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Acoustic behavior of dolphins in the Pacific Ocean: Implications for using passive acoustic methods for population studies

The Southwest Fisheries Science Center has been conducting shipboard visual line-transect cetacean surveys for over 30 years, and combined visual and acoustic surveys for seven years. Full incorporation of passive acoustics as a tool for population assessment requires an understanding of the acoustic behavior of cetaceans as well as the limitations of the methods used in these surveys. Our research summarizes data collected during seven years of combined visual and acoustic surveys throughout the central and eastern North Pacific Ocean, ranging from the Aleutian Island chain in the north, to Peru in the south. Phonations from 2.034 dolphin schools were examined to better understand the acoustic behavior of cetaceans. Equally important are the cetacean schools that were seen but not heard, and this analysis includes an examination of these groups by species, group size, geographic location, and time of day. The results of this analysis allow us to take the first steps to incorporate passive acoustics into line-transect cetacean surveys.