Foods of Little Tunny Euthynnus Alletteratus Collected Along the Southeastern and Gulf Coasts of the United States

Bulletin of the Japanese Society of Scientific Fisheries 51(8), 1207-1218 (1985)

Foods of Little Tunny Euthynnus alletteratus Collected along the Southeastern and Gulf Coasts of the United States

Charles S. MANOOCH, III,* Diane L. MASON,* and Russell S. NELSON* (Accepted December 20, 1984)

A total of 2,134 little tunny Euthynnus alletteratus were examined. Specimens ranged from 172 to 885mm fork length (FL) and were captured by hook and line and seines off the southeastern United States and from the Gulf of Mexico in 1980 and 1981. Approximately 57% (1, 212) of the stomachs contained ingested materials consisting of 20, 742 individual items, displacing 62, 961ml, and representing over 100 different categories. Fishes occurred in 66.9% of the stomachs with food, invertebrates in 30.5%, and miscellaneous items (Sargassum, seagrasses, inorganics, etc.) in 11.3%. Little tunny feed primarily in coastal waters on fishes, such as sardines, scads, and anchovies, and invertebrates. In decreasing order of importance clupeids, engraulids, unidentifiable fish, carangids, squid, stomatopods, penaeids, diogenids, stromateids, and synodontids were the most important foods in the diet, based on the index of relative importance (IRI). Diets differed with fish size (4 size classes), area of collection (8 areas) and season (4 seasons). Bray- Curtis similarity coefficients were used to compare the diet of little tunny with those of king mackerel Scomberomorus cavalla and Spanish mackerel S. maculatus collected from the same areas. Ge nerally, the little tunny diet was more similar to that of king mackerel than to that of Spanish mackerel. All three coastal pelagic predators fed extensively on clupeids, carangids, and squids. Small crustaceans were more important to the diet of little tunny, and engraulids were more fre quently eaten by Spanish mackerel.

The little tunny Euthynnus alletteratus is one of 672t.2) The species, which may attain a length three species of the genus Euthynnus found in of 1,000mm (39 to 40in.) and a weight of 12 and tropical and subtropical coastal waters of the 13kg (26 to 19lb), provides excellent sport to world. The little tunny is distributed along both anglers, but is usually caught incidentally, or fished sides of the Atlantic, including the Mediterranean for only when more desirable species are unavaila Sea; E. affinis is found throughout much of the ble. Although the flesh is very good if properly Indo-Pacific region; and E. lineatus is restricted prepared, most of it in the United States is dis to the tropical Pacific Ocean. Generally, all carded or cut into strips and used for bait. three species occur between 35°N and 35°S latitudes Because most tunas are highly desirable food and no more than several hundred miles from fishes in the world, and many species are being land. heavily exploited by fishermen, the presently un Like other scombrid fishes, including the important tunas, such as E. alletteratus, will pro mackerels and tunas, Euthynnus are important to bably receive increasing attention in the near fu the world's fisheries. From 1977 to 1981 between ture. It is important, therefore, that basic in 54,000t and 89,500t were landed annually, but formation on the life history, availability, and E. affinis contributed 87.0% and E. alletteratus and abundance be obtained for little tunny and other E. lineatus only 12.5% and 0.5% respectively, of underutilized species. Unfortunately, only limited the five year mean (69,000t).1) research has been conducted on E. alletteratus. A Although commercial and recreational fisher- synopsis of biological data on Euthynnus by men along the southeastern and Gulf of Mexico YOSHTDA3Oincludes sections on foods and feeding, coasts of the United States catch little tunny by but does not identify a quantitative study on the hook and line, gill nets, and seines, no large-scale diet of little tunny in the western Atlantic. The fishery exists in North American waters. The 1981 objectives of our research were to determine if commercial catch totaled only 120t and the 1979 the specific foods that we found in the diet of little (most recent year available) recreational catch tunny could be associated with fish size, geogra- * Beaufort Laboratory, Southeast Fisheries Center, National Marine Fisheries Service, NOAA, Beaufort, N. C. 28516-9722. 1208 MANOOCH, MASON, and NELSON phical area of collection, and season, and to com fled to the lowest taxon possible and were enu pare the diet with the diets of two other coastal merated, thus providing the relative number of pelagic species, king mackerel Scomberomorus each food type in the stomachs. Frequency of cavalla and Spanish mackerel S. maculatus. occurrence of materials was determined by count ing every stomach that contained at least one specimen or part of a specific item (taxon). Empty Methods stomachs were excluded. The volume of each From April 1980 to October 1981, 2, 134 little taxon was obtained by water displacement. tunny between 172 and 885mm fork length (FL) Larval and juvenile fish from the stomachs were were sampled from hook and line recreational identified after they had been cleared and stained, and haul seine commercial catches from North following the methods discussed by DINGERKUS Carolina to Texas. Along the southeastern and UHLER4) and TAYLOR and VAN DYKE.* United States, samples were obtained at ports in Crustaceans were identified with the assistance of North Carolina, South Carolina, Georgia, east S. G. MORGAN, University of Maryland, College central Florida, and south Florida; along the Gulf Park, MD. of Mexico coast at ports in northwest Florida, All data were analyzed as percent frequency of the Mississippi delta (Mississippi-Louisiana), occurrence, percent of total number, and percent northeast Texas, and south Texas (Fig. 1). of food volume. Once frequencies, volumes, and Samplers at all locations apportioned their efforts numbers of the various foods were obtained, the to coincide with local charter boat, head boat, importance of each major food group was judged and commercial fishing activities, primarily April on the basis of its Index of Relative Importance through November. They met the boats as a (IRI): day's catch was being unloaded and asked in IRI=(N+V)F, where dividual fishermen to let them weigh, measure, and eviscerate their catch. Fish were measured to the N=numerical percentage of a food, V=its nearest millimeter and weighed to the nearest volumetric percentage, and F=its percentage fre tenth of a kilogram. Stomachsand gonads were quency of occurrence.5) placed in labeled cloth bags or cheesecloth and Differences in the diet were evaluated as the preserved in 10% formalin. basis of IRI values according to fish size (<300 In the laboratory, stomach contents were identi mm FL; •¬300-<500; •¬500-<700; •¬700-

