Although it is believed that the harbor porpoise population is not seriously in danger at present, incidental catch of the species in gillnets continues to be the primary threat throughout its range (Hammond et al 2008). Off the eastern coast of the US, an estimated 1200 to 2900 harbor porpoises were killed annually in gillnets between 1990 and 1996 (Waring et al 1998). In the North Sea, Danish annual estimates of bycatch ranged from 2867 to 7566 between 1990 and 2002 (Vinther & Larsen 2002). In the Celtic Sea, bycatch estimates continue to be in the hundreds (ICES 2008; Northridge & Kingston 2009). In Newfoundland and Labrador, the annual level of bycatch was estimated at 2228 animals in 2003 (Benjamins et al 2007). Gillnet bycatch of the Endangered Black Sea harbor porpoise likely continues at high levels, as illegal, unreported, and unregulated fishing has increased in this area (Reeves & Notarbartolo Di Sciara 2006), and bycatch of the Critically Endangered Baltic Sea harbor porpoise is also thought to be occurring at unsustainable levels (Berggren 1994; Koschinski 2002).
Kraus et al (1997) tested the effectiveness of acoustic pingers in the Gulf of Maine to warn harbor porpoises of the presence of nets, and found that they significantly reduce bycatch. Pingers, in combination with time-area closures in this region, reduced gillnet bycatch by about half (Waring et al 2011). Pingers have also been shown to reduce harbor porpoise bycatch in the North Sea (Larsen 1999; Larsen et al 2002), the northeast Pacific (Gearin et al 2000), and the Black Sea (Goener & Bilgrin 2009). Harbor porpoises also avoided nets with active pingers in the Baltic Sea (Carlstrom et al 2009). Overall decreases in fishing effort have also contributed to fewer incidental porpoise catches in several other areas, such as Canada's Maritime Provinces (Read et al 2006; Stevenson 2003).
Berggren, P. 1994. Bycatches of the harbour porpoise (Phocoena phocoena) in the Swedish Skagerrak, Kattegat and Baltic waters, 1973-93. Reports of the International Whaling Commission (Special Issue) 15: 211-216.
Benjamins, S, J Lawson, & G Stenson. 2007. Recent harbour porpoise bycatch in gillnet fisheries in Newfoundland and Labrador, Canada. Journal of Cetacean Research and Management 9: 189-199.
Carlstrom, J, P Berggren, & NJC Tregenza. 2009. Spatial and temporal effects of pingers on porpoises. Canadian Journal of Fisheries and Aquatic Science 66: 72-82.
Gearin, PJ, L Cooke, RL Delong, ME Gosho, KM Hughes, & JL Laake. 2000. Experimental testing of acoustic alarms (pingers) to reduce bycatch of harbor porpoise, Phocoena phocoena, in the state of Washington. Journal of Cetacean Research and Management 2(1): 1-9.
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Hammond, PS, G Bearzi, A Bjorge, K Forney, L Karczmarski, T Kasuya, WF Perrin, MD Scott, JY Wang, RS Wells, & B Wilson. 2008. Phocoena phocoena. In IUCN 2012. IUCN Red List of Threatened Species. Version 2012.1. Accessed 19 September 2012. www.iucnredlist.org.
Koschinski, S. 2002. Current knowledge on harbour porpoises (Phocoena phocoena) in the Baltic Sea. Ophelia 55: 167-197.
Larsen, F. 1999. The effect of acoustic alarms on the by-catch of harbour porpoises in the Danish North Sea gill net fishery. Report of the IWC Scientific Committee SC/51/SM41.
Larsen, F, M Vinther, & C Krog. 2002. Use of pingers in the Danish North Sea wreck net fishery. Report of the International Whaling Commission Scientific Committee SC/51/SM32.
Northridge, S & A Kingston. 2009. Common dolphin bycatch in UK fisheries. Report of the International Whaling Commission SC/61/SM37.
Read, AJ, P Drinker, & S Northridge. 2006. Bycatch of marine mammals in US and global fisheries. Conservation Biology 20(1): 163-169.
Reeves, RR & G Notarbartolo Di Sciara. 2006. The status and distribution of cetaceans in the Black Sea and Mediterranean Sea. IUCN Centre for Mediterranean Cooperation, Malaga, Spain.
Vinther, M & F Larsen, 2002. Updated estimate of harbor porpoise by-catch in the Danish bottom set gillnet fishery. Report of the International Whaling Commission Scientific Committee SC/54/SM31.
Waring, GT, KD Bisack, P Clapham, T Cole, LJ Hansen, DL Palka, MC Rossman, & S Swartz. 1998. U.S. Atlantic marine mammal stock assessments - 1998. US Dep Commer NOAA Tech Memo NMFS-NEFSC.
Waring, GT, E Josephson, K Maze-Foley, & PE Rosel. 2011. U.S. Atlantic and Gulf of Mexico marine mammal stock assessments - 2011. Accessed 11 July 2012. http://nmfs.noaa.gov/pr/pdfs/sars/ao2011.pdf.