Evaluation of Fish and Mussel Assemblages, Hydrologic Characteristics, and Aquatic Habitat in Floodplain Sloughs of the Apalachicola River Before and After Habitat Enhancement

PROBLEM: River floodplains provide critical habitat areas that are used by many fishes as sources of food, cover, and spawning or nursery grounds during periods of inundation. Relatively few studies exist on the biological effects of cyclical changes in water levels associated with controlled releases on regulated streams, and in most of those cases the focus has been on the shoreline habitats and associated main-channel fauna. Even fewer studies have addressed the utilization by fishes of shallow, temporally inundated floodplain habitats of large rivers on the southeastern Coastal Plain. The Apalachicola River, the proposed area of study for this project, supports a diverse fish fauna and major sport fishery. Because the forested floodplain provides important fish habitat, and nursery areas and fish in the floodplain can be isolated by decreasing river levels, examination of habitat utilization during fluctuating hydrological cycles is needed to provide baseline data to assess restoration activities and water allocations in the basin.

OBJECTIVE: The objective of this study is to evaluate fish and mussel assemblages, hydrologic characteristics, and aquatic habitat in floodplain sloughs of the Apalachicola River to assist with excavation plans before habitat enhancement, and to determine if expected benefits were achieved after enhancement. Major tasks that will be accomplished are to: 1) evaluate benefits of enhancement by determining increases in amount of habitat or improvement in type of habitat in floodplain sloughs at different river levels, and 2) evaluate benefits of enhancement to fisheries by comparing seasonal fish utilization of connected and disconnected floodplain sloughs.

APPROACH: As each potential enhancement project reaches high-priority status, USGS staff will field check the survey elevations and excavation amounts proposed on the detailed enhancement plans prepared by the agency responsible for excavation. More than 30 sites, including both major and minor restoration projects, are currently under consideration for enhancement. The location and dimensions of hydrologic controls (i.e., sills, bars, obstructions) and water depths that will influence connectivity throughout the slough system will be determined in associated backwater areas by using either direct measurements (elevation surveys and depth soundings), or observations of connectivity, amount of flow, and direction of flow. Previously collected field data on slough connectivity (Light et al. 1998), will be analyzed if applicable, particularly data from intensive sites in that report. Hydrologic analyses of historic stage and flow records will be conducted to link all estimates of increased or improved habitat to long-term river flows. USGS staff will collect and identify larval and adult fishes, characterize community structure, estimate population abundance, and describe hydrologic conditions and other critical habitat parameters affecting fish utilization of connected and disconnected floodplain habitats. Methods for sampling habitat will involve evaluating basic physicochemical measurements (e.g., dissolved oxygen, pH, temperature), bank and substrate features, vegetation, and other parameters.