Fig. 1. Samplining areas along the southeastern United States and the Gulf of Mexico . The number at each location indicates little tunny Euthynnus alletteratus with stomach contents . * W . R. TAYLORand G. C. VAN DYKE: Unpublished manuscript . Staining and Clearing Small Verte brates for Bone and Cartilage Study. Smithsonian Institution, Washington , DC 20560. pp. 19 (1978). Foods of Little Tunny 1209

<900), area of collection, and season (spring: dividuals of the genera: Caranx, Chloroscombrus, March-May; summer: June-August; fall: Sep Decapterus, and Seriola. tember-November; and winter: December- Only one other family, Engraulidae, contributed February). significantly to the diet. Although a few of the Volumetric data by areas of collection were engraulids could be identified to species (Anchoa compared to similar data for king mackerel S. mitchilli and Anchoa hepsetus), most were only cavalla and Spanish mackerel S. maculatus by recognizable as Anchoa spp. using the Bray-Curtis similarity coefficient: In addition to feeding on mid-water or pelagic fishes, little tunny also consumed fish that are usually considered demersal as adults, but pelagic as larvae or juveniles. Representative families were Synodontidae, Batrachoidae, Chaetodontidae, Pomacentridae, Triglidae, Bothidae, Balistidae, where Xij=ith prey item for the jth predator, Xik= Tetraodontidae, and Diodontidae. Some of these ith prey item for the kth predator, and n=number were believed to be in their pelagic phase when of prey items.6) The range of Sjk is 0 to 1. Data consumed, but larger fish were probably benthic. for the mackerels were obtained from SALOMAN 2. Invertebrates and NAUGHTON.7,8) For comparisons, food data Invertebrates, almost entirely mollusks and that were usually identified to family and usually crustaceans, were of secondary importance, oc represented at least 1% of the diet were used. curring in only 30.5% of the stomachs (Table 1). When combined, the foods composed most of the Although relatively large numbers were encounter identified diet for the predator for a given area. ed (2,400, 11.6%), the volume was only 5.9% of For example, these prey accounted for 58.4% to the total, thus exemplifying their small average 89.0% of the little tunny diet, 49.6% to 88.4% of volume (about 1.5ml). the king mackerel diet, and 35.7% to 66.2% of Squids (Teuthidida), not identified to genus or the Spanish mackerel diet, depending on the area species, but probably Loliginidae, were the prin of collection. cipal mollusks eaten. They occurred in 14.4% of the stomachs, but contributed 1.2% and 3.5% Results of the number and volume, respectively. Crustaceans occurred in 17.6% of the stomachs Synopsis of Food Types 1. Fish and represented 10.3% of the total number of Fish, the dominant food, occurred in 66.9% of food items, and 2.3% of the total volume (Table the stomachs containing food (Table 1), and con 1). The mean volumetric displacement was 0.68 ml. Immature crustaceans were the smallest stituted 88.4% (18,342items) of the total number organisms consumed. Crustaceans also were of items and 93.7% (58,989ml) of the total volume. In total, 24families representing 23species were diverse; the most important by frequency of occurrence were stomatopods (6.8%), penaeids identified. While most prey fish were adults, mainly clupeids, engraulids, and carangids, some (5.7%), and anomurans (2.5%). were juveniles. Besides those identified to family 3. Miscellaneous or genus, unidentified juvenile fishes alone occurred Some material not regarded as food and pro in 8.5% of the stomachs and represented 13.1 bably consumed incidentally to fishes and inverte- of the number of all items. brates, included plant material such as Sargassum, Clupeids the most frequently eaten fish, occurred Thalassia testudinum, Zostera marina, Spartina in 22.2% of the stomachs, and constituted 5.2% patens, and objects discarded from seagoing craft. of the number and 54.7% of the food volume. Examples of the latter were a cigarette wrapper, a Adults of two species were recognizable: Bre beer tab, and corn kernels (Table 1). voortia patronus, and the far more common Sardinella aurita, which occurred in 19.4% of the Variations in Food Habits stomachs. 1. By Size The second most important, and most species Food habits changed as the fish grew larger. rich group of fishes, were the carangids, found in Fish was the dominant food category for all sizes, 13.8% of the stomachs. Five species were identi but occurred more frequently (73.9%) in larger fied, including both medium-and small-sized in than in smaller individuals (54.3%). Conversely,

Sjk=2n‡”i=1min(Xij,Xik)/ n‡”i(Xij+Xik) 1210 MANOOCH, MASON, and NELSON

Table 1. Stomach contents of 1,212 little tunny collected off the southeastern United States and Gulf of Mexico in 1980 and 1981

