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.

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