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Circadian and seasonal rhythms in the behavior of spinner dolphins (Stenella longirostris)

Authors

  • Flávio José de Lima Silva,

    1. Departamento de Ciências Biológicas, Universidade do Estado do Rio Grande do Norte, Avenida Antônio de Campos, s/n. CEP: 59600-970, Mossoró, RN, Brazil
      and
      Centro Golfinho Rotador, Caixa Postal 49, CEP: 53990-000 Fernando de Noronha, PE, Brazil
      E-mail: flavio@golfinhorotador.org.br
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  • José Martins Da Silva Jr

    1. Centro Mamíferos Aquáticos/Instituto Chico Mendes de Conservação da Biodiversidade (ICMbio), CEP: 53990-000 Fernando de Noronha, PE, Brazil
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Abstract

The present study investigated both circadian and seasonal fluctuations in the daytime activities of the spinner dolphin, Stenella longirostris, from the Fernando de Noronha Archipelago in Brazil. The number of dolphins, and aerial, and reproductive activities were documented. The observations were carried out from January 1997 to December 2001. Temporal series and rhythmic characteristics (mesor, rhythmic percentage, and acrophase) were obtained by COSINOR analysis and later compared. The dolphins entered the bay in the morning, displayed aerial and reproductive activities during daytime, and left the bay in late afternoon to the open ocean. This study indicated that the rainy season affected the three behaviors investigated decreasing the rhythms parameter and advancing the beginning of these activities. The number of individuals was higher during the dry season and the animals stayed longer inside the bay. During the dry season, there was a bimodal expression of aerial activity, expressing a longer use of the temporal niche than in the rainy season. The phases with high frequencies of aerial activity seemed associated with those showing high reproductive activity, both with peak frequencies at about 0800. The results represent an important contribution to the advancement of chronobiological studies, and to the biology of cetaceans, considering that the existence of circadian and seasonal rhythms was proven in the behavior of spinner dolphins in an area of the SW Atlantic. Moreover, it allows restricting periods of the day for the activities of tourism as a form of minimizing the impacts of the boats on the dolphins.

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