Preliminary Stock Structure of Coastal Bottlenose Dolphins along the Atlantic Coast of the US

Abstract

Recent analyses have identified multiple stocks of bottlenose dolphins along the Atlantic coast from New Jersey to central Florida. Although drawing stock boundaries is confounded by the migratory pattern of the northernmost stock and by the unequal distribution of samples both spatially and temporally, results to date indicate the likelihood of a high level of structuring. In order to estimate abundance, the offshore range of the coastal morphotype of bottlenose dolphin also has been tentatively identified. That range is different north and south of Cape Hatteras; north of Cape Hatteras, evidence suggests that the coastal morphotype generally inhabits a range from the coast to 12km from shore, while south of Cape Hatteras, the range extends to 27km. Using both sets of results (latitudinal and longitudinal), management units can be defined for the purpose of evaluating the potential effects of fisheries mortality: 1. Northern Migratory Unit: In summer, this stock is found primarily from the NC/VA state line to the northern limit of the range (NJ or NY). In winter, this stock migrates out of the northern coastal areas and at least some of the animals are found off the coast of NC, where they spatially overlap with the northern and southern NC units. 2. Northern NC Unit: In summer, this unit consists of dolphins along the coast of NC from Cape Lookout to the VA/NC line and dolphins that reside in northern estuaries in this region. There is some evidence of dolphins moving between estuaries and the coast. There may also be spatial overlap between this unit and the southern NC unit in summer, at least in the estuaries near Cape Lookout. In winter, this unit occurs along the coast or estuaries of NC, where it spatially overlaps with the migratory unit and the southern NC unit. 3. Southern NC Unit: In summer, dolphins in this unit are found primarily along the coast of NC from south of Cape Lookout, NC, to Murrell's Inlet, SC. There may also be spatial overlap between this unit and the northern NC unit in summer, at least in the estuaries near Cape Lookout. In winter, these dolphins are assumed to be in the same areas, where they may spatially overlap with the migratory unit and with the Northern NC unit. 4. South Carolina Management Units: This management unit encompasses dolphins south of Murrell’s Inlet, SC, (the southern NC Unit) and the SC/GA state line. Seasonal movements that might result in spatial overlap between this stock and any others have not been defined. 5. Georgia Management Unit: This management unit encompasses dolphins in coastal and estuarine waters of Georgia. Seasonal movements that might result in spatial overlap between this stock and any others have not been defined. 6. Northern Florida Management Unit: This management unit includes dolphins from the FL/GA state line to the north end of the Indian/Banana River Lagoon system. 7. Central Florida Management Unit: This management unit begins south of the northern management unit and has an undefined southern boundary because of lack of information south of the Indian/Banana River system. However, consistent with results from areas to the north, it is precautionary to assume that this stock does not range as far south as southern Florida.