The Indo-Pacific bottlenose dolphin is distributed in tropical to subtropical coastal waters from the Indian Ocean to the Pacific Ocean. In Japan, the dolphins have been recorded off the coast of Kagoshima, Amakusa, Mikura-jima and the Ogasawara Islands. There are also reports of the Indo-Pacific bottlenose dolphin in the waters surrounding Amami Oshima, however detailed information on these sightings is limited.

In response to this, Okinawa Churashima Foundation Research Center, Mie University and the Amami Whale and Dolphin Association has jointly conducted a survey of Indo-Pacific bottlenose dolphins. For 7 years, from 2007-2013, we analyzed the appearance and distribution of Indo-Pacific bottlenose dolphins near Amami Oshima.

We have conducted a total of 49 surveys, identifying Indo-Pacific bottlenose dolphins by the shape of their dorsal fin. We counted 33 groups made up of a total of 417 dolphins, and identified 126 individuals. As a result of the analysis, we have found that for Indo-Pacific bottlenose dolphins found throughout the year around Amami Oshima, the average (median) group size is 8 individuals (Range: 1 - 50 individuals) and over 90% of the groups are made up of less than 25 dolphins. Similar groups sizes are found in populations around Kagoshima, Ogasawara and Amakusa. Studying the distribution of the dolphins also revealed that the dolphins were usually found at an average depth of 33 meters.

The data shows that for the Indo-Pacific bottlenose dolphins that live in the waters surrounding Amami Oshima, the number of groups, the number of individuals, and their distribution does not vary across different seasons.
Furthermore, similar appearance information for the Indo-Pacific bottlenose dolphin has been reported near the islands of Kikaijima and Tokunoshima. In the future we plan to carry out surveys which include these areas to further analyze them in detail.

Authors

Noriko Funasaka, Haruna Okabe, Katsuki Oki, Kouji Tokutake, Isao Kawazu and Motoi Yoshiok (Bold letters：Foundation staff member)

Title

The occurrence and individual identification study of Indo-Pacific bottlenose dolphins Tursiops aduncus in the waters around Amami Oshima Island, southern Japan: A preliminary report

Journal

Mammal Study

DOI

http://dx.doi.org/10.3106/041.041.0307

Indo-Pacific bottlenose dolphin confirmed near waters of Amami Oshima