ESR prepress abstract  -  doi: 10.3354/esr00776

Long-term effectiveness of pingers on finless porpoises of a small population in Japan

Masao Amano*, Miku Kusumoto, Misaki Abe, Tomonari Akamatsu


ABSTRACT: Finless porpoises Neophocaena spp. are under pressure from various anthropogenic impacts due to their coastal habitat. Net fishery bycatch is considered a major risk for the populations around Japan, and mitigation measures are required. We carried out a long-term study to assess the efficiency of acoustic pingers in assisting finless porpoises to avoid fishing nets. We used a passive ultrasonic event recorder (A-tag) to obtain acoustic encounter rates of echolocating finless porpoises and compared results for the presence and absence of pinger transmissions in Omura Bay Japan over two 8-month periods (2011 and 2012). Encounter rates were significantly lower during periods when pingers were in operation, but the effect of pingers decreased with time. By the eighth month of the study in each study year, the number of encounters during the ensonified period was greater than encounters during periods without pingers, suggesting habituation. When pingers were reactivated at the study site after 4 months of silence, the encounters with the active pingers returned to the lower level observed at the beginning of the experiment. These results reveal that the pingers effectively induce avoidance in porpoises, but that this effectiveness only lasts for a few months, which is likely due to habituation; this could be remedied by several months of silence.