growth rings. Fourteen of these samples contained centra with rings which were broken or so lightly stained that ring 42 counts were not certain. Inclusion of these fourteen samples, however, did not produce any significant differences in the conclusions. The relationship between the centrum radius and the total length of the shark appears to be linear. The equation for the line is: Y = 451.0 + l58.9X (r 2 = 0.71, P l eng t h of l , 2 3 4. l ~ l l 3 . 9 mm, posses sed two rings (Tab l e 5 ) . The mean length of forty-six sharks with three incremental vertebral rings was l, 515.6 ~ 46.8 mm. Forty sharks were judged to possess four vertebral rings and averaged l ,679. 7 + 68.1 mm, while nine animals had vertebrae with five rings and an average total body length of l ,801. 6 + 118.2 mm. Only one blue shark (l ,976 mm) exhibited six centrum rings. There was a significant difference in mean total length for those sharks with 2,3, and 4 vertebral rings (P<0.05). There was, however, no significant difference in mean lengths between groups of animals with four and five vertebral rings. 43 8.0 r r- (IO) 7.0 !- e (I) r h(42) 6.0 L f-J ...... E (86) E 5.0 ~ C/) 4.0 :::> ,(98) Cl r 2.0 "' +981 1.0 I • • 2 3 4 5 6 CENTRUM RING Figure 14.-Ring radii measurements for blue sharks. The vertical line depicts the range of ring radii for each of the centrum ring counts. The horizontal line represents the mean, the box shows the 95% confidence interval, with the sample size in parentheses. TABLE 5.--Mean total length measurements for blue sharks with assigned vertebral ring counts. Displayed are the sample sizes, one standard deviation, and 95% confidence intervals around the mean total lengths for females, males, and the total. Vertebra 1 rings Sexes Character 2 3 4 5 6 Females Sample size 7 37 29 8 1 Nean total length {mm) 1 2 91 . 0 1515.1 1 6 86. 7 1797.5 1 97 6. 0 Standard deviation 21 9. 3 1 68. 1 l 81 . 4 1 63.9 95% confidence interval +202.9 +- 56.0 + 69.0 +1 37.0 Males Sample size 5 9 1 1 0 Mean total 1 ength (mm) 11 54.4 1 522.0 1 4 79. 0 1835.0 Standard deviation 51. 2 11 4. 4 95% confidence interval + 63.6 + 87.9 Total Sample size 1 2 46 30 9 1 r-tean to ta 1 length (mm) l 2 34. 1 1 51 5. 6 1679.7 l 801 . 7 1976.0 Standard deviation 1 79. 3 15 7 . 9 l 82 . 3 1 53. 8 95% confidence interval +139.9 +- 46.8 + 68.1 +118.2 45 There was no significant difference in male and female total length for each of the vertebral ring counts. The best fit logarithmic curve for males and females was as follows: males ( n=lO, ) Y = 687.6 + ln720.9X (r 2--0.57, P females(n=82), Y = 885.4 + ln575.1X (r2 =0.40, P (Fig. 15). There was no significant difference in the slopes of the male and female growth curves and therefore the data were combined (P<0.05). The growth curve for all aged blue sharks was: 2 Y = 824.0 + ln619.9X (r =0.48, P <0.01) (Fig. 16 ). The mean blue shark total length at each vertebral ring count coincides very well with the peaks in the size frequen- cy distributions for all sharks combined, with the exception of the larger size interval (Fig. 17). There was a significant difference in frequency of males and females for each of the vertebral ring counts (P <0.05). Males predominately had two or three vertebral rings, where- as most females contained three or four rings. Parasites Cursory observations were made of the stomach nematode, Anisakis sp., a liver fluke, possibly Ptychogonimus mega stomus, and the external copepod, Echthrogaleus coleoptratus. Anisakis sp. occurred in 45 (36%) of the 121 blue sharks 46 • 0""(16) 2000 • • 9 (82) • .. • • .. 1800 •• • • I • i• • • • -1600 E • E • -:::c • • ..... (!)z LIJ • ...J 1400 ...J t ~ 1- 1 ~ • FEMALES I Y =885.4 + 575.1 In X (f= 0.40) .a. MALES 1200 • Y= 687.9 + 720.9 lnX ({=0.76) 1 1 • • 1000~-----L----~------~----~------L-----~ I 2 3 4 5 6 7 NUMBER OF RINGS Figure 15.--Growth curves for 16 male and 82 female blue sharks caught in Monterey Bay. The power cu~ves generated for females (circles) and males (triangles),with their cor responding regression coefficients, are shown. 2400 47 0 / 2200 / / / / 0/ I 2000 / / " / / -.... 1800 E E -:r: I- 1600 (.!) z w .....1 .....1 1400 ~ 0 I- o---o Y= 4230(1-e-O.JJO(X+I.0:35l) 1200 •-• Y= 824.0 +In 619.9 X ((= 0.48) 1000 800 ~----~------~------~----~----~ I 2 3 4 5 6 NUMBER OF RINGS Figure 16.--Comparison of growth curves from present study and that of Stevens (1975). (-)denotes Monterey Bay sharks; (---) denotes Stevens' work. The hori zonta1 1 ine represents the mean, the open box depicts one standard deviation, and the hatched box represents the 95% confidence interval. 48 6 CJ) (!) • 2 if 5 lL 0 a:: 4 w m ~ 3 ;::) 2 2 I~ 20 - r- 15 1- t; 2 r- w - ;::) 10 - - r- fr1 E 5 - r-- - r-- r-- 0 ri 1000 1200 1400 1600 1800 2000 TOTAL LENGTH (mm) Figure 17.-Comparison of the total length histograms with lengths at a determined age for 98 blue sharks. The vertical lines in the upper graph represent the means, horizontal open boxes are one standard deviation, and the hatched boxes are the 95% confidence intervals. The frequency histogram includes males and females from all years. 49 examined for this parasite. When present, as many as 170 Anisakis sp. were found in a single stomach, although more often they numbered 10-30. Approximately ten spiral valves were examined for food and/or parasites. Flatworms pre dominated in this organ but no records were kept. The liver fluke, P. megastomus, was present in 19 (18%) of the blue sharks examined. Very rarely were there more than two per shark, but the maximum which occurred was nine. f. coleop tratus vias present on 10 (8%) of the sharks. Not more than one of these parasitic copepods usually occurred on a single shark, but occasionally as many as four were found. coleoptratus were found on all external surfaces of the shark, but were most frequently encountered on the trailing edges of the fins. DISCUSSION Catches Blue sharks, although apparently present throughout the year, become abundant in Monterey Bay during the late summer and early fall, when the surface water temperature increases. The beginning of the oceanic period and the associated rise in surface water temperature in July and August coincide with the peaks of catch per unit effort data of blue sharks in the bay. Although the catch per unit effort data is highly vari able, it does show trends for increased catches in August and therefore predicts greater abundances of blue sharks in . that month. Seasonal abundance estimates cannot be made due to the lack of year-round sampling. Occasional cursory ob servations, however, were made during monthly cruises which sampled bottom fish and pelagic birds throughout the year. Blue shark sightings at the surface were extremely rare during the winter and