Introduced Flathead Catfish Consumptive Demand on Native Fishes of the Upper Gila River, New Mexico

Predation by nonnative fish is often cited as a leading cause of declining native fish populations, but quantifying these negative interactions is difficult. Bioenergetics modeling provides a tool to estimate consumptive demand of nonnative species and to identify those that pose the greatest threats to native biota. We used bioenergetics modeling to estimate the consumptive demand of Flathead Catfish Pylodictis olivaris on native fishes in the upper Gila River, New Mexico, across an elevational gradient. Model results were coupled with measured densities and size structure of Flathead Catfish populations, as well as water temperatures, to predict its predatory threat. Potential consumption was highest at lower elevation sites because of higher water temperatures, but actual consumption was highest at mid-elevation sites because of the prevalence of larger individuals there. Potential annual consumptive demand of Flathead Catfish on native fish across our nine sampling sites ranged from 0.0 to 3.1 g/m(2), which exceeded native fish productivity at one site. Our results identify areas within the upper Gila River where introduced Flathead Catfish consumption is likely to negatively impact native fish populations.