Assisted colonization of a regionally native predator impacts benthic invertebrates in fishless mountain lakes

The intentional introduction of native cold-water trout into high-elevation fishless lakes has been considered a tool to build resilience to climate change (i.e., assisted colonization); however, ecological impacts on recipient communities are understudied. The purpose of this study was to inform native cold-water trout recovery managers by assessing potential consequences of translocating a regionally native trout (westslope cutthroat trout; Oncorhynchus clarkii lewisi) into fishless mountain lakes. This study compared littoral benthic invertebrate richness, diversity, community structure and abundance between three groups of lakes (fishless, native trout, nonnative trout) in the Canadian Rocky Mountains. While richness and diversity were preserved across all lake groups, other lines of evidence suggested that the introduction of native westslope cutthroat trout into fishless lakes can alter littoral benthic invertebrate communities in similar ways as nonnative brook trout (Salvelinus fontinalis). The community structure of cutthroat trout lakes resembled brook trout lakes compared to that of fishless lakes. For example, both trout-lake groups contained a lower density of free-swimming ameletid mayflies and a higher density of certain burrowing taxa. Risk assessments for trout-recovery actions should consider the potential for collateral damage to recipient invertebrate communities. Future research should identify possible cascading trophic effects on species subsidized by invertebrate prey.

Automated summary

The study compared the impact of introducing westslope cutthroat trout into fishless and nonnative trout lakes on littoral benthic invertebrate communities. The results showed that introducing this native trout species may alter invertebrate communities in a similar way to nonnative trout, highlighting the importance of risk assessments for trout recovery actions. Future research should focus on identifying potential cascading trophic effects on species subsidized by invertebrate prey.