Report of the International Whaling Commission (1995)


Specimens of harbour porpoises, Phocoena phocoena, from strandings and bycatches in fisheries around the British Isles between 1985 and September 1994 have been examined. Full autopsies were undertaken on most carcases, and measurements and samples taken. The date of finding, location, sex, total body length, body weight, reproductive organs and teeth of all specimens were collected during this period. A total sample of 234 individuals (including 114 males and 96 females) were aged, using decalcified thin stained sections of teeth. The sample included neonates through to animals age 24yrs. The modal age class was 0-1 yr. Preliminary investigation of the age distribution indicated higher overall survival in females, with the lowest survival in the first year of life for both sexes. Birth size appeared to be 65-70cm length and 5kg weight (neonates with unhealed umbilicus range from 60-75cm length and weight of 3-9kg). The maximum body length in the sample was 163cm in males
and 189cm in females. Maximum weights of 54kg and 81kg were recorded for males and females respectively. The inferred peak calving period is June, with high numbers of neonates and calves found stranded between June and September. Preliminary data suggest that age at sexual maturation in males is probably about 3yrs onwards. Peak testes weight was observed in June-August and peak births in June. This suggests a gestation period of approximately one year in harbour porpoise. Throughout the investigation, it has not been possible to distinguish reliably between bycatch and natural strandings.