Frequency Number of of Percent Percent Volume Percent byItem occurrence frequency items by number (62,961.3ml) volume (N=1,212) (N=20,742) Fish 811 66.9 18,342 88.4 58,988.6 93.7 Unidentifiable fish 320 26.4 1,094 5.3 6,411.0 10.2 Unidentifiable juvenile fish, 103 8.5 2,717 13.1 1,085.4 1.7 Family Ophichthidae 1 0.1 1 TR 63.0 0.1 Unidentifiable snake eel 1 0.1 1 TR 63.0 0.1 Family Clupeidae 269 22.2 1,079 5.2 34,451.1 54.7 Unidentifiable clupeid 48 4.0 107 0.5 1,758.4 2.8 Alosa sp. 1 0.1 1 TR 40.0 0.1 Brevoortia sp. 2 0.2 2 TR 17.0 TR B. patronus 1 0.1 8 TR 100.0 0.2 Sardinella aurita 235 19.4 961 4.6 32,535.7 51.7 Family Engraulidae 130 10.7 12,335 59.5 4,771.5 7.6 Anchoa spp. 128 10,6 12,271 59.2 4,707.5 7.5 A. hepsetus 4 0.3 17 0.1 27.0 TR A. mitchilli 2 0.2 47 0.2 37.0 0 .1 Family Synodontidae 8 0.7 485 2.3 257.8 0.4 Unidentifiable lizardfish 4 0.3 182 0.9 63.8 0.1 Synodussp. 2 0.2 301 1.4 89.0 0.1 S. synodus 1 0.1 1 TR 24 .0 TR Trachinocephalus myops 1 0.1 1 TR 81.0 0.1 Family Batrachoididae 1 0.1 5 TR 61.0 0.1 Porichthys plectrodon 1 0.1 5 TR 61.0 0.1 Family Exocoetidae 4 0.3 4 TR 114.8 0.2 Unidentifiable fiyingfish 1 0.1 1 TR 30.0 TR Euleptorhamphus velox 1 0.1 1 TR 2 .8 TR Hemiramphus brasiliensis 2 0.2 2 TR 82 .0 0.1 Family Belonidae 1 0.1 2 TR 70 .0 0.1 Strongylura marina 1 0.1 2 TR 70 .0 0.1 Family Atherinidae 1 0.1 2 TR 1.4 TR Menidia sp. 1 0.1 2 TR 1.4 TR Family Syngnathidae 1 0.1 3 TR 6.0 TR Hippocampus sp. 1 0.1 3 TR 6 .0 TR Family Serranidae 2 0.2 8 TR 197.0 0.3 Centropristis sp. 2 0.2 8 TR 197.0 0.3 Family Carangidae 167 13.8 478 2.3 8,201.3 13.0 Unidentifiable carangid 69 5.7 108 0 .5 1,735.3 2.8C aranx sp. 5 0 .4 7 TR 232 .0 0.4 C. crysos 1 0.1 1 TR 50 .0 0.1 Chloroscombrus chrysurus 3 0 .2 133 0.6 109.0 0.2 Decapterus punctatus 96 7.9 225 1 .1 6,032.0 9.6S eriola rivohana 1 0.1 1 TR 38.0 0.1S . zonata 1 0.1 3 TR 5.0 TRF amily Lutjanidae 5 0 .4 5 TR 194.0 0.3L utjanus sp. 2 0 .2 2 TR 29 .0 TRRh omboplites aurorubens 3 0 .2 3 TR 165.0 0.3F amily Sparidae 15 1 .2 18 0 .1 425.5 0.7Unide ntifiable porgy 2 0.2 2 TR 18.0 TRL agodon rhomboides 4 0.3 5 TR 200 .5 0.3P agrus pagrus 2 0.2 2 TR 62 .0 0.1St enotomus caprinus 7 0 .6 9 TR 145.0 0.2F amily Sciaenidae 10 0 .8 16 0.1 764 .0 1.2 Foods of Little Tunny 1211

Table 1. (Continued).

Frequency N umber ofPercent Volume Percent by Item occurrenceof frequency Percent items b y number (62,961.3ml) volume(N =1,212) (N=20,742)

Unidentifiable drum 2 0.2 3 TR 45.0 0.1 Cynoscion sp. 3 0.2 4 TR 104.0 0.2 C. nothus 1 0.1 1 TR 60.0 0.1 Menticirrhus sp. 3 0.2 7 TR 445.0 0.7 M. saxatilis 1 0.1 1 TR 110.0 0.2 Family Chaetodontidae 1 0.1 1 TR 0.6 TR Chaetodon sp. 1 0.1 1 TR 25.0 TR Family Pomacentridae 1 0.1 2 TR 25.0 TR Unidentifiable damselfish 1 0.1 2 TR 25.0 TR Family Trichiuridae 15 1.2 23 0.1 549.0 0.9 Trichiurus lepturus 15 1.2 23 0.1 549.0 0.9 Family Scombridae 1 0.1 1 TR 80.0 0.1 Unidentifiable scombrid 1 0.1 1 TR 80.0 0.1 Family Stromateidae 15 1.2 33 0.2 1,075.0 1.7 Peprilus sp. 1 0.1 4 TR 60.0 0.1 P. burti 14 1.2 29 0.1 1,015.0 1.6 Family Triglidae 1 0.1 5 TR 79.0 0.1 Prionotus sp. 1 0.1 5 TR 79.0 0.1 Family Bothidae 6 0.5 9 TR 60.0 0.1 Unidentifiable flounder 5 0.4 8 TR 35.0 TR Etropus sp. 1 0.1 1 TR 25.0 TR Family Balistidae 10 0.8 12 0.1 39.2 0.1 Unidentifiable balistid 2 0.2 2 TR 2.5 TR Unidentifiable filefish 3 0.2 4 TR 8.7 TR Unidentifiable triggerfish 3 0.3 4 TR 14.5 TR Aluterus sp. 1 0.1 1 TR 5.0 TR Monacanthus sp. 1 0.1 1 TR 8.5 TR Family Tetraodontidae 1 0.1 1 TR 4.0 TR Unidentifiable puffer 1 0.1 1 TR 4.0 TR Family Diodontidae 1 0.1 3 TR 2.0 TR Unidentifiable porcupinefish 1 0.1 3 TR 2.0 TR

