Abstract
Reactions of bottlenose dolphins, Pacific white-sided dolphins, false killer whales, Risso's dolphins, Dall's porpoises to artificial underwater sounds were observed for developing countermeasures to reduce by-catch on gill nets. Related papers published during 1980-1995 in Japan were re-visited. Various sound projectors having dominant frequencies from 2 kHz to 200 kHz with source levels reaching up to 200dB re 1μPa. Reactions of dolphins and porpoises to the sounds were observed in a pool, a net enclosure, or an open sea. Clear escaping reactions from a sound source were observed by sounds with exposed level above 170dB at the subject animal. Reactions to sounds below 160dB were not stable. The dolphins got accustomed to the sound after multiple projections. On the other hand, frequency and amplitude modulated sounds seemed to be effective even if the sound pressure level was about 120dB. Efficacy of acoustic pingers to control wild dolphins and porpoises was limited. The exposure level to change behavior was estimated above 170dB that depends on the source level of a device and distance to the animal. Acclimation for the sounds by dolphins and porpoises were not negligible. Avoiding successive transmission and amplitude/frequency modulations induced behavioral reactions.
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