The harbour porpoise Phocoena phocoena is the most common and widely distributed cetacean species in northern Europe. As the name suggests, they prefer shallow water including harbours and estuaries – being spotted in both the Bristol Channel, close to the Eco Marine office, and the Thames Estuary, where Eco Marine frequently survey.
Harbour porpoises are one of the most common cetaceans found in coastal waters around the UK, with a population of around 350,000. As one of the smallest cetacean species in the world, harbour porpoises have a typical size range of 1.4 to 1.9 m and are most easily recognised by their small triangular dorsal fin and sleek dark grey bodies. They prefer shallow coastal areas but are shy and elusive, with encounters being far less frequent than that of the friendlier common dolphin. However, this reserved species is occasionally spotted when briefly coming to the surface to breath.
Despite their small size, harbour porpoises use their powerful tails to swim up to 22 miles per hour and dive up to depths of 226 m, with a maximum dive time of 15 minutes. Feeding on fish, crustaceans, and squid, prey acquisition usually occurs at the seafloor or mid-water with a typically dive occurring at 30 m for around 5 minutes. Like other toothed whales, harbour porpoises use echolocation to hunt. Harbour porpoise emit narrowband, high-frequency (ultrasonic) clicks (NBHF) within 110-150kHz, produced in the nasal passage and emitted through the melon in a narrow 11–13-degree beam. When feeding, harbour porpoises crate a unique feeding buzz by increasingly shortening the interval between clicks and ending sound emissions in a ‘buzz’. This behaviour not only allows the animal to accurately track down a prey item but allow porpoises to be easily identified when monitoring acoustically for cetaceans in an area.
The only natural predator for the harbour porpoise is the killer whale (Orcinus orcinus), as well as being historically hunted by humans around the Baltic and Faroe Islands. Other major threats include by-catch by fishing gear, with estimates of around 1,500 deaths each year by the UK fleet alone. Furthermore, the risk of diseases arising from high levels of contaminants, principally Polychlorinated biphenyls (PCBs), is increasing. These pollutants were banned in the EU in the mid-1980s but still enter the environment from ‘open applications’, such as paints and sealants. For harbour porpoises, PCBs have shown to reduce fertility levels in male’s and supress the immune system, which may have serious consequences on population viability.
The harbour porpoise is legally protected under the EU Habitats Directive (92/43/EEC; EU, 1992). Under the Directive, all cetaceans are listed for protection with designation of Special Areas of Conservation (SACs) designed to enable their survival. However, harbour porpoises are also listed in the OSPAR Convention for the Protection of the Marine Environment of the North-east Atlantic as threatened and declining and having unfavourable conservation status in Appendix II of the Convention on the Conservation of Migratory Species of Wild Animals. Given its declining status across multiple conservation frameworks, the harbour porpoise remains a priority species for coordinated protection efforts across European waters to ensure its long-term survival.
Written by Amy Fisher
References:
Miller, L.A. and Wahlberg, M. (2013). Echolocation by the harbour porpoise: life in coastal waters. Frontiers in Physiology, 4: 52. doi:https://doi.org/10.3389/fphys.2013.00052.
Whale & Dolphin Conservation UK. (2018). Tackling Whale and Dolphin Bycatch in UK Waters. [online] Available at: https://uk.whales.org/our-goals/prevent-deaths-in-nets/tackling-whale-and-dolphin-bycatch-in-uk-waters/.
Oakley, J.A., Jenkins, R.E., Thomas, T., Williams, A.T. and Phillips, M.R. (2016). Assessing Harbour Porpoise Populations in south-west Wales, Data Issues and Implications for Conservation and Management. Ocean & Coastal Management, 119: 45–57. doi:https://doi.org/10.1016/j.ocecoaman.2015.09.011.
jncc.gov.uk. (n.d.). Bristol Channel Approaches MPA | JNCC – Adviser to Government on Nature Conservation. [online] Available at: https://jncc.gov.uk/our-work/bristol-channel-approaches-mpa/.
Williams, R.S., Curnick, D.J., Brownlow, A., Barber, J.L., Barnett, J., Davison, N.J., Deaville, R., ten Doeschate, M., Perkins, M., Jepson, P.D. and Jobling, S. (2021). Polychlorinated biphenyls are associated with reduced testes weights in harbour porpoises (Phocoena phocoena). Environment International, 150: 106303. doi:https://doi.org/10.1016/j.envint.2020.106303.