Humpback whales feed in high latitude waters during summer, and breed (mate, give birth and rear) in lower latitudes during winter. In the western North Pacific Ocean, the humpback whales feed off the coast of Russia. Their breeding grounds are in the Japanese waters of Okinawa, Amami, and Ogasawara plus the Philippines waters of the Mariana Islands. Some of the whales migrate past Hokkaido. It is possible to identify individual humpback whales based on the patterns and shapes of their flukes.
To understand the movement and interchange between domestic waters, research teams from Okinawa Churashima Foundation, Everlasting Nature of Asia (ELNA) (Tokyo Metropolis, Ogasawara Village), Ogasawara Whale Watching Association (Tokyo Metropolis Ogasawara Village), Amami Whale and Dolphin Association (Kagoshima Prefecture, Amami City), Field Science Center for Northern Biosphere, Hokkaido University (Hokkaido, Hakodate City), and the Cybermedia Center, Osaka University (Ibaraki City, Osaka Prefecture) studied photos of 3,532 humpback whale flukes taken in 4 domestic regions of water (Okinawa, Ogasawara, Amami and Hokkaido) between 1989 and 2020. An automated matching system was used to compare flukes.
The results showed 3 matching whales comparing Okinawa and Hokkaido, 225 whales comparing Okinawa and Ogasawara, 222 whales comparing Okinawa and Amami, and 36 whales comparing Ogasawara and Amami. Based on the number of these matched individuals, the indices were calculated on interchanges between waters and each region’s recurrence, and it has shown that 4 domestic water regions are most likely used by a single common group. Also, the frequency of interaction is different between areas, suggesting that two small groups may exist. One group may utilize the Philippine Sea route (Ogasawara and Mariana Islands) and the other group the East China Sea route (Amami, Okinawa and the Philippines). These discoveries are valuable for conservation of humpback whales in Japan. We will continue to collaborate with research teams, and aim to unravel the details of humpback whale population structures using DNA analysis.

Humpback whale breaching (Top Left) Characteristics of the tail fins of each whale (bottom left) and a schematic of the research results (right)

Authors

Nozomi Kobayashi, Satomi Kondo, Koki Tsujii, Katsuki Oki, Masami Hida, Haruna Okabe, Takashi Yoshikawa, Ryuta Ogawa, Chonho Lee, Naoto Higashi, Ryosuke Okamoto, Sachie Ozawa, Senzo Uchida, Yoko Mitani　(Bold letters: the Churashima Foundation Staff)

Title

Interchanges and movements of humpback whales in Japanese waters: Okinawa, Ogasawara, Amami, and Hokkaido, using an automated matching system

Journal

PLOS ONE

Journal link

https://doi.org/10.1371/journal.pone.0277761