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Foraging activity of harbour porpoises around a bottom-gillnet in a coastal fishing ground, under the risk of bycatch

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Title: Foraging activity of harbour porpoises around a bottom-gillnet in a coastal fishing ground, under the risk of bycatch
Authors: Maeda, Saki Browse this author
Sakurai, Kenji Browse this author
Akamatsu, Tomonari Browse this author →KAKEN DB
Matsuda, Ayaka Browse this author
Yamamura, Orio Browse this author →KAKEN DB
Kobayashi, Mari Browse this author
Matsuishi, Takashi Fritz Browse this author →KAKEN DB
Issue Date: Feb-2021
Publisher: The Public Library of Science (PLOS)
Journal Title: PLOS ONE
Volume: 16
Issue: 2
Start Page: e0246838
Publisher DOI: 10.1371/journal.pone.0246838
Abstract: Bycatch of harbour porpoises (Phocoena phocoena) by gillnets is a recognised threat to populations. To develop effective mitigation measures, understanding the mechanics of bycatch is essential. Previous studies in experimental conditions suggested foraging activity is an important factor influencing porpoises’ reaction to gillnets. We acoustically observed the behaviour of wild harbour porpoises around a bottom-gillnet set-up in a commercial fishing ground, especially foraging activity. Passive acoustic event recorders (A-tags) were fixed to the ends of the gillnet, and recorded for 1 392 hours. Although harbour porpoises frequently and repeatedly appeared around the net each day, incidental bycatch occurred only three times during the observations. The stomach contents of two individuals contained mainly Ammodytes sp., which were observable around the bottom-gillnet but not targeted by the fishery. A total of 276 foraging incidents were acoustically detected, and 78.2% of the foraging activity was in the bottom layer (deeper than 25 m). Porpoises appeared around the net with more frequency on the day of a bycatch incident than on the days without bycatch. These results suggest that the harbour porpoises appeared around the bottom-gillnet to forage on fish distributed in the fishing ground, but not captured by this bottom-gillnet. Thus, porpoises face the risk of becoming entangled when foraging near a gillnet, with the probability of bycatch simply increasing with the length of time spent near the net. Bycatch mitigation measures are discussed.
Type: article
Appears in Collections:水産科学院・水産科学研究院 (Graduate School of Fisheries Sciences / Faculty of Fisheries Sciences) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 松石 隆

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