Abundance Estimate for and Habitat Use by Early Juvenile Atlantic Sturgeon within the Delaware River Estuary

The Atlantic Sturgeon Acipenser oxyrinchus oxyrinchus historically supported a significant commercial fishery along the eastern coast of North America. However, overfishing led to substantial population declines with contributions from other anthropogenic impacts, including vessel strikes and contaminants that continue to impede recovery. Our work is the first to estimate the abundance of early juvenile (age 0-1), resident Atlantic Sturgeon in the Delaware River estuary. Using the Schumacher and Eschmeyer mark-recapture estimator for multiple censuses, we estimated 3,656 (95% CI = 1,935-33,041) individuals used the Delaware River estuary as a nursery in 2014. We found no significant change in mean length during the course of our study (November-December), and lengths of age 0-1 Atlantic Sturgeon ranged from 220 to 515 mm TL. Further, using a passive acoustic receiver array, we identified significant habitat areas where age-0-1 juveniles spend considerable amounts of time; this included the Marcus Hook area and some habitat use downriver and upriver of Marcus Hook at Cherry Island and the Chester Range. Our results support the idea that a spawning population of Atlantic Sturgeon exists in the Delaware River and that some level of early juvenile recruitment is continuing to persist despite current depressed population levels. Understanding trends in abundance, habitat use, and other population metrics for natal river Atlantic Sturgeon will allow for better conservation and management of the species.