nautical miles (185 km) and about 20 

 miles (37 km) west of the release 

 point, respectively. These long-term 

 recoveries suggested that the Moroc- 

 can and Iberian trap fisheries in the 

 Atlantic harvested the same stock. 



Comparison of the return rates 

 and times at liberty for fish tagged 

 from the "return" run (7.6%, five re- 

 captures after 302-683 days at lib- 

 erty) with those for fish marked dur- 

 ing the "arrival" run (4.3%, no re- 

 captures after more than 85 days at 

 liberty) suggests that fish tagged fi^om 

 the "return" run were more viable 

 than those released from the "arrival" 

 run. 



Giant and medium-sized bluefin 

 occurred in Scandinavian and North 

 Sea waters during the summer and 

 fall. It was generally believed that 

 these came, at least in part, from the 

 "return" run which was fished by the 

 traps off southern Spain and Portu- 

 gal in July and August (Sella 1929a, 

 Sara 1964). Le Gall (1929) projected 

 a northward migration route west of 

 Ireland and north of Scotland into 

 the North Sea and the Scandinavian 

 waters, on the basis of observations 

 of tuna from fishing boats along the 

 way. Sella (1929a) identified a hook 

 found in a bluefin tuna caught in 

 Oslo Fjord, Norway, as of the type 

 used in the Bay of Biscay. This find- 

 ing supported the concept of a north- 

 ward migration of bluefin tuna from 

 Iberian waters to those off 

 Scandinavia. Le Gall (1929) also 

 noted indications of a southward mi- 

 gration passing north and west of the 

 British Isles in the fall. Le Gall ( 1 927, 

 1 929) noted that the presence of blue- 

 fin in the North Sea was controlled 

 by influxes of Atlantic or Atlantic 

 slope waters with salinities of about 

 35 o/oo. These waters entered the 

 North Sea from the north. Records of 

 bluefin in the English Channel were 

 scarce, although fish occurred fre- 

 quently off its western entrance, and 

 off the western end of Cornwall. Le 

 Gall ( 1 927) noted that these fish were 

 in the feeding phase, and speculated 

 that they had spawned in the Ibero- 

 Moroccan Bay. 



The accuracy of this assumption 

 was proved by the tagging experi- 

 ments of Hamre (1965). Hamre 

 tagged 242 medium and large (150- 



250 cm long) bluefin tuna in August 

 and September 1957-1962 near 

 Bergen, Norway. Six of these fish 

 have been recaptured near Cadiz, 

 Spain, and 26 in Scandinavian wa- 

 ters (Figure 72 ) (Hamre 1965 and 

 personal communication). Four of the 

 Spanish recaptures occurred after less 

 than 10 months at liberty ("direct" 

 migrations). The other two took place 

 23 and 45 months after release, 

 respectively. If we exclude nine of 

 the local returns which were recov- 

 ered in the season of their release, 

 and thus had no opportunity to emi- 

 grate, 26% of the returns were from 

 Spain, as against 74% from local 

 waters. Bluefin were tagged off Nor- 

 way in each of the years 1957-1962, 

 but the tags used in 1957 were evi- 

 dently defective and produced no re- 

 turns at all, and only 13 fish were 

 marked in 1962. One more of the 

 fish tagged off Norway in each of the 

 other years was subsequently recap- 

 tured off Spain. These results sug- 

 gest strongly that substantial num- 

 bers of the bluefin tuna which oc- 

 curred off Norway in summer and 

 early fall also occurred off southern 

 Spain in spring and early summer, 

 presumably there to spawn. Studies 

 of the size composition of the land- 

 ings in Norway and southern Spain 

 (Hamre et al. 1968), however, indi- 

 cated that the fisheries in these two 

 areas did not harvest the same stock 

 in every year. In 1955 through I960, 

 the size composition of the Norwe- 

 gian and Spanish catches were quite 

 similar, but in 1961 through 1964, 

 they were quite different. In 1965 

 they were similar again. Hamre et al. 

 (1968) attributed these changes to a 

 subdivision of the northeast Atlantic 

 tuna population into two contingents 

 with different migratory habits in 

 1961 through 1964. 



Although it has not been dem- 

 onstrated by tag returns, Hamre 

 agreed with Le Gall (1927, 1929) 

 that the bluefin entered the North Sea 

 and Scandinavian waters from west 

 and north of the British Isles, rather 

 than through the English Channel 

 (Figure 73). 



After the disappearance of me- 

 dium-sized bluefin from the Norwe- 

 gian fishery in 1963, the northward 

 migration of the giant bluefin along 



the Norwegian coast ceased and most 

 of these fish followed the southward 

 migratory route previously used by 

 medium-sized fish (Hamre 1965). 

 Tiews (1964) and Hamre (1965) 

 agreed, on the basis of the locations 

 and periods of fishing and the sizes 

 of fish taken, that the large bluefin 

 which had arrived in July and trav- 

 elled northward along the Norwegian 

 coast from Bergen eventually left that 

 coast and migrated southward into 

 the North Sea. There they were vul- 

 nerable to the German and Danish 

 fisheries (Section IVC5 b and c). 

 When these large fish reversed their 

 migration route in 1963, predomi- 

 nantly following the Norwegian coast 

 southward rather than northward, the 

 North Sea fisheries disappeared 

 (Hamre 1971, Tiews 1975). 



The local tag returns (Hamre 

 1965, personal communication) con- 

 firmed migratory patterns (Figure 73 

 ) in Norwegian waters which Hamre 

 (1962) had also deduced from stud- 

 ies of the size composition of catches. 

 The bluefin tuna reached the coast at 

 about 62°N latitude. The larger indi- 

 viduals, which arrived in July, mi- 

 grated northward and the smaller 

 ones, which arrived in August, mi- 

 grated southward. One of the latter 

 which had been tagged near Bergen 

 was recaptured off the island of 

 Anholt in the Kattegat. In addition to 

 the nine returns in the release season, 

 nine tags were recovered after about 

 one year at liberty, three after about 

 two years, as well as single ones from 

 fish which had been at large for about 

 three, five, six, seven and eight years. 



In recent years, most of the blue- 

 fin tuna in Norwegian waters, all of 

 which have been very large, have 

 left there early in the fall. Prior to 

 1963, when medium fish were abun- 

 dant there, many of these fish did not 

 depart until late autunm. The ensu- 

 ing migration of the large bluefin 

 apparently takes them north and west 

 of the British Isles to their wintering 

 area This probably lies between lati- 

 tudes 25°N and 40°N and between 

 the African and European coasts and 

 longitude 35°W (Shingu et al. 1975, 

 Fisheries Agency of Japan 1976). The 

 size distribution of the fish in the 

 area is not known. Aloncle (1964), 

 however, reported that small to me- 



109 



