DISTRIBUTION OF TUNAS IN NORTHWESTERN ATLANTIC 



325 



that tunas were to be found in subsurface rather 

 than surface waters of the oceanic re|non. 

 Largely for this reason, the Delaware explorations 

 were conducted with longline gear. 



A brief review of tlie knowledge of eacli tuna 

 species known to inhabit the nortliwesteni At- 

 lantic follows. This review portrays the status 

 of knowledge of the tunas of Continental Shelf 

 and the oceanic regions prior to the start of DeJn- 

 irare explorations in 1957. 



BLUEFIN TUNA 



Bluefin, largest of the tunas, are common on 

 the Continental Shelf olf eastern ITnited States 

 and Canada from June througli October. Because 

 of tlieir large size, bluefin are considered highly 

 desirable game fish and have dominated tuna 

 catches of the shelf sport fishery for many years 

 (Westman and Neville, 1042). The species has 

 also dominated the commercial fisheiy. Commer- 

 cial purse seining for bluefin tuna existed in the 

 late 1930's in the Continental Shelf area north of 

 Cape Cod (Murray, 1952). and limited commercial 

 bluefin production was achieved through trapping, 

 sporadic seining, harpooning, and hook-and-line 

 fishing in the 1940's and early 1950's. In efforts 

 to help the fishery, the Bureau conducted gear 

 trails on the shelf in 1951 and 1954 with Pacific 

 coast purse seine gear and techniques (Murray, 

 1952, 1955) and in 1952-53 with longlines (Mur- 

 ray, 1953, 1954) . The "Woods Hole Oceanographic 

 Institution. Miami Marine Laboratory, and the 

 Bureau have been engaged in .studies of the life 

 history of bluefin for several years (Mather, 1959; 

 Rivas, 1954, 1955; Robins, 1957; Westman and 

 Gillx-rt. 1941 ; and Westman and Neville, 1942) . 



Bluefin had also been reported from near Ber- 

 muda by Mowbray,' but no records of this species 

 in the oceanic region adjacent to the coast of North 

 America existed prior to the Delaware work. 



Migrator^' routes taken by bluefin on their way 

 to and from their summer habitat in the inshore 

 areas and the location of their winter habitat have 

 long been subjects of considerable speculation 

 among fishermen and fishery biologists. The most 

 popular view has been that in the fall when the fish 

 head south or southeast into the oceanic region. 



' Mowbra.v. Louis S. The ganipflshes of Bormucla. Paper 

 presented at the International Gameflsh Conference, Interna- 

 tional OceanoKraphle Foundation. Nassau, 1956, 8 p. 



toward unknown spawning grounds, probably in 

 the CariblK-an Sea. Bullis and Mather (1956), 

 through examinations of bluefin ovaries, have par- 

 tially substantiated the supposition that the 

 spawning giouiids, for at least part of the bluefin 

 po])ulation, lie in the Caribbean. The migration 

 route may lead directly to the spawning grounds 

 or may be circuitous. Other workers proposed 

 that bluefin could perhaps winter in deeper waters 

 along the Continental Slope off the Middle At- 

 lantic States (Bigelow and Schroeder, 1953). 



The return migration has been linked with an 

 observed northward migration of large tuna in 

 mid-May and June along the western edge of the 

 Straits of Florida. Rivas (1951, 1954) proposed 

 that these migrants comprise the stock of large 

 fish that enter the New England and Nova Scotia 

 fisheries in late June. Rivas later (1955) stated 

 that the fish taking part in this migration ranged 

 from 300 to 700 pounds and averaged 400 to 500 

 pounds. Linking these fish with those of the 

 northern inshore fishery would, if confirmed, ac- 

 count for the large individuals, but this would 

 still leave unexplained the many small bluefin 

 common to the northern fishery. 



YELLOWFIN TUNA 



Yellowfin tuna are not common inhabitants of 

 the Continental Shelf areas and are less well- 

 known in the northwestern Atlantic than bluefin. 

 One yellowfin was taken on a trolling line from 

 the Bureau research vessel Theodore N. Gill in 

 February 1953 (Anderson, Gehringer, and Cohen, 

 1956) , north of the Bahamas. In the true oceanic 

 region between the Continental Slope of North 

 America and Bermuda, five additional records ex- 

 ist — all from trolling line captures. One of these 

 refers to a fish taken in 1949 by the Woods Hole 

 Oceanographic Institution research vessel Caryn 

 and two to yellowfin taken in 1953 by the "VYHOI 

 research vessel Aflantlfi (Mather and Gibbs, 1957) ; 

 and two to fish taken in 1954 by the Atlantis 

 (Mather, 1954). Yellowfin also were reported 

 from the Bermuda area by Mowbray (1956). 



ALBACORE 



Albacore have been reported by Goode and 

 Bean (1879) off Woods Hole and near Banquereau 

 Bank off Nova Scotia. One specimen was re- 

 portedly taken by a halibut trawl off Dexil's Island 



