Ogasawara Sea Area

The Ogasawara Islands are located about 1,000 km south of Tokyo. From north to south, there are four archipelagos: the Muroshima, Chichijima, Hahajima, and Volcanic Archipelagos, along with three isolated islands: Minamitorishima, Okinotorishima, and Nishinoshima. These islands are said to have risen out of the sea due to volcanic activity, and most of them are surrounded by steep slopes. However, despite the sudden depth, the waters around the islands are shallower than 200 meters, which is said to be the preferred depth for humpback whales. The Oceanographic Center searched for whales along the coasts of each of the four archipelagos and Nishinoshima, concentrating on waters shallower than 200 m within about 10 km of the coastline. The northern limit of the Ogasawara Islands is considered to be the northern island of the archipelago, and the southern limit is considered to be Minami Iwo Jima in the volcanic archipelago.


Migration between Ogasawara and Okinawa

In Ogasawara, we identified 1,638 photographs and 490 individuals during eight seasons from 1987 to 1994. In Okinawa, we identified 89 individuals from 240 photographs taken during six seasons between 1989 and 1994. When matching between the two areas, we found 28 who were the same whales. This means that 6% of the whales identified in Ogasawara have also been identified in Okinawa, and 31% of the whales identified in Okinawa have also been identified in Ogasawara. Of these 28 whales, 22 records occurred in different seasons with summer feeding grounds in between, while the remaining 6 whales migrated directly from Okinawa to Ogasawara during the same season. Movements between the three main breeding grounds of Mexico, Hawaii, and Japan (Ogasawara and Okinawa), only a few of the thousands of ID photos that have been compared (see Relationships with other marine areas – Breeding grounds and Feeding grounds sections for more info). The frequency of interaction between Ogasawara and Okinawa is very high. Therefore, it can be said that the whales visiting this area are a single group in the western North Pacific.



Western North Pacific breeding grounds

According to records obtained during the whaling era, the distribution range of humpback whales in the breeding area of the western North Pacific includes the Ogasawara Islands, Mariana Islands, Marshall Islands, Okinawa Islands, Taiwan, and Hainan Island. In 1990, Dr. Jim Darling conducted a survey of humpback whales in Taiwan and Saipan and concluded that there were no regular visits of humpback whales to these areas. In the Mariana Sea, recent humpback whale sightings have been limited. As for recent information on humpback whales in the Mariana area, in February 1991, a group of three humpback whales were observed in Alupang Cove, Guam (Mariana Islands), and photographs of their dorsal fins were taken. In November 1994, the Ogasawara Marine Center conducted surveys in Saipan. In March-April 1995 and January-February 1996, the Marine Center conducted visual surveys throughout the Mariana Islands with the permission of the U.S. National Marine Fisheries Service and the Federal Republic of the Northern Mariana Islands. During the survey, we learned of several sightings of whales, including a father and son, had been recorded around Saipan, Rota, Guam, and the Northern Mariana Islands, and that their songs had also been heard. In addition, in the past few years, humpback whales have been observed in Taiwan and regular migrations of humpback whales in the Philippines, which are the same as those in Ogasawara and Okinawa. The southern limit of the migration of humpback whales in the western North Pacific breeding area is presently considered to be the northern Philippines.