Igushik System 



In the Igushik system, in 1955-62 the number 

 of spawners per square kilometer of lake in 

 Ualik Lake was only slightly larger than in 

 Amanka Lake if we assign the adults spawning 

 in the interconnecting river and its branch (On- 

 goke River) to Amanka Lake. 



Snake S\stem 



Nunavaugaluk Lake is the only lake in the 

 Snake system that produces significant numbers 

 of salmon. 



Wood System 



The average numbers of spawners per square 

 kilometer in each of the four main lakes of the 

 Wood system in 1955-62 were : Aleknagik, 2,090 ; 

 Nerka, 2,430 : Beverley, 2,490 ; and Kulik, 2,040. 

 Little Togiak Lake, tributary to Lake Nerka, had 

 a slightly higher density of spawners than the 

 main lakes. 



Nuyakuk System 



The low average number of spawners per unit 

 lake area in the Nuyakuk system (table 15) is 

 largely due to the low densities in Nuyakuk 

 Lake, the largest lake in the system, where the 

 figure was only 50 spawners per square kilo- 

 meter from 1959 through 1962. 



Kvichak System 



The Kvichak is the only major sockeye salmon 

 system in Bristol Bay that has a pronounced 

 cyclic variation in number of adults in the es- 

 capement. The effects of this cycle overshadow 

 problems of distribution of the spawners within 

 each year. Over the years 1955-63, the number 

 of spawners per square kilometer of lake varied 

 from 84 — among the lowest numbers observed 

 in Bristol Bay — to 4,890 (table 16) . Peak years 

 modify the reproductive potential in subsequent 

 off years. This problem is discussed later. 



Naknek System 



Many nursery areas of the Naknek system re- 

 ceive juvenile sockeye salmon from upsystem 

 areas ; that is, from other than adjacent beaches 

 and tributary streams. Coville Lake represents 

 about 3 percent of the rearing area of the Nak- 

 nek system but has received as much as 65 per- 

 cent of the escapement in a given year. This lake 

 is at the upper end of the system, and many of 



Table 16. — Numbers of sockeye salmon in escapements and 

 spainiers per square kilometer of lake, Kvichak system, 

 1955-63 



the juvenile sockeye salmon that originate in its 

 tributaries .spend some growing time in down- 

 system lakes. North Arm basin and Brooks Lake 

 make up about 35 percent of the area of the 

 system but receive less than 10 percent of the 

 escapement, and they do not receive fry pro- 

 duced in other areas. The distribution of e.scape- 

 ment and subsequently the distribution of the 

 juveniles are considered later. 



Cliignlk System 



Chignik Lake had the greatest average con- 

 centration of spawners in the Chignik system — 

 about 14,000 per square kilometer of lake in 

 1956-62. The average for Black Lake during the 

 same period was slightly more than 4,600, about 

 the same as for the Igushik lakes. 



Karluk System 



Recently emerged fry behave in such a way in 

 the Karluk system that the total escapement is 

 assignable to Karluk Lake for consideration of 

 rearing areas. The progeny of spawners that use 

 the outlet (Karluk River) move upstream into 

 the lake, and progeny of spawners from areas 

 above O'Malley and Thumb Lakes move down 

 into Karluk Lake early in their first summer 

 of life. 



SPECIES OF FISH IN THE I..\KES 



Knowledge of the abundance of species of fi.sh 

 associated with juvenile sockeye .salmon in the 

 lakes is essential to understand the factors that 

 may affect the survival and growth of sockeye 

 .salmon. Differences in behavior and the distri- 

 bution of the habitat of the many species re- 

 quired the use of several types of collecting gear : 

 tow nets, beach seines, trap nets, gill nets, and 

 bottom and midwater trawls. 



SOCKEYE SALMON IN MAJOR RIVER SYSTEMS IN SOUTHWESTERN ALASKA 



427 



