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Marine Ecology Progress Series

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MEPS 453:241-248 (2012)  -  DOI: https://doi.org/10.3354/meps09630

Swimming patterns of wild harbour porpoises Phocoena phocoena show detection and avoidance of gillnets at very long ranges

Torben P. Nielsen1,*, Magnus Wahlberg2,3, Sanja Heikkilä2, Maria Jensen2, Puk Sabinsky2, Torben Dabelsteen1

1Department of Biology, University of Copenhagen, Universitetsparken 15, 2100 Copenhagen East, Denmark
2Marine Biological Research Laboratory, Institute of Biology, University of Southern Denmark, Hindsholmsvej 11, 5300 Kerteminde, Denmark
3Fjord & Baelt, Margrethes Plads 1, 5300 Kerteminde, Denmark

ABSTRACT: Harbour porpoises Phocoena phocoena are unintentionally caught in gillnets. Although the effectiveness of by-catch mitigation measures has been evaluated many times, only a few studies have investigated the behavioural patterns of the porpoises in relation to the presence of fishing nets. In this study, the reactions of wild harbour porpoises to a modified gillnet were visually observed. The porpoises responded to the net by avoiding it, with reactions being detectable at a distance of >80 m. The number of animals in the pods approaching the net did not affect the behaviour of individuals in relation to the net. These results strongly indicate that porpoises do not usually actively approach gillnets. The by-catch problem seems, therefore, to be caused by individual animals accidentally being caught, likely due to attention shifts or to auditory masking reducing their ability to detect the nets using echolocation.


KEY WORDS: Harbour porpoise · Phocoena phocoena · Swimming pattern · By-catch · Gillnet


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Cite this article as: Nielsen TP, Wahlberg M, Heikkilä S, Jensen M, Sabinsky P, Dabelsteen T (2012) Swimming patterns of wild harbour porpoises Phocoena phocoena show detection and avoidance of gillnets at very long ranges. Mar Ecol Prog Ser 453:241-248. https://doi.org/10.3354/meps09630

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