ATLANTIC SPOTTED DOLPHIN (Stenella frontalis): Western North Atlantic Stock

There are two species of spotted dolphin in the Western Atlantic — the Atlantic spotted dolphin, Stenella frontalis, formerly S. plagiodon (Perrin et al. 1987), and the pantropical spotted dolphin, S. attenuata. These species are difficult to differentiate at sea. Atlantic spotted dolphins are distributed in tropical and warm temperate waters of the western North Atlantic (Leatherwood et al. 1976). Their distribution is from southern New England, south through the Gulf of Mexico and the Caribbean to Venezuela (Leatherwood et al. 1976; Perrin et al. 1987). The large, heavily spotted form of the Atlantic spotted dolphin along the southeastern and Gulf coasts of the United States inhabits the continental shelf, usually being found inside or near the 200 m isobath (within 250-350 km of the coast) but sometimes coming into very shallow water adjacent to the beach. Off the northeast U.S. coast, spotted dolphins are widely distributed on the continental shelf, along the continental shelf edge, and offshore over the deep ocean south of 40 o N (CeTAP 1982). Atlantic spotted dolphins regularly occur in the inshore waters south of Chesapeake Bay and near the continental shelf edge and continental slope waters north of this region (Payne et al. 1984). Sightings have also been made along the north wall of the Gulf Stream and warm-core ring features (Waring et al. 1992). Stock structure in the western North Atlantic is unknown. POPULATION SIZE The total number of Atlantic spotted dolphins off the eastern U.S. coast is unknown. However, two population sizes are available for select regions from spring and summer 1978-82 and July-September 1995 (Table 1; Figure 1). Because S. frontalis and S. attenuata are difficult to differentiate at sea, the reported abundance estimates are for both species of spotted dolphins. A population size of 6,107 (CV=0.27) was estimated from an aerial survey program conducted fro