Invertebrates 370 30.5 2,400 11.6 3,711.1 5.9 Phylum Mollusca 201 16.6 265 1.3 2,248.5 3.6 Unidentifiable crushed shell 1 0.1 1 TR 0.2 TR Class Gastropoda 2 0.2 2 TR 2.0 TR Class Pelecypoda 8 0.7 8 TR 8.2 TR Class Cephalopoda 175 14.4 254 1.2 2,238.1 3.6 Unidentifiable cephalopod 1 0.1 1 TR 5.0 TR Order Teuthidida 175 14.4 253 1.2 2,233.1 3.5 Phylum Arthropoda 214 17.6 2,131 10.3 1,444.7 2.3 Class Crustacea 213 17.6 2,130 10.3 1,444.6 2.3 Unidentifiable crustacean 7 0.6 8 TR 2.7 TR Order Stomatopoda 82 6.8 399 1.9 264.2 0.4 Unidentifiable stomatopod 10 0.8 17 0.1 53.5 0.1 Unidentifiable larvae 63 5.2 331 1.6 29.4 TR Lysiosquilla glabriuscula 1 0.1 1 TR 6.0 TR Squilla sp. 1 0.1 1 TR 0.1 TR S. chydaea 1 0.1 1 0.1 4.0 TR S. empusa 7 0.6 17 0.1 124.6 0.2 S. empusa (larvae) 2 0.2 27 0.1 1.1 TR S. neglecta 2 0.2 4 TR 45.5 0.1 1212 MANOOCH, MASON, and NELSON

Table 1. (Continued).

Frequency Numbers of of Percent Percent Volume Percent byItem occurrence frequency items by number (62,961.3ml) volume (N= 1,212) (N=20,742) Order Amphipoda 1 0.1 1 TR TR TR Suborder Gammaridea 1 0.1 1 TR TR TR Order Decapoda 154 12.7 1,722 8.3 1,177.7 1.8 Unidentifiable decapod 2 0.2 2 TR 1.3 TR Unidentifiable zoea 2 0.2 27 0.1 1.5 TR Unidentifiable larvae 4 0.3 130 0.6 6.4 TR Suborder Natantia 99 8.2 334 1.6 1,030.8 1.5 Unidentifiable shrimp 5 0.4 11 TR 14.4 TR Section Penaeidea 69 5.7 317 1.5 1,015.2 1.6 Unidentifiable penaeid 34 2.8 61 0.3 135.0 0.4 Family Penaeidae 69 5.7 255 1.2 880.2 1.4 Parapenaeus longirostris 10 0.8 67 0.3 98.1 0.2 Penaeussp. 21 1.7 28 0.1 184.5 0.3 P. aztecus 5 0.4 32 0.1 100.5 0.2 P. duorarum 11 0,9 44 0.2 215.0 0.3 P. setiferus 8 0.7 31 0.1 83.8 0.1 Sicyonia sp. 9 0.7 10 TR 19.3 TR S. brevirostris 7 0.6 35 0.2 162.0 0.3 S. dorsalis 3 0.2 8 TR 17.0 TR Family Sergestidae (larvae) 1 0.1 1 TR TR TR Section Caridea 3 0.2 6 TR 1.2 TR Family Pasiphaeidae 1 0.1 1 TR TR TR Leptochela serratorbita 1 0.1 1 TR TR TR Family Palaemonidae 2 0.2 5 TR 1.2 TR Palaemonetes vulgaris 2 0.2 5 TR 1.2 TR Suborder Reptantia 113 9.3 1,229 5.9 137.7 0.2 Unidentifiable Reptantia 4 0.3 5 TR 5.8 TR Unidentifiable megalopa 7 0,6 90 0.4 5.4 TR Section Macrura 1 0.1 1 TR TR TR Superfamily Scyllaridea 1 0.1 1 TR TR TR (larvae) Section Anomura 30 2.5 878 4.2 54.7 0.1 Subfamily Diogeninae 23 1.9 846 4.0 54.3 0.1 (glaucothoe) Family Albuneidae 7 0.6 32 0.1 0.4 TR Albunea sp. (larvae) 7 0.6 32 0.1 0.4 TR Section Brachyura 40 3.3 255 1.2 71.8 0.1 Family Raninidae 20 1.6 218 1.0 9.2 TR Unidentifiable zoea 1 0.1 1 TR TR TR Unidentifiable megalopa 19 1.6 217 1.0 9.2 TR Family Dromiidae (megalopa) 8 0.7 12 0.1 0.6 TR Superfamily Brachyrhyncha 1 0.1 1 TR TR TR (juvenile crab) Family Portunidae 12 1.0 22 0.1 62.0 0.1 Unidentifiable portunid 3 0.2 3 TR 6.3 TR Ovalipes sp. 1 0.1 3 TR 2.6 TR Portunus sp. 6 0.5 13 0.1 47.1 0.1 P. gibbesii 2 0.2 2 TR 4 .0 TR P. sayi 1 0.1 1 TR 2 .0 TR Subfamily Parthenopinae 1 0.1 2 TR TR TR Parthenope sp. (larvae) 1 0.1 2 TR TR TR Class Insecta 1 0.1 1 TR 0 .1 TR Foods of Little Tunny 1213

