Wildlife Species Description and Significance
The Pacific Harbour Porpoise (Phocoena phocoena vomerina) is the smallest cetacean in British Columbia (BC), ranging from 1.5 to 1.6 m and 45 to 60 kg at maturity. The species has a small dorsal fin and is grey to brown dorsally, and white to greyish-white ventrally. It is typically elusive and difficult to observe in the wild, but the inshore distribution, year-round residency and proximity to populated areas in BC results in a higher probability of exposure to human-made activities and influences than most other cetaceans in the province. Strandings of Harbour Porpoises are reported more often in BC than those of other cetacean species. Regional population changes have the potential to go unnoticed because systematic surveys are spatially and temporally discontinuous, and there are no comparable data sets over long time periods.
Globally, Harbour Porpoises have a circumpolar distribution in cold temperate to subarctic waters of the northern hemisphere. In BC, Harbour Porpoises occur throughout coastal waters. They are more often found in shallow regions, but are not restricted to these habitats.
Harbour Porpoises generally occupy an ecological niche consisting of coastal shelf waters less than 150 m deep, with temperatures ranging between 6 to 17°C. In BC, they also occupy deeper waters exceeding 200 metres. Identified deep water habitats exist in southern and northern BC: in the Strait of Georgia, off the southwest coast of Haida Gwaii, and southeast of Cape St. James.
Harbour Porpoises mature by about age four—younger than most cetaceans. Parturition occurs in the spring followed by a period of mating activity in the late summer/early fall. Harbour Porpoises feed on a variety of small, schooling fish and squid, often in areas with high rates of current flow. They are prey of Transient (also known as Bigg’s) Killer Whales in BC. Predation on Harbour Porpoises by sharks is likely, but has only been reported once in BC waters. Based on telemetry, photo-identification and some genetic studies, population structure may exist in BC waters, but boundaries are not clear. It remains uncertain as to whether a single population or subpopulations of Harbour Porpoises exist within BC waters.
Population Sizes and Trends
No systematic long-term surveys of Harbour Porpoises have been carried out in BC and the total population size and recent trends are unknown. Aerial surveys flown over US inland waters of Washington State as well as over the Strait of Georgia in Canada showed a significant increase in abundance between 1996 and 2002–2003. This is consistent with anecdotal evidence suggesting that abundance in BC may have increased over the past decade. However, in waters of southeastern Alaska to the north of BC, Harbour Porpoise numbers have declined in some areas.
Threats and Limiting Factors
The overall calculated and assigned threat impact is High to Medium for Pacific Harbour Porpoise. This is a result of the combined effect of a number of low to medium-impact threats. The principal known anthropogenic threats to Harbour Porpoises are habitat degradation due to acoustic disturbance, entanglement in fishing gear, and fisheries. Other threats that are known, suspected, or predicted to have negative impacts on survival of Harbour Porpoise include shipping traffic, pollution, pathogens, predation, and habitat loss due to coastal developments. Synergistic effects of anthropogenic activities may also limit Harbour Porpoises.
Protection, Status, and Ranks
Harbour Porpoises are currently listed as Special Concern under the Species at Risk Act (SARA). Nationally they are nominally protected under the Marine Mammal Regulations. Provincially, Harbour Porpoises are a Blue-listed species (Special Concern) and in 2009 were assigned Conservation Framework Priority 4, although this provides no additional protection to the federal legislation.