Determining the northern range of the NNCES stock of bottlenose dolphins (Tursiops truncatus) through photo-identification

Abstract

The Roanoke Sound is an important summer habitat for coastal Atlantic bottlenose dolphins, including members of the Northern North Carolina Estuarine System (NNCES) stock. However, our understanding of the northern range of this stock is limited. It has been assumed that the stock occurs northward only as far as the NC/VA border, but there is considerable uncertainty in the location of this boundary. The objective of the present study was to better delineate this boundary by determining the northern range of individual dolphins sighted in Roanoke Sound. I matched individuals with high capture probabilities (n=59) in Roanoke Sound (NC-OBXCDR catalog) with individuals sighted in Norfolk, Virginia (VA-HDR catalog), the Potomac (MD-PCDP) catalog, and Cape May, NJ (NJ-CMWWRC catalog) through the MABDC. Five individuals, all likely females, were matched to VA-HDR, but none were matched to MD-PCP nor to NJ-CMWWRC. Four of the matched individuals were also sighted in the Pamlico Sound. The movements of these dolphins show some degree of seasonality, with sightings in the Roanoke Sound peaking in June but occurring from May to October, and in Virginia only in July and August. The results of my study indicate that the NC/VA border is not the northern boundary of the NNCES stock, but instead that the movement of these dolphins extends into the Chesapeake Bay. Thus, the management of this stock of dolphins should consider the threats, including by-catch, that may occur in this extended range.