spring months. Tricas (1977) collected blue sharks near Santa Catalina Island, California, and recorded the highest surface water temperatures in August and September. In conjunction with this warming trend, he found that male blue sharks represented a greater proportion of the catch while the numbers of fe males decreased, becoming absent from the catch in August. Females were again caught in September and, as the surface water temperature decreased, they soon dominated the catch {December and January). This suggests that blue shark move ments are in part determined by water temperature, and that 50 5 l males and females may react differently to this stimulus. The large proportion of females caught in Monterey Bay implies a movement of predominately female blue sharks from southern waters northward with increasing water temperatures. Numerous authors have discussed the seasonal movements and sexual segregation of this shark in response to water temperature (Suda, 1953; Neave and Hanavan, 1960; Bane, 1968; and Sciarrotta and Nelson, 1977). Temperature preferences have been presented, ranging from 11° to l7°C (Neave and Hanavan, 1960; Gubanov and Grigor'yev, 1975; and Sciarrotta and Nelson, 1977). Most authors agree that seasonal changes in temperature coincide with movements of blue sharks. In general, female blue sharks seek cooler water as an area warms while males are attracted to warmer water. Three seasonal periods have been described for the near shore coastal environment along the central California coast. A period of predominate northerly winds creating upwelling conditions, occurs from March through August (Bolin and Ab bott, 1963). Upwelling has been characterized by the move ment of the 9°C isotherm above the 100m level (Barham, 1957). With the cessation of northerly winds from September through November, surface waters show a warming trend. The stability of this water allows offshore water to move inshore creating the oceanic period. From December through February southerly winds predominate creating the convergence of water along the coast and thus downwelling. 52 In Monterey Bay, the surface water temperatures start to rise in July and peak from August to October. The surface water temperature in the middle of the bay ranged from 9.8° C (June) to 16.6° C (August) in 1976 (Lasley, 1976). In 1977, the surface temperatures ranged from 9.8° C (April) to 15.3° C (October) (Chinburg and Lasley, 1977). Female blue sharks, in particular, appear to follow the warm water transition zone as it moves north. Preference for water which is ap- proximately 14° C to 16° Cis indicated by the increased abundance of sharks in August, when the highest temperatures were recorded. It is not known why sexual segregation is apparently influenced by water temperature. Lengths Although blue sharks have been reported to measure up to 3,830 mm in total 1 ength, those caught in nearshore California waters are generally no longer than 2,100 mm. Since females become sexually mature at 2,100 to 2,400 mm in total length, the majority of the female blue sharks caught near shore are immature. The majority of blue sharks caught in this study were 1,300 to 1,900 mm in total length. Stevens (1973) col- lected 98 blue sharks in nearshore waters off England and found them to range from 1,490 to 2,300 mm in total length. Strasburg (1958) captured blue sharks in the central north Pacific and found the largest sharks in 1 ate summer and fall and the greatest numbers of fish to be 2,200 to 2,600 mm in 53 total length. These results imply that immature blue sharks predominate in nearshore water and that the adults live a more pelagic life. Weights Body weight-total length equations generated in this study are comparable to those of Stevens (1975) who found a significant difference in body weight between male and female blue sharks, although only seventeen males were analyzed. Stevens (1975) also produced a length-weight relationship which was highly correlated, whereas this relationship in the present study was not as strongly correlated. The variability in this study, as compared to Stevens, may not be entirely explained by variations in techniques. The livers of sharks not only serve as organs which per form physiological functions, such as bile formation, but also provide buoyancy and store energy. The livers of sharks can range from 3 to 25 percent of the weight of the shark, al though the average appears to be between 5 and 15 percent (Budker, 1971). The weight and volume of the liver may fluctuate based upon sex, age, state of sexual maturity, and feeding condition. The ability of the shark liver to provide a buoyant force is dependent upon the size and oil content of the liver and the specific gravity of the liver-free shark body. Bald ridge (1970) did an extensive survey of the buoyancy 54 characteristics of shark livers. He found that the density of the liver-free bodies of sharks remained relatively con stant for each species regardless of sex or size. The primary factor which affects the average densities of whole sharks was that of the buoyancy provided by the liver. Baldridge (1970) also demonstrated that larger sharks' liver-free body densities decrease with increased body size. Growth may also reduce the proportion of the total weight that the liver represents. In juvenile blue sharks in Monterey Bay, the liver re mained a constant percentage of the body weight. The rela tively stable liver weight to body weight ration during the early years may change as the animal grows older. Baldridge (1970) presented one table which depicted blue sharks as being very buoyant. The greater buoyancy possessed by blue sharks in comparison to other species may in part explain the blue shark habit of swimming at the surface. The dimorphism of the two 1 iver lobes may be a result of the shape and space available in the coelomic cavity. Dif ferences in the liver lobe weights may alter the equilibrium of the shark in the water. Other forces may be needed to counteract the possible uneven distribution of buoyancy asso ciated with the two lobes. Reproduction The blue sharks frequenting the near shore coastal waters of California are most 1 i kely immature animals. Observations 55 by a number of investigators have shown the length of sharks at maturity to be greater than 2,000 mm (Bigelow and Schroe der, 1948; Gubanov and Grigor'yev, 1975). The majority of blues caught near shore were smaller than this estimate. Most female blue sharks caught along the coast have been without young (Tricas, 1977). The occurrence of tooth cuts on the bodies of female blue sharks has been thought by Stevens (1974) to be are- sul t of mating. Stevens examined 381 sharks off England and found mating scars only on animals