EVIDENCE OF WINTER MIGRATION OF HUMPBACK WHALES TO THE HACHIJO ISLAND, IZU ARCHIPELAGO OFF THE SOUTHERN COAST OF TOKYO, JAPAN

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Abstract

<p>In the western North Pacific Ocean, humpback whales (Megaptera novaeangliae) migrate to the Okinawa (26°13′N, 127°41′E) and Ogasawara (27°04′N, 142°13′E) islands of Japan for breeding. The Hachijo Island (33°06′N, 139°47′E) is located in the Izu Archipelago —further north from known wintering grounds of those whales. In the 2015–16 winter, humpback whales were sighted around the Hachijo Island in significant numbers. This led to a monitoring project of whales around the island that was initiated from the 2016–17 winter to elucidate their migration. Here, we report the results of monitoring over two subsequent winter seasons (2016–17 and 2017–18). A survey was conducted within 5 nautical miles of the coast of the island using a dedicated vessel (12GT) for respectively 32 and 34 days in the first and second season from November to April. Humpback whales were sighted from November to March in the first season and from November to April in the second season, and a total of sightings of respectively 205 and 397 whales were recorded in the 2016–17 and 2017–18 seasons. Characteristic behaviors in the wintering grounds, such as singing and forming competitive groups, were confirmed in both seasons. Moreover, around 15% of the whales were repeatedly sighted during the same season, and six individuals observed in the first season were resighted in the second season. These results suggest that waters around the Hachijo Island are part of the winter migration grounds of humpback whales, and their migration to waters off the Hachijo area is expected to continue in the future. Long-term monitoring focusing on the social composition of groups is necessary, and additional photo-identification and genetic data should be collected to shed light on the habitat use and causes of sudden occurrence of humpback whales around this island.</p>

Journal

  • Cetacean Population Studies

    Cetacean Population Studies 3 (0), 164-174, 2021-12-28

    Publication Committee for Cetacean Population Studies

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