Table 6. --Two-way analysis of variance of abundance of juvenile sockeye salmon in tow net catches 

 in selected lakes of the Naknek system, 1961-64. The analysis involves effects of areas and time 

 where one pair of surface and deep tows for each area and time was treated as one sample except 

 for Coville Lake in 1961, when each tow was a sample. --Continued 



Year 



Source 



df 



MS 



South Bav--Cont. 



1962 



(age and I) 



1963 

 (age and I) 



Area 

 Time 



Time- area 

 Error 



Area 

 Time 



Time -area 

 Error 



1 



2 



2 



15 



2 



2 



4 



12 



indicates 101 level of significance. 

 **Indicates 5 ? <> level of significance. 



they leave the spawning grounds, although they do not 

 actually enter the ocean until the spring or early sum- 

 mer of their second or third year. As a result, the 

 numbers of age and age I sockeye salmon increase in 

 the basins closer to the outlet river, while the number 

 of juveniles in the system is declining gradually. 



I, therefore, evaluate mortality of juvenile sockeye 

 salmon in the Naknek system by examining the abun- 

 dance data for the system as a whole. For 1962 I was 

 able to calculate an average catch per tow by age class 

 each day for the system from 10 July to 29 August. 

 The sampling was done quite regularly and, in general, 

 each sampling unit shown in Figure 1 was sampled 

 once every 2 wk. By assigning the catch per tow found 

 by averaging the most recent preceding and following 

 sampling in each unit to those days on which no data 

 were collected, the weighted (by the surface area of 

 each sampling unit) rate of catch was calculated for 

 each day for the entire Naknek system. The data were 

 smoothed by a moving average of 3 (giving the middate 

 a double weight) for age and age 1 fish (Fig. 3). Three 

 general time periods of abundance for age fish appear 

 in these data: (1) the early period, when catches were 

 increasing — before 26 July; (2) the middle period, 

 when catches were generally stable — from 26 July to 

 about 10 August; and (3) the late period, when catches 

 were decreasing rapidly — after 10 August. The rate of 

 catch of age I fish decreased gradually during the sea- 

 son. 



The mean catch per tow by lake and the contribu- 

 tion of each lake to the catch for the entire system for 

 the early, middle, and late time periods were calcu- 

 lated for each year from 1961 to 1964 for age and age 

 I sockeye salmon. In 1961 and 1962 tow netting was 

 done some place in the system on most nights from 

 early July to early September, so that the averages for 

 individual time periods may represent a period of as 

 many as 20 days. In contrast, the data for the respec- 



tive periods in 1963 and 1964 were collected within 2 

 days of 10 July, 1 August, and 29 August. Therefore, 

 the figures for the early and late time periods are the 

 results of shorter periods of mortality in 1963 and 1964 

 than in 1961 and 1962. 



The weighted daily mean number of age sockeye 

 salmon caught per tow for the entire Naknek system in 

 1962 and the means for the early, middle, and late 

 periods in 1963 and for the late period only in 1961 and 

 1964 are shown in Figure 4. 



Only a general relation exists between the abun- 

 dance of age sockeye salmon in tow net catches in 

 late August and the number of resulting smolts (Table 

 7). In 1961-63 the mean number of age fish in the 

 catches ranged from 8.8 to 13.2, and the number of 

 resulting smolts (ages I and II) ranged from 11 to 16.7 

 million. Age fish were about 1 .5 times as abundant in 

 1964 as in the other years and produced an unusually 

 large number of smolts — 14.7 million age I (about 25% 



is 



E 



2°- 



£ xlO 



5 4 



15 



JULY 



25 | 



15 



AUG. 



25 5 



SEPT. 



Figure 3. — Weighted daily mean number of age and age 1 sockeye 

 salmon per standard tow in Naknek River system (all lakes combined), 

 11 July to 29 August 1962. The mean catch for the system was weighted 

 by the surface area of each sampling unit and the daily estimates were 

 smoothed by a moving average of three — (A + 2B + C) ■*■ 4. 



13 