Table 1. (Continued)

Frequency Number of of Percent Percent Volume Percent byItem occurrence frequency items by number (62,961.3ml) volume (N=1,212) (N=20,742) Order Hymmenoptera 1 0.1 1 TR 0.1 TR Unidentifiable wasp 1 0.1 1 TR 0.1 TR Phylum Echinodermata 3 0.2 3 TR 15.0 TR Class Echinoidea 2 0.2 2 TR 14.5 TR Unidentifiable urchin 2 0.2 2 TR 14.5 TR Class Asteroidea 1 0.1 1 TR 0.5 TR Unidentifiable starfish 1 0.1 1 TR 0.5 TR Subphylum Urochordata 1 0.1 1 TR 2.9 TR Class Thaliacea 1 0.1 1 TR 2.9 TR Order Salpida 1 0.1 1 TR 2.9 TR

Miscellaneous 137 11.3 261.6 0.5 Unidentifiable contents 67 5.5 199.0 0.3 Unidentifiable plant material 5 0.4 13.1 TR Unidentifiable algae 1 0.1 0.1 TR Sargassum 12 1.0 13.1 TR Thalassia testudinum 3 0.2 3.9 TR Zostera marina 7 0.6 3.2 TR Spartina patens 1 0.1 2.0 TR Pine needle 1 0.1 0.3 TR Unidentifiable seed pod 5 0.4 2.1 TR Corn kernels (yellow) 1 0.1 0.5 TR Sand 1 0.1 10.0 TR Rocks 1 0.1 0.2 TR Beer tab 1 0.1 0.1 TR Cigarette pack wrapper 1 0.1 12.0 TR Vantage cigarette pack (empty) 1 0.1 1.0 TR Wood 1 0.1 1.0 TR

invertebrates were slightly more important in the identifiable juvenile fish, squid, Penaeidea, Stoma diet of smaller fish. Selected frequency of occur topoda, and Diogeninae.

rence data by fish size are presented graphically Little tunny in the largest size category examined,

(Fig. 2). Tabular data by fish size classes are ?? 700 to <900mm FL (N=153), also contained available at the Southeast Fisheries Center's a mixture of fish and invertebrates, although fishes Beaufort Laboratory. eaten were typically larger than those consumed

The seven smallest fish examined were <300mm by the smaller fish. The 10 highest IRI values FL. Unfortunately, they contained either un were Clupeidae, crustaceans, unidentifiable fish, identified fish remains, or unidentified contents. Carangidae, Penaeidea, Diogeninae, squid, For the 278 fish between 300 and 500mm FL, Raninidae, Sciaenidae, and Stomatopoda.

invertebrates and small fish were important to the

diet. Ranked by the IRI values, the 10 most 2. By Season important foods were unidentifiable fish, crus Most little tunny (71%) were collected during taceans, unidentifiable juvenile fish, squid, un summer when charter boat anglers most actively identifiable contents, Clupeidae, Stomatopoda, pursue the species. Selected food frequency of Synodontidae, and Raninidae. occurrence data by season are presented graphi

For the third size group, •¬500 to <700mm, cally (Fig. 3). Tabular data by season of collec which contained the largest number examined tion is available at the Beaufort Laboratory.

(N=744), the 10 most significant contributors One hundred and sixteen little tunny were to the diet were Clupeidae, Engraulidae, un sampled in the spring. Fish occurred in 57.8%, identifiable fish, Carangidae, crustaceans, un invertebrates in 50.9%, and miscellaneous items 1214 MANOOCH, MASON, and NELSON

Fig. 2. Frequency of occurrence percentages for se Fig. 3. Frequency of occurrence percentages for se lected foods of little tunny Euthynnus alletteratus lected foods of little tunny Euthynnus alletteratus by predator size (mm FL). by season of collection. in 6.0% of the stomachs. Ranked by IRI values, Stomatopoda, and Penaeidea. The relative high the 10 most important food categories in the frequency for anchovies and herrings reflects their spring diet were Crustacea, Penaeidea, unidentifi emigrations from estuaries in fall. able fish, Clupeidae, squid, Carangidae, En Only 14 little tunny were sampled in winter. In graulidae, Stomatopoda, Serranidae, and vertebrates occurred in 64.3% and were more Dromiidae. frequently encountered than during the other The 860 stomachs collected during the summer three seasons. Fish occurred in 50.0%, and contained the highest diversity of contents. Fish miscellaneous items in 21.4%. By IRI ranking occurred in 67.9%, invertebrates in 30.5%, and Crustacea, unidentifiable fish, Penaeidea, Sto miscellaneous items in 7.6%. The most im matopoda, Chaetodontidae, and Diogeninae were portant foods, ranked by IRI, were Clupeidae, most important to the diet. unidentifiable fish, Carangidae, Crustacea, un identifiable juvenile fish, Engraulidae, squid, 3. By Area Stomatopoda, Diogeninae, and Penaeidea. Within two major geographic areas-south In the 222 stomachs collected during fall, fish eastern United States (North Carolina through the were found in 74.3%, invertebrates in 18.9%, Florida Keys) and the Gulf of Mexico (west coast and miscellaneous items in 13.5%. By IRI rank of Florida through Texas)-we sampled at 10 ing, the 10 most important foods were Engraulidae, locations (Fig. 1). Results for each location are Clupeidae, unidentifiable fish, Carangidae, Crus discussed below and selected foods are presented tacea, squid, unidentifiable contents, juvenile fish, graphically (Fig. 4). Tabular data by area of Foods of Little Tunny 1215

