Pacific White-Sided Dolphin

 

Status
MMPA - Pacific white-sided dolphins, like all marine mammals, are protected under the MMPA.

Taxonomy
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Cetacea
Family: Delphinidae
Genus: Lagenorhynchus
Species: obliquidens

The Atlantic white-sided dolphin (Lagenorhynchus acutus) is another species of white-sided dolphin.

Species Description
Pacific white-sided dolphins have a robust body and a very short beak. They have an unusually large, curved dorsal fin and are sometimes referred to as the "hookfin porpoise," even though they are not porpoises. Their back, fluke (tail), and lips are black, while their sides, dorsal fin, and flippers are gray. Their belly is white. On both sides of the dorsal fin, a white or light gray stripe, which resembles a pair of suspenders, extends from the eyes to the tail. Pacific white-sided dolphins can sometimes be confused with Dall's porpoise, which shares a similar distribution pattern. They are the only members of the genus Lagenorhynchusin the North Pacific Ocean.

The average adult Pacific white-sided dolphin weighs about 300-400 lbs (135-180 kg) and is between 5.5-8.0 feet (1.7-2.5 m) long. Males are generally larger than females, with males reaching an average length of 8 ft (2.5 m) and females reaching an average length of 7.5 ft (2.3 m). This species of dolphin can live for more than 40 years.

Pacific white-sided dolphins are extremely playful and highly social animals. Schools of thousands of Pacific white-sided dolphins are occasionally observed, but group size generally ranges from 10-100 animals. They are often observed "bow riding" and doing acrobatic somersaults. This species commonly associates with other cetaceans, such as Northern right whale dolphins and Risso's dolphins.

They prey on squid and small schooling fish such as capelin, sardines, and herring. This species is capable of diving more than 6 minutes to feed. They have small conical teeth that are helpful in grasping their prey. When feeding during the day, they can be seen working together as a group to herd schools of fish.

Pacific white-sided dolphins reach sexual maturity around 7-10 years of age around lengths of 5.5-6 ft (1.7-1.8 m). Gestation lasts for 12 months with calves being born in the summer months. Calves weigh approximately 30 pounds (15 kg) and are about 2.5-4 feet (1-1.2 m) in length. Females give birth less than every other year.

Habitat
Pacific white-sided dolphins are found in temperate waters of the North Pacific. They inhabit waters from the continental shelf to the deep open ocean.

Pacific White-sided Dolphin Range Map (click for larger view PDF)

Distribution
This "pelagic" species ranges in the Western Pacific Ocean from the South Bering Sea to southern Japan. In the Eastern Pacific Ocean, they range from the Gulf of Alaska to the Gulf of California. They are most common between the latitudes of 38°N and 47°N. The distribution and abundance of Pacific white-sided dolphins may be affected by large-scale oceanographic occurrences, such as El Niño and by underwater acoustic deterrent devices.

Population Trends
There are 2 stocks of Pacific white-sided dolphins in U.S. waters: California / Oregon / Washington and North Pacific stocks. The estimated population range-wide for the species is more than 900,000 animals. The current estimated population size for the California/Oregon/Washington stock of Pacific white-sided dolphins is 59,000 animals. The current population size for the North Pacific stock is 27,000 animals.

Threats
A primary threat to Pacific white-sided dolphins is incidental catch in fisheries such as in gillnets and trawls. It was estimated that 49,000-89,000 animals were incidentally "taken" between 1978-1990 in gillnets and driftnets targeting squid by Japan, Korea, and Taiwan (Folkens et al., 2002). They are sometimes killed by harpooning and drive fisheries in Japan.

Conservation Efforts
Pacific white-sided dolphins are classified as "Low Risk-Least Concern" under The International Union for Conservation of Nature and Natural Resources (IUCN) Red List. 

Regulatory Overview
This species is protected under the Marine Mammal Protection Act of 1972 as amended.