PHENOTYPIC DIFFERENCES AMONG STOCKS OF HATCHERY AND 

 WILD COHO SALMON, ONCORHYNCHUS KISUTCH, IN OREGON, 



WASHINGTON, AND CALIFORNIA 1 



R. C. Hjort and C. B. Schreck 



ABSTRACT 



Similarities in phenotypic characters (isozyme gene frequencies, life history, and morphology) 

 among 35 stocks of coho salmon, Oncorhynchus kisutch, from Oregon, Washington, and California 

 were compared by using agglomerative and divisive cluster analyses. Coho salmon stocks from 

 similar environments were phenotypically similar. Five groups of stocks were identified by the 

 agglomerative cluster analysis: 1) wild stocks from the northern Oregon coast, 2) wild stocks from 

 the southern Oregon coast, 3) stocks from hatcheries that used wild coho salmon for an egg and 

 sperm source, 4) stocks from large stream systems, and 5) hatchery stocks from the northern Oregon 

 coast. Three trends were indicated by the clustering patterns: 1) stocks that were geographically 

 close tended to be phenotypically similar, 2) stocks from large stream systems were more similar to 

 each other than to stocks from smaller stream systems, independent of geographic proximity, and 

 3) hatchery stocks were more similar to each other than to wild stocks, and wild stocks were more 

 similar to each other than to hatchery stocks. These trends may be useful to fishery managers for 

 selecting donor stocks from hatcheries for transplanting to stream systems or transferring to other 

 hatcheries. Individual phenotypic characters were correlated with characters of the stream sys- 

 tems. Results of two agglomerative cluster analyses, one of certai n characters of the stocks and one of 

 certain characters of the stream systems, demonstrated a lack of correspondence between stream 

 types and stock phenotypes. 



Genetic diversity among stocks of anadromous 

 salmonids (Simon and Larkin 1970) is a biologi- 

 cal characteristic that is more frequently dis- 

 cussed than used in fishery management. The 

 tendency to return to native streams reduces 

 gene flow among salmon populations and en- 

 ables the individual stocks to adapt to the native 

 stream systems. The mixing of stocks highly 

 adapted to their native stream systems with 

 other stocks, or transplanting them to other 

 stream systems, may reduce the rate of return or 

 survival rate of the donor stock (Ritter 1975 3 ; 

 Bams 1976). If the survival rate of a salmon stock 

 is related to its degree of adaptation to its stream 

 system, fishery managers may be able to in- 

 crease survival of hatchery fish by planting them 

 in recipient streams having native stocks geneti- 



'Oregon State University Agricultural Experiment Station 

 Technical Paper Number 5477. 



Oregon Cooperative Fishery Research Unit, Oregon State 

 University, Corvallis, OR 97331. Cooperators are Oregon State 

 University, Oregon Department of Fish and Wildlife, and U.S. 

 Fish and Wildlife Service. 



'Ritter, J. A. 1975. Lower ocean survival ratio for hatch- 

 ery reared Atlantic salmon (Salmo salar) stocks released in 

 rivers other than their native streams. Int. Counc. Explor. 

 Sea, Anadromous and Catadromous Fish Comm., C. M. 1975/ 

 M 26, 10 p. 



cally similar to the planted fish. Higher survival 

 should be especially important during the first 

 several generations, while the transplanted 

 stock is adapting to the recipient environment. 

 An additional advantage of using genetically 

 similar stocks might be a reduction in the intro- 

 gression of divergent hatchery genotypes into 

 wild stocks (Reisenbichler and Mclntyre 1977). 

 Genetic descriptions of salmon stocks could 

 benefit salmon management by assisting fishery 

 managers in selecting hatchery stocks and in 

 protecting wild stocks. Obviously, determination 

 of genetic similarity among stocks is not now pos- 

 sible for the entire genome; however, similarity 

 can be estimated by comparing genetically re- 

 lated characters. Two biochemical characters 

 that vary among stocks of coho salmon, Oncor- 

 hynehus kisutch, are transferrin (Utter et al. 

 1970) and phosphoglucose isomerase (PGI) (May 

 1975), the electrophoretic expressions both of 

 which were established by breeding studies to be 

 genetically determined. Life history and mor- 

 phological characters also vary among salmonid 

 stocks. Time of spawning (Roley 1973) and fre- 

 quency of occurrence of jacks in the population 

 (Feldmann 1974) both have a genetic basis in 



Manuscript accepted August 1981. 



FISHERY BULLETIN: VOL. 80. NO. 1. 1982. 



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