Past and Present Spatial Structure of "O. nerka" Populations in Five Sawtooth Valley Lakes: Migration Barriers and the Persistence of Sockeye and Kokanee Salmon in Redfish Lake and Beyond

Sockeye and kokanee salmon (O. nerka) were historically abundant in the Sawtooth Valley lakes in Central Idaho, USA. The decline of anadromous sockeye salmon in Redfish Lake is well-documented and the population has been the focus of restoration since 1991, following its listing as endangered under the Endangered Species Act. However, at least four other lakes supported anadromous and non-anadromous O. nerka in the Sawtooth Lake system. Relying on records from 19^th century expeditions, mid 20^th century studies and existing genetic data, we review the history of those lakes including the extirpation, or in some cases persistence, of O. nerka populations. Our work suggests that the extirpation of O. nerka in some lakes and the resulting reduction in spatial structure among the O. nerka populations in the Sawtooth Valley lakes overall can be explained by the following mechanisms: past and current fisheries management activities, harvest, local migration barriers and mainstem habitat issues. We will also present evidence of variation in size and growth of O. nerka that currently occupy three lakes in the Sawtooth Valley. The historic and current data demonstrate that in order to restore populations of O. nerka that are local adapted and resilient, we must restore the spatial complexity of Sawtooth Valley sockeye salmon.