The Pacific white-sided dolphin (Lagenorhynchus obliquidens) is a very active dolphin found in the cool to temperate waters of the North Pacific Ocean.

Taxonomy

The Pacific white-sided dolphin was named by Smithsonian mammalogist Theodore Nicholas Gill in 1865. The Pacific white-sided dolphin is morphologically similar to the dusky dolphin, which is found in the southern Pacific. Genetic analysis by Frank Cipriano suggests the two species diverged about two million years ago.

Though both are traditionally placed in the genus Lagenorhynchus, molecular analyses indicate that they are closer to dolphins of the genus Cephalorhynchus. The new genus Sagmatias has been proposed for these species.^[3]

Physical description

Pacific White-sided Dolphin named Spinnaker at Vancouver Aquarium.

The Pacific white-sided dolphin has three colors. The chin, throat and belly are creamy white. The beak, flippers, back, and dorsal fin are a dark gray. There are light gray patches on the sides and a further light gray stripe running from above the eye to below the dorsal fin where it thickens along the tail stock. A dark gray ring surrounds the eyes.

The species is an average-sized oceanic dolphin. Females weigh up to 150 kilograms (330 lb) and males 200 kilograms (440 lb) with males reaching 2.5 meters (8.2 ft) and females 2.3 meters (7.5 ft) in length. Pacific white-sided dolphins tend to be larger than dusky dolphins. Females reach maturity at 7 years. The gestation period is one year. Individuals live 40 years or more.

The Pacific white-sided dolphin is extremely active and mixes with many of the other north Pacific cetacean species. It readily approaches boats and bow-rides. Large groups are common; averaging 90 individuals, with supergroups of more than 300. Prey is mainly hake, anchovies, squid, herring, salmon and cod.

They have an average of 60 teeth.^[4]

Range and habitat

The range of the Pacific white-sided dolphin arcs across the cool to temperate waters of the north Pacific. Sightings go no further south than the South China Sea on the western side and the Baja California peninsula on the eastern. Populations may also be found in the Sea of Japan and the Sea of Okhotsk. In the northern part of the range, some individuals may be found in the Bering Sea. The dolphins appear to follow some sort of migratory pattern—on the eastern side they are most abundant in the Southern California Bight in winter, but further north (Oregon, Washington) in summer. Their preference for off-shore deep waters appears to be year-round.

The total population may be as many as 1 million. However, the tendency of Pacific White-sided Dolphins to approach boats complicates precise estimates via sampling.

Relation to humans

Protection

Pacific white-sided dolphin's brain at Okinawa Churaumi Aquarium

Until the United Nations banned certain types of fishing nets in 1993, many Pacific white-sided dolphins were killed in drift nets. One researcher estimated somewhere 50,000–89,000 individuals were killed in the twelve years to 1990. Some animals are still killed each year by Japanese hunting drives.

In popular culture

• Although overshadowed in popularity by bottlenose dolphins, Pacific White-sided Dolphins are also a part of some marine theme park shows.
• Venus Among the Fishes is a book by Elizabeth Hall, that has a female Pacific white-sided dolphin as its protagonist.

Captivity

High-jump during Pacific White-sided Dolphin show at the Vancouver Aquarium

Pacific white-sided dolphins adapt well to captivity. Almost 50 reside in dolphinariums in North America and Japan.

Natural History

These dolphins keep close company. White-sided dolphins swim in groups of ten to one hundred, and can often be seen bow-riding and doing somersaults. Members form a close-knit group and will often care for a sick or injured dolphin.

Animals that live in such big social groups develop ways to keep in touch--each dolphin identifies itself by a unique name-whistle. Staying close helps, too. Young dolphins communicate with a touch of a flipper as they swim beside adults.

See also

Cetaceans portal

Marine life portal

• List of whale and dolphin species
• Marine biology

References

• Pacific White-sided Dolphin and Dusky Dolphin by Koen van Waerebeek and Bernd Würsig Encyclopedia of Marine Mammals pp 859–60 ISBN 0-12-551340-2
• National Audubon Society: Guide to Marine Mammals of the World ISBN 0-375-41141-0
• Encyclopedia of Marine Mammals ISBN 0-12-551340-2