COSEWIC Status Reports (2003)


Species Information
The harbour porpoise is one of the smallest cetacean species, born at 80-90 cm and only occasionally reaching lengths of close to 2 m. In general, harbour porpoises are dark grey to black on the dorsal surface, and white on the belly, with no differences between males and females. They are a shy and short-lived species. The oldest individual aged in British Columbia waters was 10 years old.
Harbour porpoises are found throughout temperate and subarctic coastal waters of the northern hemisphere. In British Columbia they are found in shelf-waters throughout the province year-round, with the exception of some deep-water inlets. Density appears to be lower in deep-water basins, e.g., central Strait of Georgia.
In general, harbour porpoises have been reported to typically inhabit waters less than 200 m in depth. There is one record from British Columbia of a harbour porpoise approximately 55 km up the Fraser River, suggesting that movements into large rivers occur occasionally.
General Biology
Reproduction is seasonal, with births in British Columbia occurring from May through September. Age at sexual maturity for females is usually 3 or 4 years of age, though this is known to vary between populations, and has not been determined for the British Columbia population. Several lines of evidence suggest limited movements for harbour porpoises off western North America. This includes regional differences in pollutant ratios, cranial morphology, movements by individuals, and genetic markers. Stomach contents from stranded or incidentally caught harbour porpoises from southern British Columbia indicate that they have a diverse diet of small fish and squid, and diet overlaps strongly with that of Dall’s porpoise recovered from the same area. Squid seem to form a larger proportion of the diet of harbour porpoise in British Columbia than has been reported elsewhere. Associations with other species of cetaceans are uncommon, with some interactions being agonistic. Harbour porpoise appear to regularly hybridize with Dall’s porpoise in southern British Columbia.
Population Size and Trends
No province-wide abundance estimate is available, though a 1996 estimate for the Strait of Juan de Fuca and Strait of Georgia indicates there are likely several thousand animals. Anecdotal evidence suggests a decline in numbers in the southern part of the province between the 1940s-50s and the 1980s. Limited quantitative information did not detect a population trend through the 1980s or 1990s.
Limiting Factors and Threats
Incidental mortality in a number of fisheries in British Columbia has been documented, particularly in gillnet fisheries. The estimated number killed in salmon gillnets in southern British Columbia was <100 individuals in 2001. Harbour porpoises are known to be susceptible to disturbance by vessel traffic and loud underwater sound sources, such as acoustic harassment devices associated with aquaculture operations. Natural sources of mortality in the province include predation by sharks or killer whales (Orcinus orca). Existing protection or other status designations Harbour porpoises are listed in Appendix II of CITES (the Convention on International Trade in Endangered Species of Wild Fauna and Flora 1973), thus international trade of harbour porpoises or parts thereof by any countries which are Parties to CITES requires export permits from the country of origin. Harbour porpoises are considered "small cetaceans" by the International Whaling Commission (IWC), and are not covered by the IWC. Within Canada, harbour porpoises are managed under the Marine Mammal Regulations of the Fisheries Act.