Stomach Contents and Parasite 

 Infestation of School Bluefin Tuna 

 Thunnus thynnus Collected from 

 the Middle Atlantic Bight, Virginia* 



David B. Eggleston 



Virginia Institute of Marine Science, School of Marine Science 



The College of William and Mary, Gloucester Point. Virginia 23062 



Eleanor A. Bochenek 



Virginia Institute of Marine Science, School of Marine Science 

 The College of William and Mary, Gloucester Point, Virginia 23062 

 Present address: Louis Berger and Associates, Inc 

 100 Halsted Street, East Orange, New Jersey 07019 



In the western Atlantic Ocean, north- 

 ern bluefin tuna Thunnus thynnus 

 are distributed from Labrador and 

 Newfoundland to the Gulf of Mex- 

 ico, Caribbean Sea, and off Vene- 

 zuela and Brazil. The northern blue- 

 fin tuna is epipelagic and usually 

 oceanic, but seasonally strays near 

 the coast (Collette and Nauen 1983). 

 During June through October, these 

 tuna are common off the eastern 

 United States and Canada (Squire 

 1962) and support both commercial 

 and recreational fisheries. From 

 the end of May to August, many 

 pods of small school bluefin tuna 

 (< 100 kg) migrate past Virginia on 

 their way to more northern feed- 

 ing grounds. These tuna are caught 

 30 to 60 km off the Virginia coast 

 in the vicinity of numerous shoals 

 or "hills," by recreational anglers 

 trolling dead bait or lures on or 

 near the surface (Figley 1984). In 

 1986, 886 boats participated with 

 some degree of regularity in the 

 recreational fishery for tuna and 

 billfish out of Virginia ports (Boch- 

 enek and Lucy In press). Further 

 north, there is a recreational fish- 

 ery for giant (>200 kg) and me- 

 dium (100-200 kg) bluefin tuna, 



•Contribution no. 1580 of the Virginia Insti- 

 tute of Marine Science. 



and, to a lesser extent, school blue- 

 fin tuna (Figley 1984). 

 Bluefin tuna are opportunistic pred- 

 ators that prey upon fishes, moUusks, 

 crustaceans, and salps (Crane 1936; 

 Bigelow and Schroeder 1953; Knmi- 

 holz 1959; Dragovich 1969, 1970; 

 Mason 1976; Matthews et al. 1977; 

 Holliday 1978). Pacific bluefin tuna 

 Thunnus thynnus orienialis caught 

 off California and Baja California 

 preferred the same prey as the At- 

 lantic Ocean subspecies Thunnus 

 thynnus thynnus (Pinkas 1971). 



The spawning stock of the west- 

 em Atlantic bluefin tuna has declined 

 sharply since 1970, and both recruit- 

 ment and juvenile stock size are still 

 substantially lower than in 1970 

 (ICCAT 1987). Thus, information 

 about life-history characteristics, 

 such as trophic habits, is essential 

 for developing sound management 

 plans for this important commercial 

 and recreational fish. Mason (1976) 

 and Holliday (1978) studied the feed- 

 ing behavior of school bluefin tuna 

 captured along the eastern coast of 

 the United States; however, only 68 

 bluefin tuna stomachs were collec- 

 tively examined from fish caught off 

 or near the Virginia coast (lat 36- 

 38°N and long. 75°W). Therefore, 

 knowledge of the feeding habits of 

 school bluefin tuna off the Virginia 



coast is relatively sparse. The pres- 

 ent paper describes the findings of 

 stomach content analysis for juve- 

 nile bluefin tuna collected during 

 the summer of 1986 by recreational 

 fishermen along the mid-Atlantic 

 coast off Virginia. 



Methods and materials 



During June and July 1986, stom- 

 ach samples of 97 bluefin tuna were 

 obtained from recreational fisher- 

 men as they landed their catch at 

 Rudee Inlet, Virginia Beach, and at 

 Wachapreague on the eastern shore 

 of Virginia. Curved fork length (mm) 

 and the area of capture (Fig. 1) 

 were recorded for each fish. Fish 

 that could not be identified with a 

 specific area of capture were elim- 

 inated from the sample. Weights 

 (kg) were recorded for tuna official- 

 ly weighed on certified marina scales. 

 Stomachs were removed and placed 

 in 10% buffered formalin. Stomachs 

 were opened and designated in the 

 laboratory as either containing food 

 or empty. Stomachs containing only 

 parasites were classified as empty. 

 Stomach contents were rinsed in 

 water and stored in 10% ethanol im- 

 til identification. 



Prey items were sorted into ma- 

 jor food groups (fishes, crustaceans, 

 mollusks, and unidentifiable remains), 

 enumerated, and identified to the 

 lowest possible taxon with the aid 

 of a binocular dissecting scope. Vol- 

 umes were determined by water dis- 

 placement using a graduated cylin- 

 der and measured to the nearest 0.5 

 mL. Fishes too far digested for cer- 

 tain identification were placed in an 

 unidentified teleost category and 

 used in estimating total prey vol- 

 ume. The majority of unidentified 

 teleost material resembled remnants 

 of sand lance {Ammodytes spp.) 

 more than any other recognizable 

 species. 



Manuscript accepted 18 December 1989. 

 Fishery Bulletin, U.S. 88:389-395. 



389 



