Extirpation for Conservation: Applying Predictors of Extinction Risk to Eradicate Introduced Trout Populations for Lake Restoration

The restoration of mountain lakes affected by non-native fishes requires the removal of the introduced species. While extensive research has illuminated the physical habitats and complex food webs of mountain lake ecosystems, little is known about the self-sustaining fish populations, particularly in our study area, Waterton Lakes National Park (WLNP), Canada. We used generalized linear models to examine four population characteristics associated with the vulnerability of populations to depletion by gillnetting: 1) catch per unit effort (CPUE), 2) proportion of females, 3) proportion of mature individuals and 4) length of mature trout, as a proxy for age at maturity. There were significant differences between populations in CPUE and length of mature trout, but not in the proportion of females or mature individuals. We thus incorporated the former characteristics to rank 11 trout populations by their susceptibility to eradication. Two lakes in the Lineham basin were the best candidates for trout eradication due to their low population density and large size at maturity. The application of demographic characteristics to select introduced populations for eradication is a simple yet meaningful step in restoration commonly constrained by a lack of biological knowledge.