DISTRIBUTION OF TUNAS IN OCEANIC WATERS OF 

 THE NORTHWESTERN ATLANTIC 



By James L. Soi'iRE, Jr., Fishery Methods and Equipment Specialist 

 Bureau of Commercial Fisheries 



The increased importance attached to commer- 

 cial utilization of tunas during the past decade 

 has increased the importance of studies of the 

 habits and life histories of the principal tuna 

 species and investigations of areas known or 

 thought to be inhabited by tunas. 



Seasonal tuna fisheries have been carried out 

 for many years on the Continental Shelf between 

 Newfoundland and Cape Hatteras by commercial 

 and sport fishermen. But the short season and 

 fluctuating availability of the stocks — principally 

 bluefin and little tuna — have made commercial 

 operations economically hazardous. Since the 

 early 1950's the U.S. Bureau of Commercial Fish- 

 eries has worked to reduce the fluctuations in 

 availability through introduction and develop- 

 ment of diverse types of commercial gear. This 

 work has culminated recently near Cape Cod in 

 a successful commercial purse seining venture 

 (Squire, 1959), which, in 1959, landed 750 tons 

 of bluefin tuna in 21 days of fishing — a record 

 for the Cape Cod area. 



In addition, the Bureau and the Woods Hole 

 Oceanographic Institution have conducted re- 

 search on the life histoi-y of bluefin in attempts 

 to understand the resource more fully, but the 

 life history studies have been seriously hampered 

 by the almost complete lack of knowledge of blue- 

 fin during periods when they are absent from the 

 inshore regions. Prior to 1957, knowledge of 

 tunas in the oceanic region of the northwest At- 

 lantic was practically nonexistent, in sharp con- 

 trast to tlie extensive body of knowledge 

 concerning tunas of inshore and oceanic regions 

 of the Pacific that had been gained through con- 

 tinuing research. 



Note. — The author Is presently Flsher.v Research Biologist. 

 Tlliuron Marine Lalmratorj-. Bureau of Sport Fisheries and Wild- 

 life. U.S. Fish and Wildlife Service, Tlburon. Calif. 



.approved for publication, February 12, 19G2. 



In 1957, the Bureau's North Atlantic Fisheries 

 Exploration and Gear Research Base began an 

 investigation of tlie broad oceanic region adjacent 

 to the Continental Shelf of northeastern North 

 America. Primary objectives were to determine 

 the distribution patterns of the dominant tuna 

 species inhabiting these oceanic waters and to de- 

 tennine the availability of tunas to commercial 

 gear. Eight cruises of the Bureau research ves- 

 sel Delaware were made during the investiga- 

 tion, which was conducted intermittently from 

 March 1957 tlirough May 1960. Explorations 

 with longline gear were made during at least 

 some portion of all seasons. Represented in the 

 catches were tunas of six species — bluefin {Thun- 

 nus thynmi.s), yellowfin (Thunnus alhacares), 

 albacore {Thunnus alahinga), bigeye {Thimmis 

 ohesus), blackfin {Thunmis atlanticns), and skip- 

 jack {Euthynnus -pelamis). The first three are 

 dominant tuna species in the region explored. 



This paper firstly reviews the status of tuna 

 knowledge in the northwestern portion of the At- 

 lantic at the start of the investigation; secondly, 

 describes the exploratory methods and procedures 

 used, the physical cliaracteristics of the area ex- 

 plored, the seasonal and geographic distribution 

 of dominant tuna species of the oceanic region, 

 and the occurrence of other tuna species in the 

 region ; and thirdly, discusses the relation between 

 the tunas of the oceanic region and those of the 

 Continental Shelf. 



The investigation was facilitated greatly by co- 

 operation with Boston University and the Woods 

 Hole Oceanographic Institution. In particular, 

 acknowledgment is made of the efforts of Robert 

 H. Gibbs, Jr., Boston University, and Frank 

 J. Mather III, Woods Hole Oceanographic 

 Institution. 



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