The Pacific white-sided dolphin has a short, rounded, thick beak containing 23–32 small, rounded slightly curved teeth in each side of the upper and lower jaws. This dolphin is energetic and is frequently seen leaping, belly flopping, and somersaulting. It is a strong, fast swimmer and enthusiastic bow rider, often staying with moving vessels for extended periods. The Pacific white-sided dolphin is attractively marked. Its back is black and its sides are light gray with thin, white stripes that extend from above the eye along the sides, widening towards the tail; its belly is white. It has a black beak and lips and a black ring around each eye. Its dorsal fin is tall and sharply hooked, and is located at the center of the back. The leading edge is black and the rear portion is light gray. Its flippers are small and curved and rounded at the tips. Its flukes are notched in the centre. These dolphins reach a length of 2.1–2.4 m (8 ft) and weigh up to 150 kg (330 lbs). They are often found in large herds of 90–100, made up of animals of both sexes and all ages. Since they share the same range, they are most commonly seen with Northern right-whale dolphins and are often seen accompanying other dolphins and large whales. They are considered residents in some parts of their range, notably Monterey Bay and off southern California and northwestern Baja California. Transient groups from other areas from the fall to spring join these resident populations.
World Range and Habitat
The Pacific white-sided dolphin inhabits temperate, coastal waters in the North Pacific, avoiding both tropical and Arctic waters. Its range extends from Amchitka Island in the Aleutians, to the Gulf of Alaska south along the coast of North America to the tip of Baja California. It is abundant in Japanese waters with estimates of 30,000–50,000 in that area.
Pacific white-sided dolphins eat squid and small schooling fish such as anchovies, herring, sardines, and hake. It is believed they feed largely at night.
Sexual maturity for both sexes is reached when they are 1.8m (6ft) in length, but this can vary according to geographical location. Length at birth is 80–95cm (3.1 ft); gestation period is estimated to be 9–12 months.
Warnings and Comments
This species is no longer commercially hunted in the United States. Some are taken for food in Japan’s coastal fishery. They are difficult to catch, however, and the numbers taken are not a threat to the total population in Japanese waters. A few have been captured for display in aquariums, and unknown numbers have been accidentally killed in drift and gill nets. Population figures are unknown.