BIOLOGICAL STUDIES AND ESTIMATES OF OPTIMUM ESCAPEMENTS 



OF SOCKEYE SALMON IN THE MAJOR RIVER SYSTEMS 



IN SOUTHWESTERN ALASKA 



By Robert L. Burgnbr, Charlbs J, DiCostanzo, Robert J. Ellis, George Y. Harry, Jr., Wilbur L. Hartman, Orra E. Kerns, Jr., 



Ole a. Mathisen, and William F. Royce' 



ABSTRACT 



An inteniive reieerch program waa conducted in 1961 and 

 1962 by the Bureau of Commercial Fiiheriei Biological Lab- 

 oratory, Auke Bay, Alaska, and the Figherie) Research Insti- 

 tute, University of Washington, with the cooperation of the 

 Alaska Department of Fish and Game. Many sockeye salmon 

 river systems were studied concurrently with essentially the 

 same techniques so that systems covering the entire range of 

 production levels could be compared. The general objective of 

 this research was to determine the optimum escapement of 

 sockeye salmon for each of the major systems. This was ac- 

 complished through integration of the results of several related 

 studies; (1) summarization and analysis of historical and cur- 

 rent data on runs of adult sockeye salmon, (2) delineation and 

 description of spawning areas and estimation of their capaci- 

 ties, (3) delineation and description of the nursery areas and 

 estimation of their capacities. 



The major systems studied were the Wood, Kvichak, Nak- 

 nek, and Ugashik systems, which enter Bristol Bey; the Chig- 

 nik system, on the south side of the Alaska Peninsula; and the 

 Karluk system, on Kodiak Island. Adult sockeye salmon in the 

 commercial catches and escapements, and sockeye salmon 

 smolts, were counted and sampled. Spawning grounds were 

 surveyed to determine their size end quality and the distribu- 

 tion end ebundance of spawners. Bathymetric maps were pre- 

 pared for some of the nursery lakes. Intensive limnologicel 

 studies, including e major effort to measure primery produc- 

 tivity, were mede on meny nursery lakes. Several types of gear 

 sampled juvenile sockeye salmon end associeted species in the 

 lakes. Interim optimum or target escapements required for 

 highest production on e sustained-yield basis have been estab- 

 lished for each major system. 



The major task that the manager of a salmon 

 fishery must undertake each year is to set a tar- 

 get escapement of fish to the spawning grounds 

 for each salmon run (stock) under his manage- 

 ment. He must have such a goal as a basis for 

 numerous decisions that control the actual time, 

 place, and method of fishing. 



A correct decision is extremely valuable. The 

 number of sockeye salmon (Oncorhynchus 

 nerka) returning to a single river in Alaska 

 may exceed 20 million in a single year, and each 

 fish caught may be worth as much as $3 after 

 being canned. Sometimes the number of adults 

 returning to a system is much larger than the 

 needed escapement; sometimes it is not large 

 enough. Great year-to-year variability in the 



' The BUthort are listed alphabetically because no one Is considered 

 to be the senior author. Their addresses are: DiCostanio. Ellis, and 

 Hartman, Fishery Biologists, Bureau of Commercial Fisheries Bio- 

 logical Laboratory, Auke Bay, Alaska 99821; Burgner, Kerns, Mathi- 

 sen, and Royce, Fishery Biologists, Fisheries Research Institute, Uni- 

 verslty of Washington. Seattle 98106; and Harry, Fishery Biologist, 

 Bureau of Commercial Fisheries Biological Laboratory, Ann Arbor, 

 Mich. 48108. 



Pabllshed AprU 1969 



size of the run to a given system is common. 



The manager must divide the return between 

 catch and escapement, and he must do so in a 

 way that ensures maximum sustainable yield. 

 He must know the optimum escapement and 

 then he must set a target escapement, having in 

 mind the optimum and any modifications that 

 may be indicated by the expected characteris- 

 tics of the returning run and the expected con- 

 ditions within the spawning and nursery areas. 

 He will tend to set an escapement slightly higher 

 than the optimum because his control of the 

 fishery is not precise, and he is aware that the 

 cost of slight underfishing is probably less than 

 the cost of slight overfishing. In this way he 

 attempts to make full use of the spawning and 

 nursery areas. 



The optimum escapement is usually consid- 

 ered to be the number of adults that will yield 

 the greatest surplus of expected return over 

 needed escapement. The optimum escapement is 

 determined from the historical relation between 



FISHERY BULLETIN: VOL. 67, NO. 2 



405 



