168 



Abstract-The stomachs of 819 Atlan- 

 tic bluefin tuna (Thiinnus thynnusi 

 sampled from 1988 to 1992 were ana- 

 lyzed to compare dietary differences 

 among five feeding grounds on the 

 New England continental shelf (Jef- 

 freys Ledge, Stellwagen Bank. Cape 

 Cod Bay, Great South Channel, and 

 South of Marthas Vineyard) where a 

 majority of the U.S. Atlantic commer- 

 cial catch occurs. Spatial variation in 

 prey was expected to be a primary 

 influence on bluefin tuna distribution 

 during seasonal feeding migi'ations. 

 Sand lance iAmmodytes spp.), Atlantic 

 herring (Clupea harengus). Atlantic 

 mackerel (Scomber scombr-us), squid 

 (Cephalopoda), and bluefish (Pomato- 

 mus saltatrix) were the top prey in 

 terms of frequency of occuiTence and 

 percent prey weight for all areas com- 

 bined. Prey composition was uncorre- 

 lated between study areas, with the 

 exception of a significant association 

 between Stellwagen Bank and Great 

 South Channel, where sand lance and 

 Atlantic herring occurred most fre- 

 quently. Mean stomach-contents bio- 

 mass varied significantly for all study 

 areas, except for Great South Channel 

 and Cape Cod Bay. Jeffreys Ledge had 

 the highest mean stomach-contents bio- 

 mass (2.0 kg) among the four Gulf of 

 Maine areas and Cape Cod Bay had 

 the lowest (0.4 kg). Diet at four of 

 the five areas was dominated by one 

 or two small pelagic prey and several 

 other pelagic prey made minor contri- 

 butions. In contrast, half of the prey 

 species found in the Cape Cod Bay diet 

 were demersal species, including the 

 frequent occurrence of the sessile fig 

 sponge iSuberites ficus). Prey size selec- 

 tion was consistent over a wide range of 

 bluefin length. Age 2-4 sand lance and 

 Atlantic herring and age 0-1 squid and 

 Atlantic mackerel were common prey 

 for all sizes of bluefin tuna. This is the 

 first study to compare diet composition 

 of western Atlantic bluefin tuna among 

 discrete feeding grounds during their 

 seasonal migi'ation to the New Eng- 

 land continental shelf and to evaluate 

 predator-prey size relationships. Previ- 

 ous studies have not found a common 

 occurrence of demersal species or a pre- 

 dominance of Atlantic hening in the 

 diet of bluefin tuna. 



Differences in diet of Atlantic bluefin tuna 

 iThunnus thynnus) at five seasonal feeding grounds 

 on the New England continental shelf* 



Bradford C. Chase 



Massachusetts Division of Marine Fisheries 

 30 Emerson Avenue 

 Gloucester, Massachusetts 01930 

 E mail address brad chase gistale ma us 



Manuscript accepted 21 September 2001. 

 Fish. Bull. 100:168-180 (2002). 



Atlantic bluefin tuna iTIuinmis thyn- 

 nus) are widely distributed throughout 

 the Atlantic Ocean and have attracted 

 valuable commercial and recreational 

 fisheries in the western North Atlantic 

 during the latter half of the twentieth 

 century. The western North Atlantic 

 population is considered overfished by 

 the International Commission for the 

 Conservation of Atlantic Tunas ( NMFS, 

 1999). Bluefin tuna are the largest 

 scombrid species, and the largest tele- 

 ost occurring in the Gulf of Maine (Big- 

 elow and Schroeder, 1953). Bluefin tuna 

 migrate to coastal waters off New Eng- 

 land during warmer months, feeding 

 on local concentrations of prey. This 

 migration supports a major component 

 of the U.S. Atlantic commercial fishery 

 for bluefin tuna; from 1978 to 1992 New 

 England accounted for between TS'/r 

 and 98% of annual commercial land- 

 ings (Chase, 1992; and NMFS, 1995). 

 Substantial annual variation has been 

 seen in the harvest locations on the 

 New England continental shelf (Chase, 

 1992). Spatial variation in prey popu- 

 lations is suspected to be the primary 

 influence on these annual aggregations 

 of bluefin tuna. Adaptations in the cir- 

 culatory system of the bluefin tuna 

 allow these fish to retain metabolic 

 heat, facilitating the regulation of body 

 temperature (Carey and Teal. 1969) 

 and assisting in the efficient transfer 

 of energy from consumed prey to fast 

 growth rates and large body size. These 

 adaptive features also allow bluefin 

 tuna to make extensive migrations 

 into cold-temperate waters in search 

 of prey. Diet information is necessary 

 to improve the understanding of sea- 

 sonal movements of bluefin tuna and 

 predator-prey relationships in the New 



England continental shelf region, and 

 as a baseline for bioenergetic analyses. 

 Information on the feeding habits of 

 this economically valuable species and 

 apex predator in the western North 

 Atlantic Ocean is limited, and nearly 

 absent for the seasonal feeding grounds 

 where most U.S. Atlantic commercial 

 catches occur. 



Previous food habit studies have 

 shown that western North Atlantic 

 bluefin tuna are opportunistic feeders 

 on a wide variety of finfish, cephalo- 

 pods, and crustaceans (Crane, 19.36; 

 Krumholz. 1959; Dragovich. 1970; Ma- 

 son, 1976; Holliday, 1978; Eggleston 

 and Bochenek, 1990; Matthews et al.M. 

 Pinkas (1971) reported similar results 

 for Pacific bluefin tuna iThunnus thyn- 

 nus orientalis). These bluefin tuna food 

 habit studies either reported on small 

 numbers of samples or were qualitative 

 studies on samples distributed over a 

 broad geographic range. Previous 

 studies have not evaluated size 

 relationships between bluefin tuna 

 and their prey and the amount of 

 food consumed. The present study tar- 

 geted regions of the New England gi- 

 ant tuna (>140 kg) fishery to quan- 

 titatively analyze stomach contents 

 of bluefin tuna among discrete sea- 

 sonal feeding grounds and to investi- 

 gate predator-prey size relationships 

 for this species in the Gulf of Maine. 



Contribution 3 of the Massachusetts Divi- 

 sion of Marine Fisheries, Gloucester. MA 

 01930. 



Matthews, F. D., D. M. Damkaer, L. W. 

 Knapp, and B. B. Collette. 1977. Food 

 of western North Atlantic tunas (Thun- 

 nus) and lancetfish lAlepisaurus). Nat. 

 Oceanic Atmos. Admm. Tech. Rep. NMFS 

 SSRF-706, Washington. D.C., 19 p. 



