and this shift may have been caused by the 

 warm water (5° C. at 100 m.) being relatively 

 farther north in 1968 than in 1967 (see section 

 on environmental conditions). 



Additional information on the relative abun- 

 dance of sockeye salmon in the spring as shown 

 by commercial mesh sizes (121- and 130-mm. 

 mesh) has been obtained by Japanese research 

 cruises since 1965 (fig. 11). These data show 

 that abundance of sockeye salmon was greatest 

 in 1965, reduced in 1966 and 1967, and lowest 

 in 1968. The high abundance in 1965 reflects 

 the large return of sockeye salmon (over 60 

 million fish) to Bristol Bay that year. 



Another feature of the distribution of sock- 

 eye salmon (noted from data of 1967 in fig. 11) 

 was an apparent northward shift in main con- 

 centrations of fish from west to east. In this 

 season, fish were most concentrated from about 

 lat. 45° N. to 48° N. near long. 170° E., from 

 about lat. 47° N. to 50° N. between long. 175° 

 E. and 180°, and from about lat. 50° N. to 51° 

 N. between long. 175° W. and 170° W. 



Chum Salmon 



Chum salmon were widely distributed from 

 north to south, extending farther south than 

 sockeye salmon on the two western cruise 

 tracks (fig. 12) . To the east, on long. 164° W., 

 they were taken from about lat. 49° N. to lat. 

 54° N., the limits of fishing. 



Immature chum salmon in May, like sock- 

 eye salmon, were in the southern part of this 

 range, but maturing chums, unlike sockeye 

 salmon, extended as far south as the immatures. 

 Maturing chum salmon were in all water Areas, 

 but south of the central and western Aleutian 

 Islands they appeared to be mainly restricted 

 to the Western Subarctic and Transition waters. 

 Immatures were mainly restricted to the Trans- 

 ition water. 



In early June, south of the eastern Aleutian 

 Islands, an increase in the abundance of ma- 

 turing chum salmon indicated a migration of 

 this species through the area at the same time 

 as the migration of sockeye salmon (fig. 9). 



55°N. 



I75°E. 



180° 



I7 5°W. 



I70°W. 



I65°W. 



I60°W. 



50' 



45' 



55°N. 



50° 



45° 



40° 



Figure 12. — Relative abundance of immature and maturing chum salmon as shown by gill net catches of Jap- 

 anese and United States research vessels in May 1968. 



14 



