Feasibility assessment for translocation of imperiled bull trout populations in Glacier National Park, Montana

Abstract

Translocations are becoming an important tool for conservation and recovery of native fishes. However, many translocations have been unsuccessful likely due to inadequate feasibility assessments of abiotic and biotic factors influencing translocation success prior to implementation. This study provides a framework developed to assess the feasibility of translocating threatened bull trout Salvelinus confluentus into novel stream and lake systems in Glacier National Park, Montana (GNP). Populations of bull trout in GNP are at risk of extirpation in several lakes due to the establishment of nonnative invasive lake trout S. namaycush. Drainage-specific translocations of extant bull trout populations have been proposed as a possible management solution to these declines, but the suitability of translocation sites is unknown. This study evaluated the suitability of spawning, rearing, foraging, and overwintering habitats in three isolated headwater stream and lake systems (Logging, Camas, and Lincoln sites) to determine their suitability for bull trout translocation. A scoring framework was developed to compare the suitability of proposed translocation sites based on three major components: potential for the recipient habitat to support a translocation; potential for the translocation to negatively impact native aquatic biota; and ability of within-drainage donor populations to support a translocation. Scoring criteria were developed based on abiotic and biotic characteristics known to influence translocation success, including water temperature, habitat quantity and quality, habitat complexity, species composition, and the possibility of conducting within-drainage translocation. Based on the framework, the Camas site is the most suitable for translocation because it contains physical and biological conditions comparable to other systems supporting bull trout. The Logging site is the second most suitable site for translocation, whereas the Lincoln site is least suitable because it contains a minimal amount of stream habitat (< 300 m) and nonnative brook trout. These results will be used to prioritize and plan potential translocation strategies for imperiled bull trout populations in GNP and provide a framework for evaluating the feasibility of conducting translocations elsewhere.