Wild Harbour

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Gaskin D, Yamamoto S, Kawamura A. Harbor porpoise, Phocoena phocoena (L.), in the coastal waters of northern Japan. Fish Bull. 1993;91: 440–454.

Johnston, D. W. The effect of acoustic harassment devices on harbour porpoises ( Phocoena phocoena) in the Bay of Fundy, Canada. Biol. Conserv. 108, 113–118 (2002). Kraus SD, Read AJ, Solow A, Baldwin K, Spradlin T, Anderson E, et al. Acoustic alarms reduce porpoise mortality. Nature 1997;388: 525.

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Leeney RH, Dia IM, Dia M. Food, pharmacy, friend? Bycatch, direct take and consumption of dolphins in West Africa. Hum Ecol. 2015;43: 105–118. Dede A, Öztürk AA, Akamatsu T, Tonay AM, Öztürk B. Long-term passive acoustic monitoring revealed seasonal and diel patterns of cetacean presence in the Istanbul Strait. J Mar Biol Assoc UK. 2014;94: 1195–1202.

Bjørge A, Skern-Mauritzen M, Rossman MC. Estimated bycatch of harbour porpoise ( Phocoena phocoena) in two coastal gillnet fisheries in Norway, 2006–2008. Mitigation and implications for conservation. Biol Conserv. 2013;161: 164–173. Ruxton, G. D. Testing for departure from uniformity and estimating mean direction for circular data. Biol. Let. 13(1), 20160756 (2017). From these observations, the occurrences of bycatch can be suggested as incidental. A comparison of the BB and NB periods clarified that harbour porpoises appeared more intensively just before an incidence of bycatch. No difference in elevation/depression angle was observed between the BB and NB periods, suggesting that porpoises did not become entangled because they had dived deeper than in usual. These observations indicate that harbour porpoises risk entanglement by appearing around a bottom-gillnet, and the risk of bycatch increases with repeated appearances, which is similar to the recent report on Peruvian drift net fishery [ 46]. HP4 did not flee at all, but instead seemed to rest near the seafloor quietly, which could be an orienting response to the novel stimuli 53 (Fig. S2). Narwhals have been observed to display freeze-responses (causing them to slowly sink) in response to ship noise 17. Furthermore, a similar quiet descent has previously been reported in a porpoise exposed to a passing fast ferry 45, and porpoises, exposed to a pinger, had responses varying from extremely rapid deterrence to no reaction at all 54. Thus, porpoises may respond to exposures both with flight (predominantly in our dataset), but also with freeze-like orienting responses. Amano M, Kusumoto M, Abe M, Akamatsu T. Long-term effectiveness of pingers on a small population of finless porpoises in Japan. Endanger Species Res. 2017;32: 35–40.Kubodera T. Manual of the identification of cephalopod beaks in the Northwest Pacific. Tokyo: National Museum of Nature and Science. https://www.kahaku.go.jp/research/db/zoology/Beak-v1-3/index.html (accessed 26 November 2019); 2005. Hiley, H., Janik, V. & Götz, T. Behavioural reactions of harbour porpoises Phocoena phocoena to startle-eliciting stimuli: Movement responses and practical applications. Mar. Ecol. Prog. Ser. 672, 223–241 (2021). Brandt, M. J., Diederichs, A., Betke, K. & Nehls, G. Responses of harbour porpoises to pile driving at the Horns Rev II offshore wind farm in the Danish North Sea. Mar. Ecol. Prog. Ser. 421, 205–216 (2011). Melcón, M. L., Failla, M. & Iñíguez, M. A. Echolocation behavior of franciscana dolphins (Pontoporia blainvillei) in the wild. J. Acoust. Soc. Am. 131, 448–453 (2012). In Japan, almost 25% of fishing operators use gillnets, mostly in a small-scale gillnet fishery (vessel size of up to 5 gross tons). Especially in Hokkaido, gillnets are the most-operated fishing gear, used by more than 3 000 fishing operator households [ 25]. Around Japan, harbour porpoises are distributed mainly nearshore off Hokkaido [ 26– 29]. The Stranding Network Hokkaido (SNH), a local stranding network organised by scientists, museum curators, and fishers managed by the corresponding author M.T.F., has been collecting information on gill net bycatch along the Hokkaido coast. According to the stranding reports disclosed from SNH ( https://kujira110.com), one gillnet fisher (S. K., a co-author) reported up to 10 harbour porpoises bycatches occurred in his bottom-gillnets up to 10 times year -1. Although the total number of bycatch and incidence around Hokkaido remain unknown, because there is no obligation to report the total number of bycatch incidences. It is assumed that a substantial number of harbour porpoises are taken as bycatch around Hokkaido, drowning in gillnets could be one of the most significant threats for harbour porpoises in the Hokkaido area.

Verfuß, U. K. et al. Geographical and seasonal variation of harbour porpoise ( Phocoena phocoena) presence in the German Baltic Sea revealed by passive acoustic monitoring. J. Mar. Biol. Assoc. UK 87(1), 165–176 (2007). Elmegaard, S. L., McDonald, B. I., Teilmann, J. & Madsen, P. T. Heart rate and startle responses in diving, captive harbour porpoises ( Phocoena phocoena) exposed to transient noise and sonar. Biol. Open https://doi.org/10.1242/bio.058679 (2021). Schevill, W. E. & McBride, A. F. Evidence for echolocation in cetaceans. Deep. Res. 3, 153–154 (1956). Hammond, P. S. et al. Cetacean abundance and distribution in European Atlantic shelf waters to inform conservation and management. Biol. Conserv. 164, 107–122 (2013).

Otani S. Diving behavior and swimming speed of a free-ranging harbor porpoise, Phocoena phocoena. Mar Mamm Sci. 2000;16: 811–814. Kastelein, R. A., Steen, N., Gransier, R., Wensveen, P. J. & de Jong, C. A. F. Threshold received sound pressure levels of single 1–2 kHz and 6–7 kHz up-sweeps and down-sweeps causing startle responses in a harbor porpoise ( Phocoena phocoena). J. Acoust. Soc. Am. 131, 2325–2333 (2012).