larger than l ,800 mm. Suda (1953) also presents evidence for scarring during mating bouts. The infrequent occurrence of sharks with tooth cuts, in this study, emphasizes the immaturity of the majority of blue sharks near shore in l~onterey Bay. Female fish of many species possess reduced ovaries. In particular, certain elasmobranchs exhibit asymmetrical ovary formation, with either the left or right ovary be coming atrophied (Wourms, 1977). The majority of these s h a r k s are vi vi parous . The b l u e s h a r k was not on the l i s t, but, based upon evidence presented here, should be included. Feeding habits Blue sharks collected in t~onterey Bay fed principally upon small, epipelagic, schooling organisms. E. mordax, euphausiids, and L· opalescens are known to be abundant, concentrated food items which many vertebrate predators in 56 the bay exploit (Morejohn, et al., in press}. Non-schooling prey are also important in the blue shark diet. These organ- isms are usually classified as midwater animals which engage in vertical migrations during the night. Stevens (1973} examined 98 blue sharks taken in the fisheries off the coast of England. Fish occurred in 90% of the full stomachs, with cl upeids and mackerel (Scomber scom- brus} predominating. Other fish included the garfish (Belone belone), the scad (Tra trachurus), and the whiting ( He r 1 an g i us me r 1 an gus ) . S e p i a o ff i c i n a 1 i s wa s t h e mo s t abundant of the eight cephalopods that were consumed, and all were considered to be deep-water species. Strasburg (1958) examined the stomachs of 140 blue sharks, of which 76 were empty. The most important prey consumed by these central Pacific sharks appeared to be sardines, herring, squid, crabs, and shrimp. In the Gu1 f of Alaska, the food of 29 b1 ue sharks consisted of pomfret (Brama raii), saury (Colo1abis 1anternfish (Myctophidae), squid, shrimp (Hymenodora sp.), and salps (Salpa fusiformis) (Le Brasseur, 1964). Bigelow and Schroeder (1948), studying specimens mainly from the north Atlantic, found smaller fish and a variety of cephalopods to be the normal diet of blue sharks. The fish that were in- gested included herring, mackerel, sardines, and spiny dog fish (Squalus acanthias), as well as bottom fish. They also mention that occasionally a resting bird is taken. In the Indian Ocean, 256 sharks were examined, 59% of which had 57 empty stomachs (Gubanov and Grigor'yev, 1975). Lancetfish and squid predominated, while octopus, shrimps, and crabs were consumed infrequently. Fragments of tuna were present in blue sharks taken near the tuna fishing grounds. Appar ently the tuna were taken opportunistically off the longl ine hooks. Bane (1968) mentions that the diet of Channel Island blue sharks was basically anchovies and pipefish, but that tiley also consumed squid and squat lobster (Galatheidae). Tricas (1979) collected 81 blue sharks near Santa Catalina Island, California and found a variety of prey items in the stomachs of the fish examined. The northern anchovy (f. mordax) occurred most often, followed by bay pipefish (Syngnathus leptorhynchus) and jack mackerel (Trachurus ~ metricus). Eleven species of cephalopods were identified, the most prevalent being .tl_. heteropsis, followed by!:_.~ escens, Chiroteuthis calyx, and Onychoteuthis boreali-japon icus. A few crustaceans, algal fragments, and inorganic ma terial were also ingested. Based upon the relatively complete digestion of most of the cephalopod and fish prey in this study, and upon the available information regarding their behavior in the ocean, feeding of blue sharks on these prey species generally occurs sometime during or before the morning hours (0700-1200). This generalized feeding time coincides with the diel activity patterns of telemetered blue sharks in southern California. Sciarrotta and Nelson (1977) followed blue sharks and recorded 58 swimming activity around the Channel Islands. They found increased activity at greater depths during the late evening and night. Blue sharks also moved inshore in the twilight hours, possibly to feed. Increased feeding activity during the night has been recorded for a number of carcharinids (Nelson and Johnson, 1970). Davies and Bradley (1972) re corded observations of a blue shark and northern anchovies at depths of 275 m during the day. The majority of cephalopods were represented as beaks, which were in good condition. The presence of intact beaks implies recent ingestion, probably within a week, and thus the cephalopods were probably consumed in the vacinity of Monterey Bay. It is probable that the majority of cephalopod beaks are not passed through the spiral valve but are removed by regurgitation. Observations of everted stomachs from collected animals, even though they have no gas bladder, and the regurgitation of food particles during capture, support this hypothesis. Observations, however, have been made of squid beaks in the spiral valves of Parmaturus sp. (Cailliet, pers. comm. ) . Tricas (1979) examined digestion rates in three captive blue sharks. The sharks were fed anchovies and sacrificed after 6, 12, and 24 hours. He found that little digestion had occurred at 12 hours, and after 24 hours the anchovies appeared to be well digested. Digestion rates vary according to many factors such as: type of food, amount.of food, 59 temperature of surroundings, age or size of the animal, activity of the animal, and interval of starvation (Hathaway, 1927; Hunt, 1960; Darnell and Meierotto, 1962; Windell, 1967). Tricas (1979) did not take into account any of these factors, so his results should be interpreted carefully. Either the sharks in this study had fed during the evening and digestion is much faster than proposed by Tricas, or feeding is so spo radic that prey are taken very rarely and thus, some days have passed before the sharks were sampled. A discussion of each of the major prey items consumed follows. Engraulis mordax.--The northern anchovy was found to be the most important prey species for the blue shark in Monterey Bay from 1974 to 1977. Anchovies are considered to be one of the most abundant fishes in the northeastern Pacific Ocean (Baxter, 1967). The eggs and larvae have been collected as far out as 300 miles. Based upon relative abundance of the larvae, however, the greatest densities are found nearshore (Ahlstrom, 1967; Smith, 1972). The anchovy has dramatically increased in abundance in the last two decades and is now one of the major food sources for vertebrate predators (Baxter, 1967; Smith, 1972). The greatest concentrations are generally within 37 km of shore, over deep water basins (Mais, 1974). In southern California waters, anchovies exhibited vertical migrations to the surface during the evening (Baxter, 1967). Anchovies have also been observed in low density surface schools during daylight and appear to disperse at the surface after dark (Mais, 1974). 