release in the Aleutians area and date of recoveiT 

 in the commercial fishery and a tendency toward 

 more rapid movement by the later migrants 

 (Hartt, 1966). Many of the fish still feed actively 

 on a variety of animals when within only 100 miles 

 (185 km.) of the estuaries. 



The immature .2-age fish during their third 

 summer at sea follow a course similar to that of 

 the .2-age mature tish except that they continue 

 westward and northwestward in tlie Aleutian 

 Islands and Bering Sea areas, rather than return- 

 ing northeastward toward Bristol Bay (fig. IID). 

 They average 40 to 48 cm. long and are slimmer 

 than the .2-age mature fish. Immature salmon be- 

 gin to arrive in the Aleutian area just after the 

 mature fish ha^e passed and continue on a coui-se 

 similar to that described for their migrations in 

 the previous summer as .1-age fish. 



The earlier timing of the maturing group of 

 .2-age fish indicates tliat they segivgate from those 

 not maturing, apparently by accelerating their 

 speed or by taking a shorter route. As .1-age fisli 

 the previous summer they liad been thoroughly 

 mixed with the immature group, as verified by the 

 fact that .1-age immature fish tagged in the same 

 purse seine set frequently yield Bristol Bay re- 

 turns both 1 year and 2 yeare later (Hartt, 1966). 



The summer migrations of the .2-age immature 

 sockeye salmon can be illustrated more completely 

 by tag returns from U.S. tagging in 1964 (fig. 16) . 



Figure 16. — Recovery distribution of sockeye salmon 

 taggretl as .2-afre immature fisli in 1964 (the arrows 

 depicting returns in 1065 are merely drawn for conven- 

 ience and are not intende<l to s-how migrations during 

 the full year at lilx-rty ) . 



In 1964, substantial numbers of .2-age immature 

 fish were tagged in tlie central Aleutian area and 

 in the central Gulf of Alaska, so that together the 

 tag returns bring out the salient features of 

 migration. The 312 fish tagged south of Adak 

 Island were released between late June and mid- 

 August and were part of the characteristic sum- 

 mer migration tliat passes westward south of the 

 Aleutian Islands. The 16 liigh-.seas recoveries in 

 1964 (late July and early August) illus'trate tlie 

 westward and northwestward summer migi-ation 

 of immature fish into the western North Pacific 

 and Bering Sea. The high-seas returns of mature 

 fish in 1965 were probably en route (o Bristol Bay. 

 and tlie five Bristol Bay coastal returns together 

 witli a lack of coastal returns from areas other 

 than Bristol Bay illustrate that fish migrating 

 south of the Aleutians were primarily of Bristol 

 Bay origin. The 404 fish tagged in the central Gulf 

 (fig. 16) were released during May 1064, at wliicli 

 time the enclosed area was the ajjpareiit center of 

 abundance of .2-age immature sockeye salmon as 

 judged l)y longline sampling tliroughnut the Gulf. 

 The four coastal returns from Bristol Bay in 1965 

 demonstrate the presence of this stock and the nine 

 Gulf coastal returns indicate a mixture of all 

 major Gulf of Alaska .stocks as well. The three 

 liigh-seas returns in 1964 near the central Aleu- 

 tians, all in late July and early August., .show that 

 part of the group from the central Gulf entered 

 the mass westward migration south of the Aleu- 

 tians. In all probability these fish were the Bristol 

 Bay components of the Gulf mixture, and. thus, 

 illustrate the summer return migration from the 

 Gulf of at least some of the Bristol Bay immature 

 fish. The route followed by the Gulf of Alaska 

 stocks is not known, but they apparently did not 

 enter the migration soutli of tlie central Aleutians, 

 since tagging in that area yielded no Gulf coastal 

 returns. Thus, the data in figure 16 ilhistrate that 

 the migratory course of different salmon stocks 

 can bo discrete even though they overlap at cer- 

 tain times and places, which in turn suggests in- 

 herently different responses to whatever cues may 

 be guiding tliem even at the innnature .stage. 



The migrations of the .2-age immature sockeye 

 salmon during the remainder of their third year 

 at sea are apjiarently a repetition of tiiose in their 

 second vear. i.e.. westward or northwestward into 



454 



U.S. FISH AND WILUI/IFK SBRVICK 



