Risso's dolphins alter daily resting pattern in response to whale watching at the Azores

Authors

  • Fleur Visser,

    1. Institute for Biodiversity and Ecosystem Dynamics,
      University of Amsterdam,
      Nieuwe Achtergracht 127,
      1018 WS Amsterdam, The Netherlands
      and
      Nova Atlantis Foundation,
      Rua dr. A. Freitas Pimentel 11,
      9930-309, Santa Cruz das Ribeiras,
      Pico, Azores, Portugal
      E-mail: f.visser@uva.nl
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  • Karin L. Hartman,

    1. Nova Atlantis Foundation,
      Rua dr. A. Freitas Pimentel 11,
      9930-309, Santa Cruz das Ribeiras,
      Pico, Azores, Portugal
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  • Ente J. J. Rood,

    1. Nova Atlantis Foundation,
      Rua dr. A. Freitas Pimentel 11,
      9930-309, Santa Cruz das Ribeiras,
      Pico, Azores, Portugal
      and
      Zoological Museum,
      University of Amsterdam,
      Mauritskade 61,
      1092 AD Amsterdam, The Netherlands
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  • Arthur J. E. Hendriks,

    1. Nova Atlantis Foundation,
      Rua dr. A. Freitas Pimentel 11,
      9930-309, Santa Cruz das Ribeiras,
      Pico, Azores, Portugal
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  • Daan B. Zult,

    1. Department of Psychology,
      University of Amsterdam,
      Nieuwe Achtergracht 127,
      1018 WS Amsterdam, The Netherlands
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  • Wim J. Wolff,

    1. Department of Marine Benthic Ecology and Evolution,
      Groningen University,
      P. O. Box 14, 9750 AA Haren, The Netherlands
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  • Jef Huisman,

    1. Institute for Biodiversity and Ecosystem Dynamics,
      University of Amsterdam,
      Nieuwe Achtergracht 127,
      1018 WS Amsterdam, The Netherlands
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  • Graham J. Pierce

    1. Oceanlab,
      University of Aberdeen,
      Main Street,
      Newburgh, Aberdeenshire, AB41 6AA, United Kingdom
      and
      Instituto Español de Oceanografía,
      Centro Oceanográfico de Vigo,
      P. O. Box 1552, 36200 Vigo, Spain
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Abstract

Behavioral responses of Risso's dolphins (Grampus griseus) to whale watching vessels were studied off Pico Island, Azores. Dolphin behavior was studied from a land-based lookout, enabling observations of groups in the absence and presence of vessels. The number of whale watching vessels showed a clear seasonal pattern, dividing the whale watching period into a low season and a high season. During the low season, Risso's dolphins rested mainly in the morning and afternoon. During the high season, Risso's dolphins rested less and did so mainly at noon, when the number of active vessels was lowest. Data analysis using a generalized additive mixed model indicated that this change in resting behavior was associated with vessel abundance. When more than five vessels were present, Risso's dolphins spent significantly less time resting and socializing. During the high season, this vessel abundance was exceeded during 20% of observation days. While we cannot be sure that the observed changes in behavior have fitness consequences for Risso's dolphins, reduced resting and socializing rates can have negative impacts on the build-up of energy reserves and on reproductive success. We suggest the adoption of precautionary management measures to regulate the timing and intensity of whale watching activities.

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