Translocation of isolated species into suitable habitats may help to secure vulnerable, geographically limited species. Due to the decline of Wyoming Hornyhead Chub Nocomis biguttatus, conservation actions, such as the translocation of populations within the plausible historical range, are being considered to improve population redundancy and resiliency to disturbance events. Translocation of Wyoming Hornyhead Chub must be rigorously evaluated because a hatchery stock does not exist, so all fish used in translocations will come from the wild population. We present an approach to identify the best available translocation sites prior to translocation efforts taking place. We evaluated fish community composition and habitat conditions at 54 potential translocation sites for Hornyhead Chub within 12 streams of the North Platte River basin of Wyoming. We used two analyses to identify translocation sites that were most similar to currently occupied Hornyhead Chub sites on the Laramie River: hurdle models to predict hypothetical abundance of Hornyhead Chub at translocation sites and nonmetric multidimensional scaling with fish community and habitat conditions. Presence and abundance of Hornyhead Chub were positively related to a lack of nonnative predators and to habitat features characteristic of backwater and velocity refuge habitats (e.g., minimum water velocity and width‐to‐depth ratio). We used a rank scoring system to weight the outcomes of each analysis, and the highest‐ranking translocation sites occurred at a historically occupied locality, the Sweetwater River. Our approach may be appropriate for other at‐risk species with isolated distributions and little historical data.
Nonnative fish can have substantial negative effects on the abundance and distribution of native fishes through predation and competition. Nonnative predators are of particular interest because they represent novel threats to native prey species that are not adapted to their presence. Prey species with limited distributions or population sizes may be particularly vulnerable to the effects of nonnative predators. In the Laramie River, four nonnative predators—Brown Trout Salmo trutta, Rainbow Trout Oncorhynchus mykiss, Brook Trout Salvelinus fontinalis, and Smallmouth Bass Micropterus dolomieu are present along with a state‐imperiled population of Hornyhead Chub Nocomis biguttatus. The abundance of Hornyhead Chub has declined with increasing abundance of nonnative predators, with the probability of occurrence of Hornyhead Chub dropping drastically when Smallmouth Bass were present. All four nonnative species preyed on native cyprinids, but Smallmouth Bass relied most heavily on fish as a prey item. Isotopic niche overlap occurred between Hornyhead Chub and all of the nonnative predator species. Our results demonstrate that nonnative predators have the potential to negatively affect the abundance and distribution of Hornyhead Chub through the mechanisms of predation and competition, and predator identity is important in determining the extent of effects. Smallmouth Bass are a greater concern than nonnative salmonids because of their more piscivorous behavior, and their recent upstream expansion may be limiting the downstream distribution of Hornyhead Chub in the Laramie River.
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