from offshore inhibits the further 

 progress of some groups of small and 

 medium tuna travelling northward 

 from the wintering area. These fish 

 eventually find themselves in the 

 cooler upwelling waters off the cen- 

 tral Moroccan coast, but completely 

 surrounded by tropical water. Most 

 of them stay in this cool water rather 

 than continuing northward through 

 the warmer water (Aloncle 1964). 



The return to summer feeding 

 areas completes the migratory cycle 

 of the medium and large bluefin of 

 the eastern Atlantic. The hypotheti- 

 cal three phase migration is compli- 

 cated by the entrapment of some me- 

 dium fish off central Morocco, and 

 the entry of larger fish into the Medi- 

 terranean to spawn. 



ii. Small Fish 



Thirty-four small bluefin tuna 

 have been tagged in the Bay of Biscay 

 and off Portugal since 1960 (Aloncle 

 1973). Three of these were recap- 

 tured locally, and two off the north- 

 eastern United States. One of the lo- 

 cal returns was from a small bluefin 

 tagged off Cape St. Vincent (south- 

 western comer of Portugal) in early 

 June and recaptured in the Bay of 

 Biscay 83 days later (Figure 74). 

 This migration supports Aloncle's 

 (1964) hypothesis that small bluefin 

 migrate seasonally from the Ibero- 

 Moroccan Bay in spring to the Bay 

 of Biscay in summer. The transatlan- 

 tic returns will be discussed in part 3 

 of this section. 



The results of tagging off the 

 Atlantic coast of Morocco (Lamboeuf 

 1975) also support Aloncle's (1964) 

 theory. During 1972 and 1973, 63 

 bluefin, 41-73 cm long, were tagged 

 and released there: 1 5 in June, one in 

 July, 25 in August and 2 1 in Novem- 

 ber. Eleven returns resulted, includ- 

 ing five from Moroccan waters and 

 six from other areas (Figure 74). 



During 1973 two fish, of which 

 one had been marked in June and the 

 other in August (at ages of approxi- 

 mately 1 1 and 14 months, respec- 

 tively), were recaptured off the south- 

 western coast of Portugal in October 

 and September, respectively. Four 

 others, of which three were tagged in 

 August 1972 (at ages of about 13 

 months) and one in November 1972, 

 (age about 17 months) were recap- 



tured in the Bay of Biscay in June- 

 August 1973. These important results 

 indicate that both the minor fall fish- 

 ery off the west coast of Portugal and 

 the much more important one which 

 takes place in the Bay of Biscay dur- 

 ing the warm season draw recruits 

 from off the Atlantic coast of Mo- 

 rocco. These few returns suggest that 

 fish recruit to the former fishery at 

 age 1 and to the latter at age 2. These 

 ages of recruitment are in accord with 

 the age groups which have been pre- 

 dominant in the landings of ihe re- 

 spective fisheries. The tendency for 

 the maximum catches of 

 "cachorretas" (age 1 hiuefin) in the 

 Portuguese trap fishery to have oc- 

 curred in late August suggests that 

 the indicated migration from off Mo- 

 rocco in summer to off western Por- 

 tugal in the fall may sometimes have 

 passed along the south coast of Por- 

 tugal en route. 



Local returns showed two south- 

 westward movements from the 

 Larache-Casablanca area toward Cap 

 Blanc in August-September 1972 and 

 two northward migrations from off 

 Agadir to off Essaouira in Novem- 

 ber-December 1972. 



Lamboeuf (1975), considering 

 these results and observations of the 

 movement of the fishery and the sizes 

 of fish caught, formulated the fol- 

 lowing hypothesis: 



Bluefin spawned off Morocco by 

 the adult "arrival" tuna in spring or 

 earlv summer remain offshore in fa- 

 vorable waters (18°C-22"C). They 

 occasionally approach the coast when 

 hydrological conditions allow this. 

 Having attained 1 year of age and 50 

 to 60 cm in length, they frequent the 

 coast from June through August, 

 moving from north to south during 

 this period. They then disappear, hav- 

 ing been driven offshore by the cold 

 waters in the Safi-Essaouira region, 



6S* 



6}« 



55« 



i1° 



Figure 73. Possible paths of bluefin tuna entering the North Sea and Scandinavian 

 waters from west and north of the British Isles, rather than through the English 

 Channel. 



Ill 



