They also noted the findings of Hamre 

 et al. ( 1 966, 1 968, 1 97 1 ) wh ich showed 

 that there were considerable differences, 

 in both the trends of the catches and 

 their size composition, between the fish- 

 eries for large bluefin in the eastern 

 Atlantic and those in the Mediterra- 

 nean. These authors concluded tenta- 

 tively that the respective fisheries were 

 supported by different stocks. Mather 

 et al. (1974) noted, however, that the 

 catches of many Mediterranean trap 

 fisheries had recently declined drasti- 

 cally, and the sizes of the fish taken had 

 increased markedly. Thus, afler a con- 

 siderable lag, they appeared to have 

 followed the trends of the northeastern 

 Atlantic large fish fisheries. 



Mather et al. ( 1 974) generally sup- 

 ported Sara's hypothesis, but also pos- 

 tulated a migration of newborn fish 

 from the western Mediterranean to the 

 Atlantic coast of Morocco in October 

 and November. They pointed out that 

 this was the most plausible explanation 

 available for the continued productiv- 

 ity of the fisheries for small bluefm off 

 the coast of Morocco and in the Bay of 

 Biscay, and cited evidence that such a 

 migration actually occurred. They also 

 recommended the tagging of very small 

 bluefin in the western Mediterranean 

 and off the Atlantic coast of Morocco 

 in order to test this hypothesis and de- 

 termine the sources of recruitment to 

 the major eastern Atlantic fishery for 

 small bluefin in the Bay of Biscay. The 

 Mediterranean phase of this recommen- 

 dation has not been attempted, but a 

 small-scale tagging operation was car- 

 ried out most successfiilly off the At- 

 lantic coast of Morocco in 1972 and 

 1 973. This showed that at least some of 

 the recruitment to the Bay of Biscay 

 fishery was indeed drawn from the Mo- 

 roccan coast (Lamboeuf 1975). This 

 important and relatively inexpensive 

 achievement further emphasizes the de- 

 sirability of conducting similar experi- 

 ments in the western Mediterranean. 

 Results which would be of great im- 

 portance in identifying the bluefin 

 stocks in this critical area should be 

 obtained quickly and at modest cost. 



Important new information on the 

 question of the eastern Atlantic-Medi- 

 terranean bluefin stocks has become 

 available recently. The progression of 

 Japanese longline catch rates in the area 

 and season of the "arrival" and "re- 



turn" runs and the overall estimate of 

 the sizes of the fish taken (Shingu et al. 

 1974) strongly support Sard's (1973) 

 migratory theory. 



The failure of the expedition "Mo- 

 roc-Iberia 1" to find early stages of 

 bluefin in the ibero-Moroccan Bay 

 (Rodriguez-Roda 1975) and the dis- 

 covery of new spawning areas in the 

 Mediterranean (Duclerc et al. 1973, 

 Scaccini et al. 1975, Piccinetti et al. 

 1976) emphasize the probable depen- 

 dence of the eastern Atlantic fisheries 

 on recruitment from tlie Mediterranean. 

 We therefore now attach even greater 

 importance to the spawning migration 

 of large and some medium (as indi- 

 cated by tag returns in Rodriguez-Roda 

 1969a) bluefin from the eastern Atlan- 

 tic into the Mediterranean, and the re- 

 cruitment of newborn fish from the 

 Mediterranean to the eastern Atlantic 

 fisheries. We conclude that the eastern 

 Atlantic and Mediterranean bluefin con- 

 stitute a stock which tends to separate 

 into two components, one in each wa- 

 ter mass, in its years of immaturity and 

 its earlier ones of maturity, and to spawn 

 in the Mediterranean and spend the rest 

 of the year in the Atlantic when the fish 

 exceed about 9 years in age and 1 00 kg 

 to 150 kg in weight. 



The status of the relatively small 

 groups of large bluefin which occupy 

 the Mediterranean throughout the year 

 is unclear. Those in the western Medi- 

 terranean could well be contingents of 

 fish which have chanced upon a good 

 feeding area and dropped out of the 

 normal migratory pattern. The group 

 of large bluefin which reproduces in 

 the Black Sea and winters in the Sea of 

 Marmara is more likely, in our opin- 

 ion, to be the nucleus of a separate 

 population. 



Mather et al. ( 1 974) noted that the 

 situation with regard to bluefin tuna in 

 the Atlantic and connected seas other 

 than the Mediterranean (North Sea, and 

 the Baltic and its approaches, the Car- 

 ibbean, and the Gulf of Mexico) was 

 also extremely complex. They stated 

 some arguments for a single stock oc- 

 cupying the entire ocean, and others 

 for two stocks, with spawning areas on 

 the east and west sides of the Atlantic. 



The arguments for a single stock 

 were as follows: 



Flucmations in catches, and trends 

 in their size composition, appear to be 



rather similar throughout the ocean. A 

 correlation analysis, based on the dubi- 

 ous assumption that the sizes of the fish 

 caught in the two fisheries were the 

 same, showed a positive correlation in 

 the catch per unit of effort between the 

 small fish fisheries in the northwestern 

 Atlantic and in the Bay of Biscay 

 (Sakagawa and Coan 1 974). 



Tag returns have traced several 

 transatlantic migrations of small and 

 large bluefin tuna, as well as several 

 other migrations between widely sepa- 

 rated localities in the Atlantic. 



Studies of heart muscle protein 

 from bluefin tuna collected on opposite 

 sides of the Atlantic showed no differ- 

 ences in the characteristics which were 

 studied. The growth rates for bluefin 

 tuna in the Mediterranean, the eastern 

 Atlantic, and the western Atlantic ap- 

 pear to be similar. 



The arguments for separate east- 

 em and westem Atlantic stocks were as 

 follows: 



Bluefin of all sizes are found on 

 both sides of the ocean, with the excep- 

 tion that very few larvae or small (less 

 than 10 cm) juveniles have been found 

 in the eastern Atlantic. 



Bluefin spawn on both sides of the 

 Atlantic (whether the bluefin which ar- 

 rive in the Ibero-Moroccan Gulf with 

 ripening gonads and depart with spent 

 gonads actually spawn in that area or in 

 the Mediterranean seems irrelevant in 

 this context). There is no evidence of 

 extensive spawning in mid-Atlantic wa- 

 ters. Spawning in the eastern Atlantic 

 (and/or the Mediterranean) is later than 

 spawning in the western Atlantic. 



There is no correlation between 

 trap catches in the eastern Atlantic and 

 Japanese longline catches in the west- 

 ern Atlantic (Sakagawa and Coan 

 1974). 



The patterns of spring and sum- 

 mer-early fall distribution of bluefin 

 tuna on the two sides of the Atlantic are 

 quite similar. 



The principal exceptions were at- 

 tributed to different spawning habits. 

 Spawning occurs later in the eastern 

 Atlantic (Ibero-Moroccan Bay and/or 

 Mediterranean) (about the end of June) 

 than in the corresponding westem At- 

 lantic spawning area (Bahamas, Gulf 

 of Mexico) (May, early June). The "re- 

 turn" (spent fish) run in the Straits of 

 Florida occurs in May-June, whereas 



141 



