measurements proved to be useful in final analysis. 



The most extensive data on size of juvenile sockeye 

 salmon came from collections made with tow nets. 

 These data, in the form of average lengths and length 

 frequencies, have been used to relate changes in aver- 

 age size with time (apparent growth) to abundance of 

 sockeye salmon and other species and in some in- 

 stances to investigate the effects of migrations. 



Average lengths of juvenile sockeye salmon in 

 catches were used to calculate "growth" curve equa- 

 tions which describe the average size by age class each 

 day. After trying several mathematical models and 

 visually examining the fit of the curves to the actual 

 data, I selected a second-degree polynomial 

 (Snedecor, 1956), in which length is related to time in 

 days since 30 May (i.e. 1 June = day 1 ; 1 July = day 3 1 ; 

 and 1 September = day 93). The equations describing 

 the average length have been used to: (1) calculate the 

 average size on other than dates of sampling by extrapo- 

 lation or interpolation; (2) make estimates of size from 

 combined data for sampling areas within a basin; and (3 ) 

 plot graphs (apparent-growth curves) describing the 

 changes in length during a season. 



Juvenile Sockeye Salmon 



Curves depicting the average lengths of juvenile 

 sockeye salmon in the summers from 1961 to 1963 for 

 all basins and 1961 to 1964 for Coville Lake are pre- 



sented in this section as each lake is discussed. Be- 

 cause of known differences between the average size 

 of migrating and nonmigrating fish, probable size- 

 related differences in mortality, and known variations 

 in time of recruitment of fry from the spawning 

 grounds, the curves represent only "apparent 

 growth." 



A comparison of the average size of the fish from 

 different areas supplies part of the knowledge needed 

 to understand differences in apparent growth, but for a 

 more complete understanding knowledge of the length 

 frequency composition of the population is also 

 needed. Graphs of the percent frequency of juvenile 

 sockeye salmon by 3-mm size groups by time periods 

 have been prepared for 1961 to 1964. The length fre- 

 quencies offish sampled will be discussed and related 

 to their average lengths for each lake. 



The mean fork length of age and age I sockeye 

 salmon on 20 August and 1 September 1961-64 by 

 sampling area and lake are summarized in Table 21 for 

 each basin. The sizes used are those estimated from 

 the calculated growth curves rather than the empirical 

 data even when collections were made on 20 August or 

 1 September. The dates 20 August and 1 September 

 were selected for comparison for different reasons — 20 

 August is late enough in the season to indicate growth 

 conditions for the summer and early enough to avoid 

 most sampling problems caused by the early fall 

 storms; 1 September is the date used in much of the 



Table 21. --Mean fork lengths of age and age I sockeye salmon in each lake of the Naknek River 

 system and in Coville and Grosvenor Rivers on August 20 and September 1, 1961-64. (Weighted by 

 abundance and average size in each sampling area.) 



Age 



Coville Lake 

 Coville River 

 Grosvenor Lake 

 Grosvenor River 

 Iliuk Arm 

 South Bay 

 West End 

 North Arm 

 Northwest Basin 

 Brooks Lake 



Age I 



Coville Lake 

 Coville River 

 Grosvenor Lake 

 Grosvenor River 

 Iliuk Arm 

 South Bay 

 West End 

 North Arm 

 Northwest Basin 

 Brooks Lake 



84.3 

 84.5 



83.4 

 83.8 



79.9 

 81.9 



94.0 



33 



