Harbour Porpoise – Phocoena phocoena
Habitat: Subtropical to too temperate and subarctic waters, usually but not exclusively over the continental shelf at depths of 20 – 100 m. Commonly found in coastal bays, estuaries, around headlands, in tidal channels; in most parts of NW Europe, most common cetacean within 10 km of coast.
Description: Small rotund body, small head, no obvious forehead or beak. 19 – 28 pairs of small, spade-shaped teeth in each jaw. Dark grey back with paler grey patch on flanks and white belly, although colouration on back and sides variable. Grey line from flippers to jawline. Short, slightly rounded flippers. Upper and lower jaws, chin, flippers, flukes grey or blackish. Low triangular dorsal fin centrally placed on back. Flukes have central notch.
Size: 145 – 160 cm, females larger; male maximum 163 cm, female maximum 189 cm. Smallest cetacean in British waters.
Weight: 50 – 55 kg; male maximum 54 kg, female maximum 81 kg.
Lifespan: 12 years, maximum of 24.
Distribution: Cool subtropical to subarctic seas of Northern Hemisphere. In E North Atlantic, widely distributed over continental shelf from Barents Sea, south to coasts of Portugal and Spain, off west Africa from Morocco to Senegal. Isolated population in Black Sea. Occurs year round in coastal waters of British Isles, peaks in July – October, and along South coast of England, in January – April.
Became scarce in S North Sea, English Channel, Bay of Biscay in 1960s; sharp increase in late 1980s – 90s, peaking in 2005/6. Sudden change not well understood, but probably reflects shift in distribution caused by decrease in sandeels further north, recovering in some North Sea herring stocks, or combination of both.
Diet & Feeding: Varies geographically and seasonally. Primarily small schooling fish. Takes small cephalopods but less often than fish. Little known about feeding methods. Captive individuals require 4 – 9.5 % body weight in food per day.
Breeding: Young born May – August, though some early as March, peaks in June. Mating season April – September, peaks in July – August. Gestation period 10 – 11 months; lactation period up to 10 months with calves taking solid food from 2 – 3 months; calving interval 1 – 2 years. Age at sexual maturity 3 – 5 years, little difference between sexes.
Conservation Status & Population: Listed by IUCN as vulnerable. Estimated population 341,366 in 1994 from North Sea, Baltic, Channel, and Celtic Sea. Repeat survey in 2005 over larger area gave estimate of 386,000.
Exposed to variety of human activities. Formerly hunted in drive fisheries in Baltic and off Faroes. Major threats currently fishery conflicts. Incidentally caught in variety of fishing gear including fixed nets, traps, herring weirs, trawls, drift nets, purse seines. Estimated 6 % of population caught each year in English and French bottom-set gillnet fisheries. Sound disturbance and ship strikes occur due to living in vicinity of vessel traffic.
Smallest British cetacean. Rarely leaps clear of water. Short blunt head, no beak, small triangular dorsal fin. Teeth spade shaped – in all delphinids, they are conical.
Vocalisations: High frequency sounds for echolocation and communication, but not FM whistles typical of delphinids. Click trains produced in 2 narrow frequency bands; one weaker and of longer duration at 1 – 20 kHz, one at 120 – 160 kHz of shorter duration. Repetition rates of pulses range between 0.5 – 1000 clicks /s.