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The Harbour Porpoise

The harbour porpoise {Phocoena phocoena L.), a representative of the marinę mammals, is the only species of cetaceans living in the Baltic Sea. It belongs to the toothed whales suborder (Odontoceti), like dolphins, killer whales, and sperm whales. It inhabits the Coastal areas of the seas and oceans in the temperate zone of the northern hemisphere. It lives in smali groups, of 2 - 3 individuals. Sometimes, during predation or migration, harbour porpoises gather in larger groups, even up to 50 individuals. Harbour porpoises are the world's smallest cetaceans. Baltic harbour porpoises measure up to 170 cm in length and their lifespan is 15 years. They breed in the warm season, when they reach the age of 5 - 6 years, producing one young, usually every second season. Harbour porpoises have a naked body, black in the dorsal part and becoming lighter in colour, down to white on the belly and lower part of the head. All their fins are black.

Harbour porpoises swim at 17-22 km per hour. They come up to the surface for 1-1.5 seconds to exhale and take a breath. What you can see above the water surface are just the top parts of their heads and their small triangular dorsal fins. During foraging they can stay under water for a few minutes. In Polish waters they feed on the small fish inhabiting the coastal area, such as herrings, sprats, gobies, and sand eels, sometimes also small cods and flad fishes. Baltic harbour porpoises belong to an isolated population, and most probably do not crossbreed with the porpoises living in the Danish Straits and the North Sea.

Harbour porpoises are rare in the Polish waters of the Baltic. Their presence in this region is documented chiefly by fishermen's reports of finds of dead porpoises, usually very young ones (less than two-year old) in nets or stranded on the beach. In general people in Poland do not know very much about these "Baltic dolphins", even though harbour porpoises have inhabited our coastal seas for as long as the Polish State has existed.

Like seals, harbour porpoises have been hunted by man ever since humans first settled in the Baltic region. Even as late as the 18th and 19th century there were porpoise-hunters' guilds with large memberships. They did especially well in Denmark. The configuration of bays and straits helped to drive harbour porpoises into shallows, where nets would be put up cutting off their escape routes. The inhabitants of the southern shores of the Baltic were also engaged in porpoise-hunting. The municipal charter of Hel (1378) levied an annual tax on the townspeople on the catches brought home by each of their fishing boats.

In the 1920s and 30s porpoises were regarded as nuisances that depleted the fishing-grounds and damaged nets. The fishing statistics kept for the Bay of Gdańsk up to the 1930s, when there was a reward for every harbour porpoise killed, show that their population was very large. From the records of payments we know that in the period of 1922-1939 at least 720 porpoises fell victim to fishermen's nets in the fishing grounds used by Polish trawlers and boats. Since the 1950s, for reasons unknown, their numbers in Baltic waters have fallen dramatically. Only about a hundred porpoises have been seen over the past fifty years.

Neither the exact number of the Baltic porpoise population nor the range of its habitat is known. The most recent data, for 1994, refer only to the North Sea and the Danish Straits. Estimates of about 200 thousand harbour porpoises were given for the North Sea, over 40 thousand for the Kattegat, and 6 thousand for the Belts. A year later an attempt was made to supplement the data for the Baltic proper. According to the estimates, there were about 600 harbour porpoises inhabiting the coastal waters off Germany and southern Sweden. The latest Swedish estimates say that there are only 100 porpoises left in the south-western part of the Baltic. The present-day harbour porpoise habitat in the Baltic is believed to be limited only to the south-western part, whereas the occurrence of harbour porpoises in the north-eastern Baltic may be observed only sporadically. In the Polish waters harbour porpoises are most often spotted in the Bay of Gdańsk and Puck area. In 2000 the International Council for the Exploration of the Sea (ICES) issued a statement that in comparison with the negligible number of sightings now coming from other parts of the Baltic, the current number of observations being reported from the Puck Bay made this area an important habitat for the survival of the Baltic harbour porpoise population.

The threats to the survival of Baltic harbour porpoises are extremely grave. If their death rate does not fall, in the next few decades they will become extinct. As for now, harbour porpoises are most imperilled by the fishing equipment. 61 cases of bycatch have been officially reported in Poland since 1990, but the actual waste is much larger. Harbour porpoises and other marine mammals, when ensnared in a net, are no longer able to breathe and suffocate within about a quarter. In the last decade there have been only two cases of fishermen managing to save a porpoise trapped in a net.

Evidently, the biggest danger to harbour porpoises is posed by semi-drift nets for salmon and bottom gillnets, which account for about the majority of the porpoise depletion in the Baltic. Made of soft, often almost invisible synthetic fibres, they are an obstacle hard to notice and avoid to harbour porpoises. The holes in nets are big enough to ensnare the mouth of a harbour porpoise that happens to swim into such a net. The animal's desperate attempts to free itself from the trap, the stress, and sudden shortage of air cause death by suffocation. Another threat to harbour porpoises stems from marine pollution, which weakens their immune system and makes them prone to disease.

There is a growing risk of harbour porpoises colliding at surface level with fast vessels such as hovercraft, motorboats, and water-scooters, which are increasing in number. Underwater there is a growing noise level due to echolocation systems, turbines and motors, and the detonation of underwater ammunition in military testing grounds. The echo- sounding equipment and sonars used in navigation, fishing, and by the military work at frequencies used by these marine mammals for communication. This disturbs, or even permanently damages their biological hydrolocation system, which increases mortality.

Harbour porpoise conservation has been given the highest priority. Harbour porpoises are under strict protection both in Europe and in Poland, e.g. in line with the Directive of 26th September 2001 issued by the Polish Minister of the Environment, and the ASCOBANS (Agreement on the Conservation of Small Cetaceans on the Baltic and North Seas), ratified also by Poland. Being an ASCOBANS signatory, Poland has been bound to protect harbour porpoises and responsibly use the regions of the sea in which they live. We have also undertaken to conduct research on the harbour porpoise population and to identify existing and potential threats to the species. Under the ASCOBANS agreement we are also obliged to conduct education programmes on the subject of harbour porpoises and to collect data on porpoise sightings and cases of harbour porpoises being washed ashore. Fishermen should have access to information to help them report cases of porpoises being trapped in nets, and also to bring in dead porpoises for research.

If you catch a harbour porpoise or a dolphin, or see one on the beach or out at sea off the Polish coast, call the Hel Marine Station of Gdańsk University. The number of our 24-hour emergency line is 0 - 601 88 99 40. We come out immediately to rescue live animals!

Iwona Kuklik
Marine Station of the Institute of Oceanography, Gdańsk Universit