Dall's porpoise

Phocoenoides dalli
Other names: 
  • White-flanked porpoise
  • True's porpoise
Maximum length: 
  • Male: 2.4m
  • Female: 2.2m
  • Calf: 1m
Maximum weight: 
  • Male: 200 kg
  • Female: Unknown
  • Calf: Unknown
Diet: 
  • Surface and mid-water fish
  • Myctophids and gonatid squid
Estimated population: 
1.2 million
IUCN Listing: 
LC
CITES Appendix: 
II
CMS Appendix: 
II
Classification: 

Dall's porpoises have been extensively exploited over the years and remain one of the main species hunted by Japanese fishermen with catch rates reaching as high as 40,000 individuals a year. Two subspecies are currently recognised; P. d. dalli, (Dalli's type) which is more widespread, and P. d. truei (Truei's type) which is restricted to the western sector of the species range. Although both display a piebald appearance, these two subspecies show variation in both colour and size.

Appearance: 

The Dall's porpoise is the largest species of porpoise and has a robust compact body. It has a relatively small head with a short beak with an upturned mouthline and a rather flat forehead. The forward-leaning, triangular dorsal fin has a broad base and may have a hooked tip. The pale white/grey patch on the top looks like 'frosting' and it is a distinctive feature of this animal. Small rounded flippers are set close to the head and it has a thick tailstock and keel which is more exaggerated in males. The notched flukes sometimes have a white upper trailing edge. Colouration varies between subspecies. The dalli-subspecies is black with a bright white patch extending along the side and belly from just below the dorsal fin to the middle of the tail stock whilst the white patch on the truei-subspecies starts further forward, just in front of the flippers. Due to their distinctive colouration, Dall's porpoises are not easily confused with other species of cetacean.

Behaviour: 

The Dall's porpoise has an extremely ‘un-porpoise-like' behaviour. Most members of this Family are quiet and shy, preferring to avoid boats while the Dall's porpoise actively seeks out large fast moving vessels. The Dall's porpoise is the fastest swimming small cetacean, and in short bursts can reach speeds of up to 55 km/h, surfacing rapidly producing a distinctive spray of water called a ‘rooster tail'. They are eager bow-riders but will not stay long with boats moving slower than 20 km/h. While it is a very active swimmer it rarely breaches or engages in other forms of acrobatic display. Generally found in groups of fewer than 20 animals, aggregations of more than 1,000 individuals have been seen. Often found to associate with Pacific white-sided dolphins and long-finned pilot whales, Dall's porpoises are predominantly an oceanic species however they can be found in more coastal waters where deep water is closer to the shore. They feed at night on fish and cephalopods in waters as deep as 500m.

Distribution: 

The Dall's porpoise is found in the colder waters of the North Pacific Ocean and the Japan, Bering and Okhotsk Seas. The dalli-subspecies is found from the US-Mexico border in the south to approximately 60°N and from Central Japan to the Bering and Okhotsk Seas. The truei-subspecies is found only in the West Pacific between 35°N and 54°N. The greatest threat to this species is undoubtedly the directed hunts undertaken by the Japanese, whilst other threats include bycatch and chemical pollution. Dall's porpoises are reported to have been found with high levels of organochlorines and this may affect reproduction. The IUCN Red List classifies this species as of Least Concern.

Distribution map: