Study on the social structure of Tappanaga off Muroran based on individual identification

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We collected the sighting records of Tappanaga, northern form of short-finned pilot whales, from fishing and dolphin-watching boats. Tappanaga appears in Sanriku waters in July to August, expands its range up to the coast of Hokkaido in September to October, and then migrates south to disappear from Sanriku waters in January through April. Observation researches were carried out off Sanriku coast and Muroran, Hokkaido in June though September every year. Behavioral observation revealed that Tappanaga did not show diurnal pattern in the behavior, and one behavioral pattern tended to last long. Photographs for individual identification have been examining, but the preliminary analyses indicated that the proportion of adult males in a school varied 5-12%, suggesting the inter-school transfer. Females with calves accounted 15-21% of whales in a school which percentage was higher than that reported before. Suction-cup attached tag was able to be attached to two whales and recovered 6 hour data from one of them. The whale made shallow dives in the daytime but deep dives over l00m in the night. Most of dive durations were limited below 200 sec and the relationship between depth and duration changed around 200 sec. These suggest some metabolic restriction in the dive duration of 200 sec. Two patterns in dive profiles were found and Tappanaga is supposed to use two patterns separately. Same call types were heard in the same group of a school, while call types were not shared in the different schools. This suggest the existence of individual-or group-discriminating vocalizations.