60 Anchovies, together with euphausiids, were the least digested prey. This fact along with their daily schooling pattern, indicates that anchovies may be preyed upon through out the day. Their ranking as the most important prey spe cies may be in large part a consequence of the time of in gestion. Because anchovies may be consumed at the time of day when blue sharks were collected, they were often undi gested and therefore occupied a greater volume than other prey. Merluccius he biology of the pacific hake, 1-1. productus, may predispose this fish to predation by the blue shark. !'1_. productus is found from the Gulf of Alaska to the Gulf of California, although the greatest concentra tions occur between British Columbia and Baja California (Alverson and Larkins, 1969). !'1_. productus has been caught as deep as 800 m (Clemens and Wilby, 1961) but is usually found from near the surface to depths of 600 m. In Monterey Bay, hake is the third most abundant and most frequently oc curring pelagic vertebrate caught in midwater trawls which are fished deeper than 64 m (Cailliet, Karpov, and Ambrose, in press). These samples were all taken on summer nights. M. productus was only the seventh most frequently occurring animal in depths of less than 64 m. The diel vertical move ments of !'1_. productus have been thought to be associated with prey habits. The principal prey species, one of which is 61 L· spinifera, make night-time vertical migrations to the sur- face and are preyed upon at this time by M. productus. As morning approaches, both euphausiids and M. productus move to greater depths. The digestive state of ingested !:1· productus found in blue shark stomachs, implies that the hake were eaten many hours before the sharks were caught. This, as well as the vertical migratory habits of!:!· productus, provides evidence that hake are fed upon during the evening, when they are near the surface. Euphausiids.--Blue shark predation upon euphausiids was sporadic and was probably a result of the variable availabil- ity of this prey. The importance of euphausiids in the diet of blue sharks caught in ~lonterey Bay reflects both their local and seasonal abundance and distribution. Euphausiids are known to be vertical migrators which move to the surface at night, but may also swarm at the sur face during the day (Alton and Blackburn, 1972; Youngbl uth, 1976). Swarms of l· spinifera and f. pacifica have been observed along the California coast (Boden, et al ., 1955; Brinton, 1962). Brinton, in his classic account on Pacific euphausiids, reported a range for I· spinifera from the Gulf of Alaska south to Baja California. He also stated that sur- face shoals are prevalent from north of San Francisco south ward to the Channel Islands, California. The peak of shoal formation was from July to September. Brinton (1962) found 62 no evidence of diurnal vertical migration in I· spinifera, and thought they were restricted to the upper 100 m. In his discussion of E. pacifica, Brinton (1976) proposes a range for this species from the Gulf of Alaska southward to Baja California, with the heaviest nearshore concentrations off central California. Swarms were observed north of Point Conception and consisted of spawning and spawned-out speci mens. This species was found mainly in the upper 280 m and may make an upward night-time migration to within 140 m of the surface. The factors which govern the phenomenon of swarming have not been completely examined. Komaki (1967) reviewed surface swarming accounts and investigated some of the pos sible stimuli which could trigger swarm formation. He re lated surface swarms to cold water temperatures and the move ment of this water mass toward shore. This hypothesis seems feasible with regard to the Monterey Bay situation, and the surface euphausiid swarms would provide a handy surface food supply for blue sharks. Surface swarms of euphausiids were observed in Monterey Bay in the morning hours on eleven different occasions (Ap pendix B). All observations occurred in July and August. This corresponds to the end of upwelling and the beginning of the oceanic period when offshore waters move onshore. The weather conditions, at different observations, were variable enough to possibly negate their effect on swarming. The 63 ;warms were concentrated at the mouth of the Monterey sub marine canyon (Fig. 18). I· spinifera was present in ten of the sightings, and f. pacifica was identified once. Surface swarms were of various sizes, the largest covering approxi mately a 200 by 200 m area. Blue sharks were observed in six of the eleven swarms spotted, swimming through the swarms, with mouths agape. Normally the shark would be seen swimming slowly through the mass, until the swarm would apparently change direction. The shark waul d then quickly alter its course to make another "pass" through the swarm. The utilization of this concentrated, easily caught food item, tends to obscure general feeding habits. In 1976, when I· spinifera was ranked as the most important prey, a single day's collection greatly biased the sample towards euphausiids. On that day, 26 July, nine of the twelve collected blue sharks contained T. spinifera and six had ingested great quantities of this species, numbers ranging from 600 to 2,179 individuals. It was later discovered that there was a surface swarm ofT. spinifera in close proximity to the collection site. The inclusion of this sample tends to overestimate euphausiid predation in Monterey Bay, unless euphausiid distribution can be shown to be random throughout the area. Random distribu tion does not appear to be the case: the swarms seem to con centrate in one area. Therefore, the importance of euphausi ids found in Monterey Bay blue sharks may be an overestimation of 64 122° w 50' 43' 37° 1••*•• CQPI!Ofa ' •••... Wot•nrwille 50' AO' BAY NAUTICAL Ill L ES 0 I 2 Depth in fathom• Figure 18.-Locations of observed surface s.warms of euphaus iids. 65 the overall blue shark utilization of this food source. The consumption of swarming euphausiids was not limited to blue sharks. On ten occasions, other organisms were ob served either feeding directly on euphausiids or preying upon euphausiid predators. Usually surface swarms are easily spotted since the water's surface boils from active fish pre dation. Fish species that were observed feeding on euphausiids include: juvenile jacksmelt (Atherinopsis californiensis) and juvenile sablefish (Anoplopoma fimbria). Marine birds were active in either euphausiid or fish capture. Birds such as the sooty shearwater (Puffinus griseus), rus spp., and Forster's tern (Sterna forsteri) would head-dip for euphausiids. The murre (Uria aalge), Brandt's cormorant (Phalacrocorax ~ cillatus), and the rhinoceros auklet (Cerorhinca monocerata} were observed surface-diving into the euphausiid swarms. Cephalopods.