Development and Employment of Environmental DNA Methods for the Detection of Bull Sharks (\u3ci\u3eCarcharhinus leucas\u3c/i\u3e) in a Freshwater and Estuarine Interface in the Mobile-Tensaw Delta and Mobile Bay, Alabama

Species conservation and management is influenced by the quality of monitoring methods employed, especially when targeting elusive, but ecologically significant species, like elasmobranchs. Bull Sharks (Carcharhinus leucas) are highly mobile predators that rely on estuaries and freshwater rivers for maturation, resources, and refuge; their ability to withstand changing environmental conditions may mean they are linking ecosystems through their habitat usage and movements. Rather than setting nets or attaching acoustic monitoring devices, which can be expensive, time-consuming, and invasive, the analysis of environmental DNA (eDNA) for tracing species presence was used to target C. leucasDNA. The present research compared and developed methods to capture and isolate eDNA from northern Gulf of Mexico waters and designed a genetic assay to specifically target C. leucasDNA in concentrations as low as 0.6 copies/μL using Droplet Digital™ PCR. The optimal methods determined were employed for samples collected from Mobile Bay, Alabama and the Mobile-Tensaw Delta during two distinct seasons to determine if C. leucaswas providing linkage between these two regions and if there appeared to be preferential usage of one area over others. Field samples showed strong positive detections for target DNA in the Mobile-Tensaw Delta during the summer season and no strong positive detections during the winter seasons, indicating C. leucasis likely using freshwater habitat in the Mobile-Tensaw Delta when temperatures are favorable, but additional sampling is required to make more robust conclusions about the extent to which C. leucasis serving as a mobile link between these two habitats