collection are available at the Beaufort Laboratory. Stomachs of 47 little tunny collected off Cape Lookout, North Carolina were examined. Ranked by IRI values, the most important foods were Crustacea, unidentifiable fish, squid, unidentifiable Reptantia, Stomatopoda, Engraulidae, unidenti fiable juvenile fish, Belonidae, Clupeidae, and Diogeninae. Fish occurred in 55.3% of the stomachs, invertebrates in 48.9%, and miscellane ous in 10.6%. Thirty-two fish were collected off South Carolina. The major foods were Clupeidae, unidentifiable fish, squid, Crustacea, Stomatopoda, unidentifiable juvenile fish, Carangidae, and Syngnathidae. Fish occurred in 90.6% of the stomachs, invertebrates in 31.2%, and miscel laneous items in 3.1%. One hundred and twenty-eight were collected from the east central coast of Florida area. Fishes, invertebrates, and miscellaneous items were en countered in 73.4%, 26.6%, and 3.1% of the stomachs, respectively. Clupeidae, Crustacea, Diogeninae, unidentifiable fish, squid, Raninidae, Stomatopoda, unidentifiable juvenile fish, En graulidae, and Carangidae ranked as the 10 most important contributors to the diet. One hundred and seventy were collected from the South Florida area. Fish occurred in 64.1%, Fig. 4. Frequency of occurrence percentages for se invertebrates in 52.3%, and miscellaneous in lected foods of little tunny Euthynnus alletteratus 10.0%. Crustaceans were found in 43.5% of the by area of collection (1=North Carolina, 2= stomachs. The 10 most important groups were South Carolina, 3=east coast of Florida, 4= Crustacea, unidentifiable fish, Penaeidea, En south Florida, 5=northwest Florida, 6= graulidae, Stomatopoda, Carangidae, Clupeidae, Mississippi Delta, 7=northeast Texas, and 8= squid, unidentifiable juvenile fish, and Balistidae. south Texas). From the Gulf of Mexico, 835 fish were collected, most (739) were from the northwest Florida area. Fish were found in 81.5%, invertebrates in 24.0%, Table 2. Bray-Curtis diet overlap values for three and miscellaneous items in 10.4%. By number, species of coastal pelagic fishes, by volume, by Anchoa, Synodus, and Decapterus were the most area important genera of fishes, and squid, stomatopods, and diogeninae glaucothoes were the most abund Little tunny Little tunny King ant invertebrates. The 10 highest ranked food Areas vs King vs Spanish macheral mackerel mackerel vs Spanishmackerel groups were Clupeidae, Engraulidae, Carangidae, unidentifiable fish, unidentifiable juvenile fish, Carolinas 0.426 0.109 0.172 squid, Crustacea, unidentifiable contents, Stomato East poda, and Synodontidae. Florida 0.410 0.496 0.704 In the 67 fish collected off Louisiana and Mis South sissippi, fish occurred in 83.6%, invertebrates in Florida 0.325 - - 56.7% and miscellanea in only 6.0%. Chloro Northwest scombrus chrysurus, raninid megalopa, Anchoa sp. Florida 0.427 0.478 0.474 and Parapenaeus longirostris were the most Mississippi/ numerous foods identified. Index of relative im Louisiana 0.213 0.212 0.461 Texas 0.516 0.360 0.558 portance ranking revealed Crustacea, unidenti 1216 MANOOCH, MASON, and NELSON fiable fish, Penaeidea, Stromateidae, Carangidae, the northeast Texas fish, invertebrates were im Stomatopoda, Sciaenidae, Sparidae, squid, and portant to the diet of little tunny sampled from Engraulidae as the most important groups. south Texas. The 10 highest ranked IRI cate Of the three fish obtained from the northeast gories were Crustacea, Trichiuridae, Penaeidea, coast of Texas, the frequency of occurrences for unidentifiable fish, Stomatopoda, squid, Portuni fishes and invertebrates were equal (66.7%). The dae, Caridea, Triglidae, and Raninidae. Thus 7 major contributors to the diet were Crustacea, of the 10 were invertebrates. unidentifiable fish, Clupeidae, Sciaenidae, Penaei dea, Stomatopoda, Batrachoididae, and Bothidae. 4. Between Coastal Pelagic Species In the 26 collected from south Texas, fish, in Volumetric data by area were compared with vertebrates, and miscellaneous items occurred in those of king mackerel and Spanish mackerel by 92.3%, 88.5%, and 7.7%, respectively. As with the Bray-Curtis similarity coefficient6-8) (Table 2).

