Abstract
The extraordinary productivity of fish and invertebrates on the floodplains of tropical rivers has been well documented, and large predatory fishes are known to take advantage of prey moving into river channels during falling-water periods. To quantify relationships between river flow and the abundance and body condition (weight relative to length) of a representative predator, electrofishing sampling for common snook Centropomus undecimalis was conducted in the Peace River, Florida, USA, during 2005 and 2007-2013. In years with at least average flows or higher, snook abundance increased up to 3-fold and body condition increased 1.2-fold from summer (high-water) to fall (falling-water). Snook consumed large numbers of fish species whose life histories are tied to inundated floodplains. During a year of severe drought, when floodplain inundation was minor, snook diet was comprised primarily of one small-bodied species, and snook abundance and body condition did not increase between sampling periods. Over the 8 yr record, mean annual abundance and body condition of snook were positively related to mean annual river flow (R-2 = 0.88) and the number of days that river level exceeded a specific threshold (R-2 = 0.70), respectively. A portion of the snook population moves from the estuary into rivers to take advantage of abundant food resources derived from riverine habitats. These results demonstrate a connection between riverine prey production and the body condition and movement patterns of a euryhaline predator and highlight a pathway for energy transfer from freshwater floodplains to estuarine and marine habitats.