Diet Composition and Overlap in a Mixed Warm- and Coldwater Fish Community

Abstract

ABSTRACT In Twin Lakes, Washington, illegal introductions of largemouth bass (Micropterus salmoides) and golden shiner (Notemigonus crysoleucas) are feared to be impacting economically important rainbow trout (Oncorhynchus mykiss) and brook trout (Salvelinus fontinalis) populations. We evaluated the stomach contents of 69 golden shiner, 146 rainbow trout, 83 brook trout, and 561 largemouth bass during summer stratification in 2004 and 2005, to determine community diet composition and overlap when food resources were partitioned thermally and spatially. Gut content data revealed some diet overlap but also illustrated distinct resource partitioning among all species but not between salmonids. Rainbow and brook trout had similar pelagic based diets of zooplankton and chaoborids, with high estimated diet overlap. Largemouth bass ≥300 mm was piscivorous and consumed principally golden shiner, with some consumption of rainbow and brook trout during late spring and early fall. Largemouth bass ≤299 mm primarily consumed benthic invertebrates in littoral macrophyte beds. Golden shiner diet contained both littoral and pelagic items, consisting of algae, benthic invertebrates, and zooplankton. Preferential differences in temperature, dissolved oxygen, and habitat as well as species size and ontogeny may all contribute to resource partitioning in the Twin Lakes.