FISHERY BULLETIN: VOL. 72, NO. 2 



162°E 165°E 



170°E 



17 5°W 



170°W 



160,702 

 0.12 



50° 



45°- 



5,267 

 



1,837 

 



93,962 

 



12,923 

 



24,295 

 0.41 



25,362 

 



25,889 



30,902 

 0.32 



162,525 

 0.43 



228,440 

 



977 

 , 



122,646 

 3.02 



159,557 

 0.50 



11,494 

 



394,944 

 2.03 



40,728 

 0.74 



vliji^' 



UPPER NUMBER — NUMBER OF TANS FISHED 



LOWER NUMBER- TAG RECOVERIES PER 10,000 TANS FISHED 



60° 



55° 



50° 



-45° 



162°E 165°E 



170°E 



175°E 



180° 



175°W 



170°W 



Figure 17. — Fishing effort and tag recoveries per unit of effort 

 by the Japanese mothership fleet in 2° by 5° areas and for the 

 period of 21 July to 10 August (data from Fisheries Agency 

 of Japan, 1966 and Fisheries Research Institute, 1964). 



There is some doubt about the true proportion of 

 immature sockeye salmon remaining in the North 

 Pacific Ocean in comparison to those moving to 

 the Bering Sea. The rates of return from the high- 

 seas fleet was 3.5% of age .1 fish and 5.1% of 

 age .2 fish, rather low rates considering the total 

 fishing effort, although the small age .1 fish 

 even with tags affixed may not be vulnerable to 

 the fishery with its large-mesh gill nets. By way 

 of comparison tag returns of 8.9% were made on 

 the high seas of maturing fish from tagging 

 experiments in the central and western Aleutian 

 Islands area in 1960 (Hartt, 1966). 



Because of the dynamic nature of the ocean 

 migration of salmon (the rate of travel of those 

 recovered in 1964 ranged from 2 to 50 nautical 

 miles per day and averaged 17 nautical miles per 

 day), it is possible that the fish recovered in the 

 North Pacific Ocean after an extended period had 

 migrated extensively and reentered the fishing 

 area south of the Aleutian Islands. We do not 

 know if the immature salmon make such a migra- 

 tion in the summer. It is known, however, that 



immature sockeye salmon become more widely 

 distributed in the Bering Sea in August compared 

 to their distribution in July (see Machidori, foot- 

 note 7), a pattern which might argue against the 

 possibility of a return migration to the North 

 Pacific Ocean in July or even by early August. 



In relation to oceanographic features, the age .1 

 fish in summer were found primarily in the Ridge 

 Area water south of the Alaska Peninsula and 

 eastern Aleutian Islands but were located in both 

 the Ridge Area and the Alaskan Stream south 

 of the central and western Aleutian Islands (Bak- 

 kala, 1971). Ridge Area waters in summer were 

 also found to have greater concentrations of food 

 organisms than other water areas of the Subarctic 

 Pacific Region (McAlister et al., 1969, 1970). 



In summary, the evidence from distribution 

 studies indicates that movements of Bristol Bay 

 immatures in June are northward from areas they 

 occupy in spring to waters they occupy in 

 summer — generally between lat. 50''N and the 

 Aleutian Islands and Alaska Peninsula. The 

 majority of Bristol Bay fish appears to remain 

 in these waters through the summer, but some 

 smaller proportion continues northward or north- 

 westward into the Bering Sea. Thus, the distribu- 

 tion of immatures is seen to shift northward 

 from spring to summer but not extensively on an 

 east-west plane. 



Conflicting with this hypothesis of summer 

 distribution is other evidence which has indicated 

 that migrations in the North Pacific are pre- 

 dominantly and continuously westward through- 

 out the summer (Royce et al., 1968), implying 

 that the population of Bristol Bay immatures is 

 displaced to the west during the summer and 

 leaves waters of the northeastern Pacific Ocean. 

 Direct evidence of immature sockeye salmon 

 migrating long distances across the North Pacific 

 from the northeast Pacific is provided by tag 

 recoveries on the high seas of age .2 immature 

 fish. Three immature sockeye salmon were tagged 

 in the northeast Pacific near long. 145^W in May 

 and recovered in the central Aleutian Islands area 

 in July and August of the same year. Similarly, 

 two immature sockeye tagged south of Unalaska 

 Island in late June were recovered in the western 

 Aleutian Islands area, one near 171°E in late 

 July and one near 173°E in early August of the 

 same year. Such long migrations across the North 

 Pacific have not been demonstrated by the age 

 .1 fish. The apparent contradiction of the two lines 

 of evidence cannot satisfactorily be resolved at 



604 



