FRENCH and BAKKALA: NEW MODEL OF OCEAN MIGRATIONS 



present. It may be that the Bristol Bay popula- 

 tion of immatures actually shifts to the west in 

 the summer but to a limited degree, or the 

 movements of the fish are not constant from year 

 to year. Our inability to readily identify stocks of 

 sockeye at sea and the limited sampling make 

 such movements difficult to detect. Another possi- 

 bility is that migrations are not as directional as 

 some evidence would imply but rather more 

 variable; a yet undetected recirculation (or 

 eastward movement) of immatures may also be 

 occurring to maintain a broad east-west distri- 

 bution of immatures throughout the summer. 



Information on the distribution and movements 

 of age .1 fish in the fall and early winter is 

 limited. The only catch data available are from 

 south of the western Aleutian Islands (Figure 18). 

 Age .1 fish were still abundant in this area in 

 October and November. It is unknown whether 

 these sockeye had remained in the North Pacific 

 Ocean through the summer and fall or were, at 

 least in part, fish that had returned from the 

 Bering Sea. 



Immature and Maturing Age .2 (January -June) 



During their second winter at sea, the sockeye 

 (now age .2 fish) either remain in the northern 

 part of the North Pacific Ocean or move into 

 southern areas depending on their maturation 

 schedule (if they mature as age .2 fish the follow- 

 ing summer or not). Generally most age .2 

 sockeye mature; the percentage maturing has 

 been estimated as ranging from 60 to 80% 

 each year (Royce et al., 1968). Separation of the 

 immature age .2 fish is evident at least by mid- 

 winter. Catch data from winter cruises show a 

 partial separation of the two groups of age .2 

 sockeye in most areas fished (Figures 19 and 20). 

 This may represent the period when the immature 

 component of the age .2 group are in the process 

 of separating from the maturing group by moving 

 south, leaving the matures in the more northerly 

 waters. 



By spring, separation of immature and matur- 

 ing age .2 sockeye is much more pronounced 

 (French, Bakkala, Osako, and Ito, 1971). It was 

 shown that in the northeastern Pacific Ocean im- 

 mature sockeye were not taken north of about 

 lat. 49"" in April and only appeared in catches 

 in this area in late May and June. Maturing 

 sockeye, however, were taken throughout the area 

 from lat. 49"" to 54''N. In the western and central 



Aleutian area along long. ITS^E and 175^W, im- 

 matures were primarily south of lat. 48^N, and 

 matures were caught mainly north of this 

 latitude in May. 



On the basis of the winter and spring catch 

 data, we surmise that in winter, age .2 immature 

 sockeye start migrating to southern waters and by 

 spring become well separated from the maturing 

 fish. Maturing sockeye tend to remain in 

 northern waters throughout the winter and 

 spring. They are found primarily in Ridge Area 

 water and waters of the Western Subarctic 

 Intrusion Area (Bakkala and French, 1971). 



Most of the maturing Bristol Bay population 

 probably shifts eastward in Ridge or Western 

 Subarctic Intrusion Area waters during the fall 

 or winter. Evidence of eastward movement is 

 provided by comparing results of sampling south 

 of Adak Island in summer 1969 with those from 

 south of the Aleutians in spring 1970 (Figure 21). 

 On the basis of age composition, magnitude of 

 catches, and historical tagging data from this 

 area, we conclude that the large numbers of sock- 

 eye taken near long. 176^W in July and August 

 were primarily Bristol Bay fish; some of these 

 sockeye undoubtedly moved even farther west, 

 and others were probably already to the west of 

 Adak Island. In spring 1970, sampling demon- 

 strated that most maturing sockeye were east of 

 long. 175^W indicating that many of the fish 

 located west of long. 175°W in the previous 

 summer had returned east of long. 175''W by 

 spring. 



The location of concentrations of Bristol Bay 

 sockeye in spring (which is influenced by the 

 extent of their eastward movement in fall or 

 winter) determines the main migration routes 

 taken to reach Bristol Bay; probably the largest 

 part of the population is located east of long. 

 175^W, and the main migration is through passes 

 east of long. 175°W. This conclusion was also 

 indicated by Kondo et al. (1965). (We do not know 

 the relative abundance or distribution of Bristol 

 Bay sockeye that may be in the Bering Sea in 

 late winter or early spring prior to the time of 

 migration.) The intrusion of the Western Sub- 

 arctic Gyre or northward shift of the Western 

 Subarctic Current may affect the westward dis- 

 tribution of Bristol Bay sockeye or the eastward 

 distribution of Asian sockeye in some years. For 

 example, the percentage of Bristol Bay fish in 

 catches by the Japanese mothership fleet in the 

 area where Asian and Bristol Bay sockeye salmon 



605 



