Spotting gar using imaging sonar: The effects of river–floodplain habitat connectivity on a lepisosteid assemblage

Objective: Anthropogenic modifications, such as levee construction and other flood control structures, have decoupled Louisiana’s floodplains from the seasonal flood pulse, influencing aquatic food web dynamics. Many of Louisiana’s fish species rely on timing, magnitude, and duration of the Mississippi River flood pulse to trigger key aspects of their life histories. At the Richard K. Yancey Wildlife Management Area, 283 ha of Mississippi River floodplain are undergoing weir and culvert repair to retain water depth and improve water quality for native Louisiana fishes, with particular focus on large nongame species, such as gars (Lepisosteidae). Methods: Beginning in summer 2021, we conducted high-resolution imaging sonar monitoring of gar abundance, size-class distribution, and habitat use across seasons at four sites through a latitudinal gradient of decreasing hydrologic connectivity. We tested the hypothesis that the degree of river–floodplain connectivity, mediated by seasonal inundation levels and proximity to the Mississippi River, affects the abundance and size-class distribution of gar in the floodplain. Results: Our study demonstrated size-class-dependent use of floodplain habitats that was mediated by inundation level but not by the distance from the Mississippi River. Our results suggest that remaining pools of water, when disconnected from the main-stem river, are likely to provide both nursery and refuge habitats to floodplain-associated gar. Conclusions: Continued monitoring efforts will provide additional data to better describe the complex interactions between floodplain-associated fishes and habitat use in relation to inundation level and hydrologic restoration efforts.