Harbour porpoises species vary in size across a geographical range, with males generally being slightly smaller than females of the same age.
Adult length averages 1.4 metres with a maximum of 1.8 metres. Adult weight averages about 41kg. Calves are about 75cm long at birth, with an average weight of 5kg (Watson, 1981).
Maximum longevity is reported as 24 years in the United Kingdom (Lockyer, 1995b), but most do not live beyond 10 years (Jefferson et al, 2008).
The species matures very quickly, with females being able to reproduce at around 14 months old, and males at around 3 years (Watson, 1981).
Reproduction is extremely seasonal in all populations of harbour porpoises, with ovulation and conception occurring in spring or summer (Read, 1999).
Gestation is 10-11 months, calves are nursed for around 8-12 months and females may become pregnant again the following season (Watson, 1981; Jefferson et al, 2008).
White sharks and killer whales are the two major predators of harbour porpoises (Read, 1998).
In some areas, harbour porpoises have been taken heavily by humans, with their meat being used for human and animal consumption, and their oil for lamps and lubricants (Nowak, 2003).