Abstract
The group definition for an animal population is important for building associations among individuals (i.e., social network). Indo-Pacific bottlenose dolphins (Tursiops aduncus) have a society with high fission–fusion dynamics that changes their group memberships over time, making it difficult to define groups clearly. In addition, current group definitions of small delphinid species are mainly related to boat-based or land-based surveys, and few definitions exist for underwater surveys. We propose a group definition for underwater observations after comparing 234 group transitions from 44 surveys of simultaneous boat-based and underwater observations targeting the resident Indo-Pacific bottlenose dolphins around Mikura Island, Japan. Our results highly matched group transitions between boat-based and underwater observations when all video-recorded dolphins during one encounter (from entering to exiting the water) were defined as a group, and groups with at least one shared individual during one survey were treated as the same group. This definition successfully produced highly similar association indices to boat observation. This is useful for underwater surveys of highly maneuverable delphinids, especially for commercial-tour-based studies in which researchers do not have the full decision-making authority for the observations.
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Data availability
The datasets generated and/or analyzed during the current study are available from the corresponding author upon reasonable request.
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Acknowledgements
We are grateful to the dolphin-watching tour captains and guides, volunteers, and members of the identification research for Mikura dolphins (MBK and MIDO). Mikura-jima Iruka Kyoukai, Mikura Island Tourist Information Center, and the Mikurashima Tourism Association provided logistical support. We thank the people of Mikura Island for their kind support during our stay there. We also thank Mai Sakai (Kindai University) and Taiga Yodo (Mie University) for their comments and advice on this study, and Yuria Kasanuki for helping us collect and sort the data from 2000. We would also thank three reviewers for their insightful and helpful comments on this manuscript. This work was partially supported by JSPS KAKENHI Grant Number 18K05782 for the TM.
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This study was conducted in accordance with voluntary regulatory rules for sustainable dolphin swimming programs developed by program operators on Mikura Island. Mikurashima Village granted permission to enter the protected sea area around Mikura Island. The Mikurashima Tourism Association approved all the research protocols for underwater observations. To minimize disturbance, we followed a noninvasive approach for observation in accordance with the Guidelines to Study Wild Animals of the Wildlife Research Center of Kyoto University. In most cases, the dolphins did not exhibit unusual behavior during our observations. We did not use scuba tanks, never attempted to touch the dolphins, and never fed them.
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Morisaka, T., Furuichi, T., Kogi, K. et al. Group definition for underwater observation of wild Indo-Pacific bottlenose dolphins. J Ethol 41, 141–151 (2023). https://doi.org/10.1007/s10164-023-00780-7
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DOI: https://doi.org/10.1007/s10164-023-00780-7