Abstract
Euryhaline predatory fishes use river systems in south Florida, but the degree to which they compete with resident freshwater fish predators is unknown. The objectives of this study were to determine the abundance, distribution, habitat, and diet of a large diadromous euryhaline predator (common snook Centropomus undecimalis) in a southwest Florida river relative to large freshwater predators. Fish were electrofished in the mainstem of the Peace River 2007–2010, and gastric lavage was used to acquire stomach contents. Common snook and resident freshwater predators were found throughout the river. Common snook were most abundant in the lower section of the river, whereas the two dominant freshwater species, Florida gar Lepisosteus platyrhincus and largemouth bass Micropterus salmoides, were most abundant in the upper section. Both euryhaline and freshwater predators had affinities for structure (e.g., snags) and ate similar prey (predominantly crayfish Procambarus spp. and brown hoplo Hoplosternum littorale). Separate niches likely resulted from innate differences in seasonal movement patterns (e.g., spawning locations), habitat preferences (e.g., water depth and flow), and tolerance of environmental conditions (e.g., temperature) that either spatially separated common snook from freshwater predators or reduced competition for resources.