--Although represented mainly by beaks, a variety of cephalopods were found to be important prey items of blue sharks in Montery Bay. L. opalescens was one of the few squids which was found in some early stage of digestion. L. opalescens ranges from British Columbia south to the tip of Baja California (Fields, 1965). This species is consid ered to be mainly neritic and is thought to stay near the bottom during the day and disperse during the night (Roper and Young, 1975). Recent work by Karpov (1977), however, reveals a feeding activity peak around noon, which may ren der these squid available to blue sharks during the day. 66 This availability may be demonstrated by the presence of un digested l· opalescens in the stomach of sampled sharks. L. apalescens is the mast abundant pelagic organism in summer midwater tra~1ls in Monterey Bay (Cailliet, Karpav, and Am- brose, in press). This species spawns in shallow sandy areas near Monterey. Tricas (1979) and Sciarrotta and Nelson (1977), working in southern California, have observed blue sharks mov ing inshore in the evening to prey on shoals of l· opalescens. Discussions with the local Monterey squid fishermen revealed some presence of blue sharks in the evening, but the sharks were not considered to be abundant near the squid spawning grounds. Gonatus spp. were not identified to species, since the beaks are not distinctive enough. This genus was the most abundant of the squids, with many species exhibiting a mid water existence and demonstrating some vertical migration. Gonatus berryi and §_. ~have both been captured in Mon terey Bay and therefore are possible prey (Anderson, 1978). Octopoteuthis deletron, Histioteuthis heteropsis, and Onychoteuthis boreali-japonicus all undergo some sort of ver tical migration, bringing them near the surface at night (Pearcy, 1965; Young, 1972). The majority of these animals stay below 200 m during the day. Vampyrotheuthis infernalis is distributed worldwide and considered to be a deepwater cephalopod. This species appar- ently does not go through a vertical migration, but remains 67 below 800 m; generally it is caught in trawls between 800 and 2,000 m (Lu and Clarke, 1975; Young, 1978). In general, it appears that predation on cephalopods would occur at night when the cephalopods are near the sur face. Increased activity patterns shown in other studies and the availability of near surface cephalopods, make night time feeding probable. Predation on V. infernalis indicates feeding at depths in excess of 800 m. The condition of ceph alopod beaks and the species identifications can be used to predict feeding areas and times (Clarke and Stevens, 1974). Age and growth The fncremental rings of blue shark vertebrae can be distinguished and measured. These rings are composed of concentrations of calcium salts, usually carbonate, phosphate, or chloride (Stevens, 1975). Jones and Geen (1977), using X-ray spectrometry, have found periodic peaks of calcium and phosphorus In vertebrae of Sgualus acanthias, which they attributed to the position of rings. The periodic deposition of these salts may be a result of several factors, including temperature, salinity, food, and light {Simkiss, 1974). The seasonal movement of blue sharks into ~lonterey Bay and colder northern waters may expose these animals to all of those fac tors found to contribute to ring formation. Therefore, it is reasonable to assume that ring formation may be annual and correspond to the change in water temperature, food, light, 68 and salinity experienced in the northward migration of blue sharks to Monterey Bay. Vertebral growth corresponds directly with growth of the animal. Stevens (1975) found a 1 inear relationship between centrum radii and total 1 ength in blue sharks. Stevens' data for blue sharks caught off England show less variability and faster centrum growth than the data for sharks caught in Nonterey Bay. There is very 1 ittl e error associ a ted with measuring total length or centrum radius, so it appears that the differences between centrum growth of Monterey Bay and England's blue sharks are real, assuming the samples are representative of those of Stevens. The position of the rings with relation to the center of the vertebra (ring radius) is fairly constant. In comparison to Stevens' (1975) work, this study shows that the position of each vertebral ring is similar unti 1 the fourth and fifth ring. Sharks from this study had smaller radii at higher ring counts. This fact, along with the smaller centrum radius, provides evidence that the growth rates of the vertebrae from Monterey Bay sharks may be less than those of the sharks an alyzed by Stevens. Based upon the relationship of centrum radii to total length, back calculations can be made to estimate total body length for each ring radius. The variability of the centrum radi us-tata 1 1 ength relationship was, however, tao great to reliably predict such values. 69 Stevens' (1975) growth data on blue sharks are the only comparable information on this species. He examined 81 blue sharks caught off England using a similar method to that one described in the present study. Stevens did not separate the sexes because of the small number of males, and used the von Bertalanffy equation to describe growth. He also compared his growth curves with a curve he generated from the length-fre- quency data of Aasen (1966). The growth curves generated from Stevens • and Aasen's data agree rather well. The growth curve for blue sharks caught in Monterey Bay seems to differ from that of Stevens with increasing shark age. In this study, blue shark growth starts to level off or slow considerably at about four to five years of age. On the other hand, the growth curve of Stevens' continues to rise, creating quite a difference in projected size at age five. The difference in growth equations may be real due to natural causes, or an artifact due to discrepancies in the interpretation of rings or in the use of two different equa- tions to depict growth. It is possible that there is a significant difference in growth between northeastern Atlan- tic and northeastern Pacific blue sharks. Variation in temperature, food supply and composition, movements, age at maturity, and populations may produce differences in growth. The above variables, however, are somewhat similar in the two studies. The interpretation of rings and 70 processing of the vertebrae may account for some variability. Although Stevens examined two vertebrae which were processed in the present study and