Pacific white-sided dolphin

Lagenorhynchus obliquidens
Other names: 
  • Hook-finned porpoise
  • White-striped dolphin
  • Lag
  • Pacific-striped dolphin
Maximum length: 
  • Male: 2.5m
  • Female: 2.4m
  • Calf: 0.9m
Maximum weight: 
  • Male: 200kg
  • Female: 150kg
  • Calf: Unknown
Diet: 
  • Small schooling fish (including hake, anchovies, saury and mackerel)
  • Squid
Estimated population: 
Unknown
IUCN Listing: 
LC
CITES Appendix: 
II
CMS Appendix: 
Not Listed
Classification: 

The Pacific-white-sided dolphin is very similar in appearance to its close relative the dusky dolphin (L. obscurus) though their ranges do not overlap. In recent years, there was the suggestion that it was in fact a sub-species of the dusky dolphin however genetic studies have made this assertion redundant. Indeed it is considered that before long the genus Lagenorhynchus will include only the white-beaked dolphin (L. albirostris), with other members being reclassified as being of the genus Sagmatias.

Appearance: 

The Pacific white-sided dolphin has a robust body with a very short stubby beak and black lips. The dorsal fin is one of the most distinguishing characteristics of this species being tall, falcate, and bicoloured with a black leading edge fading to grey on the trailing edge. The large flippers are similarly coloured with rounded tips. Overall the Pacific white-sided dolphin is dark grey or black in colour. As its name suggests, it has a greyish thoracic patch which extends down the sides to just below the dorsal fin. Thin greyish stripes under the dorsal fin meet and broaden along the tailstock. The throat and belly are bright white. The eye is surrounded by a dark patch and there is a black stripe running from the face to the flippers and down to the anus, separating the white underside from the greyish flanks. Several colour morphs exist throughout the species range. The Pacific white-sided dolphin may be confused with the common dolphin, but the latter has a more pronounced beak and different colour pattern, whilst the former can usually be easily identified by its diagnostic dorsal fin.  

Behaviour: 

Pacific white-sided dolphins are extremely agile, acrobatic and social. Generally traveling in groups of tens or hundreds of individuals, they can be seen in herds of 2,000 or more. Groups are often segregated according to sex and age. They associate with many other species including northern right-whale dolphins, Risso's dolphins, sea lions, and seals. They are avid bow and wake riders, and are known to actively approach boats. They can be seen performing leaps, flips, spins, somersaults, and they often porpoise at high speeds. Large groups travelling at high speeds create a lot of surface disturbance that is visible from a great distance.

Distribution: 

The Pacific white-sided dolphin is found in the cool temperate waters of the North Pacific and adjoining seas. It prefers deep, offshore waters around the continental shelf although they can also be found in more nearshore waters. In recent decades the major threat to this species was bycatch in drift and gill-net fisheries operated on the high seas. Many thousands of individuals were killed before the fisheries were banned in 1993. Bycatch in other fisheries however remains a threat. Pacific white-sided dolphins have also been taken in small numbers off the coast of Japan, and that country is considering starting regular hunting of this species again. Other threats include prey depletion, marine debris and the impacts of climate change. There is no reliable global population estimate for this species and the IUCN categorises this species as of ‘Least Concern'.

Distribution map: