| Last modified: Thursday September 24th, 1999 |
Harbor porpoisePhocoena phocoena (Linneaus, 1758) |
The harbor porpoise is generally considered to be a single species. Some have suggested three subspecies: Phocoena phocoena relicta in the Azov and Black Seas, Phocoena phocoena phocoena in the North Atlantic and Phocoena phocoena vomerina in the North Pacific (Klinowksa, 1991). However, this subdivision is not widely accepted.
The harbor porpoise is a small, stocky animal.The dorsal side is brown or
dark grey, converging to a lighter grey on the flanks. The triangular dorsal
fin is located in the middle of the back (Minasian et al, 1984). The average
length is 1.5 m. with a maximum size of about 2 m. Females are slightly larger
than males. They weigh 45-65 kg, with a maximum of 90 kg (Evans, 1987; Peet et
al., 1992).
The harbor porpoise is a coastal species, limited to the cold temperate and subarctic waters of the Northern Hemisphere. In the Eastern North Atlantic it ranges from the Kara Sea south to Senegal, Africa, including the North Sea, the Baltic Sea and the Western Mediterranean. There is an isolated population in the Black Sea. In the Western North Atlantic, this species ranges from southern Greenland to North Carolina, USA. and there is also a population around Iceland. In the Eastern Pacific, it ranges from Alaska (up to Point Barrow) south to California. In the Western Pacific, the species ranges from the Bering Sea to northern Japan (Klinowksa, 1991). There is no clear migration. Most of the travelling seems to be related to movement of food resources.
The maximum age for harbor porpoises is about 17 years. The mean age at sexual maturity for females is 3.1 to 3.4 years. Pregnancy lasts about 10.6 months, followed by 8 to 12 months of lactation (Palka et al, 1996).
The harbor porpoise population in the North Sea has declined considerably since the second World War (Verwey, 1975), but seems to have recovered slightly (Reijnders et al, 1996).
| Region | Abundance |
|---|---|
| Gulf of Maine - Bay of Fundy | 47,200 |
| Iceland | 27,000 |
| North Norway, Barents Sea | 11,000 |
| Kattegat, Skagerrak and Bælt areas | 36,000 |
| Baltic Sea | unknown, low |
| North Sea | 279,300 |
| Ireland and Western UK | 32,280 |
The diet of the harbor porpoise is varied and differs geographically and seasonally. Common prey species include herring, hake, lantern fish, capelin as well as cephalopods (Palka et al, 1996). Also anchovy and loligo are taken (Sekiguchi, 1995). Total food intake is between 4 and 9.5% of the total body weight, representing between 8000 and 25000 kJ/day (Kastelein, Hardeman and Boer, 1997). Harbor porpoises have been observed swimming into schools of fish. When large schools of fish are available, the porpoises seem to concentrate around them (Baptist and Witte, 1996).
In the past, the harbor porpoise has been hunted throughout its range for food and oil. There has been a major fishery for this species in the Lille Bælt in Denmark from the 1830s until the second World War, in which several hundred to more than thousand animals were taken annually. There has also been a drive fishery in the Black Sea. Before the second World War, this fishery took 100,000-300,000 animals per year, which declined to 5,000-7,000 per year in the mid-1960s. This fishery targeted harbor porpoises, common dolphins and bottlenose dolphins. The composition of the catch is unknown. The Turkish fisheries, which was suspended in 1983, took 34,000-44,000 animals per year between 1976 and 1981. Harbor porpoises made up about 80% of the total catch (Klinowksa, 1991)
Currently, the main threat for the harbor porpoise is the high level of bycatch. The International Whaling Commission (1996) reports the following bycatch estimates for the North Atlantic:
| Region | Bycatch |
|---|---|
| Gulf of Maine - Bay of Fundy | 1,000-4,000 |
| Greenland | > 700 |
| Kattegat, Skagerrak and Bælt areas | > 250 |
| Baltic Sea | ~ 10 |
| North Sea | 4,000-5,000 |
| Ireland and Western UK | 2,000 |
The IWC concluded that the current bycatch in the North Sea may not be sustainable. In the area where most of the bycatch occurs, 3.1% of the population is killed this way annually. Recently, the Agreement on the Conservation of Small Cetaceans of the Baltic and North Seas (ASCOBANS) was set up to provide an international platform for the conservation of among others the harbor porpoise. A number of countries already signed and ratified this agreement.
Also, most of the common prey species of the harbor porpoise (herring, mackerel, sprat, pilchard, whiting, cod) are also commercially exploited species. In addition to the threats of entanglement, this also means that depletion of food resource by fisheries is a risk (Hutchinson, 1996).
In areas where the harbor porpoise is relatively abundant, strandings of sick and injured animals are not uncommon. Animals stranding on the Western European coastline are usually transfered to the rehabilitation center at the Dolfinarium in Harderwijk, the Netherlands. The park has a dedicated rehabilitation center for small cetaceans since 1991. See Kastelein, Bakker and Staal (1997) for details on the rehabilitation process.
The pictures on this page were taken at the Fjord- og Bælt Centret in Kerteminde, Denmark. At this aquarium, two harbor porpoises (incidentally caught animals) are kept for research purposes. The research is aimed at reducing bycatches.
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