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Decline in local abundance of bottlenose dolphins (Tursiops truncatus) in the Bay of Islands, New Zealand

Authors

  • Gabriela Tezanos-Pinto,

    Corresponding authorCurrent affiliation:
    1. Coastal-Marine Research Group, Institute of Natural and Mathematical Sciences, Massey University, Auckland, New Zealand
    • School of Biological Sciences, The University of Auckland, Auckland, New Zealand
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  • Rochelle Constantine,

    1. School of Biological Sciences, The University of Auckland, Auckland, New Zealand
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  • Lyndon Brooks,

    1. Southern Cross University Whale Research Group, Marine Ecology Research Centre, Southern Cross University, New South Wales, Australia
    Current affiliation:
    1. British Antarctic Survey, Cambridge, England
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  • Jennifer A. Jackson,

    1. School of Biological Sciences, The University of Auckland, Auckland, New Zealand
    2. Hatfield Marine Science Center, Oregon State University, Newport, Oregon, U.S.A
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  • Fabiana Mourão,

    1. School of Biological Sciences, The University of Auckland, Auckland, New Zealand
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  • Sarah Wells,

    1. School of Biological Sciences, The University of Auckland, Auckland, New Zealand
    Current affiliation:
    1. Ecology and Conservation Group, Massey University, Auckland, New Zealand
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  • C. Scott Baker

    1. School of Biological Sciences, The University of Auckland, Auckland, New Zealand
    2. Hatfield Marine Science Center, Oregon State University, Newport, Oregon, U.S.A
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Corresponding author (e-mail: gaby@pachamama.co.nz).

Abstract

Regional populations of bottlenose dolphins (Tursiops truncatus) around New Zealand are genetically isolated from each other and the species was recently classified as nationally endangered based on relatively small population sizes and reports of high calf mortality. Here, we estimate the abundance and trends in one of these regional populations, the Bay of Islands, using a photo-identification database collected from 1997 to 1999 and from 2003 to 2006, containing a total of 3,841 records of 317 individual dolphins. Estimates of abundance obtained with the robust design fluctuated widely but showed a significant decline in the number of dolphins present in the bay over time (7.5% annual rate of decline). Temporary emigration was random and fluctuated considerably (γ  =  0.18, SE = 0.07 to γ  =  0.84, SE = 0.06). Apparent survival was estimated at 0.928 (CI = 0.911–0.942). Seasonal estimates (26 seasons) obtained in POPAN also showed a significant decline in abundance (5.8% annual rate of decline). Despite the decline observed in local abundance, dolphins continue to be found regularly in the Bay of Islands, suggesting that fewer dolphins use the bay on regular basis. Consequently, it seems that a change in habitat use, mortality and possibly low recruitment could underlie the apparent local decline.

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