dium fish occurred between the Ca- 

 nary Islands and Morocco in winter. 



Many medium and some large 

 bluetln are captured in the Bay of 

 Biscay from mid- July to mid-August, 

 or early September (Creac'h 1952, 

 Le Gall 1954, Bard et al. 1973, Dao 

 and Bessineton 1974, Cort 1975, 

 1977). Some of the smaller fish may 

 spawn on their arrival in the Bay 

 (Cort 1977), but this is primarily a 

 feeding concentration. Where these 

 bluefin go after they leave the Bay of 

 Biscay is uncertain. Cort ( 1 976) con- 

 jectured that those in age groups 6 to 

 9 continued their northward migra- 

 tion to Norwegian waters, whereas 

 those in age groups 4 and 5 followed 

 a different, probably more southerly, 

 route. The migration of age groups 

 6-9 to Scandinavian waters may well 

 have taken place in years prior to 

 1963, but fish of these ages have not 

 been important in the Norwegian 

 catches since then (Hamre 1971). 



The European landings of me- 

 dium bluefin in the Bay of Biscay 

 have increased markedly since 1973, 

 perhaps in consequence of substan- 

 tial fishing effort by Japanese longline 

 vessels in the area (Cort and Cendrero 

 1975, Cort 1976, Fisheries Agency 

 of Japan 1976, Shingu and Hisada 

 1976). 



It is unfortunate that adequate 

 size composition data for Bay of Bis- 

 cay landings in the 1960s are not 

 available. It would have been of in- 

 terest to note whether the departure 

 of the medium fish from the Norwe- 

 gian fishery in 1963 through failure 

 of recruitment (Hamre 1971) was re- 

 flected by any increase in their avail- 

 ability in the Bay of Biscay. 



The medium and large bluefin 

 which leave the Bay of Biscay in 

 August or early September presum- 

 ably reach the wintering area de- 

 scribed above in late fall or early 

 winter, but their whereabouts in the 

 meantime is unknown. Possibly some 

 of them join the concentration off the 

 central Moroccan coast, along with 

 others which may have gone there 

 directly after spawning in the Ibero- 

 Moroccan Bay (Aloncle 1964). 



In April the medium and large 

 bluefin begin to migrate from their 

 wintering area to their spawning 



grounds. Most of the kirgc t1sh and 

 some of the older mediums partici- 

 pate in the "arrival" run, assembling 

 in the Ibero-Moroccan Bay in May 

 and June. One contingent of them, 

 mainly the individuals weighing less 

 than 150 kg, presumably spawns 

 there, along with a portion of the 

 larger fish. Apparently many of the 

 latter, however, enter the Mediterra- 

 nean, spawn there in June or early 

 July, and make a "return" run into 

 the Atlantic in July and August. Most 

 of the larger fish which have re- 

 mained in the Ibero-Moroccan Bay 

 also join this "return" run. 



Some of the smaller individuals 

 may spawn off the Moroccan coast 



\\b'\\e en route to the Ba\' of Biscay 

 (Aloncle 1964). Others may spawn 

 after arriving there (Con 1 977), thus 

 actually spawning in their feeding 

 area. 



Most of the large "return" fish 

 migrate from the Ibero-Moroccan 

 Bay around the British Isles to their 

 summer feeding area in Norwegian 

 waters. Many of the smaller ones, 

 including most of those which have 

 spawned in that Bay, proceed to the 

 Bay of Biscay, but others may join 

 the concentration off the central Mo- 

 roccan coast. This gathering is occa- 

 sioned when the impingement on the 

 northern coast of Morocco of a tongue 

 of warm (over 21°C) tropical water 



Figure 72. Geographic distribution of bluefin tag release and recapture data from 

 Norwegian tagging studies and hook recovery data in the eastem Atlantic. 



110 



