Harbour porpoise. Also known as herring hog, sea pig, and common porpoise
Harbour porpoises are coastal species that are typically found in relatively shallow waters to about 150 meters. However, there have been sightings of harbour porpoise in much deeper areas, for example, in Georgia Strait, harbour porpoise have been observed in waters over 400 meters deep.
The harbour porpoise has a Northern Hemisphere, circumpolar distribution and is found in the Pacific and Atlantic Oceans, and in the Black Sea and Sea of Azov. This species inhabits the cold-temperate, sub-arctic neritic waters of North America, Russia and Eurasia; as well as some mid North Atlantic landmasses, such as the Faeroe Islands, Greenland and Iceland. They are typically found in coastal ocean waters, although they have been reported to swim up rivers while pursuing prey.
of 1.4 to 1.9 meters long and weigh between 45-60 kg.
Harbour porpoises are grayish-brown on their backs and sides, with white undersides. There are often gray stripes or flecks within the white pigmentation, especially in the throat region. A distinctive lateral grey – brown stripe extends from the corner of the mouth to beginning of the pectoral flipper on both sides of the animal. The width and pigmentation of this stripe varies among individuals, and is rarely visible on wild, healthy animals.
A harbour porpoise’s life expectancy is typically around 8-12 years, however, some have been reported to have lived 20 years.
Behaviour (e.g. sounds, foraging):
Harbour porpoise surface with a gentle rolling motion. They infrequently breach or display at the surface, however when feeding along tide lines, they will often surface quickly creating a low splash. Unlike Dall’s porpoise, harbour porpoises rarely approach vessels that are underway and are often considered shy. However, the harbour porpoises of southern British Columbia have been observed to occasionally exhibit vessel curiosity, especially when clustered in large aggregations. During these aggregations, they have been observed to “surf” in the vessel’s stern wake.
Harbour porpoise can emit a very broad frequency range (40 Hz to at least 150 kHz) of sounds. Some are within our hearing range (sonic) and others are above the frequency range that humans can hear (ultrasonic). They use slow, repeated echolocation clicks for navigation and rapid bursts of echolocation to focus in on prey or other items of interest. Harbour porpoises have also been reported to use whistles, which may have social or communication significance.
Harbour porpoise’s diet preferences often overlap with species that are commercially important to humans. They typically eat a variety of fish and squid between 10 – 25 centimeters in length, such as herring, hake, codfishes, and also on small squid (cephalopod). Pacific cephalopod prey species consumed include the market squid or opal squid, also known as calamari.
Harbour porpoise feed on prey both within the water column and on the sea floor. Like other odontocetes, they cannot chew, so they must swallow their prey whole. It has been proposed, that harbour porpoise may go for larger fish, but will attack them from behind and bite through them at the gills, ingesting the body without the head. Experiments at the Harderwijk rehabilitation center for stranded harbour porpoise in the Netherlands have shown that harbour porpoise actually create negative pressure in their mouths, using their tongues, to suck the fish into their mouths. This would reduce the likelihood that a live fish could escape. They also manipulate fish to swallow them headfirst. Some harbour porpoises have died by trying to eat prey that is too large to swallow.
Harbour porpoise give birth to one calf every year to every other year after a 10-11 month gestation period. Lactation lasts for approximately 9 months but calves will start to consume solid food at about 5 months of age. Calves may stay with their mothers for up to another 9 months post-weaning. Groups of 2 –3 animals are very common in British Columbia and it is possible that these groups are mothers with their growing calves. Reproduction is thought to be based on sperm competition, rather than competition between males for females. This is because the testes of a male harbour porpoise are exceptionally large during the reproductive season and may account for 4-6% of his body weight. This means that a 50kg male, will have approximately 2 kg testes!
Globally, there are an estimated 700,000 harbour porpoises in our oceans at minimum. That is a conservative estimate, as the most recent population assessment was completed in 2016.
Under Canada’s Species At Risk Act, the harbour porpoise is classified as a species of Special Concern in both the Atlantic and Pacific Oceans. The harbour porpoise is considered particularly sensitive to human activities. Conservation threats include anthropogenic noise, entanglements, and other fisheries activities.