Estimating detection probability and population changes for conservation of finless porpoises

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The finless porpoise, a kind of toothed whales, is exposed to human activities. The existence of this species is threatened. Abundance, which is essential information for conservation, has been estimated using sighting surveys. Because the detection probability on the track line, g(0), is hard to be grasped, abundance estimates have been given under an assumption of g(0)=1. We developed a method to estimate g(0) using a combination of acoustic surveys and sighting surveys. We carried out an aerial sighting survey in Ohmura Bay, Nagasaki Prefecture, Japan, in 2010. A population decrease was not detected over these 10 years.