340 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



(BuUis, 1955; Backus, Springer, and Arnold, 

 1956) . Other sharks probably also attack the line- 

 caught tuna. 



SUMMARY 



From 1957-60, tuna explorations were carried 

 out, intermittently, to determine the distribution 

 of tunas in the oceanic portion of the northwest- 

 em Atlantic and to assess tlie availability of tunas 

 to commercial gear. Major effort was expended 

 in the Gulf Stream proper. Longline gear, 

 fished from the Bureau vessel Delaware at 111 

 stations, caught bluefiji, yellowfin, albacore, skip- 

 jack, and bigeye tunas. 



Temperature studies show that the Gulf Stream 

 system provides the environmental conditions 

 favorable for the presence of tunas in the oceanic 

 portion of the northwestern Atlantic. Bluefin, 

 preferring cooler water, are the dominant tuna 

 in the vicinity of the Gulf Stream in winter and 

 spring. Longline catches indicate that a commer- 

 cial fishei-y for bluefin might be profitable in those 

 seasons. Bluefin disappear from the oceanic re- 

 gion in late spring or early summer, and yellow- 

 fin, preferring warmer water, are the dominant 

 tuna in summer and fall. 



A sharp temperature gradient on the edge of 

 the Gulf Stream allows tunas of two or more spe- 

 cies with dissimilar temperature requirements to 

 exist within short distances and yet be distinctly 

 separated. 



Temperatures at calculated fishing depths at 

 stations where subsurface yellowfin were taken in 

 the northwestern Atlantic were comparable to 

 temperatures of the surface water at positions in 

 the Pacific where surface-dwelling yellowfin were 

 taken. 



Shark damage was light. A liigher percentage 

 of yellowfin (to 20.6 percent) than bluefin (to 12.5 

 percent) was attacked at any one exploratory sta- 

 tion. Whitetip sharks appear to be responsible 

 for a large share of shark damage to tunas in the 

 western Atlantic. 



LITERATURE CITED 



Andekson, William W., Jack W. Gf.hringek, and Ed- 

 ward Cohen. 



1956. Physical oceanographic, biological, and chemi- 

 cal data South Atlantic coast of the United 

 States, M/V Theodore N. QUI cruise 1. U.S. Fish 

 and Wildlife Service, Special Scientific Report — 

 Fisheries No. 178, 160 p. 



Backus, Richard H., Stewabt Springer, and Edgar L. 

 Arnold, Jr. 



1956. A contribution to the natural history of the 

 white-tip shark, Pterolamiops longimanus 

 (Poey). Deep-Sea Research, vol. 3, no. 3, p. 

 17&-188. 

 BiGELOW, Henry B., and William C. Schroedek. 



19.j3. Fishes of the Gulf of Maine. U.S. Fish and 

 Wildlife Service, Fishery Bulletin 74, vol. 53, p. 

 1-577. 

 Blunt, C. E., Jr., and James D. Messersmith. 



1960. Tuna tagging in the eastern tropical Pacific, 

 1952-59. California Fish and Game, vol. 46, no. 3, 

 p. 301-369. 

 Bullis, Harvet R., Jr. 



1955. Preliminary report on exploratory longline 

 fishing for tuna in the Gulf of Mexico and the 

 Caribbean Sea; Part I— Exploratory fishing by 

 the Oregon. U.S. Fish and Wildlife Service, 

 Commercial Fisheries Review, vol. 17, no. 10 (Oc- 

 tober), p. 1-15. 



Bullis, Harvey R., Jr., and F. J. Mather III. 



1956. Tunas of the genus Thttnnns of the Northern 

 Caribbean. American Museum Novitates, no. 

 1765, 12 p. 



Captiva, Francis J. 



1955. Preliminary report on exploratory longline 

 fishing for tuna in the Gulf of Mexico and the 

 Caribbean Sea : Part II — Longline gear used in 

 yellowfin tuna explorations. U.S. Fish and 

 Wildlife Service, Commercial Fisheries Review, 

 vol. 17, no. 10 (October), p. 16-20. 



Day, C. Godfrey. 



1959. Oceanographic observations 1957, east coast of 

 the United States. U.S. Fish and Wildlife Serv- 

 ice, Special Scientific Report — Fisheries no. 282, 

 123 p. 



GooDE, George B., and Tarleton H. Bean. 



1879. A list of fishes of Essex County, including 

 those of Massachusetts Bay, according to the 

 latest results of the work of the U.S. Fish Com- 

 mission. Bulletin Essex Institute, vol. 11, p. 

 1-38. 



Iselin, C. O'D. 



1960. The Gulf Stream system. Oceanus, vol. 6, no. 

 4, p. 20-23. Woods Hole Oceanographic Institu- 

 tion, Woods Hole, Mass. 



Iversen, Edwin S., and Howard O. Yoshida. 



19.56. Longline fishing for tuna in the central 

 equatorial Pacific, 1954. U.S. Fish & Wildlife 

 Service, Special Scientific Report— Fisheries No. 

 184, 33 p. 

 Mather, Frank J., Ill 



19.54. Northerly occurrences of warm water fishes in 

 the western North Atlantic. Copeia, no. 4 (Octo- 

 ber), p. 292-293. 

 19.59. A preliminary report on biometric studies of 

 tunas (genus Thunuus) of the western North 

 Atlantic. (Mimeographed) Woods Hole Ocean- 

 ographic Institution, Woods Hole, Mass., June 19, 

 1959, 9 p. 



