Reservoir communities in the intermountain west are typically dominated by a mix of introduced fishes. Due to the non-coevolved interactions present in these communities, energy flow and trophic interactions may not facilitate optimal growth and survival for all species. It is difficult to predict how well each species will survive in such novel communities. One such community is in Jordanelle Reservoir in northern Utah, USA. Recently, low survival and recruitment of stocked rainbow trout (Onchorhynchus mykiss) have been observed in Jordanelle Reservoir.

We characterize the food web structure of the fish community in Jordanelle reservoir to infer competitive or predatory interactions that might lead to a poor return of stocked rainbow trout.

We performed a stable isotope analysis on the fish community in Jordanelle Reservoir and carried out niche space analyses using the software package Stable Isotope Bayesian Ellipse (SIBER) in R.

Small rainbow trout exhibit high competitive overlap with brown trout (Salmo trutta), smallmouth bass (Micropterus dolomieu), and yellow perch (Perca flavescens). In addition, large brown trout and large smallmouth bass may feed heavily on small rainbow trout.

Food web analysis suggests that rainbow trout encounter a highly competitive and potentially high predation environment in Jordanelle reservoir, leading to observed low return rates.