Fish Assemblages in the Oligohaline Stretch of a Southwest Florida River during Periods of Extreme Freshwater Inflow Variation

Maintenance or restoration of the oligohaline stretch (i.e., salinity 0.5-5 psu) of coastal rivers is becoming an increasingly important goal of water managers striving to balance human consumption of water with the ecological integrity of estuaries. The objectives of this study were to compare fish assemblage structure and species abundance of the oligohaline stretch to those of the lower river mouth during periods of varying freshwater inflow (wet and dry periods) in one of southwest Florida's largest rivers, the Peace River. The abundance of several estuarine residents and estuarine transients captured in 21.3-m seinesSand Seatrout Cynoscion arenarius, Tidewater Mojarra Eucinostomus harengulus, Red Drum Sciaenops ocellatus, and Spot Leiostomus xanthuruswere similar between river sections, which is consistent with the premise that the oligohaline stretch is an extension of the juvenile habitat known to be important for fish in lower rivers. Estuarine residents known to have affinities for marsh habitatEastern Mosquitofish Gambusia holbrooki, Rainwater Killifish Lucania parva, and Sailfin Molly Poecilia latipinnawere at least an order of magnitude more abundant in the oligohaline stretch, probably the result of greater production at low salinity, greater marsh area, or less competition. During a dry period, the oligohaline fish assemblage became more similar to the assemblage of the lower river mouth. Reductions in the abundance of species characteristic of the oligohaline stretch were offset by increases in the abundance of Bay Anchovy Anchoa mitchilli. This study provides information to managers that can be used in the restoration of oligohaline waters by identifying characteristic fishes in the oligohaline stretch of a large river, providing insight into how this river section functions as fish habitat, and determining the changes in fish assemblages that occur during low freshwater inflow conditions.