concurred with the ring counts, it is possible that errors were made in distinguishing annular rings. A more plausible explanation is connected to the two growth equations used. Stevens used a von Bertalanffy equa tion with L~ estimated based upon present literature values. The use of large L~ values, which were not incorporated into equations used in this study, may account for the discrepancy in the gro\vth lfnes at older ages .. The equation used in this study, therefore, may better explain growth at younger ages ( 2 to 6) . There are insufficient samples to recognize significant differences in male/female growth rates. The growth curves generated for males and females predict larger males, with higher growth rates. Holden and Meadows (1 g52) found di f ferences in growth rates of male and female Squalus acanthias. The growth curves show that males have a greater growth rate until age five, whereupon the rate of growth in the males declines below that of the females. Moss (1972) has reported on differential growth equations for male and female ~1ustelus canis. Growth was similar at approximately one year of age. Thereafter, females grew more rapidly reaching a maximum of 1, 500 mm compared to a maximum 1 ength in males of 1,100 mm. LITERATURE CITED Aasen, 0. 1966. Blahaiem, Prionace glauca (Linnaeus). 1758 Fisken og havet, 1:1-15. Abbott, D. P., and R. Albee. 1967. 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R., and J.D. Stevens. 1974. Cephalopods, blue sharks, and migration. J. Mar. Bio1. Ass. U.K., 54: 949-957. Clemens, W. A., and G. V. Wilby. 1961. Fishes of the Pacific coast of Canada. 2nd Ed. Fish. Res. Bd. Can. Bull., 68: 1-443. Daiber, F. C. 1960. A technique for age determination in th skate, Raja eglanteria. Copeia, 1960(3):258-260. 73 Darnell, R. M., and R. R. Meierotto. 1962. Determination of feeding chronology in fishes. Trans. Am. Fish. Soc., 91 (3):313-320. Davies, I. E., and R. P. Bradley. 1972. Deep observations of anchovy and blue sharks from Deeps tar 4000. Fish. Bull., 70(2):510. DeWitt, F. A., and G. M. Cailliet. 1972. Feeding habits of two b r is t l e mo u t h f i shes , Cy c loth one a c c l i n i dens and f._. signata. Copeia, 1972:868-871. Fields, W. G. 1965. The structure, development, food rela- tions, reproduction, and life history of the squid Lol igo opalescens Berry. Calif. Fish and Game, Fish Bull., 131: l-108. Gubanov, Y. P., and V. N. Grigor'yev. 1975. Observations on the distribution and biology of the blue shark Prionace glauca (Carcharinidae) of the Indian Ocean. J. Ichthy., 15(1):37-43. Hart, J. L. 1973. Pacific Fishes of Canada. Fish. Res. Bd. Can. Bull., 180:1-740. Hathaway, E. S. 1927. The relation of temperature to the quantity of food consumed by fishes. Ecology, 8:428-434. Holden, r~. J. 1972. The growth rates of Raja brachyura, _8_. clavata, and R. montagui as determined from tagging data. J. Const. Int-:- Explor. Mer, 34(2):161-168. 1973. Are long-term sustainable fisheries for el as- mobranchs possible? Rapp. P. V. Reun. Cons. Int. Explor. ~1er, 164:360-367. Holden, M. J., and P. S. Meadows. 1962. The structure of the spine of the spur dogfish (Sgual us acanthi as L.) and its use for age determination. J. Mar. Biol. Ass. U.K., 42: 179-197. Hunt, B. P. 1960. Digestion rate and food consumption of Florida Gar, Warmouth, and Largemouth Bass. Trans. Am. Fish. Soc., 89(2):206-210. Hurtubia, J. 1973. Trophic diversity measurement in sympatric predatory species. Ecology, 54:419-424. Jones, B. C., and G. H. Geen. 1977. Age determination of an elasmobranch (Sgualus acanthias) by X-ray spectrometry. J . F i s h . Res . Bd . Can ad a , 3 4 ( 1 ) : 4 4-4 8. 74 Karpov, K. A. 1977. Feeding habits of the market squid, Loligo opalescens. Unpubl. M.S. thesis, Calif. State Uni v., Fresno, 91 pp. Kashiwada, J., C. W. Recksiek, and K. Karpov. In press. Beaks of the market squid, Lol igo opalescens, as tools for predator studies. Calif. Fish and Game,Fish Bull. Komaki, Y. 1967. On the surface swarming of euphausiid crus- taceans. Pacific Science, XVI:433-448. Lat~arca, M. J. 1966. A simple technique for demonstrating calcified annuli in the vertebrae of large elasmobranchs. Copeia, 1966(2):351-352. Lasley, S. R. 1976. California cooperative oceanic fisheries investigations hydrographic data report, Monterey Bay, January to December, 1976. Moss Landing Marine Laboratories Tech. Publ., 77-1:1-117. LeBrasseur, R. J. 1964. Stomach contents of blue sharks (Prionace glauca L.) taken in the Gulf of Alaska. J. Fish. Res. Bd. Canada, 21(4):861-862. Lu, C. C., and M. R. Clarke. 1975. Vertical distribution of cephalopods at 40°N, 53°N, and 60°N at 20°W in the north Atlantic. J. l·iar. Biol. Ass. U.K., 52:143-163. t~ais, K. F. 1974. Pelagic fish surveys in the California Current, California. Calif. Fish and Game, Fish Bull., 162:1-72. l·lcKenzie, R. A., and S. N. Tibbs. 1964. A morphometric de- scription of blue shark (Prionace glauca) from Canadian Atlantic waters. J. Fish. Res. Bd. Canada, 21 (4):865- 86 6. Miller, D. J., and R.N. Lea. 1972. Guide to the coastal marine fishes of California. Calif. Fish and Game, Fish Bull., 157:1-249. Morejohn, G. V., J. T. Harvey, and L. D. Krasnow. In press. The importance of Lo1 igo opalescens in the food web of marine vertebrates in Monterey Bay, California. Calif. Fish and Game, Fish Bull. Moss, S. A. 1972. Tooth replacement and body growth rates in the smooth dogfish, Mustelus canis (Mitchell). Copeia, 1972(4): 808-811. Neave, F., and M.G. Hanavan. 1960. Seasonal distribution of some epipelagic fishes in the Gulf of Alaska region. J. Fish. Res. Bd. Canada, 17(2):221-233. 75 Nelson, D. R., and R. H. Johnson. 1970. Diel activity rhythms in the nocturnal bottom dwelling sharks, Heterodontus francisci and Cephaloscyllium ventriosum. Copeia, 1974(4): 732-739. Pearcy, W. G. 1965. Species composition and distribution of pelagic cephalopods from the Pacific Ocean off Oregon. Pacific Science, XlX:261-266. Pinkas, L., ~1. S. Oliphant, and L. K. Iverson. 1971. Food habits of albacore, bluefin tuna, and bonito in Calif- ornia waters. Calif. Fish and Game, Fish Bull., 152: 1-105. Ronsivalli, L. J. 1978. Sharks and their utilization. Mar. Fish Rev., 40(2):1-13. Roper, C. F. E., and R. E. Young. 1975. Vertical distribution of pelagic cephalopods. Smithsonian Contr. Zoo., 209:1- 51. Sciarrotta, T. C., and D. R. Nelson. 1977. Diel behavior of the blue shark, Prionace glauca,near Santa Catalina Is- land, California. Fish. Bull., 75(3):519-527. Simkiss, K. 1974. Calcium metabolism of fish in relation to aging. Pp. 1-12, in Aging of Fish (T. B. Bagenal, ed.). Unwin Brothers LimiTed, England. Smith, P. E. 1972. The increase in spawning biomass of northern anchovy, Engraulis mordax. Fish. Bull., 72(3): 849-874. Sakal, R. R., and F. J. Rohlf. 