Life history and possible genetic origins of rainbow trout from Packwood Lake, Washington

Abstract

Life history and electrophoretic data were collected for an iso1ated, lacustrine popu1ation of rainbow trout from Packwood Lake, Washington. Spawning activity peaked in the lake outlet in late May and tributaries in mid-June. Eighty-four percent of the spawners were age IV or V. Females represented 63 percent of the total run. Only one of the 16 enzyme loci examined in Packwood Lake rainbow trout was polymorphic, LDH-4. Genetic comparisons indicated that Packwood rainbow are more similar to "inland" steelhead (rainbow) stocks than they were to "coastal" steelhead (rainbow) stocks. This unanticipated finding was hypothesized as evidence that colonization of Packwood Lake by an "inland" form of rainbow trout took place shortly after the last Pleistocene ice retreat. Further, that isolation from invading "coastal" stocks occurred due to subsequent geologic events. It is suggested· that Packwood rainbow are unique and that their genetic integrity be preserved for future reference and study.