Abstract
A number of local populations of finless porpoises (Neophocaena phocaenoides) are widely distributed throughout the warm coastal waters of Asia. The Omura Bay population, consisting of approximately 300 individuals, is the smallest of five populations inhabiting Japanese waters. It is a relatively new population that established after the global warming that took place approximately 9000 years ago. To observe whether these porpoises appear in the major corridor to the ocean from Omura Bay, we used acoustic monitoring to record occurrences of finless porpoises from November 2007 to May 2009. A stereo acoustic event recorder recorded the intensity and the sound source direction of biosonar signals, providing independent traces of sound sources corresponding to each detected animal. A total of 226 individuals were detected over the 1.5-year monitoring period, of which 76% occurred at night and 73% occurred during March and April. We compared the presence of porpoises to the Japanese anchovy catch in Omura Bay and the Hario Strait over the same period. Results suggested that possible reductions in anchovy resources in the bay could attract porpoises to the outside of their normal habitat. In total, 70% of the porpoise recordings took place when the tidal current was moving out of Omura Bay. Porpoises might follow the prey that are transported out of the bay due to the strong outbound current. The finless porpoises confined to the bay might extend their swimming area if prey is available.
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Acknowledgments
We thank Fumio Hamaguchi (Hamaguchi Marine Service) for the deployment of the monitoring system. Takeshita Suisan Co. Ltd., Segawa Fisheries Cooperative Association, Sasebo City Fisheries Cooperative provided the data of fisheries statistics and shared their various knowledge of fisheries in the study site with us. Professor Hideaki Nakata, Mr. Hirokazu Suzaki and the members of Nakata Laboratory at Nagasaki University kindly allowed using long-term water temperature data of the study site. Natural Environmental Division of Nagasaki Prefectural Government supported our project. We specially thank Kunio Shirakihara, Miki Shirakihara, Hideyoshi Yoshida for their valuable comments on this manuscript. This research was supported by Grant-in-Aid for Scientific Research (B) 19405005, Research and Development Program for New Bio-industry Initiatives and Resource conservation of Eastern Asia Estuary.
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Communicated by S. Garthe.
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Akamatsu, T., Nakamura, K., Kawabe, R. et al. Seasonal and diurnal presence of finless porpoises at a corridor to the ocean from their habitat. Mar Biol 157, 1879–1887 (2010). https://doi.org/10.1007/s00227-010-1459-8
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DOI: https://doi.org/10.1007/s00227-010-1459-8