Genetic composition of anadromous fisheries stocks have developed over millennia to match the unique fluctuating conditions of each particular river system. Beginning in the 1930s, salmonid eggs, fry, or fingerlings were often transplanted to the Smith River from other watersheds. This has probably altered the genetic composition of fish to some extent. Because introduced stocks usually have lower survival rates than native stocks, inter-breeding of native and introduced stocks has presumably reduced the attunement of native stocks to their home river system. This may have temporarily or permanently lowered the survival rate of native stocks and perhaps makes their survival less certain (Sedell and Luchessa 1981). Others state that planted stocks did not become permanently established in the Smith River and that remaining stocks are predominantly native (McCain et al. 1995). Besides presumed influences on genetics, hatchery fish can also hurt native stocks by competing for food and cover, spreading disease, and increasing the number of predators.

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