Table 3. Volumes (%) of the major foods identified in the diets of little tunny, king mackerel, and Spanish mackerel, by area of collection

Food Little King Spanish Food Little King Spanisht unny mackerel mackerel Tunny Mackerel Mackerel Carolinas Northwest Clupeidae 44.8 21.1 4.3 Clupeidae 62.1 14.8 8.8 Squid 20.6 5.5 - Carangidae 15,2 38.4 12.7 Belonidae 4.7 - - Engraulidae 8.9 - 6.0 Squillidae 3.2 - - Squid 2.8 10.6 2.3 Engraulidae 1.9 - 29.7 Scombridae - 0.9 - Scombridae - 6.2 - Sparidae - - 4.2 Carangidae - 5.6 3.3 Sciaenidae - - 1.7 Serranidae - 2.7 - Mississippi/Louisiana Synodontidae - 2.4 - Stromateidae 25.0 - - Exocoetidae - 2.3 - Sciaenidae 10.2 43.0 3.6 Sparidae - 2.0 - Penaeidea 9.7 - 1.5 Mugilidae - 1.8 - Carangidae 5.5 10.4 3.7 Atherinidae - - 1.5 Serranidae 4.9 - - East Coast of Florida Synodontidae 3.9 - - Clupeidae 66.0 39.7 33.3 Sparidae 3.7 1.1 3.1 Squid 10.9 1.8 0.6 Sauillidae 3.3 - - Diogeninae Triglidae 1.7 - - (glaucothoe) 1.8 - - Ophichthidae 1.6 - - Engraulidae 0.9 4.7 14.8 Clupeidae - 26 .8 21.8 Exocoetidae - 3.9 0.8 Scombridae - 3.1 - Mugilidae - 3.0 - Trichiuridae - 3.1 - Carangidae - 1.0 11.3 Pomatomidae - 0 .9 - South Florida Engraulidae - - 7.8 Carangidae 12.5 - Haemulidae - - 1.2 Penaeidea 11.3 9.1 Texas Clupeidae 11.2 4.4 Trichiuridae 31 .2 24.9 9.0 Engraulidae 9.4 - Penaeidea 17.9 1.8 2.0 Squid 5.2 - Sciaenidae 14.2 1.2 7.8 Scombridaei 3.7 3.7 Clupeidae 5.1 10.9 7.9 Exocoetidae 3.5 34.6 Squillidae 3.2 - - Balistidae 1.8 - Pomacentridae 1.4 - - Lutjanidae - 10.9 Squid 1.4 2.9 2.4 Mugilidae - 3.2 Carangidae - 12.6 15.6 Serranidae - 1.7 Scombridae - 1.8 - Lutjanidae - 1.4 - Balistidae - 1.4 - Engraulidae - - 21.5 Foods of Little Tunny 1217

The diet of little tunny was generally more similar it goes a step further by evaluating the diets by to king mackerel than to Spanish mackerel. The fish size, area of collection, and season, and by coefficients for little tunny/king mackerel ranged comparing the similarity of the diets of three from 0.213 to 0.516, but 0.109 to 0.496 for little members of the coastal pelagic community. tunny/Spanish mackerel. The diet of the two We found the diet of little tunny to be very mackerels overlapped substantially. Similarity diverse, consisting of many types of fishes and coefficients ranged from 0.172 to 0.704 (Table 2). invertebrates that usually occur in schools or that The major foods that could be identified, and aggregate in the water column of nearshore coastal thus used to calculate the Bray-Curtis similarity waters. For the entire region, North Carolina coefficients are listed by area in Table 3. Several through Texas, the most important foods by fre general observations may be made by inspecting quency of occurrence, number, and volume com this table. First, the little tunny diet included bined were clupeids, engraulids, carangids, squids, more crustaceans, particularly smaller ones, such stomatopods, penaeids, diogenids, stromateids, as stomatopods, dromiid and raninid megalopa, and synodontids. Other researchers studying the and diogenid glaucothoe, than did those of king foods of little tunny on both sides of the Atlantic and Spanish mackerels. Second, engraulids were Ocean also found fishes, squids, and crustaceans far more important in the diet of Spanish mackerel to form the bulk of the diet.3,10,11) than for either little tunny or king mackerel. And As we expected, diets changed with area and third, squids, clupeids, and carangids seemed to season of collection, and to a lesser extent with be important foods of all three species. size of little tunny. The species appears to be relatively non-selective in its feeding. Since major prey items (i.e. schooling fishes, immature Discussion crustaceans, and squids) are patchily distributed, The little tunny is but one of several species of the little tunny concentrates its feeding activity coastal pelagic scombrids (others are king and on spatially and temporally localized high-density Spanish mackerels and Atlantic bonito Sarda prey aggregations. sarda) that are important to fisheries along the The Bray-Curtis similarity coefficient was southeastern and Gulf of Mexico coasts of the selected to evaluate the diet overlap of three coastal United States. These fishes, which compose a pelagic fishes because it is considered to be the only dynamic, seasonally fluctuating subsystem, migrate index that exhibits the "correct" amount of simi through the inshore waters of the region. They larity,12) and because it is not affected by joint occur in the neritic zone, intertidal to the Con absences of a prey species.13) Although little tinental Shelf break, and therefore generally in tunny, king mackerel, and Spanish mackerel feed habit water shoreward of the oceanic pelagics such on similar foods (i.e., fishes, squids and crus as the tunas and billfishes. Migrations generally taceans), the diet of little tunny and king mack follow the temperate zone pattern of southward erel is usually most alike than that of little and in fall and winter, and northward in spring and Spanish mackerel. This similarity may be ex summer as the species follow prey and favorable plained in several ways. First, little tunny and water temperatures.9) king mackerel are more often caught together than Food habit studies of migratory fishes are are little tunny and Spanish mackerel. Thus, the difficult because one must consider many variables, confounding variables of time and area are not as including predator size, buccal cavity and gill pronounced. MANOOCH et a1.14) found that raker morphologies, and temporal and spatial anglers on North Carolina charter boats caught distributions of the prey as well as the predators. little tunny and king mackerel in spring and fall, Determining what a migratory marine fish perfers whereas Spanish mackerel were more frequently to eat is an almost impossible task, because very landed in summer. Another factor may be fish little is known about the quantitative abundance size. Little tunny and king mackerel are generally of the foods at a specific time or location. In larger than Spanish mackerel; therefore, their fact, scientists are only now beginning to ascertain foods would more closely reflect a predator size what foods constitute the diets of marine fishes prey size correlation. When the mackerls do co important to recreational and commercial fisheries. occur, however, their diets may reveal considerable Although our study follows the basic approach overlap. This may be due to comparable gill of determining what foods were found in stomachs, apparatus morphology. 1218 MANOOCH, MASON, and NELSON

