Abstract
Very little is known about the ecology of common bottlenose dolphins (Tursiops truncatus) living in oceanic waters. This study investigated the ranging and residence patterns of bottlenose dolphins occurring in the Azores (Portugal), the most isolated archipelago in the North Atlantic. Data were collected during standardized boat-based surveys conducted over a 6-year period in an area of approximately 5,400 km2 (main study area). To investigate the extent of movements of individual animals, non-systematic surveys were also conducted outside this area. Only 44 individuals out of 966 identified were frequently sighted within and between years. The remaining individuals were either temporary migrants from within or outside the archipelago, or transients. Resident dolphins showed strong geographic fidelity to the area. Long-distance movements (of almost 300 km), consistent with foraging or exploratory trips, were observed among non-resident dolphins. Home range size was estimated for 31 individuals sighted ≥10 times. Range areas of these dolphins varied in size and location, but considerable overlap was observed in the areas used, suggesting the absence of habitat partitioning between resident and non-resident dolphins. Estimates of home range size of bottlenose dolphins in the Azores were found to be considerably larger than those previously reported for this species. It is hypothesized that dolphins living in the Azores carry out extensive movements and have large home ranges in response to the lower density and patchy distribution of prey compared to other areas. The extensive ranging behaviour and the lack of territoriality provide an opportunity for interbreeding between dolphins associated with different islands, thus preventing genetic differentiation within the population of the Azores.
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Acknowledgments
This research was funded by the Portuguese Science and Technology Foundation (FCT), under the CETAMARH project (POCTI/BSE/38991/01), by an EU-LIFE program (B4-3200/98/509), and by an Interreg program (Interreg IIIBMAC/4.2/A2). We are also grateful to FCT for funding M. A. S. doctoral grant (SFRH/BD/8609/2002) and post-doctoral grants (SFRH/BPD/29841/2006), and S. M. M. and M. I. S. research grants through the CETAMARH project. We are thankful to the skippers (Filipe Goulart, P. Martins, V. Rosa, R. Bettencourt and N. Serpa), crew members, students and volunteers that helped us throughout this study. We also thank David Lusseau and three anonymous reviewers for their comments on an early draft of the manuscript. IMAR-DOP/UAç is the R&D Unit #531 funded through the pluri-annual and programmatic funding schemes of FCT-MCTES and DRCT-Azores. This research was conducted under license of the Environment Directorate of the Regional Government of the Azores.
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Silva, M.A., Prieto, R., Magalhães, S. et al. Ranging patterns of bottlenose dolphins living in oceanic waters: implications for population structure. Mar Biol 156, 179–192 (2008). https://doi.org/10.1007/s00227-008-1075-z
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DOI: https://doi.org/10.1007/s00227-008-1075-z