the "return" run off southern Spain and 

 Portugal occurs in July-August. This 

 accounts for the later arrival in north- 

 em summering areas of the medium 

 and large bluefin in the eastern Atlan- 

 tic, as against the western Atlantic. 



Also, the spawners in the Ibero- 

 Moroccan Bay and in the Mediterra- 

 nean, although predominantly large, in- 

 clude medium-sized and reportedly, 

 even small fish, whereas all of those 

 which spawn in the Bahamas-Gulf of 

 Mexico area are giant fish (over 122 



kg). 



Tag return data indicated that west 

 to east transatlantic migrations of small 

 bluefin tuna are the exception rather 

 than the rule. As of the end of 1972, 

 about 9,700 small bluefin had been 

 tagged in the Middle Atlantic Bight. 

 Disregarding 1,112 local recaptures 

 within less than six months of release, 

 1,201 returns were from the release 

 area as against 40 fi-om the eastern At- 

 lantic. 



Recoveries from large bluefin tuna 

 tagged off the Bahamas were more nu- 

 merous in the eastern Atlantic (8) than 

 in the westem Atlantic (5), but, with 

 the collapse of the eastern Atlantic fish- 

 eries and increased effort in the west- 

 em North Atlantic, the trend in recov- 

 eries has reversed itself As witli the 

 transatlantic migrations of small blue- 

 fin, those of large bluefin appear to be 

 important in some years and negligible 

 in others. There have been no transat- 

 lantic returns from numerous taggings 

 of large bluefin off New England, 

 Canada, Norway, and Spain. 



Preliminary comparisons of exten- 

 sive data on the extemal morphology 

 of bluefin tuna from the eastern and 

 westem Atlantic indicate that there are 

 slight morphometric and meristic dif- 

 ferences between fish from the respec- 

 tive areas. 



There is little evidence for a sepa- 

 rate stock of bluefin tuna in the South 

 Atlantic. The oceanic distribution of 

 the species appears to be continuous 

 from off eastern Brazil to off New En- 

 gland and eastern Canada. 



Also, the more significant Japa- 

 nese longline catches of bluefin tuna 

 appeared to progress seasonally from 

 off eastern Brazil in March and April to 

 off Cape Hatteras by the end of June. 

 Furthermore, two bluefin tuna tagged 

 in the Straits of Florida have been re- 



captured in the westem South Atlantic, 

 one offeastemmost Brazil, and the other 

 off Argentina. No evidence that blue- 

 fin spawn in the South Atlantic has 

 come to our attention. 



Mather et al. (1974) concluded 

 from the above infonnation that the 

 evidence was insufficient to perm it clear 

 cut conclusions, but believed that the 

 most probable combinations were: 



1. A single Atlantic or Atlantic- 

 Mediterranean stock and one or more 

 essentially Mediterranean stocks. 



2. Two Atlantic spawning stocks, 

 one spawning in the westem Atlantic 

 and the other spawning in the eastern 

 Atlantic and/or the Mediterranean, with 

 one or more essentially Mediterranean 

 stocks. 



They believed that the greatest 

 weight of evidence appeared to favor 

 the second arrangement. They noted, 

 however, that for management purposes 

 it must be recognized that important 

 interchanges between the two proposed 

 Atlantic stocks occur on an apparently 

 erratic and unpredictable basis. 



They noted that the problem of the 

 stock structure of Atlantic bluefin is 

 one of enormous complexity. With the 

 existing depressed state of most of the 

 fisheries, and the consequent diminu- 

 tion or termination of research on the 

 species in several nations, there was no 

 prospect that it could be solved defini- 

 tively in the foreseeable future. They 

 concluded that management of the spe- 

 cies should be undertaken on the basis 

 of the best information now available, 

 if its commercial extinction was to be 

 avoided. 



Conservation measures for Atlan- 

 tic bluefin were finally enacted by 

 ICCATin 1975. Also, under the stimu- 

 lus of this organization, research on 

 bluefin tuna in several nations has ac- 

 tually increased. Unlbrtunately, how- 

 ever, the failure of the fisheries in the 

 Federal Republic of Germany, Nor- 

 way and Portugal has forced some of 

 the most competent experts on the blue- 

 fin into other fields. 



Continued tagging in the western 

 Atlantic by the Woods Hole Oceano- 

 graphic Institution has yielded results 

 of great value in determining the mi- 

 gratory patterns of the bluefin in that 

 area. Recent tag relums have finally 

 and definitely connected the spawning 

 occurrence of eiant bluefin in the Gulf 



of Mexico with the migratory passage 

 of similar fish through the Straits of 

 Florida and their summer feeding oc- 

 currence in New England and Cana- 

 dian waters. All of these migrations 

 were recorded through taggings of gi- 

 ant fish. An even more significant re- 

 turn connected the Cape Hatteras-Cape 

 Cod area, the only known nursery 

 ground for young bluefin in the west- 

 em Atlantic with the region's most im- 

 portant known spawning ground in the 

 Gulf of Mexico. Another important 

 group of recent returns connected the 

 Cape Hatteras-Cape Cod summer con- 

 centration of small fish with their pre- 

 viously unknown wintering area in oce- 

 anic waters near the edge of the conti- 

 nental shell" east of this summer habi- 

 tat. Previous retums had connected the 

 nursery area south of Cape Cod with 

 the summer habitat of larger bluefin 

 north of this cape, and the offshore 

 winter and spring habitat of the me- 

 dium bluefin with their warm season 

 feeding grounds north and south of 

 Cape Cod. These retums collectively 

 indicate a cohesive and self-sufficient 

 westem Atlantic bluefin population. 

 The most important remaining link to 

 be established among the occurrences 

 of bluefin in the westem North Atlantic 

 would be the migration of newborn 

 bluefin from the Gulf of Mexico to the 

 Cape Hatteras-Cape Cod area. It would 

 be well worth the effort to tag some age 

 fish in the Gulf, or in the Straits of 

 Florida. Other important but more dif- 

 ficult objectives of tagging westem At- 

 lantic bluefin are to learn more about 

 the extent of their normal oceanic dis- 

 tributions, and to estimate the frequency 

 and importance of their transatlantic 

 migrations. 



In regard to the latter, the infre- 

 quency of west to east transatlantic mi- 

 grations of small bluefin has become 

 increasing!) apparent. The last tag re- 

 tum revealing such a migration was 

 from a fish tagged in 1967 and recap- 

 tured in 1968. More than 4,400 small 

 bluefin have been marked in the west- 

 em North Atlantic in the years 1968- 

 1975. Not one of these tags has been 

 returned from the eastern Atlantic, al- 

 though 935 have been recovered in the 

 westem part of the ocean in the years 

 1 969- 1 976 Transatlantic migrations of 

 small bluefin, at least in the west to east 

 direction, have become increasingly 



142 



