Ecology and comparison of coastal and offshore bottlenose dolphins (Tursiops truncatus) in California
Maddalena Bearzi A B , Charles A. Saylan A and Alice Hwang A
+ Author Affiliations
- Author Affiliations
A Ocean Conservation Society, PO Box 12860, Marina del Rey, CA 90295, USA.
B Corresponding author. Email: mbearzi@earthlink.net
Marine and Freshwater Research 60(6) 584-593 https://doi.org/10.1071/MF08279
Submitted: 3 October 2008 Accepted: 28 January 2009 Published: 19 June 2009
Abstract
Populations of coastal and offshore bottlenose dolphins (Tursiops truncatus) are considered to differ ecologically, with implications for their protection and management. We assessed occurrence, distribution and behaviour of coastal and offshore populations of dolphins during a photo-identification study in Santa Monica Bay and nearby areas (1997–2007). Bottlenose dolphins occurred year-round and were encountered on 44.2% of all surveys (n = 425). We photo-identified 647 individuals; of these, 375 (58.0%) were coastal (<1 km from shore), 241 (37.2%) offshore (1–65 km from shore) and 31 were both (4.8%). Dolphins mostly travel (69.0%) and travel-dive (61.5%), with offshore dolphins socialising more (22.6%) than coastal. There were low re-sighting rates for both coastal and offshore dolphins. Low re-sighting rates of coastal individuals provide little evidence of year-round site fidelity, suggesting their range is greater than the study area. Several individuals were re-sighted between and over 1-year periods, often foraging. This suggests that coastal dolphins: (1) are highly mobile within inshore waters, but spend time foraging in the study area, and (2) range >1 km from shore, contrary to what has been previously reported.
Additional keywords: behaviour, conservation, distribution, feeding, habitat, occurrence, photo-identification.
Acknowledgements
The manuscript was improved through reviews by D. Maldini, G. Bearzi and two anonymous referees. The field research was funded by Ocean Conservation Society (1997–2005) and Santa Monica Bay Restoration Commission (2006–2007). Thanks to all the Los Angeles Dolphin Project assistants. Special acknowledgements to ESRI for the ArcGis software, Maptech for the PC Chart Navigator software and IFAW for the Logger software. This study was conducted following guidelines of the American Society of Mammalogists. Fieldwork was conducted following the laws of California and the General Authorisation for Scientific Research issued by the National Oceanic and Atmospheric Administration (files #856–1366 and #8561835, Silver Spring, MD, USA).
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