Quantifying the Potential for Biological Control of An Explosive Prey Base by Predatory Fishes in a Novel Food Web of a High Elevation, Western Reservoir

Artificial species assemblages contribute to novel and complex trophic interactions.  In Scofield Reservoir, Utah, the potential for a population explosion of Utah chub prompted managers to shift the stocking program from exclusively rainbow trout, to include tiger trout and Bear Lake cutthroat trout as biological controls.  However, these latter introductions appear to lead to an overall decline in trout condition, and the structure and stability of the food web is unknown.  We initiated a multi-faceted study consisting of field observations, theoretical comparisons of gape limitation, and bioenergetic simulations, to estimate predator demand versus prey supply.  A substantial proportion of chub outgrow the gape limit of trout predators; chub greater than 247mm in length are not susceptible to predation.  Further, stable isotope and diet analyses demonstrate the potential for competition among and between trophic levels.  Large tiger trout and cutthroat trout occupy top trophic positions indicating considerable piscivory and considerable niche overlap.  Rainbow trout niche space overlaps substantially with Utah chub, indicating a similar trophic niche.  These findings contribute to our understanding of food web dynamics in novel aquatic systems, and will aid managers in optimizing sport fish growth and survival, potential control of Utah chub, and in turn, angler satisfaction.