1969. Biometry. 1~. H. Free- man and Co, San Francisco, 776 pp. Stevens, J. D. 1973. Stomach contents of the blue shark (Prionace gl auca L.) off south-west England. J. ~1ar. Biol. Ass. U.K., 53:357-361. 1974. The occurrence and significance of tooth cuts on the blue shark (Prionace glauca L.) from British waters. J. Mar. Biol. Ass. U.K., 54:373-378. ---. 1975. Vertebral rings as a means of age determination in the blue shark (Prionace glauca L.). J. Mar. Biol. Ass. U.K., 55:657-665. 1976. First results of shark tagging in the north- east Atlantic, 1972-1975. J. Mar. Biol. Ass. U.K., 56: 929-937. 76 Strasburg , D. W. 1 9 58. Di s t r i but i on , a bun dance , and habits of pelagic sharks in the central Pacific ocean. Fish. Bull., 138(58):335-361. Suda, A. 1953. Ecological study of the blue shark (Prionace glauca Linne.). South Seas Area Fish Res. Lab. Rept., 26(1):1-11. Tricas, T. C. 1977. Food habits, movements, and seasonal abundance of the blue shark, Prionace gl auca (Carchar hinidae), in southern California waters. Unpubl. M.S. thesis, Calif. State Univ., Long Beach, 79 pp. ---. 1979. Relationships of the blue shark, Prionace glauca, and its prey species near Santa Catalina Island, California. Fish. Bull., 77(1):175-182. Williams, T., and B. C. Bedford. 1974. The use of otoliths for age determination. Pp. 114-123, in The Aging of Fish (T. B. Bagenal, ed.). Unwin BrothersLimited, England, 234 pp. Windell, J. T. 1967. Rate of digestion in fishes. Pp. 151- 173, in The Biological Basis of Freshwater Fish Production (S.D-.Gerking, ed.). Blackwell, S. W. Publ., Oxnard. Wourms, J. P. 1977. Reproduction and development in chon- drichthyan fishes. Am. Zool., 17(2):379-410. Young, R. E. 1972. The systematics and areal distribution of pelagic cephalopods from the seas off southern Calif- ornia. Smithsonian Contr. Zool., 97:1-159. ----. 1978. Vertical distribution and photosensitive vesicles of pelagic cephalopods from Hawaiian waters. Fish. Bull., 76(3):583-615. Youngbluth, M. J. 1976. Vertical distdbution and diel migra- tion of euphausiids in the central region of the Califor- nia Current. Fish. Bull., 74(4):925-936. Zar, J. H. 1975. Biostatistical Analysis. Prentice-Hall, Inc., Englewood Cliffs, N.J., 620 pp. APPENDIX 77 APPENDIX A.-Prionace g]auca catch records for Monterey Bay, California (1975-1977). Weather & sea N Caught Length of Oa te location conditions Method (CPUE) time fishing Comments 29 Jan 75 l21°49.8'W Long] ine 0 3 hrs R/V Artemia, 75 fm, 2/3 47°BO,O'N (0935-1235) vertical,. 1/3 horizontal. 3 bait cans w/ anchovyf hooks w/ squid. 13 Jul 76 1Bl 0 53.2'W Fog, visibility Long1i"e 1 3 hrs R/ V Orca, 60 fm, 2 addi 56°49.3'N 2-3 mi. ca im, ( '33) (0920-1230) tionar!b1ue sharks ob swell; 0-2 ft SW served. 17 Jul 76 121°so.o•w Overcast, fogt longline 0 3 hrs 2 blues in associ at ian 3B 0 50,0'N wind:0-5 knots W, (091 0-1210) w/ T. spinifera. Top or swell ;0-2 ft SW. jacksmelt and l. feeding also. 26 Jul 76 1Bl 0 53.2'W Longline 1 1 h r 1 blue spotted 1/2 mi SW 56°49.3'N (1) {0845-0930) of Moss Landing harbor. 26 Jul 76 " Handline 11 2, 5 h rs In association w/ T. ( 4 '4) (1000-1230) spinifera, sometimis in groups of 4-5. circling through euphausiids, 28 Jul 76 121°47,7'W Overcast, glassy. Handline 0 2 h rs 25 blues seen in area, 36°47.3'N swe11:0-1 ft. (0830-1 030) man y !'~~9..~.2.. 30 Jul 76 l21°46.5'W Calm, high fog, longline 4 3 hrs 36°47.2'N swell :0-1 ft, ( 1. 3) (0930-1230) wind:0-3 knots. 4 Aug 76 121°5o.s•w Clear, warm,callil, Longline 6 2. 5 h rs 30°49,4'N seas:0-1 ft NW. ( 2 '4) (0900-1130) APPENDIX A.--continued. Weather & sea # Caught Length of Date location conditions Method ( C PUE) time fishing Comments 5 Aug 75 121 SJ.S'W Overcast, wind: Longline & 1 5 3 h rs 36°46.2'N 5-10 knots, Handline ( 5. 3) {0900-1200) seas:1-3 ft W. 9 Aug 75 121°50.0' w Handline 0 1 • 5 h rs Sharks at surface, juve 36°45.2'N (0900-1030) nile sablefish feeding on bait. 12 Aug 75 121°52.0'W Calm, fog, vis- Handline 11 2 . 5 h rs ln association w/ l. 36°48.8'N ibility 8 mi. ( 4.4) (0900-1130) occidenta1is, L.heermani 1 wind:0-3 knots W, t. ~n seus, Pelecanus seas:l-3 ft W. occldenta1is, Phalacro corax, l. argentatus, S. forsterl, A. affinis, A. nm~ aTld l· sprili fera, 13 Aug 76 121° 50.2' w Calm, wind:l-2 Handline 1 hr Euphausiids at surface 36° 48. 8' N knots W, seas; (1200-1300) in one area, jacksmei t 1-4 ft w, high feeding on euphausiids, fog. visibility: !!· ~ & J:. griseus s mi. feeding on E. mordax. 20 Aug 76 121~51.7'\l Seas:l-3 ft W, Handline 0 2 hrs T. spinifera at surface 36 49.7'N wind:0-2 knots SW. (0900-11 00) over large area, S. fors~ teri and P. griseus teei! ~on euPhaus i 1 ds, 4 blues seen in vicinity at 1 HS. 23 Aug 75 121°51.8'W Calm and sunny, Handline 0 2.5 hrs 10 blues observed all 36°47.3'N wind:0-2 knots W, (0900-1130) day, only 1 attracted to swell:l-2 ft NW. chum, rafts of ashy petrels (2-3,000). APPENDIX A.--continued. Weather & sea # Caught Length of Date Location conditions Method (CPUE) time fishing Comments l 0 Sep 76 l21°52.7'W light fog,glassy, Handline 0 3 hrs 36°49.6'N wind:O~ swells: (0830-1130) 1-2 ft NW. 10 Jan 77 121°55. 3' w Partly cloudy, Observation Observed 6 blues on J6°50.4'N swell :2-4 ft, surface. wind:2-4 knots E. 11 Jan 77 l21°47.7'W Overcast, swe 11 : Obse rva ti on Surface temperature l4°C, 36°47.3'N 2-4 ft w, wind: i blue observed at sur 5-6 knots E. face. 21 Jan 77 121°55.3'W Wind:2-5 knots Observation Observed 3 blu s, water 35°50.4' r~ SE, swe 11 : 1-3 temperature 15 0C. ft w, 40% cover. 5 Apr 77 121°SO.B'W Observation Dave Streig reported 36°44.S'N first sighting of blue this year. 17 Jun 77 l21°55.3'W Calm, Swell :0-1 Handline 0 2 h rs I blue sighted feeding 36°30.4'N ft, 100% cover. (0900-1100) on euphausiids~ swdrms (260 -5 mil of l· spinifera at sur face. 11 Jun 77 121°55.3'W " 0 " 2 blues sighted. 36°80. 4' H (270 -7.5 mi) 21 Jun 77 121°52.9'W Light breeze, Handline 0 2 hrs Covered approx. 20 mi. 36°44. 7'N 100% cover, swell: (0830-1 030) observed only 1 blue, 2-4 ft. got 8-9 mi out. 29 Jun 77 Observation Observed 4 blues while otter trawling. (X) 0 APPENDIX A.--Continued. Weather & sea U Caught Length of oa te Location conditions Method (CPU E) time fishing Comments 4 Jul 77 121•sz.O'W Clear, swell: Handline 0 1.5 hrs No blues spotted all day. 36"48.2'N 2-4 ft, wind: (0900-1030) f. pacifica at surface. 1-2 knots. 6 Jul 77 121 '53.2'W Partly cloudy, Handline 0 2.5 hrs spinifera at surface. 36"51.8'N swell :1-2 ft SW (0800-1030) 11 Jul 77 121°53.2'W 100% cover, Handline 4 2 hrs Observed zig-zag approach 36°44.2'N swell :1-3 ft SW, ( 2) (0900-11 00) of blue about 30m from wind: lig~t. boat, each zig was 5 m and got 6 m closer w/ each turn. 12 Jul 17 121 '56.2'W 100% cover, wind: Handline 1 2 hrs 36"47.7'N 2-3 knots W, (0.5) (0830-1030) 15 Jul 77 12l 0 44.6'W 100% cover, Handline 1 0 2 h rs 3 blues observed on 36'45.8'N glassy, swell: ( 5) (0800-1000) route. 