The meager information avail- 

 able (Rivas 1954, Mather 1963a, 

 Mather et al. 1974) indicates that the 

 passage of these young of the year 

 through the Straits peaks m late July 

 and August. Since no age fish have 

 been tagged in these waters, this mi- 

 gration is strictly hypothetical. It does, 

 however, fit the known facts of ex- 

 tensive spawning in the Gulf of 

 Mexico and the tendency of age 1 

 bluefin to concentrate almost exclu- 

 sively in the Cape Hatteras-Cape Cod 

 area in the summer. Age bluefin do 

 occasionally appear in numbers, for 

 a few weeks at a time, between late 

 July and early November in some 

 part of this northern nursery area, but 

 there has been no way to determine 

 where these fish had been spawned 



Thirty age bluefin (42-48 cm 

 long) were marked during an unusu- 

 ally strong concentration of young of 

 the year off Brielle, New Jersey, in 

 October 1973. Four of these have 

 been recaptured off New Jersey, one 

 in August 1974, and the others in 

 June or July 1975 (Mather and Ma- 

 son 1976). These returns proved that 

 bluefin which visited the nursery area 

 at age were actually recruited to the 

 group of small (ages 1 -4) fish which 

 supported the fisheries there in ensu- 

 ing seasons 



The first sustained and regular 

 concentration of these very small 

 bluefin known to us begins in late 

 June or early July between Cape 

 Hatteras and Cape Cod, when the 

 fish are almost exactly one year old 

 The important question of how they 

 reach that area remains to be an- 

 swered. 



3. TRANS-ATLAlVnC AND 

 TRANS-EQUATORIAL 

 MIGRATIONS, AND 

 ATLANTIC STOCKS 



a. Introduction 



Transatlantic migrations of blue- 

 fm tuna have been demonstrated by 

 tag returns showing migrations of 40 

 small (ages 1 and 2 when tagged) 

 individuals between the New York 

 Bight (New Jersey to Cape Cod) and 

 the Bay of Biscay (Table 34, and 

 migrations of 9 large (over 122 kg) 



individuals from the Straits ofFIorida 

 to Norwegian waters (Table 28) 



Two transequatonal migrations 

 have been recorded for giant bluefin 

 which were tagged off the northwest- 

 em Bahamas and recaptured off the 

 South Atlantic coasts of South 

 America (Table 28). 



Biometnc comparisons of blue- 

 fin tuna fi"om various parts of the 

 Atlantic and the Mediterranean have 

 been made and biochemical charac- 

 teristics of bluefin tuna from various 

 parts of the Atlantic have been com- 

 pared. 



In the following parts of this sec- 

 tion we will present the data for these 

 migrations (Figure 75) and some re- 

 lated factors, and consider their im- 

 plications. Finally we will discuss the 

 identity of the stocks in the Atlantic 

 Ocean 



b. Trans- Atlantic Migrations 



L Giant Fish 



Nine giant bluefin which had 

 been tagged off the Bahamas have 

 been recaptured in Norwegian wa- 

 ters. Four of these recaptures repre- 

 sented "direct" migrations since the 

 fish had been at liberty for less than 

 four months The other five indicated 

 longer periods at liberty, which were 

 approximately as follows: 15.3 

 months for two fish, 26.5 months for 

 two, and 86.6 months for the remain- 

 ing one Thus when the fish in the 

 second group ("indirect" migrants) 

 had crossed the Atlantic, or whether 

 they had done so more than once, is 

 uncertain The release (May 9-June 

 15) and recapture (August 4-October 

 6) dates show that the "direct" mi- 

 grants had crossed the Atlantic dur- 

 ing the warm season One of these 

 made the trip of at least 4,200 nauti- 

 cal miles (7,800 km) in a maximum 

 of 50 days, at a rate of 84 nautical 

 miles (155 km) per day, or 3 5 knots 

 (6 5 km per hr) 



These transatlantic migrations of 

 giant bluefin were not randomly dis- 

 tributed over the years Five of the 

 nine fish were released in the years 

 1960-1962, two in the years 1972- 

 1973 and only two in the other 15 

 years in which bluefin tuna were 

 tagged in the Bahamas 



Four of these migrations defi- 

 nitely occurred in the following years 



(numbers in parentheses indicate 

 number of migrations, if greater than 

 one): 1961(2), 1962, 1967. The other 

 five could have occurred in the fol- 

 lowing years 1960-1962(2) (migra- 

 tions in 1 962 are considered improb- 

 able because of the fat condition of 

 the fish when they were recaptured), 

 1969-1976, 1972-1973, and 1973- 

 1974. Unfortunately, no body condi- 

 tion data have been reported for the 

 tagged fish recaptured since 1962. 

 Likewise, the weekly distributions of 

 body condition data for tlie landings 

 in northwestern Europe since then 

 are not available. The tag return data, 

 however, suggest another pulse of 

 west to east migrations m the period 

 1 972- 1 976 This may account for the 

 somewhat increased availability of 

 giant tuna off Norway since their vir- 

 tual disappearance in 1973. 



The fish which made the direct 

 migrations, between May and early 

 October, must have spent much of 

 this time in deep oceanic waters 

 where food is relatively scarce. Nor- 

 mally, large bluefin tuna are concen- 

 trated in the coastal areas in the more 

 northerly part of their ranges m sum- 

 mer and early fall, where they are 

 feeding heavily (Sections 1VC2 and 

 IVC4) 



The two "direct" transatlantic mi- 

 grants which were exammed after re- 

 capture were very lean, m contrast to 

 the fat condition typical of large blue- 

 fin which have spent the summer m 

 coastal waters (Rivas 1955, Mather 

 1962, Tiews 1964). Such lean blue- 

 fin, called "long-tailed bluefin" (J. 

 Ilamre, personal communication) by 

 the local fishermen, had previously 

 been observed among late season 

 catches off Norway and in the North 

 Sea, but there had been no explana- 

 tion for their unusual body condi- 

 tion 



Hamre (in Mather 1962) and 

 Tiews (1964) assumed that the lean 

 condition of the recaptured fish re- 

 sulted from their having passed much 

 of the summer in relatively barren 

 oceanic waters, instead of the rich 

 coastal feeding grounds They con- 

 cluded that the "long-tailed bluefin" 

 were actually fish which had been 

 recruited from the western Atlantic 

 during the years in which they were 

 captured Using extensive body con- 



129 



