Harbour porpoise

Description

  • Robust, human-sized body
  • Dark back, lighter sides and belly
  • Large triangular-shaped dorsal fin

When it surfaces: The spout is not visible. With its small size and rapid, splashless swimming, it creates the impression that it is rolling across the water’s surface. It swims alone or in small groups.

Marsouin commun

Phocoena phocoena

Other names: Common porpoise, puffing pig, herring hog

Suborder: Toothed whales (Odontoceti)

Length: 1.5 to 2 m

Weight: 45 to 50 kg, up to 65 kg

Social behaviour: Sometimes solitary or in pairs but usually in groups of 5 to 10 individuals

Life expectancy: 10 to 13 years

Dive time: 1 to 3 minutes, up to 12 minutes

Observations: Regular in the Gulf and Estuary

Global range: Coastal waters of the Northern Hemisphere

Global population: Unknown, probably declining

Status in Canada: Special Concern


Life is short, but intense!

Of all the cetaceans of the St. Lawrence, harbour porpoises are the smallest and have the shortest life spans. Their lives seem to revolve around urgency and performance, with one dominant driver for both sexes: reproduction.

Population, range and habitat

In the St. Lawrence

In summer (end of June to end of September), harbour porpoises frequent coastal zones of the Gulf and the Estuary. They can often be found in fjords, bays, estuaries and ports (hence their name). In the Gulf of St. Lawrence, the population is estimated at over 20,000 individuals.

Migration

The harbour porpoise’s winter habitat is poorly understood. They are believed to move offshore to avoid ice. According to an analysis of bycatch conducted in the 1970s, some individuals are believed to spend the winter in the Estuary.

In the world

The harbour porpoise inhabits temperate and subarctic coastal waters of the Northern Hemisphere. The population of the Northwest Atlantic is divided into four sub-populations: those of the Gulf of St. Lawrence; the Bay of Fundy and Gulf of Maine; Newfoundland and Labrador; and Greenland. The species is also present in the North Pacific. There is even a population in the Black Sea (a sea bordering several Eastern European countries, Russia and Turkey) and in the Sea of Azov (an extension of the Black Sea).

Status

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) designated the harbour porpoise of the Northwest Atlantic “threatened” in 1990. The status of the population was reviewed in 2003 and is now classified “special concern”. Due to a decline in the fishing industry and efforts made to reduce incidental catches in the Bay of Fundy, the COSEWIC considers that fewer harbour porpoises are dying accidentally. The Committee maintains however that incidental catches still represent a potentially limiting factor for this population and that the situation warrants monitoring.

The International Union for Conservation of Nature (IUCN) has designated the harbour porpoise of “least concern”, whereas in the United States, the species is not included in the List of Endangered and Threatened Wildlife under the Endangered Species Act.

None of these statuses applies specifically to the sub-population of the St. Lawrence. The species does appear however in the List of threatened or vulnerable species in Quebec under the Act Respecting Threatened or Vulnerable Species.

Behaviour

Feeding

The harbour porpoise searches for its food in the water column (small schooling fish such as capelin, herring, pollock, mackerel) and on the seabed (squid and crustaceans).

On the surface

Its rapid swimming movement creates the impression that it is rolling on the surface. Its spout (etymologically, “porpoise” means “sea hog”) can only be heard in calm weather. Although a slow swimmer, the harbour porpoise can cover vast distances in a day. Once they surface, porpoises sometimes remain motionless for a few seconds before diving again. They rarely leap out of the water. Harbour porpoises are wary and not usually curious toward boats.

Diving

Their short dives generally do not exceed 5 minutes, reaching depths varying between 15 and 130 m (documented record: 226 m).

Social

Harbour porpoises are gregarious, living in small groups of 2 to 5 individuals that can gather in herds of a few dozen or even a few hundred individuals. These groupings are most certainly linked to feeding. Expansive territories of thousands of square kilometres can be used by harbour porpoises, which are highly mobile.

Vocalization

The porpoise emits repeated clicks but also low-pitched sounds which are believed to be used for communication and echolocation.

Reproduction

Males reach sexual maturity between 3 and 4 years of age and females, between the ages of 2 and 4. The reproductive strategy of males is based on sperm competition and they are well endowed for the purpose, with testicles reaching impressive proportions during the reproduction season: from 4 to 7% of their body mass (e.g. 3 kg for a body mass of 45 kg). He who produces the most sperm will be entitled to repetitively mate with one or more females. Mating takes place between July and August. Gestation lasts about 10 months. Calving occurs annually in spring and early summer (peaking in June). Nursing lasts between 8 and 12 months. Harbour porpoise cows are amongst the few cetaceans that are able to give birth every year, meaning that they are simultaneously pregnant and lactating for the majority of their adult life…an enormous physiological investment!

About scientific research

Harbour porpoises’ coastal habits and our fishing methods don’t make a good match. In the early 1990s, thousands of incidental catches in fishing nets prompted fears for the species’ survival. Mortalities have in all likelihood declined since the cod fishing moratorium implemented in the St. Lawrence in 1993, but the threat may still be a concern for the population’s recovery, according to the work of Véronique Lesage of Fisheries and Oceans Canada.

In the news

Fin the latest articles about the harbour porpoise.