Abstract
ESR Endangered Species Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials ESR 32:35-40 (2017) - DOI: https://doi.org/10.3354/esr00776 Long-term effectiveness of pingers on a small population of finless porpoises in Japan Masao Amano1,*, Miku Kusumoto1, Misaki Abe1, Tomonari Akamatsu2,3 1Graduate School of Fisheries and Environmental Sciences, Nagasaki University, Nagasaki 852-8521, Japan 2NRIFS, Fisheries Research Agency, Fukuura, Kanazawa, Yokohama, Kanagawa 236-8648, Japan 3CREST, Japan Science and Technology Agency, Gobancho, Chiyoda-ku, Tokyo 102-0075, Japan *Corresponding author: m-amano@nagasaki-u.ac.jp 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 reducing the encounter rates of narrow-ridged finless porpoises with 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-mo 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 that during periods without pingers, suggesting habituation. When pingers were reactivated at the study site after 4 mo 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 which could be mitigated by alternating periods of several months of silence between periods of active pinger use. KEY WORDS: Bycatch · Pinger · Neophocaena asiaeorientalis · Small cetacean · Bioacoustics Full text in pdf format PreviousNextCite this article as: Amano M, Kusumoto M, Abe M, Akamatsu T (2017) Long-term effectiveness of pingers on a small population of finless porpoises in Japan. Endang Species Res 32:35-40. https://doi.org/10.3354/esr00776 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in ESR Vol. 32. Online publication date: January 12, 2017 Print ISSN: 1863-5407; Online ISSN: 1613-4796 Copyright © 2017 Inter-Research.
Highlights
Of the various anthropogenic impacts on populations of small coastal cetaceans, which include habitat loss and degradation, and collision with vessels, bycatch in net fisheries is considered the most serious in many habitats (Read et al 2006)
Experimental setup of the A-tag and pingers at a set net repeated from April to December 2011, after which we set a 4 mo silent period and began the 2 wk on/2 wk off cycle again at the end of April 2012 to examine whether the habituation that may have occurred during the first year trial period is mitigated
The GLM for the 2 years clearly indicated that the presence of pingers significantly decreased the number of encounters of finless porpoises with the set net (Table 1), implying that pingers may be effective in reducing bycatch of finless porpoises in the gillnet fisheries, as is evident for harbor porpoises (Dawson et al 2013)
Summary
Of the various anthropogenic impacts on populations of small coastal cetaceans, which include habitat loss and degradation, and collision with vessels, bycatch in net fisheries is considered the most serious in many habitats (Read et al 2006). Various measures to reduce bycatch in terms of regulations of scale and period have been proposed, e.g. banning of the fishery, time/area fishery closure, improvement of fishing gear, and use of deterrent devices. Finless porpoises Neophocaena spp. are primarily coastal odontocetes that are distributed in inshore waters and several large rivers in southern and eastern Asia Their usual habitats are waters shallower than the 50 m isobath with soft-bottom substrates (Shirakihara et al 1994, Amano et al 2003, Jefferson & Hung 2004). There are many small - scale gillnet and set net fisheries operating along the coast of Omura Bay, and a fishery ban or closure, either here or elsewhere in Japan, is usually unacceptable, as fishermen and the Japanese government are less conscious of marine mammal conservation and reluctant to adopt strong management measures without unequivocal evidence of threats. To evaluate the longterm effectiveness of acoustic pingers for mitigating bycatch of finless porpoises, a 2-yr experiment using a passive acoustic echolocation event recorder was carried out in Omura Bay
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