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

Fleur Visser, Karin L. Hartman, Ente J. J. Rood, Arthur J. E. Hendriks, Daan B. Zult, Wim J. Wolff, Jef Huisman, Graham J. Pierce

Research output: Contribution to journalArticlepeer-review

47 Citations (Scopus)
12 Downloads (Pure)


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.

Original languageEnglish
Pages (from-to)366-381
Number of pages16
JournalMarine Mammal Science
Issue number2
Early online date15 Jul 2010
Publication statusPublished - Apr 2011


  • Risso's dolphin
  • Grampus griseus
  • whale watching
  • Azores
  • behavioral budget
  • land observations
  • resting behavior
  • bottle-nosed dolphins
  • Orcinus-orca
  • sampling methods
  • Tursiops SPP.
  • New-Zealand
  • tour boats
  • behavior
  • disturbance
  • Florida
  • model


Dive into the research topics of 'Risso's dolphins alter daily resting pattern in response to whale watching at the Azores'. Together they form a unique fingerprint.

Cite this