Lisa Moulton and Sandra DeMaria

Harbor porpoises are the smallest cetaceans alive today. They are a very unique species, in that they live in very cold habitats yet are minute in comparison to other cetaceans, which live in the same climates.

They are in the order Cetacea, suborder Odonotocete, and their scientific name is Phocoena phocoena. They are usually 1.5m long and weigh 60kg, but some may reach 1.8m long and 68kg. They have a beak-less profile and low, triangular dorsal fin with tubers along the edges. The back of the harbor porpoise varies from dark gray to black, while its belly may be light gray to white. The fins, tail and dorsal fin are all gray with two stripes that extend from the eyes to the interior angle of the fins. The harbor porpoise is known for the characteristic puffing sound it makes on exhalation, described as being much softer than the usual cetacean spouting.

Their habitat ranges from Cape Hatteras, North Carolina, to Greenland, and also in Alaska, Canada and as far south as Monterey Bay, California. They have been found in many rivers in Europe, as well as the Baltic, Mediterranean and Azov seas. The North Atlantic population is estimated to contain 15,300 (+/- 2552) individuals from the south of Maine to the Border of New Brunswick, and 35,000-57,000 individuals off the coasts of Newfoundland and Labrador (MMSC, 1998).

Harbor porpoises are known to inhabit bays, oceanic canals, and of course, harbors. They live in cold waters preferring water temperatures of 5 to 16 degrees Celsius (MMSC, 1998). In addition, they like turbulent, shallow waters that change direction frequently. They are primarily benthic feeders, (i.e. bottom feeders), feeding mostly on small, smooth, non-spiny fish such as herring, cod, and whiting. They feed in small groups using herding techniques to capture prey.

The harbor porpoise has a life expectancy of about 13 years, however few today live past age 8 (MMSC, 1998). Females reach sexual maturity at about age 3 to 4 years. Mating occurs during the months of July and August (Ellis, 1982). Harbor porpoises are one of the few species that have male and female bonding that suggests monogamy. The gestation period is approximately 10 to 11 months, and an adult female gives birth to one calf per year (Harrison, 1997). This birthing frequency is high in comparison to most cetaceans, which may give birth to only one calf every other year to every three years. In harbor porpoise families, the calf and mother have a very close bond and the mother will nurse for approximately 8 months.

Several unusual physiological characteristics enable harbor porpoises to persist in such harsh, cold environments. Their small size is atypical for cold waters (where a high surface area to volume ratio can lead to rapid heat loss). A comparison study was completed between the harbor porpoise and a fin whale, Balaenoptera physalus, by Kanwisher (1983). Both whales live in the same very cold waters however the fin whale has approximately 10,000 times the mass of the harbor porpoise. Studies showed the small porpoise had only 25% of its body weight in the form of muscle, while almost half its weight was composed of blubber. The fin whale ratios were very different; its weight comprised of 50% muscle and only one quarter blubber. Metabolic rates in the harbor porpoise were equally remarkable as theirs range between 2 to 3 times that of terrestrial mammals of the same weight. This accounts for why they must consume at least 10% of their body weight daily in food. High energy and food demands limit their migration and restrict their movements to only hundreds of square miles versus thousands of miles for most other cetaceans (Read, 1985).

All this metabolic activity requires greater oxygen demands as well, causing the porpoises to rise to the surface and breathe often, consuming three times more oxygen than the same sized terrestrial mammal (Kanwisher, 1983). They may surface as often as 8 times per minute with short, shallow breaths being taken each time (Harrison, 1974). The shallow waters and short breaths limit dives to only about 4 minutes.

Many of the problems associated with the poor life expectancy in harbor porpoises have centered on the commercial fishing industry. For harbor porpoises, gill nets can pose a serious life threat and they can easily drown in such devices. One study reported 4.3 % of the population the Bay of Fundy and Gulf of Maine are killed each year in gill nets (Read, 1990). Recently, techniques for reducing the likelihood of harbor porpoise captures in gill nets have been to place "pinging" devices on nets, allowing the porpoises to use their echolocation abilities to avoid entanglement. Early studies indicate these "pings" are working and do not affect commercial fishery catches (Read, 1990). Other problems have been postulated as causes for the decline of the harbor porpoises in some areas. Waters off the coast of New Brunswick have been warming slightly each year, which may be a cause of their decline in the Northern Atlantic (Read, 1985). Many researchers have questioned how these warming trends may affect the porpoises. Some feel the porpoises simply cannot thermoregulate in warmer waters, while others question whether the problem lies in food resources. No studies have been conclusive on either hypothesis (Forney, 1995).

Other habitats that are changing are the Bay of Fundy and the Gulf of Maine, where organochloride levels are high. Such toxins affect reproductive outputs of the harbor porpoises and may be affecting their numbers (Gaskin, 1985). During the 1980s, another threat arose when the Indians of the Pleasant Point Reserve tribe of Northern Maine were hunting porpoises as a food resource.

Harbor porpoises have been protected under the Canadian Fisheries Act since 1982. They have been listed as a threatened species in U.S. waters since 1990 (EEL, 1998). Efforts to clean up major harbors and their surrounding areas have helped to increase their numbers. The fishing industry’s commitment to prevent net entanglements has also helped the population to recover somewhat.

The harbor porpoise remains a threatened species in virtually all its habitats. Its status as the smallest cetacean makes it a very unique species worth preserving.

Ellis, Richard. Dolphins and Porpoises. Alfred A. Knopf, NY: 1982.

Environmental Education Link. Endangered Species. http://eelink.net/hrbprps.html

Forney, K.A. 1995. A decline in the abundance of harbor porpoise, Phocoena phocoena, in nearshore waters off California, 1986-1993. Fishery Bulletin. 93(4):741-48.

Gaskin, David E. and A.P. Watson. 1985. The harbor porpoise, Phocoena phocoena, in Fish Harbor, New Brunswick, Canada: occupancy, distrubution, and movements. Fishery Bulletin. 83(3): 427-42.

Harrison, R.J.. Functional Anatomy of Marine Mammals (vol.2). Academic Press, London: 1974.

Harrison, R.J.. Functional Anatomy of Marine Mammals (vol.3). Academic Press, London: 1977.

Kanwisher, John W. and Sam H. Ridgeway. 1983. The physiological ecology of whales and porpoises. Scientific American, 248: 110-20.

Marine Mammal Stranding Center. Info: Harbor Porpoise. http://www/mmsc.org/porpoise-harbor.html.

Read, Andrew J. and David E. Gaskin. 1990. Changes in growth and reproduction of harbor porpoises, Phocoena phocoena, from the Bay of Fundy. Canadian Journal of Fisheries and Aquatic Science. 47:2158-63.

Read, Andrew J. and David E. Gaskin. 1985. Radio tracking the movements and activities of harbor porpoises, Phocoena phocoena (L.), in the Bay of Fundy. Canadian Journal of Fisheries and Aquatic Science. 83(4): 543-52.

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