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Defining bottlenose dolphin (Tursiops truncatus) stocks based on environmental, physical, and behavioral characteristics

Authors

  • Jacalyn L. Toth,

    1. Marine Field Station,
      Institute of Marine and Coastal Sciences,
      Rutgers University,
      c/o 132 Great Bay Boulevard,
      Tuckerton, New Jersey 08087–2004, U.S.A.
      E-mail: toth@marine.rutgers.edu
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  • Aleta A. Hohn,

    1. NOAA, National Marine Fisheries Service,
      Southeast Fisheries Science Center at the NOAA Beaufort Laboratory,
      101 Pivers Island Road,
      Beaufort, North Carolina 28516, U.S.A.
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  • Kenneth W. Able,

    1. Marine Field Station,
      Institute of Marine and Coastal Sciences,
      Rutgers University,
      c/o 132 Great Bay Boulevard,
      Tuckerton, New Jersey 08087–2004, U.S.A.
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  • Antoinette M. Gorgone

    1. NOAA, National Marine Fisheries Service,
      Southeast Fisheries Science Center at the NOAA Beaufort Laboratory,
      101 Pivers Island Road,
      Beaufort, North Carolina 28516, U.S.A.
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Abstract

The population structure of bottlenose dolphins, Tursiops truncatus, along the U.S. Atlantic coast has recently been redefined from one homogenous population into five coastal stocks. Local studies indicate even finer structure, primarily based on isolation of dolphins inhabiting estuaries. We identified population structuring of non-estuarine coastal bottlenose dolphins during a study in New Jersey, the northern range along the Atlantic Coast. Using photo-identification and distribution survey results, an analysis identified two major clusters of individuals significantly separated by five variables (distance from shoreline, group size, occurrence of the barnacle Xenobalanus globicipitis, avoidance behavior, and individual coloration). Sightings assigned to cluster 1 occurred in nearshore shallow waters (0–1.9 km, = 3.5 m), and those assigned to cluster 2 occurred further offshore in deeper waters (1.9–6 km, = 9.5 m). Only eight of 194 individuals (4%) were identified in both regions. Collectively, this suggests an occurrence of two stocks that are spatially, physically, and behaviorally distinguishable over a small distance. These results indicate that complexity in Tursiops population structure is not limited to latitudinal gradients or barriers created by estuarine habitats, but also by partitioning of habitat as a function of distance from shore and depth over small distances.

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