Harbour porpoises

The only resident cetacean in Baltic waters

The harbour porpoise (Phocaena phocaena) is the only whale breeding in the Baltic Sea. Harbour porpoises are timid animals, usually seen swimming alone or in small pods. They can be difficult to spot because of their dark colouring, small size, and low dorsal fin. Porpoises can dive to depths of 60 metres, navigating and locating their prey by sonar.

Two main harbour porpoise populations, each differing significantly from the porpoises in the North Sea, have been identified in Baltic waters. The population living in the transitional waters linking the Baltic Sea to the North Sea - the Skagerrak, the Kattegat, the Belt Sea, the Sound and the westernmost Baltic Proper - seems to be doing well. Their total population, including the eastern Skagerrak, may number over 36,000.

Much less is known about the distinct harbour porpoise population based in the Baltic Proper. However, historical records and current estimates suggest that this population has declined markedly over the past 100 years, from between 10,000 and 20,000 to perhaps about 600 today. The present population may be classed as vulnerable or endangered.

	Reports submitted by the public during the summer of 2001 included sightings of porpoises as far north as Vaasa on the east coast of the Gulf of Bothnia.

	Threats facing porpoises in the Baltic · Fisheries by-catch represents a major threat to harbour porpoises, but the figures published for by-catches can be unreliable, so the full extent of this threat is not known. · Harbour porpoises can easily become stranded, especially if they are sick, or after they have been tangled in fishing nets and disoriented. · Other threats include hazardous substances, acoustic disturbances, shipping and possibly also electro-magnetic fields around marine cables. · Disturbance during the construction and operation of offshore wind farms is another potential threat. · Cold winters force porpoises to abandon waters which regularly freeze over. Porpoises disappeared from northern parts of the Baltic during the 1940s for this reason.

 Action to help porpoises

	HELCOM Recommendation 17/2 concerns protecting the harbour porpoise in the Baltic Marine Area. Priority is to be given to changing fishing practices to prevent accidental by-catch, especially concerning salmon drift nets and bottom-set gill-nets. Protected areas may also be designated if surveys reveal that this could help.

	Abundance of harbour porpoises and other cetaceans in the North Sea and adjacent waters, Journal of Applied Ecology 2002, 39, 361-376. Geographical variation in harbour porpoises skulls: support for a separate non-migratory population in the Baltic Proper], Ophelia 56 (1): 1-12 (June 2002)