Many species of porpoises travel in large lively groups. The harbour porpoise (Phocoena phocoena) doesn’t fit this description. The harbour porpoise is a secretive retiring species that travel alone or in small groups, shies away from boat traffic, and does not make spectacular leaps.
Nevertheless, the harbour porpoise is widespread and often encountered in the northern temperate waters of the world. This reserved porpoise frequents the shallow waters of the Pacific as far north as Arctic Alaska. Its habitat in the western Pacific Ocean ranges from the Aleutian Islands at least as far south as Japan.
As its name implies, it stays close to coastal areas or river estuaries, and as such, is the most familiar porpoise to whale watchers.
In the eastern Pacific, it occurs from the Pribilof Islands to southern California. The eastern Pacific subspecies P. p. vomerina occasionally reach the Mackenzie River’s mouth in the Northwest Territories of Canada, and there are infrequent sightings of the western Pacific subspecies near Taiwan.
Sightings of marked individuals suggest inshore and offshore populations that are possibly genetically distinct. There is also some genetic evidence to suggest little mixing of populations and hence little migration along the Pacific coast of North America.
The harbour porpoise represents one of the oldest marine mammals, the true porpoises or Phocoenidae that arose in the late Miocene epoch 5 to 23 million years ago.
Feeding And Reproduction Behaviour
Harbour porpoises feed mostly on small schooling fish, especially herring, pollack, hake, sardine, cod, and sprake, but have been known to eat squid and crustaceans in certain places. They tend to feed close to the sea bottom, at least for seas less than 200 metres deep.
Porpoises are promiscuous maters; the males produce large amounts of sperm, possibly for sperm competition. Females become sexually mature by their third or fourth year and can calve each year for several consecutive years, being pregnant and lactating at the same time.
The gestation period of the porpoise is usually 10–11 months. Calves are weaned at around 8–12 months, after being born in late spring and summer.
Harbour Porpoise Conservation
There is some concern that harbour porpoise populations have declined as a result of fisheries bycatch (accidental catch by fisheries targeting other species).
The Atlantic population is designated as threatened by the Committee on the Status of Endangered Wildlife in Canada and the Pacific population is designated as a special concern. The porpoise is designated as a strategic stock under the U.S. Marine Mammal Protection Act.
The IUCN Red List of Threatened Species has less concern for the species as it does for some stocks that have been severely depleted in particular in the Black Sea region where it might be endangered. The major concern is that the harbour porpoise sometimes becomes tangled in fishing nets and some have carried high loads of industrial contaminants in some areas. The Pacific population in the USA is estimated to be about 100,000 animals.
References:
- Baird, R.W., and T.J. Guenther. 1995. Account of harbour porpoise (Phocoena phocoena) strandings and bycatches along the coast of British Columbia. Reports of the International Whaling Commission Special Issue 16:159-168
- Baird, R. W. 2003. COSEWIC Assessment and update status report on the harbour porpoise Phocoena phocoena. Canadian Wildlife Service, Ottawa.
- Calambokidis, J., J.L. Laake, and S.D. Osmek. 1997. Aerial surveys for marine mammals in Washington and British Columbia inside waters. Final report to the National Marine Mammal Laboratory, Seattle, WA 98115.
- Gaskin, D. E., M. Holdrinet and R. Frank. 1971. Organochlorine pesticide residues in harbour porpoises from the Bay of Fundy region. Nature 233: 499-500.
- Hall, A.M. 2004. Seasonal abundance, distribution and prey species of harbour porpoise (Phocoena phocoena) in southern Vancouver Island waters. MSc thesis. Department of Zoology, University of British Columbia, Vancouver, B.C.
- Otani, S. Y. Naito, A. Kawamura, M. Kawasaki, S. Nishiwaki, and A. Kato. 1998. Diving behavior and performance of harbor porpoises, Phocoena phocoena, in Funka Bay, Hokkaido, Japan. Marine Mammal Science 14: 209–220
- Reynolds, JE and SE Rommel. 1999. Biology of marine mammals. Smithsonian.
- Rice DW 1998. Marine mammals of the world: systematics and distribution. Society for Marine Mammalogy, Special Publication Number 4 (Wartzok D, Ed.), Lawrence, KS. USA.
- Rosel, P. E., A. E. Dizon, and M. G. Haygood. 1995. Variability of the mitochondrial control region in populations of the harbour porpoise, Phocoena phocoena, on inter-oceanic and regional scales. Can J. Fish. Aquat Sci. 52:1210-1219.
- Wilson, D. E. and S. Ruff. 1999. The Smithsonian book of North American mammals. UBC press, Vancouver.
- Yurick, D. B. and D. E. Gaskin. 1987. Morphometric and meristic compariions of skulls of th harbour porpoise Phocoena phocoena L. from the North Atlantic and North Pacific. Ophelia 27: 53-75.