18 Jul 77 121 '44.6'W 1001 cover, wind: Handline 0 1. 5 h rs 1 blue observed. 36'45 .8' tl 2-3 knots W, (0830-1000) swell: 2-4 ft NW. 20 Jul 77 121'56.0'W Clear and sunny, Handline 2 1.75 hrs B blues observed near 36"47.5'N swell:l-3 ft WNW ( 1. 1) (0845-1030) boat but not caught. 21 Jul 77 121 '52.0'W 5eas:2-4 ft w/ Handline 0 0.5 hrs Windy as hell, ended 36'44.9'N 1-3 ft swell from (0900-0930) operations early. W, winds:2-5 knots. 27 Jul 77 121'5l.B'W lOOX cover, wind: Handline 0 1.75 hrs Phytoplankton appear to 36"46.6'N 0, swell:l-3 ft W. (0845-1030) be blooming. APPENDIX A.--continued. Weather & sea # Caught Length of Oa te Location conditions Method (CPUE) time fishing Comments 29 Ju1 77 121 '54. 2' w CJear1 small Handline 0 1 . 75 h rs 4 blues observed. 36'50.3'N crafts up, swell: (0815-1000) 2-4 ft, wind:0-2. 3 Aug 77 121'53.2'W 100% cover, wind: Handline 0 2.5 hrs l blue observed on way 36'46.1'N 0, swell:0-1 ft, (0840-1110) out, 250' (7 mi), ob calm. served l· spinifera ag gregation w/ blues as sociated (10-15). 5 Aug 77 121'52.0'W 100% cover, calm, Handline 6 l. 5 h rs 36'46.7'N swell :0-2 ft W, ( 4 ) (0900-1030) wind:O. 6 Aug 77 121'50.6'W Overcast, no Handline 0 1 hr 36'50. 1' N wind, swell :1-3 ft. (0830-0930) 6 Aug 77 Ml 270' Clear skies, no Handline 0 2. 5 h rs Nightlight station; sc 1 50 ° wind, swell:0-1 (2330-0300) ~· opalescens schools of 360' ft w. about lOO individuals. 8Aug77 121'53.2'W Overcast, calm. Handline & 8 2 hrs Many blues spotted in 36'48.B'N 1-3 ft w. Longline ( 4 ) (0930-1130) area, at least 1 caught on longline. 10 Aug 77 121'54.2'W Overcast(lOO%), Handline & 11 2 h rs 10 blues caught on R/V 36'49.3'N no wind, s we 11 : longl ine (5,5) (0810-1000) Orca, 1 on long1ine. 1-2 ft. 11 Aug 77 121'51.6'W Overcast but Handline 0 1 • 5 h rs J b1ue swam byf no 36'45.5'N clear horizontally. (2300-0030) response to chum. 00 N APPENDIX A .-{anti nued. Weather & sea N Caught Length of Date Location conditions Method (CPU E) time fishing Comments 14 Aug 77 121'53.7'W 100% cover~ wind~ Hand! ine 5 2 hrs Number of blues in area. 36'49. l'N 1-3 knots S, ( 2. 5) (0830-1030) llOO:spotted T. s~lnifera swell :0-2 ft w. swarm at 260'\4 m ), 30 blues associated w/ eu phausiids. 15 Aug 77 121'53.0'W Clear, swe11:2-4 Handline 2 2 hrs 36"45.3'N ft, 1-ft chop, ( 1 ) (0830-1030) wind:0-4 knots NNE. 18 Aug 77 121'54.2'W Swell :2-4 ft W, Handline & 0 1. 5 hrs a blues observed~ none 36'47.7'N winds:2-4 knots. Longline (0930-11 00) caught. 19 Aug 77 12l 0 54.6'W Swell :1-3 ft W, Handline 4 1 • 5 hrs 36°49.3'N no wind. ( 2. 7) (ogoo-1030) 22 Aug 77 121 '53.9'W Overcast, swell: Handline 0 1 • 5 hrs 2 blues caught but got 36'4g.J'N 1-3ft, no wind. (ogoo-1030) away. 23 Aug 77 121 '52,5'W Handline 0 1. 2 hrs Observed a few blues. 36"49.0'N ( 0850-1000) 24 Aug 77 121"53.7'W Overcast, low Handline 0 1. 2 hrs Few blues observed. 36'47.0'N fog, swell;l-2 (0845-1000) ft, calm and glassy. 26 Aug 77 121 '5l.O'W Swell :3-5 ft WNW, Handline 2 1 . 5 h rs 36°48.3'N wind:light, clear. ( 1 . 3) (0900-1030) (f) w APPENDIX A.--continued. Weather & sea # Caught Length of Oa te location conditions. Method (CPU E) time fishing Comments 29 Aug 77 121'50.4'W Swell :3-6 ft WNW, Handline & 6 2 hrs 36'50.2'N wind slight. Rod & Reel ( 3) (0900-1100) 8 Se p 77 121'52.2'W Foggy, swell: 2-3 Handline 0 2 h rs 2 blues observed. 36'47.4'N ft w. calm. ( OB00-1 000) 12 Sep 77 121 •ss.o•w No winds, swe 11 : Handline 0 1.5 hrs Some blues caught and 36'49.0'N 1-2 ft. (ogoo-1030) 10 s t' many observed. 1 5 Sep 77 121'55.0'W Overcast, swell : Handline 1 1 • 5 h rs Few blues investigated 36'4g, 0' N 0-1 ft, ca. 1m. (0. 7) (0900-1030) chum. 22 Sep 77 121'51./'W 95% overcast, Handline 1 I hr 1 blue went to chum w/in 36'50.3'N swell :3-4 ft w, (1) (0845-1000) 5 minutes after placed no wind. in water. 14 De t 77 121 '56.0' w Handline 3 1.5 hrs Caught w{in 15 minutes 36'48./'tl ( 2) (1000-1130) of placement of chum in water. APPENDIX B.-Euphausiid observations in Monterey Bay, California (1976-1977). Weather & sea Species associ a ted Gate conditions Location Time Euphausi i d wi t h euphausiids Comments 1 7 Ju 1 76 Overcast, some 36° 50.0 N 1000 Thlsanoessa A theri noes affinis 1 fog, wind; 0~5 121° 50.5 W ~inifera Larus heerman1 knots w, s we 11; Prfiinace glauca 0-2 ft. sw. 26 Ju1 76 unknown 36° 4g.O'N 0930 Thr_sanoessa glauca 121° 50.2'W spinifera 12 Aug 76 High fog, vis- 36° 48.0'N ThJ<:sanoes sa Prionace g1auca ability: 8 mi. , 1 21 ° 50. 5' w Sf!inifera ~~lopoma fimbria wind: 0-3 knots Ather1noes affinls w, seas: 1-3 ft. [arus occ1dental is w. raru.5 heermani PUTtTnus gnseus Pe1ecanus occidental is Pha1 acrocorax ~en1ci 11atus La rus argentatus Sterna torsteri 1 3 Aug 76 Overcast, high 36° 49.0'N 1200 I!!.rsanoessa Atherinoes affinis fog, wind; 1 -2 121° 5l.O'W s~Tnlfera Ur1a ulJl~ knots w, seas: ~ffi n~,t grise us 1 -4 ft. w. 20 Aug 76 Patchy fog, some 36° 49.0'N 0830 Th,l':sanoessa Eupha us i ids seat- sun~ wind: 0-2 121° 51. J I W s~inifera tered over 1 a rge knots sw. seas: area. Zalophus 1 -3 ft. w. california11us ~ Phocoenoides d a 1 1 i observed i" area. "'m APPENDIX B.-Continued. Weather & sea Species associated Oa te conditions location Time Euphausiids with euphausiids Comments 17 Jun 77 Overcast. calm, 3 49.4'N 1000 Thys~noessa Prionace glauca Unidentified small swell :0-1 ft. 121 51.2'W ~nifera fish observed feed ing in euphausiid aggregation. 4 Jul 77 Clear, swell: 36° 48.5'N 0930 Euphausia Atherinops affinis g,.pacifica ·cone. in 2-4ft.,. wind: 121° 51.2'W 22cifi ca larus occidentalis and area 200x200 m. 1-2 knots. PeTecanus occi den- Pelican feeding on ta 11 s fish. 6 Jul 71 Partly cloudy, 36° 50.2'N 0740 Thysanoessa T. spinifera at sur swell: 1-2 ft. 121° 52.0'W sp1n1fera face 1n D.Sxl m SW, no wind. swarms. Small fish feeding 1n swarms. 11 Jul 77 100% overcast, 36° 44.6'N 1835 Thysanoessa Puffinus griseus r.spinifera in scat~ swell: 1-3ft. 121° 51.5'W spinifera Puffinus creatopus tered numbers. 3 Aug 77 100% overcast1 36° 48.6'N 1030 Thysanoessa Lo1 igo opa1escens !·•pinifera In lOOx no wind. swell; 121° 52.5'W illnifer!_ Puffinus griseus 100m area. L.~ 0-1 ft., visa Pelecanus occiden- escens obserVed feed b i 1 ity: 2 mi. ta 11 s lng on euphausiids larus argentatus from below. P.!l..!.i seus feeding On L.oejlescens when i"va1 able. H Aug 77 100% ovarcast. 36° 48.0'N 1100 Thysanoessa Atherinops affinis Large fish, prob- wind: 1-3 knots 121° 49.0'W spinifera Pn on ace ill.J!.E..! ab 1 y Trachurus S, swell: 0-2 larus sp. s~mmetricus, swim ft. w. BaTile-noptera acuto- m1ng through small rostrata swarm of euphausiids. 00 en