Lagenorhynchus obliquidens
Pacific white-sided dolphin

Pacific white-sided dolphins have a primarily temperate distribution, remaining north of the tropics and south of the colder waters caused by arctic currents. Their range is from the Aleutian Islands through the Gulf of Alaska to the tip of Baja California in the eastern Pacific; and from Japan to the Kuril Islnads in the western Pacific.

They are usually seen in deep waters up to 160 km (100 miles ) offshore. There seem to be local migrations inshore in the winter months.

Pacific white-sided dolphins have torpedo-shaped bodies which help them move quickly through water. Body length of Pacific white-sided dolphins ranges from 150 to 310 cm. Their coloration is one of their most distinguishing features, they are black or dark gray on the dorsal surface with a white underside, and have bicolored fins and flippers. This coloration is believed to act as a form of camouflage in their aquatic environment.

Pods are made up of one dominant male and a number of other males and females. The dominant male mates with reproductively available females.

Female Pacific white-sided dolphins reach sexual maturity around 5-6 years of age, males are sexually mature at 8-10 years. Generally breeding occurs in the summer or fall, and gestation lasts approximately 11-12 months. Females give brith to a single calf, which is almost 3 feet long and can weigh up to 14 pounds.

Pacific white-sided dolphins are highly gregarious, sometimes seen in schools of 1000 or more. It is more common to find them in groups of 50. When a group member is ill or hurt, other members of the group will seldom leave their side.

Pacific white-sided dolphins eat fish that live in large schools, such as anchovies, herring, smelt, capelin, and mackerel. They feed in groups of 10-20 dolphins, each adult eating about 9 kilograms (20 lbs ) of food each day.

Pacific white-sided dolphins are not considered to be endangered. A recent estimate of the population of these mammals in the central North Pacific ranged between a minimum of about 500,000, to a maximum of 930,000. Therefore there is not any immediate danger for the extiction of these animals. They are hunted by Japanese coastal fishermen in the East China and Japan seas and taken accidentally in the North Pacific purse-seine fishery.