Abstract
Research strategies for investigating the freshwater-inflow requirements of estuarine fishes often integrate life-history information and correlative analyses of inflow and fish abundance. In tidal rivers, however, some fish have affinities for embayments, oxbows, and smaller tributaries, often referred to collectively as river "back-waters". The objective of this study was to determine whether freshwater and estuarine fish assemblages differed between backwaters and the mainstem of the tidal Caloosahatchee River, a highly managed river system located in an urban setting in southwest Florida. Nonmetric multidimensional scaling of 21.3-m seine data revealed that fish assemblages did indeed differ between the backwater and mainstem habitats in each of three river sections. Univariate analyses identified species that differed in abundance between the habitats, which included ecologically and economically important fishes in the region. For example, striped mullet Mugil cephalus and pinfish Lagodon rhomboides were more abundant along the river's mainstem; common snook Centropomus undecimalis and bluegill Lepomis macrochirus were more abundant in the river's backwaters. For those species that were more abundant along the mainstem of the river or showed no difference, studies that measure changes in the distribution and abundance of these species with varying inflow along the mainstem of the river are justified. However, for species that were more abundant in backwater areas, geomorphological features should be considered in the design of studies that assess factors affecting fish use.