Determining trophic interactions in a complex lake food web using a size-dependent analysis of stable isotopes and stomach contents

Authors: Kevin L. Landom, Todd A. Crowl

Year: 2008 (xl)

Abstract

The product of a series of successful nonnative fish introductions in Utah Lake, UT, is an incredibly complex and specious food web dominated by nonnative fishes. The establishment of nonnative fishes is partially responsible for the eradication of native minnow species, extreme reduction in native sucker populations, and degradation of habitat. Our goal was to construct an empirically-based food web model to determine which species pose the greatest threat to conservation of the Utah Lake aquatic ecosystem. We used stable isotopes in conjunction with seasonal quantification of stomach contents to determine ontogenetic trophic interactions within the complex nonnative food web. We identify three problematic species. White bass, Morone chrysops, are extremely abundant, become piscivorous as young-of-year, and are the primary predation threat to small native fishes. Although stomach contents provided little insight into the feeding relationships of fathead minnow, Pimephales promelas, the Á¤¹⁵N signature places them near the top trophic level, warranting concern regarding their effect on larval fish and egg survival. Common carp, Cyprinus carpio, are a carbon sink within the food web. Young carp grow extremely fast, making them unavailable as prey for most piscivores. Adult carp are relatively long lived and withhold energy from the rest of the food web until death. Our results will be used to assist conservation biologists in evaluating the cost-benefit potential of various management strategies.