Salmon Supplementation: Demography, Evolution, and Risk Assessment
Abstract.—Salmon supplementation aims to integrate the wild and hatchery populations by deliberately allowing returning hatchery adults to stray to the natural spawning ground and, in some protocols, by taking adults of natural spawning origin for hatchery broodstock. If the population becomes truly integrated, this puts a different light on concerns about effects of “hatchery” fish on “wild” fish because the result will just be one population with a common gene pool. In this integrated population, the basis for an assessment of the genetic effect would be a comparison of the natural spawning performance of the supplemented population compared to that of an unsupplemented “control.” Actual, experimental supplementation programs have not yet measured the right quantities with the right design to provide an empirical assessment. Theoretical modeling shows that an integrated breeding program still has the potential for domestication selection during the hatchery phase, which can reduce the natural spawning performance of the stock relative to its presupplementation performance. The models predict that, all other things being equal, the erosion of natural spawning performance will increase with the frequency of natural spawning by hatchery spawned fish and the frequency of hatchery spawned fish in the hatchery broodstock. This should put more of a premium on adherence to a definite protocol, and on effective monitoring of actual supplementation experiments in order to quantify the inherent trade-offs between competing adaptations to the life cycle resulting from hatchery spawning versus the life cycle resulting from natural spawning.