Development of a Stage-Specific Floodplain Inundation Model to Predict Suitable Spawning Habitat Availability for Assessing Alligator Gar Recruitment Success

Alligator Gar historically ranged throughout the Mississippi River Basin and in coastal river basins of the Gulf of Mexico from Florida to Mexico, but have seen a large reduction in populations in many parts of their range.  Hydrologic alteration of river systems in which river-floodplain connectivity has been reduced is thought to be a main contributor to these declines. In order to better conserve this species, it is important that we understand how hydrologic processes influence floodplain connectivity and ultimately recruitment success of Alligator Gar.  Utilizing a HEC-RAS 1-dimensional hydraulic model and LIDAR derived digital elevation models, a high resolution floodplain inundation model was developed for the middle Trinity River, Texas and used to quantify suitable Alligator Gar spawning habitat availability by river stage.  This model was then applied to a hydrologic time series analysis where adult Alligator Gar year class structure was utilized to develop relationships between hydrologic characteristics (flood pulse timing, duration, magnitude, and frequency), spawning habitat availability, and successful recruitment.  This information will be used to inform instream flow recommendations to support this species.