REISENBICHLER and PHELPS: GENETIC VARIATION IN CHINOOK AND COHO SALMON 



stocks unless strong evidence exists to the con- 

 trary. 



Our data suggested that summer chinook 

 salmon were distinct from fall chinook salmon 

 (P = 0.06, Table 5). Electrophoretic differences 

 between distinct runs or life history types of chi- 

 nook salmon were also found within the Nanaimo 

 River system (Carl and Healey 1984) and within 

 the Columbia River system (Kristiansson and 

 Mclntyre 1976). Summer-run fish from different 

 streams along the north coast were not suffi- 

 ciently similar to form a cluster separate from the 

 fall-run fish (Figs. 4, 5), and the differences 

 among populations of summer-run fish may be as 

 great as the differences between summer- and 

 fall-run fish. Unfortunately the small number of 

 populations precluded rigorous comparison of 

 these differences. 



The (significant) variation in allele frequencies 

 between year classes of juvenile chinook salmon 

 may have been exaggerated by variation between 

 years in the proportion of fish from the three dif- 

 ferent runs. This possibility illustrates the need 

 for sampling adult chinook salmon (only adults 

 can be distinguished according to run) in river 

 systems where juveniles from different runs occur 

 together. Of course, the utility of sampling adults 

 to genetically describe wild populations is com- 

 promised if adult hatchery and wild fish occur 

 together and cannot be reliably separated. 



The gene diversity analysis for coho salmon 

 showed that diversity within drainages was eight 

 to nine times the diversity among broods, with or 

 without Pnp-1 included in the analysis, and sug- 

 gested that separate breeding units exist within 

 drainages as well as between drainages. Separate 

 breeding units within drainages were also sug- 

 gested by the likelihood ratio analysis. 



Hatchery Fish Versus Wild Fish 



Analysis of variance for hatchery and wild chi- 

 nook salmon, and the cluster analyses for both 

 chinook and coho salmon showed that the hatch- 

 ery populations of the north coast were geneti- 

 cally distinct from the populations of wild fish. 

 Indeed, coho salmon from Snow Creek or from the 

 Snohomish River were more similar to wild coho 

 salmon from the north coast than were coho 

 salmon from Quinault National Fish Hatchery 

 (Fig. 7). 



The differences between hatchery and wild fish 

 were to be expected because the hatchery popula- 

 tions were developed with fish from locations in 



addition to the local stream or exclusive of the 

 local stream. Among chinook salmon, fall-run 

 fish at Soleduck Hatchery were the most similar 

 to wild fish (Fig. 5), probably because the Sole- 

 duck Hatchery population was the only hatchery 

 population developed primarily with local fish 

 (Houston fn. 3). Fall coho salmon at Soleduck 

 Hatchery were also primarily developed with 

 local fish but were not included in the analysis 

 because of missing data. We would expect these 

 coho salmon to be more similar to wild fish than 

 were the coho salmon from Quinault National 

 Fish Hatchery — and that expectation held for al- 

 lele frequencies at Ada-2 and Ldh-4 , and was not 

 countered by evidence from any other loci (App. 

 Table A2). 



It is reasonable to assume that interbreeding 

 with fall chinook salmon (or fall coho salmon) 

 from Soleduck Hatchery will cause less reduction 

 of fitness and less genetic change for wild fish 

 than will interbreeding with the other (less simi- 

 lar) hatchery fish (Helle 1981; Reisenbichler 

 1984). The observed differences between fall chi- 

 nook salmon at Soleduck Hatchery and wild fish 

 probably exist because few wild fish are included 

 in the hatchery brood stock. Data for steelhead, 

 Salmo gairdneri, (Reisenbichler and Phelps 

 1985^) illustrate that the continued use of wild 

 fish in the hatchery brood stock and avoidance of 

 selective breeding are necessary to maintain a 

 hatchery population that is genetically similar to 

 wild fish. Where hatchery populations can be 

 managed separately from wild populations and 

 where few hatchery fish stray onto natural 

 spawning areas, perhaps there is little reason to 

 ensure that hatchery fish are genetically similar 

 to wild fish. However, where substantial numbers 

 of hatchery fish successfully spawn in streams 

 and where genetic resources are to be conserved, 

 hatchery fish should be as genetically similar as 

 possible to the wild fish (e.g., Helle 1981). 



ACKNOWLEDGMENTS 



We are grateful to the many persons who pro- 

 vided advice, information, samples, or other assis- 

 tance. The efforts of Scott Corley and Kurt Nelson 

 are especially appreciated. Dave Agee, Susan 

 Glenn, Denny Offutt, and Dave Teel assisted with 

 portions of the electrophoretic analysis. Carl 



SReisenbichler, R. R., and S. R. Phelps. 1985. Genetic 

 structure of steelhead, Salmo gairdneri , from the north coast of 

 Washington State. Unpubl. rep. National Fishery Research 

 Center, Seattle, WA. 



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