UTTER ET AL.: STOCK COMPOSITION OF 1983 CHINOOK SALMON 



and brights contribute to oceanic fisheries (Pacific 

 Fishery Management Council 1981^) the persisting 

 prime condition of brights makes them highly 

 favored in river fisheries. 



An ideal program for harvest management of 

 Chinook salmon would include the capability of iden- 

 tifying the abundance and distribution of distinct 

 breeding groups (such as component stocks of the 

 tule and bright runs of the Columbia River) in a par- 

 ticular fishery. This capability would permit adjust- 

 ments of regulations to permit both protection of 

 weaker stocks and more optimal harvest of abun- 

 dant stocks, depending on their proportions in a 

 fishery. Current information based primarily on data 

 from coded wire tags provides a broad and general 

 overview of hatchery stocks, but lacks details to im- 

 pose differential harvest regulations adequately and 

 does not yield information on wild populations. In 

 addition, a sufficient number of tags must accum- 

 ulate in the fishery or in terminal areas before any 

 quantitative interpretation can be made concerning 

 stock distribution. This requirement coupled with 

 the lag time between field collection and tag de- 

 coding has precluded in-season regulatory adjust- 

 ments based on relative stock strengths. 



The ability to estimate component stocks in stock 

 mixtures based on genetic profiles of contributing 

 groups has recently been developed and applied 

 (Grant et al. 1980; Fournier et al. 1984; Beacham 

 et al. 1985; Pella and Milner 1987). Numerous esti- 

 mates of stock mixtures of chinook salmon have 

 been made using a genetic stock identification (GSI) 

 procedure described by Milner et al. (1983). These 

 applications (Miller et al. 1983; Milner et al. 1985) 

 have substantially increased the ability to manage 

 stock mixtures of chinook salmon. 



The genetic procedures provide estimates of stock 

 composition with greater detail and precision than 

 has previously been possible when the following two 

 conditions are met. First, known genetic differences 

 (presently identifiable by electrophoretic methods, 

 among other techniques) must exist among popula- 

 tions contributing to a particular stock mixture. Sec- 

 ond, a data base of calculated genotypic frequencies 

 (based on a sufficient number of genetic systems) 

 must be developed for those populations that are 

 likely to compose a fishery. 



The GSI procedure obtains maximum likelihood 

 estimates of stock composition using the genotypic 



'Pacific Fishery Management Council. 1981. Proposed plan 

 for managing the 1981 salmon fisheries off the coast of Califor- 

 nia, Oregon, and Washington. Pacific Fishery Management Coun- 

 cil, 526 S.W. Mill St., Portland, OR 97201. 



frequencies of the data base and of the stock mix- 

 ture. The GSI analysis of the May 1982 troll fish- 

 ery off the Washington coast using a data base for 

 California through British Columbia provided the 

 most detailed analysis of an oceanic salmon fishery 

 to date (Miller et al. 1983). 



This paper follows a general description of the GSI 

 and its application to stock mixtures of salmonids 

 provided in Milner et al. (1985). Estimates of stock 

 composition were obtained from samples collected 

 from fisheries off the Washington coast during the 

 spring and summer of 1983. A particular focus was 

 given to the fall runs of the Columbia River because 

 of the major contributions these runs have histori- 

 cally made to oceanic fisheries. This information is 

 intended to provide managers and biologists with 

 better insights into the life histories of chinook salm- 

 on populations in this area of intermingling, and to 

 initiate a continuing record of this species' oceanic 

 distribution and relative abundance. 



MATERIALS AND METHODS 



The procedures used in this study are outlined 

 below. Many of the details required for specific ap- 

 plication are necessarily omitted, but are available 

 in the referenced sources. 



Baseline Populations 



Data were obtained from 88 collections taken from 

 British Columbia through California and repre- 

 sented distinct breeding units in most cases (Table 

 1). Intact juveniles or samples of tissues (eye and 

 liver were the tissues of interest in the present 

 study) from adult fish were taken in the field and 

 transported frozen (usually on dry ice) to the labora- 

 tory for further processing prior to electrophoresis. 



Methods used for detection of electrophotetic vari- 

 ants followed procedures outlined in Utter et al. 

 (1974) and May et al. (1979). The three buffer sys- 

 tems used included: 



1) A Tris-boric acid-EDTA gel and tray buffer, 

 pH 8.5 (Markert and Faulhaber 1965). 



2) An amine citric acid gel and tray buffer, pH 

 6.5 (Clayton and Tretiak 1972). 



3) A Tris-citric acid-lithium hydroxide-boric acid 

 gel buffer, and a lithium hydroxide-boric acid tray 

 buffer, pH 8.5 (Ridgway et al. 1970). 



A system of nomenclature for locus and allelic 

 designations followed Allendorf and Utter (1979). 



15 



