DUML surveys for the stock discrimination of bottlenose dolphins along the Outer Banks of North Carolina 2011-2012

Original provider: Duke University Marine Laboratory Dataset credits: Duke University Marine Laboratory Abstract: Four stocks of bottlenose dolphins (<i>Tursiops truncatus</i>) have been described in the waters of North Carolina: the Northern Migratory (NM); Southern Migratory (SM); Northern NC Estuarine System (NNCES); and Southern NC Estuarine System (SNCES) stocks (Waring et al. 2013). The two migratory stocks occur in coastal shelf waters, but dolphins from the two estuarine stocks also occur in near-shore coastal waters. During summer, dolphins from both the SM and NNCES stocks are vulnerable to by-catch in small-mesh gill nets set in coastal waters, primarily gill nets set for Spanish mackerel very close to shore along the Outer Banks. Little is currently known about the degree of overlap of dolphins from these two stocks along the Outer Banks, which hampers our ability to assess the true impact of these by-catches. In this research project we photographed and collected biopsy samples of bottlenose dolphins from both the SM and NNCES stocks in coastal waters along the Outer Banks during the summer and early autumn of 2011 and 2012. We sampled dolphins from both stocks to determine: (1) their distribution patterns; (2) the degree of overlap between NNCES and SM stocks; and (3) specifically, how far from shore the NNCES animals are found. Almost all of the groups we encountered were from the SM stock; we only encountered four groups of NNCES dolphins during these surveys. In general, estuarine animals were observed in relatively small groups, close to shore, in shallow water and in relatively close proximity to an inlet. Sighting and biopsy locations were significantly closer to shore (p=0.00278 and p=0.00091, respectively) and shallower (p=0.00117) for the NNCES stock than the SM stock. We note, however, that these conclusions should be tempered by the small sample of estuarine animals we observed. Nevertheless, all four sightings of estuarine dolphins occurred within 500-m of shore and in waters less than 4-m deep. The distribution of the two stocks overlapped in waters very close to shore, but we did not observe any estuarine groups beyond 500 m. from shore.<br><br> This work was funded by the North Carolina Sea Grant Bycatch Reduction Marine Mammal Project. This research was conducted under General Authorization Number 16185 from the NMFS held by Dr. Andrew Read, allowing the close approach to bottlenose dolphins for research purposes.<br><br> Reference: <a href="http://www.nmfs.noaa.gov/pr/sars/pdf/ao2012.pdf">Waring G.T., E. Josephson, K. Maze-Foley and P.E. Rosel (eds.) 2013. U.S. Atlantic and Gulf of Mexico Marine Mammal Stock Assessments – 2012.</a> Accessed 28 September 2013.