One of the smallest cetacean species, harbour porpoises are generally inconspicuous in their behaviour. They are usually found in small groups, and generally surface quickly without showing too much of their body above the water surface1. As such, they are not often the primary target of dolphin watching activities. However, as one of the most common whale or dolphin species in Europe and both coasts of North America, whale watchers in either of these regions have a good chance of catching a glimpse of this compact and enigmatic porpoise. The porpoises’ nearshore distribution allows them to be observed from land in many places, including the Netherlands, where they are the target of a unique land-based form of whale watching that allows watchers to listen to harbour porpoise vocalisations in real-time (see the ‘harbour porpoise studio’ case study on this site). They can also be observed from the Golden Gate bridge or ferries crossing the San Francisco Bay.
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Harbour porpoise Phocoena phocoena
Not to be confused with:
Harbour porpoises are fairly distinct from all other species with which they share habitat. There are no other species of porpoise in the North Atlantic with which they could be confused, and all other cetacean species in the Atlantic are much larger. In the North Pacific, harbour porpoises share habitat with Dall’s porpoises, and indeed, hybrids are known to occur between the species, usually the result of a Dall’s mother and a harbour porpoise father2. However, in the absence of hybridization Dall’s porpoises can be easily distinguished from harbour porpoises by their striking black and white pattern and the white blaze on the dorsal fin.
Distribution
There are currently three formally recognised subspecies of harbour porpoises: The Pacific harbour porpoise (Phocoena phocoena vomerina), the Atlantic harbor porpoise, (P. p. phocoena), and the Black Sea Harbor Porpoise (P. p. relicta)3. A fourth subspecies has been proposed for harbour porpoises found around the Iberian Peninsula and north Africa (P. p. meridionalis). Throughout its range the species is found in cool temperate or subpolar waters, usually coastal areas and depths of less than 100m.
Native to the following countries: Belgium; Bulgaria; Cabo Verde; Canada; China; Denmark; Estonia; Finland; France; Georgia; Germany; Gibraltar; Iceland; Ireland; Japan; Latvia; Lithuania; Mauritania; Morocco; Netherlands; Norway; Poland; Portugal; Romania; Russian Federation; Senegal; Spain; Sweden; Tunisia; Turkey; Ukraine; United Kingdom; United States
Presence uncertain in: Democratic People's Republic of Korea, Republic of Korea.
Biology and Ecology
Feeding
Harbour porpoises have a high metabolic rate, so they need to eat often, and rely on prey with high caloric content. As such, in most areas they predominantly feed on fish species with a high fat content like herring, sprat, anchovies, whiting and sand eels1,4,5. However, different populations have varying prey preferences. Recently they have been observed to feed on cod off the coast of Greenland 1, and in other areas they are also known to feed on squid and crustaceans1. Although harbour porpoises normally feed alone or in very small groups, in some cases they have been observed working together to corral or herd fish while feeding1.
Social structure, Reproduction and growth
Harbour porpoises are usually found in small groups of up to five or six individuals1,2,6. However larger (temporary) aggregations have also been observed in some locations. Gestation lasts 10.5 months, and calves are roughly 70-80cm at birth, weighing only 5 kg7. Calves are dependent on their mothers for milk until they are roughly a year old, but may start to catch their own prey (e.g. small crustaceans and fish) long before they are fully weaned7. Both males and females become sexually mature by the age of three or four years, but have very short average life spans of only 8-10 years1,7. In the Atlantic females can produce calves every year during their short reproductive phase, but in the Pacific it appears to be more common for them to have calves every other year1.
Research, threats and conservation
Harbour porpoises are hunted and eaten by killer whales and sharks. However, they are also attacked by gray seals8 and bottlenose dolphins9,10, that kill them without eating them, possibly driven by competition for prey11. While there is still a limited hunt for harbour porpoises in Greenland12,13, bycatch in fishing gear is the most pervasive threat that faces harbour porpoises throughout their range, with gillnets presenting the greatest risk14-17. Harbour porpoises’ coastal distribution, often in areas with high population densities, also exposes them to a range of other threats, including chemical pollution18, underwater noise from vessels and construction19, habitat degradation and depletion of prey by overfishing1,14.
Conservation status
Because the harbour porpoise is found close to shore in countries that are generally well-resourced and have the capacity to conduct regular surveys, population estimates are available for many parts of the species’ range12,20,21. The combined estimates indicate that there are over a million harbour porpoises globally throughout their range. As such, the species is globally designated as Least Concern on the IUCN Red List of Threatened species14. However, there are notable exceptions: the Baltic Sea population is considered Critically Endangered15, and the Black Sea population is designated as Endangered16. There is also increasing concern about the Iberian Peninsula harbour porpoise population. In all three cases, fisheries bycatch is considered the main cause of continued population declines15,16,22.
Harbour porpoises and whale watching
Harbour porpoises are rarely the primary target of whale or dolphin watching operations. However, because they are so common in North American and European coastal waters, they are often encountered during whale watching or marine-based wildlife tours in those areas. Harbour porpoises can be observed in Canada, Denmark; France; Ireland; Norway; Portugal; Spain; the United Kingdom, and the United States.
