MAIN-STEM AND TRIBUTARY SAMPLING OF 

 RED SALMON SCALES FOR POPULATION STUDIES 



by 

 Ted S. Y. Koo and Howard D. Smith 



ABSTRACT 



Comparison of freshwater age composition by scale studies was 

 made on red salmon sannpled at two locations: (1) in the Kvichak River 

 before fish dispersed into the lake system, and (2) on spawning grounds 

 after fish had spawned. Kvichak River samples in 1956 and 1957 had higher 

 percentages of 1 -winter -in-lake fish than did spawning ground samples. 

 The discrepancy was believed to be due to difficulties in obtaining repre- 

 sentative samples and proper weighting from spawning grounds. The 1958 

 samples from both locations were comparable, probably as a mere coinci- 

 dence. 



It is concluded that although spawning ground sannpling is essential 

 to studies of population density, distribution, and subpopulations in a 

 lake system, it is difficult, if not impossible, to obtain and weight the 

 samples so that they are representative of the whole escapennent. The 

 proper place to sample the entire escapement is in a trunk river, such as 

 the Kvichak River in the Kvichak system. 



INTRODUCTION 



Age and size composition of red salmon 

 (Oncorhynchus nerka) runs of Bristol Bay, 

 Alaska may be determined only if both 

 catch and escapement are sannpled, be- 

 cause the commercial gear, restricted 

 by regulation to gill nets of 5 1/2-inch 

 mesh or larger, is highly selective on 

 size, and therefore on age and sex of 

 the fish. In the average runs, the com- 

 mercial gear takes a higher proportion 

 of the larger fish which have spent 3 

 years in the ocean, whereas more of the 

 small fish escape. Catch is usually 

 sampled at a cannery where fish are 

 landed; escapement may be sampled at 

 two places--first in the main river before 



dispersing to the spawning grounds, and 

 second on the spawning grounds after 

 fish have spawned. 



The purpose of this paper is to deter- 

 mine whether or not spawning ground 

 sampling can represent the entire escape- 

 ment. If the objective is to study popula- 

 tion density, time and geographical 

 distribution, and subpopulations, spawn- 

 ing grounds are the place to sample. If 

 it is to study sex ratio, age composition, 

 and other characteristics of the popula- 

 tion as a whole, the logical place to sample 

 is in the trunk river or main stem where 

 the entire escapement ascends within a 

 relatively short period and can be ade- 

 quately sampled. 



iContribution No. 58, College of Fisheries, University of Washington. 



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