What's a harbour porpoise?

The harbour porpoise is a small marine mammal, a cousin of the dolphin, found in temperate and cold waters throughout the northern hemisphere. In the Baltic Sea, there are two populations of harbour porpoise: one in the western Baltic Sea (the Kattegat, the Belt Sea, the Sound and the German Baltic) and another in the Baltic proper. The harbour porpoise is the only cetacean that permanently resides in the Baltic Sea.

Dramatic population decline

Over the past 100 years, the population in the Baltic proper (the green area of the map above) has declined dramatically, and only around 500 individuals remain today. This population may be facing extinction. The western Baltic Sea harbour porpoise population is stable, but also assessed as vulnerable.

In the 19th and early 20th centuries, harbour porpoises were widespread throughout the entire Baltic Sea, with sightings not uncommon in the Gulf of Finland and even in the northeastern part of the Gulf of Bothnia. They were actively hunted until the end of the 19th century, with catches as large as 2 000 individuals per year, and possibly even more.

Threats

Today, porpoises in the Baltic Sea face a wide range of threats.

• Bycatch is the greatest concern. Porpoises get entangled and drown in gillnets, trawls, and other fishing gear.
• Pollution also affects harbour porpoises, with substances such as PCBs affecting pregnancy rates. Porpoises in the Baltic proper area carry higher levels of PCBs compared to porpoises from Kattegat and Skagerrak. However, PBC levels in the Baltic Sea seem to be declining, so they may have less of an impact in the future.
• Underwater noise: Harbour porpoises have very good hearing, and they rely on sound for their orientation, communication and foraging. They also use echolocation to find prey. Because of this, underwater noise from human activities such as shipping, construction, sonars etc. is likely to affect porpoises.
• Lack of food due to overfishing is another threat to harbour porpoises.

For more details and references, see HELCOM’s Red List species information sheet on the harbour porpoise and the recent State of the Baltic Sea report.

What is HELCOM doing about this?

• Evaluation of the state of the harbour porpoise: Currently, HELCOM is developing precise ways of evaluating the state of the harbour porpoise in the Baltic Sea. Solid scientific data and clear definitions, in the form of a core indicator, will help understand what the status is for harbour porpoises and how the status may be changing.
• A reporting system and database on sightings, by-catches and strandings is already in place, created in cooperation between HELCOM and ASCOBANS.
• National commitments: Each HELCOM member has committed to protect the harbour porpoise in the Baltic Sea by avoiding by-catch, collecting and analyzing data, establishing Marine Protected Areas, and cooperating with other organizations and conventions. This commitment was set down in the HELCOM Recommendation 17/2 on harbour porpoise adopted in 1996 and updated in 2020.
• Agreements: the harbour porpoise is also covered by other agreements, such as the Baltic Sea Action Plan and the declaration from the 2018 Ministerial Meeting, which include commitments to improving the status of threatened species, taking action on by-catch, and improving the network of Marine Protected Areas. When it comes to by-catch, a core indicator on drowned mammals and waterbirds is under development.
• The 2018 Ministerial Meeting also decided to develop an action plan on underwater noise. This will complement the existing roadmap, which includes work on monitoring noise as well as investigating the impact of noise on marine species. The plan is due to be adopted in October 2021 during the next HELCOM Ministerial Meeting.
• In general, HELCOM is continuously addressing other threats to the harbour porpoise in the Baltic Sea through its work on reducing input of hazardous substances, on sustainable fishing practices, or on clean and safe shipping.

Watch the video address by Rüdiger Strempel, Executive Secretary of HELCOM, on the occasion of the “International Day of the Baltic Harbour Porpoise”:

What is HELCOM

HELCOM – the Helsinki Commission, or the Baltic Marine Environment Protection Commission – is an intergovernmental organization of the nine Baltic Sea coastal countries and the European Union, working together since 1974 to protect the marine environment of the Baltic Sea. HELCOM operates through conducting research, developing objectives and agreements, and following up on those objectives and agreements.