ROGERS: JUVENILE SOCKEYE SALMON 



Area A 



Agulowak River 



LAKE ALEKNAGIK 



SCALE IN KILOMETERS 



DEPTH IN METERS 



4^ 



Area C 



Wood 

 River 



Figure 2. — Beach seine stations and lake sampling areas in Lake Aleknagik. 



that were easily separated from the length fre- 

 quencies. The mean lengths were converted to 

 equivalent live lengths so as to adjust for the 

 shrinkage due to preservation (Rogers, 1964). 

 These were plotted by date and examined for 

 determination of the most suitable growth 

 model. A curvilinear relationship was indicated, 

 and regressions of natural logarithm (In) mean 

 length on coded date (1 June = 1, 1 July = 31, 

 etc.) were calculated through weighting the 

 observations with geometric mean catch. A 

 weighting procedure was used because (1) vari- 

 ance of the means tended to increase during 

 the season as a result of the decline in catch 

 (hence sample size) and (2) the accuracy of 

 mean lengths from beach seine samples as 

 estimates of mean length in the population 

 tended to decrease in midsummer as the fish 

 moved offshore. Annual growth rate and fish 



size in given periods were estimated from the 

 regressions. 



The beach seine catch data were analyzed 

 through logarithmic transformation. An analy- 

 sis of variance was conducted with the catches 

 made in the first four periods of sampling (20 

 June-19 July) for the purpose of determining 

 the significance of observed variation associated 

 with location (station and lake area), date, and 

 year. The last two periods ( 21 July-5 August) 

 were excluded from the analysis since the 

 catches of sockeye salmon fry in these periods 

 were obviously lower than those in the other 

 periods and age fish of the longer lived species 

 often appear at this time. 



Mortality rate in a population is estimated 

 commonly from changes in catch with time 

 when catch per unit of effort can be reasonably 

 assumed to be proportional at all times to true 



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