Density-habitat relationships of mangrove creek fishes within the southeastern saline Everglades (USA), with reference to managed freshwater releases

The Comprehensive Everglades Restoration Plan aims to make considerable changes to the quantity, quality, and timing of freshwater delivery to the southeastern saline Everglades (SESE), a mangrove ecosystem located between the freshwater Everglades and downstream estuarine embayments. Whereas fishes inhabiting seasonally-inundated areas of the SESE and the shorelines of downstream embayments have been examined, those utilizing the creeks connecting these ecotones have not. To evaluate the functional role of the creek habitat and the possible impact of future hydrologic changes on the fishes inhabiting them, 228 underwater visual surveys were performed at three locations of the SESE over a three-year period. Fish abundance data was related to structural habitat, water level, and salinity over various time periods. The SESE contains taxa from both the freshwater Everglades and downstream embayments, but does not appear to function as a nursery for most fishery taxa. Abiotic variability and fish diversity increased with distance from major freshwater sources. Though there were significant differences in the physical structure of mangrove trees among locations, few meaningful correlations between these parameters and the density of individual fish taxa were found. Small prey-base fishes (<10 cm TL) utilize the expansive ephemeral wetlands (i.e., upper mangle) during wet periods, and were concentrated into deeper creeks when these wetlands became dry. Densities of these fishes increase on the upper mangle with increased flooding (hydroperiod), and we observed greater densities of larger species in the creeks when hydroperiods exceeded 240 days. Based on these results, we recommend that water management create water releases which result in a wet period of ca. 240 days, followed by a gradual dry period lasting ca. 90 days.