FISHERY BULLETIN: VOL. 72, NO. 2 



coastal tag returns have provided information for 

 describing the migrations of sockeye salmon 

 through most of their life at sea. 



DISTRIBUTION AND MIGRATION 



OF BRISTOL BAY SOCKEYE 



SALMON INFERRED FROM 



HIGH-SEAS CATCHES 



The apparent relative abundance of sockeye 

 salmon taken in gill nets, purse seines, and long- 

 lines from synoptic sampling over periods of time 

 and large areas of the ocean furnish much 

 information on movements and distribution offish. 

 This information coupled with the age composi- 

 tion of the catches and tagging data provides 

 important links for formulating migration pat- 

 terns of the stock. 



First Year at Sea 



Juveniles Age .0 (July-December)^ 



Juvenile salmon, age .0 fish after leaving the 

 rivers of Bristol Bay, move southwest along the 

 north side of the Alaska Peninsula throughout 

 summer, but substantial numbers remain in the 

 eastern Bering Sea until sometime after the 

 middle of September (Hartt et al., 1967; Hartt, 

 Dell, and Smith, 1969; Straty and Jaenicke, 

 1969'*). Sampling with purse seines indicates that 

 the juveniles do not make a rapid directional 

 migration at this stage of life but disperse slowly 

 toward the southwest as they move back and 

 forth with the tides. By mid-September the juve- 

 niles are still present in large numbers east of 

 long. 165°W extending at least 167 km offshore. 

 The length of time that the juveniles spend in 

 the eastern Bering Sea and their restricted dis- 

 tribution are probably due to the local abundance 

 and availability of food. During this period of 

 late summer, growth is rapid as the fish, averag- 

 ing 17 to 18 cm long, feed on the abundant 

 supply of zooplankton and larval fish (Hartt et al., 

 1967). 



The migration routes of the juvenile sockeye 



^Age designation used are those suggested by Koo (1962). 

 The numeral preceding the dot indicates number of winters 

 in fresh water; the numeral following the dot indicates number 

 of winters at sea. 



■•Straty, R. R., and H. W. Jaenicke. 1969. Estuarine ecology 

 of sockeye salmon in Bristol Bay. Bur. Commer. Fish. Biol. 

 Lab., Auke Bay, Alaska. (Unpubl. manuscr.) 



as they leave the eastern Bering Sea is unknown 

 due to lack of sampling in fall and early winter. 



Immatures Age .1 (January-June) 



The small sockeye were next taken as age .1 

 fish (an additional year is added on 1 January 

 regardless of state of annulus formation) in winter 

 catches in the North Pacific Ocean at various 

 locations; a few specimens have been taken in 

 the south-central Bering Sea. Bakkala (1971) 

 has summarized winter gill-net catches of age .1 

 fish for 1962-67 by research vessels of the North- 

 west Fisheries Center, NMFS. To his data we 

 have added catches made in the winters of 1969 

 and 1970 (Figure 4).^ These data illustrate that 

 main catches of age .1 sockeye were made near 

 lat. 46°30'N in the central North Pacific and 

 between lat. 48° and 51°N in the northeastern 

 Pacific from long. 165° to 155°W. A good catch 

 was also made near lat. 50°N at 175° and 170°W. 

 Relatively small numbers offish were taken in 

 the Bering Sea during sampling in late January 

 and early February 1963 and near long. 170°E 

 in February 1965. (Stations shown on long. 170°E 

 represent stations fished as far west as long. 

 167°18'E.) 



There were no tagging data to indicate area of 

 origin of the age .1 fish taken in the winter. We 

 can surmise their origin, however, on the basis 

 of the freshwater age composition of catches, at 

 least for some years. The largest catches of age .1 

 fish occurred in 1965 (10 and 16 March) near 

 lat. 46°30'N between long. 175°E and 180°. CPUE 

 (see footnote 5 for definition of catch per unit 

 effort) of 16 and 13 were the largest made during 

 the years of winter sampling. Most of these fish 

 (78% of the catch) were age 2.1 (a salmon of age 

 2.1 has spent two winters in fresh water after 

 hatching and one winter in the ocean). Later 

 in the year in the samples taken south of Adak 

 Island (where tag returns indicate that Bristol 

 Bay fish predominate) , the 2 . 1 age-group made up 

 approximately 75% of the catch of age .1 fish. 

 One year later this same group, now age 2.2 fish, 

 made up about 70% of the mature age .2 fish 

 in the 1966 run to Bristol Bay. That same year 

 the age composition of the mature Asian sockeye 



sin this and other figures the catch per unit of effort 

 (CPUE) of gill nets is the value of the sums of the average 

 catch per shackle of each mesh size. A shackle is approxi- 

 mately 91.5 m long. 



592 



