from those from Tunisia in many 

 characters. Arico and Genovese 

 (1953) and Genovese (1957, 1958) 

 compared morphological data for 

 spawning and feeding tunas taken off 

 northeastern Sicily with similar data 

 for bluefm taken off Tunisia and 

 southern Portugal and in the North 

 Sea. They concluded that the two 

 Sicilian samples were from a single 

 Tyrrhenian stock which was distinct 

 from the fish from the other three 

 areas and also from smaller samples 

 taken off the Mediterranean coast of 

 France, and off Algeria. 



Tiews ( 1 963) summarized, com- 

 pared and discussed these data and 

 studies. He found that only the dif- 

 ferences in head length, pectoral fin 

 length and number of finlets support 

 the case for the existence of separate 

 stocks on the European side of the 

 Atlantic. In view of the long and rapid 

 migrations of bluefm demonstrated 

 by tagging experiments, however, he 

 did not believe that the above differ- 

 ences would stand up under critical 

 inspection. He predicted that further 

 studies would prove the existence of 

 a single bluefin population in the east- 

 em North Atlantic. 



Genetic and biochemical char- 

 acteristics of bluefin tuna from the 

 eastern Atlantic and the Mediterra- 

 nean have also been investigated and 

 compared. Keyvanfar ( 1 962) studied 

 the serology and immunology of 

 bluefm tuna from the Atlantic and 

 Mediterranean coasts of France. In- 

 dividual differences in immunology 

 between Mediterranean samples were 

 found but the samples were too few 

 in number, particularly those from 

 the Atlantic, to furnish any inter- 

 pretation on migatory tendencies. Lee 

 (1965) provided further information 

 on the serology and immunology of 

 the bluefm from the French Mediter- 

 ranean coast and ( 1 968) comparisons 

 of the immunology of bluefin tuna 

 from the eastern Atlantic (30 speci- 

 mens) and the Mediterranean (72 

 specimens). Lee found individual dif- 

 ferences even within the samples 

 from the Atlantic and those from the 

 Mediterranean. She also found that 

 the percentage of individuals with no 

 antigens and those with one or sev- 

 eral differed in the two lots. She con- 

 cluded that one might consider the 



presence in the Gulf of Lion 

 (Mediterranean) of certain individu- 

 als which belong to a race or to a 

 population different from that ob- 

 served in the Bay of Biscay. 



These biometric and biochemi- 

 cal studies provided interesting 

 information, but, in our opinion, they 

 were inconclusive in determining 

 whether the bluefin in the Mediterra- 

 nean and eastern Atlantic constituted 

 a single or separate stocks, or to what 

 degree mixing occurred. 



In summarizing his extensive 

 studies of the fisheries and migra- 

 tions and other aspects of the biology 

 of the species, Sella (i929a, 1930) 

 proposed the following four phase 

 migratory cycle for bluefin tuna: 



a. Gathering of bluefin in May-June 



in relatively limited spawning ar- 

 eas in the southern part of its 

 range (Mediterranean, Ibero-Mo- 

 roccan Bay) 



b. Post-spawning dispersion, mainly 



northward, with the maximum 

 extension of their habitat occur- 

 ring in the wannest part of the 

 summer and autumn. 



c. New reduction in habitat with the 



coming of winter. This distribu- 

 tion was not well known, because 

 the fish were farther below the 

 surface, but was presumed to be 

 considerably reduced, with ma- 

 jor withdrawal from the more 

 northerly area. 



d. In March-April, immediately pre- 



ceding the reproductive period, 

 the tuna made another northward 

 migration which was much more 

 limited than that in summer-au- 

 tumn. They appeared en masse 

 off the north coasts of the Medi- 

 terranean and the Spanish coast 

 of the Bay of Biscay. 

 The subsequent development of 

 fisheries covering nearly all suitable 

 waters of the Atlantic, and modem 

 research, including tagging and track- 

 ing with sonar, have shown how ac- 

 curate Sella's concept was. The only 

 dubious point is his fourth phase, the 

 pre-spawning northward migration. 

 This probably consists of immature 

 fish and the younger mature ones, 

 concerning whose spawning habits 

 little was known then (Sella 1929a), 



or indeed, even now (Sara 1973). 

 Both authors indicated, however, that 

 these smaller reproducers spawned 

 later than the larger ones. 



Sara (1964, 1973) has proposed 

 a hypothesis which reconciles many 

 of the seemingly contradictory facts 

 in regard to the relationships between 

 eastern Atlantic and Mediterranean 

 bluefin tuna. He believed that a num- 

 ber, determined by the environmen- 

 tal conditions existing then and in 

 the preceding few weeks, of large 

 (over 100 kg) bluefin tuna gathered 

 in the ibero-Moroccan Bay in late 

 April and early May, "hesitating" 

 (Lenier 1959) there. Then a portion 

 of these, the number again depen- 

 dent on environmental conditions, 

 entered the Mediterranean to spawn, 

 and subsequently returned to the At- 

 lantic. 



Lozano Cabo (1958) and Aloncle 

 (1964) showed that the average sizes 

 of the bluefin taken in the Atlantic 

 traps, both in Morocco and along the 

 south coasts of Portugal and Spain, 

 varied inversely with the distance of 

 the trap from the Strait of Gibraltar. 

 The largest bluefin (by average 

 weight) have been taken by the traps 

 of Tarifa and Cape Spartel, at the 

 very entrance to the Mediterranean. 

 Actually, more small fish were taken 

 in the more westerly and southerly 

 traps. This was a good indication that 

 the larger bluefin were more apt to 

 enter the Mediterranean than the 

 smaller ones, just as Sara ( 1 973) hy- 

 pothesized. 



Sara (1973) stated, moreover, 

 that daily catch records collected con- 

 tinuously during the fishing seasons 

 for several years showed that the first 

 catches of the Cape Spartel trap, at 

 the entrance of the Strait, consistently 

 preceded the first of the traps off 

 western Sicily by from seven to nine 

 days. This 900 nautical mile (1,675 

 km) itinerary would require average 

 speeds between 4.2 and 5.4 knots 

 (7.7- 1 0.0 km/hr). This range does not 

 differ greatly from the migrating 

 speeds observed by Lozano Cabo 

 ( 1 959b), less than seven knots ( 1 3.0 

 km/hr), and by Rivas (1955, 1976), 

 four knots (7,4 km/hr), or from the 

 average speed of a giant bluefin which 

 migrated from the Bahamas to Nor- 

 way in 50 days (Mather 1969), 3.5 



103 



