Survival and Propensity for Homing as Affected by Presence or Absence of Locally Adapted Paternal Genes in Two Transplanted Populations of Pink Salmon (Oncorhynchus gorbuscha)

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Abstract
An experiment was carried out on pink salmon (O. gorbuscha) at the Tsolum River, Comox Bay, British Columbia [Canada] comparing an introduced pure donor stock with a hybrid stock created by crossing females from the donor with males of the local residual stock. Progeny of both treatments were raised in gravel incubators and released as unfed fry. On return from the ocean, marked fish were recaptured from catch and escapement. At the fry stage times of emergence differed, but mean fry lengths, weights and stages of development were the same in both treatments. Survivals from fry to returning (coastal) adult were identical and comparable to that of other years, as was timing of adult migrations. Large differences occurred in returns to the river. At the hatchery stream the expected relative rate of return of the hybrid was p = 0.53, observed .cxa.p = 0.91. Returns to the river below the hatchery stream also favored the local genotype, but less strongly. Imprinting alone brought back some pure donor stock; addition of the local male genetic complement improved the return to the natal river system to a normal level; and the male complement alone was not sufficient to achieve normal accuracy of return to the natal tributary within the system. Hybrid transplants may hold considerable potential for salmon rehabilitation and enhancement, but genetic and managerial implications should be carefully evaluated. Possibilities exist of seriously affecting fitness and abundance of other stocks and ecosystems.

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