tions of bluefin tuna in the north At- 

 lantic (Sella 1 93 1 , Rivas 1 955, Squire 

 1963). Since the economic impor- 

 tance of the species in the western 

 Atlantic has been slight until recent 

 years, the history of research on its 

 migrations there is brief in compari- 

 son with that in the eastern Atlantic 

 and the Mediterranean. 



b. Large Fish 



Few deductions about the mi- 

 gration of large bluefm tuna in the 

 western Atlantic have been published. 

 The summer and early fall occur- 

 rences of bluefin tuna off northeast- 

 em North America (off the United 

 States coast from New Jersey to 

 Maine, and off Nova Scotia and New 

 Brunswick in Canada) have long been 

 known (Farrington 1939). A periodic 

 northward migration of "giant" blue- 

 fin through the Straits of Florida 

 (mainly along the northwestern edge 

 of the Great Bahamas Bank near Cat 

 Cay and Bimini) was discovered by 

 sport fishermen in the 1930s and it 

 was soon concluded that these fish 

 were among those which subse- 

 quently occurred off northeastern 

 North America in summer and early 

 fall (Farrington 1939, Mowbray 

 1949). 



At the Oceanic Fisheries Con- 

 ference held at the Bermuda Biologi- 

 cal Station for Research, May 28-3 1 , 

 1951, (transcript of tape recordings 

 available at Woods Hole Oceano- 

 graphic Institution) Schuck and 

 Mather presented their views on sev- 

 eral aspects of the biology of bluefin 

 tuna in the western North Atlantic. 

 They described the behavior of the 

 giant bluefin tuna in the Straits of 

 Florida as observed during flights 

 made with L. R. Rivas in U.S. Coast 

 Guard aircraft. These observations 

 confirmed that the visible schools 

 were virtually all travelling north- 

 ward, as reported by the sport fisher- 

 men. Schuck and Mather also showed 

 that the times of the passage of the 

 giant tuna through the Straits of 

 Florida and their arrival in New En- 

 gland waters were consistent with a 

 migration between the two areas. Fi- 

 nally, they presented preliminary re- 

 sults of biometric studies which 

 showed that the fish taken in the 

 Straits ofFlorida were similar to those 

 taken in New England waters, except 



in regard to body condition. The fish 

 taken off New England in the begin- 

 ning of the season were similar in 

 body proportions to those taken in 

 the Straits of Florida. As the season 

 advanced, however, the fish off New 

 England fed heavily and gained 

 weight rapidly. Therefore tiie fish 

 taken there in August, September and 

 October became progressively 

 heavier in proportion to their length 

 than those taken in the Straits of 

 Florida. The ratios of their girth and 

 depth to their length consequently 

 also became greater than the corre- 

 sponding ratios for fish taken in the 

 southern area. 



Rivas (1955), in a similar study, 

 compared the morphological charac- 

 teristics of samples of bluefin tuna of 

 similar sizes taken in the Straits of 

 Florida in May 1 952- 1954(19 speci- 

 mens) and at Wedgeport, Nova 

 Scotia, in October 1952 and August 

 1953 (nine specimens). He found no 

 significant differences between these 

 samples, except those attributable to 

 the normal seasonal change in body 

 condition experienced by bluefin 

 tuna. These fish lost considerable 

 weight during the spawning process 

 and related migrations, then fed so 

 heavily during the summer and early 

 fall that their length-weight ratio was 

 at a minimum in September-Octo- 

 ber. The lean condition of the fish 

 taken in the early part of each season 

 at Wedgeport was consistent with 

 their having come from the Straits of 

 Florida. In addition, Rivas showed 

 that the times of arrival of giant blue- 

 fin tuna off Cape Cod, Massachu- 

 setts, and Wedgeport were consistent 

 with the time of departure and esti- 

 mated average speed (3.5 knots, or 

 6.5 km/hr) and direction of travel of 

 the individuals passing the Bahamas. 

 Thus he presented a case, which he 

 considered strong, but not conclu- 

 sive, for a northward migration of 

 giant bluefin from the Straits of 

 Florida in May-June to New England 

 and Nova Scotia waters in summer 

 or early fall. 



Exploratory and commercial 

 longline fishing has provided impor- 

 tant information on the temporal and 

 areal distribution of bluefin in the 

 oceanic waters of the v\estern Atlan- 

 tic since 1956 (see Sections IVC2 



and IVC3). The records of occur- 

 rences during the cold season (No- 

 vember-April), when their where- 

 abouts had previously been virtually 

 unknown, were especially valuable. 

 This information has been used in 

 conjunction with tagging results in 

 developing new hypotheses c the 

 migrations of the species (Mather 

 1969, 1974, Mather etal. 1974). 



Continuous tagging of western 

 Atlantic bluefin began in 1954. Since 

 then, about 1 , 100 giant fish have been 

 marked off the northwestern Baha- 

 mas (Straits of Florida) and 15 of 

 these fish have been recaptured over 

 a very extensive area — four off 

 northeastern North America, two off 

 eastern South America, and nine off 

 Norway (Table 28) (Mather 1962, 

 1969; FAO 1972, Mason et al. 

 1977). Cooperating sport fishermen 

 provided the effective tagging in this 

 effort. A few fish have been marked 

 during exploratory fishing cruises in 

 this general area, but none of the tags 

 have been returned. 



The four returns off North America 

 were from ofTMary land to off the Nova 

 Scotian banks (Figure 76); only one 

 was from an area known as a tuna 

 fishing ground. This return was from 

 a giant released in early June 1973, 

 in the Bimini-Cat Cay area (north- 

 western Bahamas) and recaptured 

 about 18 nautical miles (33 km) 

 northeast of Gloucester, Massa- 

 chusetts, a well-known center for 

 small boat tuna fishing, in early July 

 1974. Since it had been at liberty for 

 13 months, this was not a "direct" 

 migration. If it is regarded as a sec- 

 ond retracing of an annual migratory 

 cycle, however, the fish would have 

 passed through the Straits ofFlorida 

 again in May or June 1974, and its 

 ensuing migration would have fitted 

 the proposed pattern. The other three 

 recaptures were incidental or acci- 

 dental catches by vessels fishing for 

 other species. While they could be 

 interpreted as representing incom- 

 plete migrations toward the New En- 

 gland or Canadian feeding areas, 

 there is an element of doubt in each 

 case. One return was from a fish re- 

 captured about 48 nautical miles (89 

 km) east-southeast of Ocean City, 

 Maryland, in April 1973, 23 months 

 after it had been released off the 



113 



