ABUNDANCE AND SIZE OF JUVENILE SOCKEYE 



SALMON, ONCORHYNCHUS NERKA, AND 



ASSOCIATED SPECIES IN LAKE ALEKNAGIK, ALASKA, 



IN RELATION TO THEIR ENVIRONMENT^ 



Donald e. Rogers ^ 



ABSTRACT 



Juvenile sockeye salmon, Oncorhynchus nerkci, and associated fish in the littoral of Lake 

 Aleknagik (Bristol Bay, Alaska) were sampled systematically from spring to midsummer 

 (1962-72) with a beach seine. Apparent mortality rate and relative abundance were estimated 

 from catches. Juvenile sockeye salmon and threespine stickleback comprised the majority 

 of the population, and slimy sculpin, ninespine stickleback, and Arctic char fry the remain- 

 der. The annual abundance of juvenile sockeye salmon was related to the abundance of 

 parent spawners. No correlation was evident among the annual estimates of abundance of 

 the five species. 



Age was determined from length-frequency distributions, and growth rates were calculated 

 for sockeye salmon (age 0), Arctic char (age 0), and threespine stickleback (age I). The 

 mean lengths of sockeye salmon fry and char fry on 20 June were positively correlated with 

 water temperature, whereas the mean length of threespine stickleback (age I) on this date 

 was inversely correlated with the average catch of sockeye salmon fry in the previous year. 

 The mean lengths of all species on 20 July were inversely correlated with the mean catch of 

 sockeye salmon fry. A limited capacity of the Lake littoral to sustain growth of individual 

 fish was indicated. 



The annual commercial catch of anadromous 

 sockeye salmon, Oncorhynchus nerka Walbaum, 

 from the Nushagak District of Bristol Bay de- 

 clined from an average of about 5 million fish 

 in the early 1900's to only about 1 million in 

 recent years (Mathisen, 1971). Since the early 

 1950's, the Fisheries Research Institute has 

 studied the freshwater life of the stock to under- 

 stand the factors controlling the average abun- 

 dance and annual variation in abundance of the 

 adult run. We have assumed that a significant 

 portion of the variation is related to the varia- 

 tion in abundance and growth of juveniles, 

 especially fry (age 0), and have concentrated 

 effort on the Wood River lake system because it 



• Contribution No. 389, College of Fisheries, University 

 of Washington, Seattle, Wash. 



2 Fisheries Research Institute, College of Fisheries, 

 University of Washington, Seattle, WA 98195. 



has been the major producer among the river 

 systems in the District (Figure 1). 



The sockeye salmon fry inhabit different 

 parts of each lake from spring to fall. From mid- 

 May to mid-June, when the ice breaks up, to 

 mid-July, they reside along the shore and in 

 shallow bays; in mid-July they begin to move 

 offshore; and from mid-August through Sep- 

 tember they occupy the pelagic areas (Burgner, 

 1962). Accordingly, the populations are sampled 

 during early summer through beach seining 

 and during August and September through tow- 

 netting and echo sounding (Rogers, 1967). 

 Beach seine sampling has been conducted 

 throughout the District but has been concen- 

 trated in Lake Aleknagik. The catch and length 

 statistics for sockeye salmon fry from an exten- 

 sive effort in the lake in 1962 were analyzed by 

 Pella (1968). and the catch statistics for five 

 species of fish from 1964 through 1966 were 

 examined by Waters (1969). 



Manuscript accepted March 1973. 



FISHERY BULLETIN: VOL. 71, NO. 4, 1973. 



1061 



