24 



S 



?22 



IT 



w 20 



a. 



u. 



u. 16 

 o 



rr 14 



UJ 



m 



z 10 



z 



uj 8 

 o 6 



UJ 



£ 4 

 o 

 uj 2 



15 

 JULY 



I 



15 

 AUG. 



5 



SEPT. 



Figure 4. — Weighted daily mean number of age sockeye salmon per 

 standard tow in Naknek River system (all lakes combined) for 1962 and 

 means for early, middle, and late periods for 1963 and for late period 

 only in 1961 and 1964. (See Fig. 3 for explanation of weighting proce- 

 dure.) 



more than in the previous high year) and 20.8 million 

 age I and age II combined. 



The systemwide average catch per tow of age I 

 sockeye salmon generally declined slowly from July 

 through August each year and the abundance after 10 

 August ranged from 2.0 to 5.4 from 1961 to 1964 (Table 

 7). A decrease in abundance of age I fish was expected 

 because of a continuing outmigration of smolts during 

 the summer and natural mortalities. The range of 

 abundance of age I fish after 10 August each year was 

 similar to the range in abundance of age II smolts the 

 next spring (age III smolts are rare in the Naknek 

 system). 



Comparative Abundance among Lakes 



Although age and age I sockeye salmon were 

 commonly captured together, the abundance of each 

 age class is considered separately because of differ- 

 ences in behavior and distribution among the lakes. 



The general picture of the relative seasonal abun- 

 dance of age and age I sockeye salmon in tow net 

 catches in each lake for 1961-63 are shown in Figures 5 

 and 6. Because it was not always feasible to maintain 

 the sampling schedule, the data in Figures 5 and 6 are 

 not complete for all years and all time periods. The 

 great difference in the scale of the ordinates of Figures 

 5 and 6 should be noted: only general sampling periods 

 are indicated in the graphs because I wish to consider 

 only the seasonal trends in abundance. 



The most marked changes in the abundance of age 

 fish (and changes involving the greatest numbers of 

 fish) are the decreases in Coville Lake and concurrent 

 increases in Iliuk Arm for each time period (Fig. 5); 

 similar but much smaller increases for age fish ap- 

 pear in Grosvenor Lake and South Bay. The decrease 

 in abundance of age fish in Coville Lake and the 

 increase in the other lakes are due in part to an ob- 

 served downsystem migration of age fish. This sum- 

 mer outmigration is probably significant in Coville 

 Lake, but the significance of these fish to the rest of 

 the system is uncertain (discussed in more detail later). 

 Part of the increase in numbers of age fish downlake 

 from Coville Lake was due to a continuing recruitment 

 of fry from spawning grounds directly tributary to the 

 lakes, as indicated by the occurrence of the small fish 

 in samples taken in late July and most of August in all 

 years. 



The abundance of age fish in each lake in July is 



Table 7. --Mean number of age and age I sockeye salmon taken in tow nets in the Naknek River 

 system (all lakes combined) in August 1961-64 and resulting numbers of smolts produced. Age 

 fish in August can become age I or age II smolts, but age I fish in August can become only age 

 II smolts (rarely age III). 



Stewart, Donald M. (editor). 1969. 

 Dep. Fish Game, Inform. Leafl. 154. 



1967 Bristol Bay red salmon smolt studies. Alaska 



14 



