ESTIMATING RED SALMON ESCAPEMENTS BY SAMPLE COUNTS 



FROM OBSERVATION TOWERS 



By Clarence Dale Becker, Fishery Biologist 



Fisheries Researcli Institute, College of Fisheries, 

 University of Washington, Seattle, Wash. 



The Kvichak Eiver system of western Alaska 

 is tlie foremost producer of red or sockeye salmon, 

 Oncorhynchus nerka (Walbaum), for the Bristol 

 Bay commercial fishery. Since 1955, a series of 

 biological investifrations on the red salmon of this 

 system has been conducted by the Fisheries Re- 

 search Institute of the University of Washintrton. 

 A major aspect of the investigation has been to 

 estimate the numbers of adult red salmon which 

 compose the annual spawning escapement. 



The metliod of estimation developed by the 

 Institute involves systematic visual sample counts 

 of tlie transient bands of migrants, taken in the 

 main river after the fish have passed through the 

 fishery and before they have dispersed throughout 

 the spawning grounds. Wlien the numbers of Hsh 

 in the commercial catch are added, the total return 

 can be determined. In addition, when the data 

 are coupled with age analysis of scale samples from 

 botli the catch and the escapement, accurate esti- 

 mates can be made of the number of atlults in each 

 age group returning from a given year of spawn- 

 ing and from a given year of seaward migration. 



It is file pur])ose of this report to: (1) describe 

 in detail tiie counting method, (2) summarize the 

 counts from the years 1955 to 1959, and (3) discuss 

 the factors influencing the estimation. The tech- 

 niques discussed are the results of 5 years of re- 

 search on the Kvichak. 



This method of estimating a salmon escapement 

 from tower counts made from observation towers 

 in Bristol Bay, Alaska, was proposed by W. F. 

 Tliompson in the spring of 1953, and he organized 

 the initial ex[)eriment on tlie Wood River in that 

 same suiinner ( Fisjieries Research Institute, 1955; 

 Tliompson and Clancy, 1959) . The success of this 

 method promptecl repetition the following year. 



Note. — Aiipruveil for puliliciitlon ,Inn, .'JO, 1961. 

 letin 192. 



Fishery Biil- 



with expansion to the Kvichak River system in 

 1955. In 1956 and 1957, tlie Bureau of Commercial 

 Fisheries, U.S. Fish and Wildlife Service, com- 

 pared estimates from tower counts with those from 

 the weirs on the Egegik River and found insignifi- 

 cant differences in total numbers of fish (Bureau of 

 Commercial Fisheries, 1956 and 1957). In 1957, 

 for the first time the escapements to all major red 

 salmon streams in Bristol Bay were assessed from 

 intermittent visual counts made from towers along 

 the river banks. 



Tiie Kvichak River is about 57 miles long, drain- 

 ing from Iliamna Lake and following a twisting 

 course tlirough flat tundra country before flowing 

 into Kvichak Bay (fig. 1). Its lower 43 miles is 

 influenced by tides and the river has a mean depth 

 of about 10 feet. From the head of tidewater, a 

 broad area of numerous shallow channels called 

 the Kaskanak Flats extends upriver 8 miles. From 

 the flats to the outlet of Iliamna Lake, a distance of 

 4 miles, the river is restricted to a deeper channel 

 that contains a few islands and gravel bars. 



The system drains a watei'shed of 7,700 square 

 miles, which includes a profusion of lakes and 

 connecting or tributary streams. Iliamna Lake 

 alone is 77 miles long and from 8 to 20 miles wide. 

 Clark Lake, connected to Iliamna Lake by the 

 Newhalen River, is 52 miles long and from 1 to 

 4 miles wide (U.S. Army Corps of Engineers, 

 1957). Extensive red salmon spawning grounds 

 are distributed in streams, in spring ponds, and 

 on beaches throughout the area. 



As the Kvichak River empties into the ocean it is 

 joined by first the Alagnak and then the Xaknek 

 River. These streams each sustain their own 

 populations of red salmon, which mix as they 

 arrive from ocean feeding grounds and encounter 

 the commercial fishery in the Kvichak-Naknek 

 district. 



355 



