Abstract
Calving can be a critical period for cetaceans. Areas providing security for vulnerable calves, and high food availability for lactating females can be critical habitats requiring specific conservation measures. Here, we test the hypothesis that calving and nursing habitat could be defined for Risso’s dolphins (Grampus griseus). We investigated the spatial and temporal preferences of this species around Pico Island, Azores, using data gathered from land-based surveys and dedicated at-sea observations between 2004 and 2007. We divided observed pods into three groups: (1) those with newborn and young calves, (2) those with older calves or juveniles and (3) those consisting only of adults or sub-adults. We analysed eco-geographical variables and incorporated them into a presence-only spatial distribution model to evaluate differences in habitat suitability among the groups. We identified 694 pods of Risso’s dolphins overall. On the 267 pods observed in the first and second groups, 136 calves or juveniles were identified, of which 22 were newborns. The peak of the calving season was between June and August. The pods with newborn calves were larger and closer to shore, whereas the other groups were more widely dispersed offshore. Our results support the definition of critical habitat areas for this species, but we suggest widening the geographical coverage for better mapping around the island and throughout the archipelago generally. Conservation measures can, nevertheless, be implemented immediately, in order to reduce human impacts on a vulnerable component of the Risso’s dolphin population
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Acknowledgments
We gratefully thank the following NGOs, companies and private persons for their financial support during our studies: The Netherlands : WWF, Greenpeace, Burgers ZOO, Stichting Lucy Burgers, Federation International Nature Conservation, Wing, Liesbeth-Feikema, Taco van der Harst, Fam. van Hooff, Anna Tiepel and Marloes Hartman. We thank Arthur Hendriks and Fleur Visser for their contribution to the setup of the long term research on Risso’s dolphins in Pico. David Janiger provided us with some important literature and several colleagues, students and volunteers helped us collecting and processing data; a special thank you here for Lisa Steiner, Britta Adam and Anja Wittich. Fernando Tempera and the Department of Oceanography and Fisheries at the University of the Azores kindly shared a 50 m resolution grid for the study area. Mark Simmonds and Chris Yesson are particularly acknowledged by their useful comments on earlier versions of this manuscript and for revising the English. This project was carried out under scientific license numbers 4/CN/2004 and 9/CN/2005, issued to the Nova Atlantis Foundation by the Azorean Department of the Environment. This research was partially supported by the European Regional Development Fund (ERDF) through the COMPETE—Operational Competitiveness Programme and national funds through FCT—Foundation for Science and Technology, under the project “PEst-C/MAR/LA0015/2011”. Karin Hartman is supported by the Azores Regional Fund for Science (FRC) Ph.D. Grant M3.1.2/F/014/2009. Marc Fernandez is supported with Grants M3.1.5/F/004/2009 and M3.1.2/F/028/2011.
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Hartman, K.L., Fernandez, M. & Azevedo, J.M.N. Spatial segregation of calving and nursing Risso’s dolphins (Grampus griseus) in the Azores, and its conservation implications. Mar Biol 161, 1419–1428 (2014). https://doi.org/10.1007/s00227-014-2430-x
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DOI: https://doi.org/10.1007/s00227-014-2430-x