20 



LlI (T 



CD 



3 



o ^ 14 



2- 



liJ 10 

 8 



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UJ ^ 



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 ^ o 



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15 

 JULY 



25 



15 

 AUG. 



25 



5 

 SEPT. 



Figure 7. — Weighted daily mean catch of juvenile sockeye salmon per tow in Naknek system, all lakes com- 

 bined, 1962. The mean catch for the system has been weighted by the size of each sampling area, and 

 the daily estimates have been smoothed by a moving average of three — (A + 2B — C) — 4. 



would be somewhat higher if data from North 

 Arm, which is not involved in the interlake 

 movement, were omitted. The weighted mean 

 catch of age I juveniles for the system was 

 greatest in the earliest tows, July 11 to 20, and 

 declined gradually during the summer. 



Within lakes of the Naknek system we found 

 a wide range in numbers of adult spawners per 

 unit area of lake and also in the abundance of 

 their progeny. Coville Lake had an escapement 

 of about 6,600 adults per square kilometer in 

 1961 ; Brooks Lake had 267 ; and North Arm had 

 55. In July 1962 (before the presmolt interlake 

 migrations) the average number of age sock- 

 eye salmon in tow net catches was 150 in Coville 

 Lake, 2 in Brooks Lake, and 0.5 in North Arm. 

 The abundance of spawning adults (table 15) 

 and of age juveniles in these three lakes nearly 

 cover the range found in southwestern Alaska. 



Studies of juvenile salmon in the Naknek sys- 

 tem have run too few years to determine the rela- 

 tion between the abundance of age sockeye 

 salmon and the size of the parent population. The 

 escapement to the Naknek system in 1960 was 

 828,000 spawners, and the average catch of age 

 sockeye per tow in 1961 (in late August) was 

 about 9.5. The escapement in 1961 was about 



350,000, and the average catch per tow in 1962 

 was about 11.6. 



The age composition and mean fork lengths of 

 juvenile sockeye salmon on September 1 are pre- 

 sented for the Naknek and Karluk systems in 

 table 21 by lake or sampling area. The average 

 lengths of age sockeye salmon in the Naknek 

 system were greater in 1962 than in 1961, al- 

 though the numbers of age and age I fish in 

 the system were essentially the same, as indi- 

 cated by tow net catches in 1961 and 1962 and 

 the smolt emigration in 1962 and 1963. The aver- 

 age catches per tow were 9.5 and 11.6 age fish 

 on August 20, and the smolt migrations were 8 

 million age I and 8 million age II in 1962 and 6 

 million age I and 8 million age II in 1963. 



The year-to-year variation in basic produc- 

 tivity of the lakes of the Naknek system may 

 cause marked differences in growth of juvenile 

 .sockeye salmon independent of their abundance. 

 As was shown earlier in this report, basic pro- 

 ductivity was comparatively low in 1961 and 

 high in 1962. The resulting apparent growth of 

 juvenile sockeye salmon reflected these differ- 

 ences. 



The variation among mean lengths of age 

 sockeve salmon in the several basins of the Nak- 



434 



U.S. FISH .A.ND WILDLIFE SERVICE 



