Pacific White-Sided Dolphin - Credit: NOAA Fisheries
Pacific White-Sided Dolphin - Credit: NOAA Fisheries
About the Species
Pacific white-sided dolphins, known for the distinct coloring that give them their name, are a playful and highly social marine mammal. They are also sometimes known as the “hookfin porpoise” because of their large, curved dorsal fin, though they are not technically porpoises.
In the United States, Pacific white-sided dolphins live off the coasts of California, Oregon, Washington, and Alaska. They can be seen travelling in schools of thousands, but group sizes are usually between 10 and 100 animals. These extremely playful dolphins are often seen “bow riding” (swimming near the front part of a ship) and jumping, somersaulting, or even spinning in the air.
Pacific white-sided dolphins in the United States are not endangered or threatened, but they are protected under the Marine Mammal Protection Act. A primary threat to Pacific white-sided dolphins is entanglement in fishing gear, such as gillnets and trawls.
NOAA Fisheries is dedicated to the conservation and protection of Pacific white-sided dolphins. We are working to help conserve this species through collaborative management, integrated science, partnerships, and outreach.
Population Status
NOAA Fisheries estimates the population size for Pacific white-sided dolphins in its stock assessment reports. In all, there are three stocks of Pacific white-sided dolphins in U.S. waters. Population trends for the North Pacific stock off the coast of Alaska are unknown. A survey of the two stocks off the coasts of Washington, Oregon, and California from 2008 to 2014 found a population of more than 21,000 dolphins.
Protected Status
CITES Appendix II
MMPA Protected
Appearance
These dolphins have a robust body, short rostrum (snout), and large dorsal fin compared to their overall body size. Their back, flukes (tail), and lips are black; their sides, dorsal fin, and flippers are gray; and their belly is white. They have a white or light gray stripe along their sides that extends from their eye to their tail, sometimes referred to as "suspenders." Pacific white-sided dolphins are most likely to be confused with common dolphins and Dall’s porpoises because they have similar large light-colored flank patches.
The average adult Pacific white-sided dolphin weighs about 300 to 400 pounds and is between 5.5 and 8 feet long, with males being generally larger than females.
Behavior and Diet
Pacific white-sided dolphins feed on a variety of prey, such as squid and small schooling fish (capelin, sardines, and herring). They can dive underwater for more than 6 minutes to feed. They have small conical teeth that help them catch and hold on to their prey; each tooth row contains 23 to 36 pairs of teeth. Instead of using their teeth to chew their food, dolphins use their teeth to grip food before swallowing it whole—head first—so the spines of the fish do not catch in their throats. Pacific white-sided dolphins often work together as a group to herd schools of fish. Each adult eats about 20 pounds of food a day.
Where They Live
Pacific white-sided dolphins are pelagic, meaning they live in the open ocean and nearshore waters, but are unlikely to be found close to shore. They live in the temperate waters of the North Pacific Ocean. In the United States, they are found off the coast of California, Oregon, Washington, and Alaska. Worldwide, they are found in the southern Bering Sea (around the Aleutian Islands), Sea of Okhotsk, Sea of Japan, and Yellow and East China Seas to the south of Japan.
Lifespan & Reproduction
The Pacific white-sided dolphin can live more than 40 years. Males reach sexual maturity around 10 years and females around 8 to 11. They mate and give birth from late spring to fall, except in the central Pacific, where calves are born in late winter to spring. Gestation is usually 9 to 12 months, and calves weigh about 30 pounds at birth and are about 3 to 4 feet. Mothers nurse their calves for up to 18 months and females usually give birth every 3 years.
Threats
Interactions with Fishing Gear
One of the main threats to the Pacific white-sided dolphin is entanglement in fishing gear. Dolphins can become entangled or captured in commercial fishing gear such as gillnets, seines, trawls, trap pots, and longlines.
Before a 1933 United Nations moratorium that banned large-scale drift nets, Pacific white-sided dolphins were often captured by Japanese fisheries. In addition, every year between 1978 and 1991, thousands of Pacific white-sided dolphins suffered mortality and serious injury when caught incidentally in high-seas fisheries for salmon and squid. These fisheries were closed in 1991 and no other large-scale fisheries have operated in the central North Pacific since 1991.
Ocean Noise
Low-frequency underwater noise pollution can interrupt the normal behavior of Pacific white-sided dolphins. Noise interference hinders their ability to use sound, which in turn disturbs their ability to communicate, choose mates, find food, avoid predators, and navigate.
Scientific Classification
| Animalia |
Chordata |
Mammalia |
Cetacea |
Delphinidae |
Lagenorhynchus |
obliquidens |
