Harbour porpoise (Pacific Ocean population) COSEWIC assessment and status report: chapter 16

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Species Information

Name, Classification and Taxonomy

Three subspecies of harbour porpoise, Phocoena phocoena (Linnaeus 1758), are generally recognized (Rice 1998), P. p. phocoena in the North Atlantic, P. p. vomerina in the eastern North Pacific, and an unnamed subspecies in the western North Pacific (see also Amano and Miyazaki 1992). Genetic evidence suggests that the North Pacific and North Atlantic populations have been isolated for between 1 and 5 million years (Rosel et al. 1995; Wang et al. 1996).

Morphological Description

The harbour porpoise (Figure 1) is one of the smallest cetacean species. In British Columbia they are approximately 80-90 centimetres at birth, and occasionally reach lengths of close to 2 metres (Baird and Guenther 1995). Females grow faster and reach greater lengths than males (Read and Tolley 1997). In general, harbour porpoises are dark grey to black in colour on the dorsal surface, and white on the belly, with no differences in colouration between males and females (Koopman and Gaskin 1994). They are distinguished fairly easily from the other two relatively common small cetaceans on the British Columbia coast (Pacific white-sided dolphins, Lagenorhynchus obliquidens, and Dall’s porpoise, Phocoenoides dalli), due to differences in colour pattern and body shape, as well as behaviour. Harbour porpoises typically travel in smaller groups (usually 1-8 individuals) than white-sided dolphins, usually avoid boats, and normally show very little of their body above water. Hybrids with Dall’s porpoise (see Baird et al. 1998: Willis et al. 2004) can consistently be seen in some areas around southern Vancouver Island (e.g., 4 or 5 individual hybrids can often be seen in one day in Boundary Pass or Haro Strait; Baird, personal observations), and could easily be misidentified as harbour porpoise from a distance (e.g., from aerial surveys). At close range they are fairly easy to discriminate, as the hybrids are a lighter grey, regularly bowride on vessels, and commonly associate with Dall’s porpoises.