Conservation Ecology of Indo-Pacific bottlenose dolphins in Amakusa, western Kyushu, Japan

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A year-round resident population of bottlenose dolphins is known to inhabit the coastal waters of Amakusa, western Kyushu, Japan. We confirmed that most of individuals moved in 2000 from waters near Tsujishima Island in Kumamoto prefecture to Nagashima Island in Kagoshima prefecture. Distance between both islands is 60 km. At the beginning, the objective of this study was to investigate causes of such habitat shift, but they returned to Tsujishima in 2001 and only a portion of individuals has remained near Nagashima. Recent taxonomic re-examinations has shown that botllenose dolphins are separated into two species : Tursiops aduncus and T. truncatus. We needed to identify the species of bottlenose dolphins off Amakusa. The final objectives of this study on bottlenose dolphins in the coastal waters of Amakusa were 1) to identify the species. 2) to estimate the population size and 3) to clarify their habitat utilization.Morphological and genetic examination of specimens showed that the species is T. aduncus (Shirakihara et al. 2003). We estimated that the population size was 218 individuals using techniques of photo-identification and mark-recapture (Shirakihara et al. 2002). Behavioral observation and theodolite tracking showed as follows. In the daytime, this population utilizes shallow waters with depth less than 20 m and tends to move regularly along the coast. We guessed that in the daytime it takes rest and from near sunset it begins to move to the waters suitable for conducting night activities, which are not the open sea facing East China Sea.This population is subject to negative stress from dolphin watching. To evaluate whether the population size will decrease or not is an important work to continue in future.