Mississippi River-floodplain connectivity level mediates fish assemblage dynamics

The life histories of many Louisiana fishes are tied to the timing, magnitude, and duration of the Mississippi River flood pulse. Anthropogenic modifications designed to control and restrict flood waters have decoupled Louisiana’s floodplains from the seasonal flood pulse, influencing the aquatic food web. Culvert and rock weir repair within the Richard K. Yancey Wildlife Management Area aims to improve water quality and maintain appropriate water depth for native Louisiana fishes. In this study we conducted high-resolution imaging sonar (ARIS Explorer 3000) monitoring of the floodplain fish assemblage across seasons prior to hydrologic restoration. Imaging sonars may be used to obtain quantitative ecological and behavioral information without the selectivity biases of traditional techniques through the recording of continuous video-like datasets that are not constrained by environmental factors such as turbidity. Our first objective was to test the hypothesis that seasonal inundation levels and proximity to the Mississippi River affect the abundance and size class distribution of the floodplain-associated fish assemblage. Our second objective was to characterize species composition and ecological function of each acoustically-detected size class using historical fisheries datasets collected by the Louisiana Department of Wildlife and Fisheries. To do so, we employed the multi-gear mean standardization technique for standardizing catch per unit effort of passive and active gear types used within the historical dataset in order to produce a non-exhaustive list of potentially recorded species by the imaging sonar. Our study demonstrated a size class dependent use of floodplain habitats mediated by inundation level, but not the distance from the Mississippi River. Our results illustrated a trend of increased detections of all size classes during high-water connected-spring and summer periods, as well as during disconnected-summer periods immediately following the seasonal flood pulse. Continued monitoring of the fish assemblage will provide additional data to better describe the complex dynamic patterns the floodplain fish assemblage may exhibit in response to the seasonal flood pulse and hydrologic restoration efforts.