FISHERY BULLETIN: VOL. 71, NO. 4 



Table 1. — Dates of ice breakup, surface water temperatures, and relative lake levels during beach seine sampling 



in Lake Aleknagik. 1962 through 1972. 



population size. A frequent source of error is 

 the variation in availability of the fish popula- 

 tion to the sampling net. Beach seine catches 

 of sockeye salmon fry and threespine stickleback 

 decline seasonally as a result of movement off- 

 shore and mortality. Apparent mortality rates 

 were estimated from linear regressions of In 

 mean catch on coded date. 



The data were examined through stepwise 

 multiple regression and linear correlation tech- 

 niques for determination of significant relation- 

 ships among the physical and biological param- 

 eters. 



RESULTS 



Climatological observations for the Wood 

 River lake system are given in Rogers, Siler, 

 and Croker (1970). The average date of ice 

 breakup from 1951 to 1972 is 1 June, and the 

 range in dates is from 14 May to 16 June. A 

 summary of physical data collected in connec- 



tion with the beach seine sampling in Lake 

 Aleknagik is given in Table 1. Lake level usually 

 rises rapidly after ice breakup until mid-June 

 and declines through the summer. Inshore sur- 

 face water temperatures rise gradually from ice 

 breakup to late July and then level off. Water 

 temperatures are lower on the average in the 

 upper third of the lake (area A) than elsewhere. 

 From 1962 to 1972 the average surface water 

 temperatures during 20 June- 19 July were 9.1°, 

 10.3°, and 10.7° C in areas A, B, and C, 

 respectively. 



Fish of 24 species have been collected in Lake 

 Aleknagik, but only juvenile sockeye salmon 

 and threespine stickleback have been greatly 

 predominant in beach seine catches (Table 2). 

 These two species are also the only ones that 

 become pelagic in midsummer. Three other 

 species appear in significant numbers in the 

 catches: ninespine stickleback, PinigitiKs puiig- 

 itius Linnaeus; slimy sculpin, Coitus cognatus 



Table 2. — Sums of geometric mean beach seine catches of five fish species by lake area. 



Lake Aleknagik, 1962 through 1972. 



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