data on past spawning populations. Finally, we 

 consider the question — is the capacity of the 

 spawning grounds to produce young sockeye 

 salmon less than or greater than the capacity 

 of the lakes to rear them? 



MEASURES OF ESCAPEMENT 



Statistics on the escapements of sockeye salm- 

 on to the major river systems of southwestern 

 Alaska are incomplete before 1955. Between 

 1900 and 1933, escapement counts were ob- 

 tained at weirs in a few rivers. Since the late 

 1930's, rough estimates of escapements have 

 been made by ground and aerial surveys. Weirs 

 were reinstalled in the Chignik and Ugashik 

 Rivers in 1949, in the Naknek River in 1950, 

 and in the Egegik River in 1952. Intensive 

 ground and aerial surveys of spawning grounds 

 in the Wood system were started in 1946. On 

 the Wood River in 1953, FRI first used observa- 

 tion towers to obtain sample counts for estimat- 

 ing escapements of migrating adult salmon. This 

 technique has supplanted weirs in most areas 

 and was extended to the Kvichak River in 1955 ; 

 the Egegik in 1956 ; the Naknek, Ugashik, and 

 Alagnak in 1957; the Igushik in 1958; the 

 Nuyakuk in 1959; and the Snake in 1960 (fig. 

 2). Since 1921, weirs have been used in Karluk 

 River except in 1958 and 1959 when counting 

 towers were used. A weir is still used in the 

 Chignik River. 



Size of Escapements 



Estimates of the size of escapements to the 

 several river systems in 1955-62 (table 8) pro- 

 vide an index of the relative production of each 

 system. Escapements may vary widely within a 

 system and may be cyclic in some. For instance, 

 in the Kvichak system (which is the only sys- 

 tem with clearly defined cycles of abundance of 

 sockeye salmon) the escapement in 1960 was 

 almost 60 times that in 1955. In each of the next 

 three largest systems — Wood, Naknek, and 

 Egegik — ^the greatest escapements were only six 

 to eight times the smallest. The escapements to 

 Chignik and Karluk Rivers have not varied as 

 much — in the Karluk system the largest was 

 about four times the smallest, and in the Chignik 

 system it was only twice the smallest. 



Distribution of Spawners within Systems 



Sockeye salmon use four major types of 

 spawning grounds : streams tributary to lakes, 



Table 8.— Estimates of sockeye salmon escapements: to major 

 river systems of southwestern Alaska, 1955-6:i 



I Thousands of fishj 



' Aerial survey estimates by FRI. 



rivers between lakes, outlet rivers (trunk 

 streams), and lake beaches. The relative im- 

 portance of each type varies among systems and 

 from year to year within systems. 



Variation may be considerable in the age com- 

 position of sockeye salmon that use the different 

 types of spawning grounds within a given sys- 

 tem. The most striking diflference is in the num- 

 ber of years the salmon have spent in the ocean. 

 Although most adult sockeye salmon are 2- or 

 3-ocean fish (i.e., remain in the ocean 2 or 3 

 years before they return to spawn) , the propor- 

 tion varies among groups of fish occupying 

 specific spawning areas from year to year. 

 Three-ocean fish are larger than 2-ocean and 

 are more susceptible to capture by the gill nets 

 in Bristol Bay. 



Natural fluctuations in the relative abun- 

 dance of various components of a stock, com- 

 bined with selective effects of the fishery, often 

 lead to poor distribution of the escapement 

 among the spawning grounds. The total escape- 

 ment may be adequate for a system, but if the 

 distribution of the escapement does not conform 

 to the relative spawning capacities of various 

 grounds, some grounds will be underutilized and 

 others will be overutilized. Various races and 

 age groups of sockeye salmon bound for the 

 many spawning grounds of a system may pass 

 through the fishery at different times. There- 

 fore, the fishery that operates at different in- 

 tensities through each season could harvest 

 components at different rates — for example, 

 through a combination of net selectivity and 

 closed fishing times. This section examines the 

 evidence bearing on these problems in the sock- 

 eye salmon systems of southwestern Alaska. 



Igushik system. — The type of spawning 

 grounds used varies greatly from lake to lake 



SOCKEYE SALMON IN MAJOR RIVER SYSTEMS IN SOUTHWESTERN ALASKA 



419 