The feeding behavior of little tunny has been University of Maryland for identifying crustaceans, noted by other researchers. BULLIS and JUHL15) and A. POWELL, Beaufort Laboratory, for identi reported a "phalanx orientation" of little tunny fying larval fishes. feeding near the Lesser Antilles. The phalanx was composed of three fish tightly aligned side by References side. The fish attacked a school of dwarf herring Jenkinsia lamprotaenia without breaking phalanx 1) FAO: 1981 Yearb. Fish. Stat., 52, 357 pp. (1983). formation. Additional little tunny joined the pre 2) Fisheries of the United States, 1981: U. S. Natl. dators until 14 or 15 fish were aligned. A study Mar. Fish. Serv., Curr. Fish. Stat., 8200, 131 off Florida by WICKLUND16)reported on a school pp. (1982). of 20 and a group of four little tunny feeding on 3) H. O. YOSHIDA: U.S. Natl. Mar. Fish. Serv., bigeye scad Selar crumenophthalmus and herring Circ., 429; and, FAO Fish Synop., 122, 57 pp. Clupea sp. The predators forced the prey to the (1979). bottom where they were attacked. The little 4) G. DINGERKUSand C. D. UHLER: Stain Technol., tunny swam swiftly to the bottom, and at the last 52, 229-232 (1977). 5) L. PINKAS,M. S. OLIPHANT,and I. L. K. IVERSON: moment turned sharply, viciously snapping up the Calif. Dep. Fish Game, Fish. Bull., 152, 1-105 scad and herring, and stirring up clouds of sedi (1971). ment. Feeding continued all day until 1800h. 6) D. F. BOESCH: Va. Inst. Mar. Sci., Spec. Sci. and then resumed the next morning at 1030h. Rep., 77, 115 pp. (1977). Fishermen along the southeastern and Gulf of 7) C. H. SALOMANand S. P. NAUGHTON: NOAA Mexico coasts of the United States have often been Tech. Memo., NMFS-SEFC, 126, 25 pp. (1983). perplexed by the catchability of little tunny on 8) C. H. SALOMANand S. P. NAUGHTON: NOAA hook and line. On some occasions the species Tech. Memo., NMFS-SEFC, 128, 22 pp. (1983). readily strikes artificial lures, while at other times 9) G. R. HUNTSMANand C. S. MANOOCH,III: in "Marine Recreational Fisheries it is very reluctant to bite. We believe that when , 3" (ed. by H. little tunny are feeding on immature crustaceans, Clepper), Sport Fishing Institute, Washington, trolling or casting lures are not effective. How D. C., pp. 97-106. ever, when the species is feeding on fishes and 10) J. E. RANDALL: Stud. Trop. Oceanogr., 5, 753- squids it is easily taken with hook and line. One 754 (1967). 11) A. DRAGOVICH: U. S. Fish Wildl. Serv., Spec. can only tell by trying. Sci. Rep. Fish., 593, 21 pp. (1969). 12) S. A. BLOOM: Mar. Ecol. Prog. Ser., 5, 125-128 Acknowledgments (1981). 13) J. G. FIELD, K. R. CLARKE,and R. M. WARWICK: We wish to thank E. NAKAMARA,Director of the Mar. Ecol. Prog. Ser., 8, 37-52 (1982). NMFS, Southeast Fisheries Center, Panama City 14) C. S. MANOOCH,III, L. E. ABBAS,and J. L . Ross: Laboratory, Panama City, Florida and his staff Mar. Fish. Rev., 43(8), 1-11 (1981). 15) H. R. BULLIS, JR. and R. JUHL: Trans. Am. for providing most of the biological materials , J. WITZIG, NMFS, Southeast Fisheries Center Fish. Soc., 96, 122-125 (1967). , 16) R. I. WICKLUND: Underwater Nat., 5(2), 30-31 Beaufort Laboratory for his suggestions and re (1968). view of our statistical methods, S. G. MORGAN,