In the Netherlands a unique form of land-based dolphin watching allows observers to spot harbour porpoises from shore, and listen to their vocalisations in real-time. Learn more about this in the case study featured in this handbook.
References
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- Bjørge, A. & Tolley, K.A. in Encyclopedia of Marine Mammals Vol. Third Edition (eds B Würsig, J.G.M. Thewissen, & K.M. Kovacs) 448-451 (Academic Press, Elsevier, 2018 ).
- Jefferson, T. A., Webber, M. A. & Pitman, R. L. Marine Mammals of the World: a Comprehensive Guide to their Identification. Second Edition. (San Diego: Academic Press, 2015).
- Committee on Taxonomy. List of marine mammal species and subspecies. Society for Marine Mammalogy, www.marinemammalscience.org, consulted on 11 June 2020. (2020).
- Borjesson, P., Berggren, P. & Ganning, B. Diet of harbor porpoises in the Kattegat and Skagerrak seas: Accounting for individual variation and sample size. Marine Mammal Science 19, 38-58 (2003).
- Santos, M. B. & Pierce, G. J. The diet of harbour porpoise (Phocoena phocoena) in the northeast Atlantic. Oceanography and Marine Biology: an Annual Review 41, 355-390 (2003).
- Bouveroux, T. et al. Modelling fine-scale distribution and relative abundance of harbour porpoises in the Southern Bight of the North Sea using platform-of-opportunity data. Journal of the Marine Biological Association of the United Kingdom, 1-9, doi:10.1017/S0025315420000326 (2020).
- Lockyer, C. Harbour porpoises (Phocoena phocoena) in the North Atlantic: Biological parameters. NAMMCO Scientific Publications 5, 71-89 (2003).
- Leopold, M. F. et al. Exposing the grey seal as a major predator of harbour porpoises. Proceedings of the Royal Society B: Biological Sciences 282, 20142429, doi:doi:10.1098/rspb.2014.2429 (2015).
- Jacobson, E. K., Forney, K. A. & Harvey, J. T. Acoustic evidence that harbor porpoises (Phocoena phocoena) avoid bottlenose dolphins (Tursiops truncatus). Marine Mammal Science 31, 386-397, doi:10.1111/mms.12154 (2015).
- Barnett, J. et al. Postmortem evidence of interactions of bottlenose dolphins (Tursiops truncatus) with other dolphin species in south-west England. Veterinary Record 165, 441-444 (2009).
- Spitz, J., Rousseau, Y., Ridoux, V. & Preen, A. R. Diet overlap between harbour porpoise and bottlenose dolphin: An argument in favour of interference competition for food? Estuarine, Coastal and Shelf Science 70, 259-270 (2006).
- NAMMCO. Report of the NAMMCO Scientific Committee Working Group on Harbour Porpoise. 32 (North Atlantic Marine Mammal Commission, Copenhagen, Denmark, 2019).
- NAMMCO. Report of the Meeting of the Management Committee for Cetaceans, March 2018. 17 (North Atlantic Marine Mammal Commission Tromsø, Norway, 2018).
- Braulik, G., Minton, G., Amano, M. & Bjorge, A. in The IUCN Red List of Threatened Species 2020 (eds R. Reeves & B. Taylor) (In press).
- Hammond, P. S. et al. Pocoena Phocoena (Baltic Sea subpopulation). The IUCN Red List of Threatened Species e.T17031A98831650 (2016).
- Birkun Jr, A. & Frantzis, A. Phocoena phocoena ssp. relicta. . The IUCN Red List of Threatened Species Downloaded on 28 January 2019. (2008).
- Scheidat, M., Couperus, B. & Siemensma, M. Electronic monitoring of incidental bycatch of harbour porpoise (Phocoena phocoena) in the Dutch bottom set gillnet fishery (September 2013 to March 2017). 79 (Wageningen University and Research, Wageningen, Netherlands, 2018).
- Covaci, A. et al. Determination of organohalogenated contaminants in liver of harbour porpoises (Phocoena phocoena) stranded on the Belgian North Sea coast. Marine Pollution Bulletin 44 1157-1165 (2002).
- Tougaard, J., Carstensen, J., Teilmann, J., Skov, H. & Rasmussen, P. Pile driving zone of responsiveness extends beyond 20 km for harbor porpoises (Phocoena phocoena). Journal of the Acoustic Society of America 126, 11-14 (2009).
- Carretta, J. V. et al. U.S. Pacific marine mammal stock assessments: 2017. 161 (2018).
- Hayes, S. A. et al. US Atlantic and Gulf of Mexico marine mammal stock assessments—2017. 282 (National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Northeast Fisheries Science Center, Woods Hole, Massechusetts, 2018).
- Read, F., Santos, M. B., Ferreira, M., Lopez, A. & Pierce, G. J. Harbour porpoise (Phocoena phocoena) and fisheries interactions in the north-west Iberian Peninsula. document presented to the Scientific Committee of the International Whaling Commission, 24 (2020).