Study on the Life History of Finless Porpoise Living in the Coastal Waters of Nagasaki.

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1. ON THE DISTRIBUTION AND MIGRATION(1) OMURA BAYA pattern of the seasonal migration was discussed by some data from sighting surveys. Namely, the finless porpoises aggregate in Southeast area of this bay in Winter and spread over in the whole bay in Summer. But, data were not sufficient to discuss the migration in detail. Moreover, we could not find out any evidence to prove whether they go out from this bay or not.(2) ARIAKE SOUND AND TACHIBANA BAYSighting surveys at every stations of these areas for two years clarified a following pattern of the seasonal migration. They migrate between the inner part of Ariake Sound and Tachibana Bay, and have a tendency to aggregate in the inner part of Ariake Sound in Winter.2. RELATION WITH FISHERIESTheir food was consisted of many kinds of small aquatic animals, namely fish, mollusca, crustacean and etc. The catch of these preys of this porpoise was decreasing in Omura Bay, but this tendency was not clear in Ariake Sound and Tachibana Bay.3. LIFE HISTORYA parturition season of this porpoise estimated from the dates collecting neonates or fetuses was from Autumn to Winter. Then, it seems that the aggregation in Winter is related with breeding. Males (3.5 years old) mature earlier than females (7-8 years old). The oldest individual (female) was 25.5 years old.4. POPULATIONIt was very difficult to decide the accurate number, because the number of porpoises sight was a few. However, we can say that the population in Omura Bay was in a critical situation (its size of several tens to a hundred) and much smaller than the population in Ariake Sound and Tachibana Bay.