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Gill, 1865 - Pacific white-sided dolphin

Distinctive Characteristics

Pacific white-sided dolphins, like all members of the genus Lagenorhynchus, are stocky animals with very short, thick snouts. The large flippers have slightly rounded tips. The dorsal fin, the species' most diagnostic feature, is prominent, strongly recurved, and bi-coloured.

The dark grey back and sides are distinctly set off from the white belly by a black border. Light grey streaks beginning on the sides of the melon sweep downwards behind the eye and expand into large grey thoracic patches. Grey “suspender stripes”, whichstart above the eyes, widen to bands on the sides of the tail stock. The lips are black.

Each tooth row contains 23 to 36 pairs of relatively fine, sharply pointed teeth.

Can be confused with

Pacific white-sided dolphins are most likely to be confused with common dolphins, because both species are found in large schools and have large light coloured flank patches. Beak length and specifics of the colour pattern are the best keys to distinguishing them.

Size

Adults of this species reach 2.5 m in length, with males slightly larger than females. Maximum weight is about 180 kg. Length at birth is unknown, but is thought to be about 1 m.

Geographical Distribution

Pacific white-sided dolphins inhabit temperate waters of the North Pacific and some adjacent seas. Although they are widely distributed in deep offshore waters, they also extend onto the continental shelf and very near shore in some areas. They reach their southern limits at the mouth of the Gulf of California (and occasionally venture northward to or beyond La Paz) and Taiwan. On both eastern and western sides of the Pacific, separate local stocks have been documented.

Biology and Behaviour

Often seen in large herds of hundreds or even thousands, these highly gregarious dolphins are also commonly seen with other species, especially northern right whale dolphins and Risso's dolphins. They are highly acrobatic and playful, commonly bowriding, and often leaping, flipping, or somersaulting.

Calving apparently occurs during a protracted summer breeding season, which extends into autumn.

They feed mostly on small schooling fish and squid. There is evidence that these dolphins feed mostly on deep scattering layer (DSL) organisms, sometimes using cooperative foraging techniques.

Exploitation

In the western Pacific, Japanese drive and harpoon fisheries take hundreds or thousands of Pacific white-sided dolphins in most years. Exploitation in the eastern Pacific has been limited to occasional incidental capture in fishing nets, and small numbers taken in a fishery for live animals. In the central Pacific, white-sided dolphins were recently killed in substantial numbers in the Asian pelagic driftnet fisheries for squid. The annual kill was on the order of 8000 to 10,000 per year.

IUCN Status

Insufficiently known.

Pacific white-sided dolphin (Lagenorhynchus obliquidens)