Abstract.- We analyzed the pro- 

 tein products of 78 isozyme loci in 37 

 populations of chinook salmon Onco- 

 rhynchus tshawytscha from Califor- 

 nia and Oregon. Allele frequencies at 

 47 polymorphic loci revealed substan- 

 tial genetic variability within the study 

 area. The collections of chinook salm- 

 on studied could be differentiated 

 into five major groups located in the 

 following geographical areas: (1) 

 Smith River- Southern Oregon area, 

 (2) Middle Oregon Rivers. (3) Kla- 

 math-Trinity Basin, (4) Eel River- 

 California Coastal area, and (5) 

 Sacramento-San Joaquin Basin. 

 Average heterozygosity estimates 

 were lowest in collections from the 

 Klamath-Trinity area and highest in 

 the Oregon populations. Gene diver- 

 sity analysis indicated that differ- 

 ences among fish within samples 

 accounted for 89.4% of the total 

 diversity, whereas intersample dif- 

 ferences accounted for 10.6 %. Esti- 

 mates of the average level of histor- 

 ical gene flow between populations 

 ranged from 15.57 migrants per 

 generation in the Sacramento-San 

 Joaquin River system to 3.97 in the 

 Klamath-Trinity Basin; an overall 

 estimate of number of salmon ex- 

 changing genes between populations 

 per generation was 2.11. Although 

 these data appeared to reflect pri- 

 marily population structures existing 

 prior to the 20th century, evidence 

 of some effects of hatchery manage- 

 ment and transplantations was 

 detected. 



Geographic variation in population 

 genetic structure of cFiinool< salmon 

 from California and Oregon 



Graham A.E. Gall 

 Devin Bartley 

 Boyd Bentley 



Department of Animal Science 



University of California. Davis, California 95616 



Jon BrodzJak 



Graduate Group in Applied Matfiematics and Institute of Theoretical Dynamics 

 University of California, Davis. California 95616 



Richard Gomulkiewicz 



Graduate Group in Applied Matfiematics and Institute of Thieoretical Dynamics 



University of California, Davis, California 95616 



Present address: Department of Zoology, University of Texas, Austin, Texas 78712 



Marc Mangel 



Department of Zoology and Center for Population Biology 

 University of California, Davis, California 95616 



Manuscript accepted 13 August 1991. 

 Fishery Bulletin, U.S. 90:77-100 (1992). 



Chinook salmon Oncorhynchus tsha- 

 wytscha is the most abundant and 

 commercially important species of 

 Pacific salmon native to California 

 and Oregon (Moyle 1976), but stocks 

 have dechned (Netboy 1974), in some 

 cases to near extinction. Efforts to 

 manage and preserve the chinook 

 fishery have involved traditional 

 methods such as tag and recapture 

 estimations and restrictive fishing 

 regtilations. Recently, however, pop- 

 ulation genetic analysis of Pacific 

 salmon has emerged as a major tool 

 in fishery management to estimate 

 population subdivision, migration, 

 gene flow, and stock composition of 

 ocean fisheries (Ryman and Utter 

 1987). 



Genetic studies on chinook salmon 

 have refined our understanding of 

 these populations. Examination of 

 large numbers of polymorphic loci 

 revealed geographic associations 

 among populations of chinook salmon 

 (Gharrett et al. 1987, Utter et al. 

 1989, Bartley and Gall 1990, Shaklee 



et al. 1990b). Genetic differences 

 among chinook salmon stocks from 

 different geographic areas are being 

 used to identify the stock composition 

 of mixed ocean salmon fisheries 

 (Pella and Milner 1987, Utter et al. 

 1987, Shaklee et al. 1990b, Brodziak 

 et al. 1992). In addition, genetic 

 studies have indicated the effects of 

 climate and geological events on the 

 population structure of chinook 

 salmon (Gharrett et al. 1987, Bartley 

 and Gall 1990). 



Utter et al. (1989) and Bartley and 

 Gall (1990) recently described Cali- 

 fornia populations of chinook salmon 

 using data sets with 53 isozyme loci 

 for 35 populations, and 25 polymor- 

 phic loci for eight populations, respec- 

 tively. The objectives of the study 

 reported here were to further refine 

 the description of chinook salmon 

 populations in California and south- 

 ern Oregon, expand the baseline 

 genetic data available for genetic 

 stock-identification studies (Shaklee 

 et al. 1990b, Brodziak et al. 1992), 



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