Loss of Exploited, Indigenous Populations of Lake Trout, Salvelinus namaycush, by Stocking of Non-Native Stocks

Abstract

A deterministic, age-structured population model was developed to explore the combined effects of exploitation and stocking of hatchery-reared lake trout on native lake trout populations. Stocking of non-native lake trout at moderate to high exploitation rates caused loss of the recipient population, even when the stocked fish did not reproduce or interbreed with the native fish. If hatchery fish reproduce, their progeny mask the loss of the wild stock. At exploitation and stocking rates typical of lake trout populations in Ontario, the wild stock was replaced by the hatchery stock in a few generations. Native stocks having weak recruitment are least resistant to displacement by hatchery stocks and are also the most likely to be subjected to stocking. Evidence from several field studies in Ontario generally provided support for our stock displacement hypothesis and modelling results. Extensive stocking of a few domesticated hatchery stocks has the potential to reduce genetic heterogeneity through loss of locally adapted stocks of lake trout. We suggest that emphasis should be placed on protecting the genetic integrity of the remaining self-sustaining wild stocks, and that a moratorium be considered on supplementation stocking of these populations, especially with non-native hatchery-reared stocks.