Recent observations of humpback whales (Megaptera novaeangliae) in Japanese waters off Ogasawara and Okinawa

Abstract

The current status of humpback whales in waters off Ogasawara and Okinawa islands, Japan, and the relationship of these populations to each other and to humpback whales in the central-eastern North Pacific were investigated. Fluke-identification photographs collected from 1987 to 1990 were analyzed to estimate abundance and determine individual behavior patterns, and were compared with humpback photoidentifications from other regions. In total, 177 humpbacks were identified. At the end of the study period the rate of discovery of "new" whales was still high, suggesting a substantially larger overall population. Whales were commonly sighted throughout the Ogasawara archipelago from December to May, and were present during the same period near the Kerama Islands, Okinawa. Humpback whales were not regularly seen near Saipan in the Northern Mariana Islands, or near Kenting, Taiwan. Repeat sightings of individuals indicate that some whales were present for extended periods off Ogasawara. The predominant behavior patterns were those related to calving and mating. Two whales were identified in both the Okinawa and Ogasawara regions in different years, suggesting that both regions are used by the same population. Identification of one whale in both Japan and Hawaii (reported elsewhere) indicates the potential for mixing of western and eastern North Pacific humpback populations; the overall matching effort to date suggests that this interchange is relatively small.