Pacific White-Sided Dolphin
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.
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.
- Throughout Its Range
These dolphins have a robust body, short rostrum (snout), and large dorsal fin compared to their overall body size. Their back, fluke (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 the eye to the 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. Females usually give birth every 3 years.
Interactions with Fishing Gear
One of the main threats to the Pacific white-sided dolphin is getting caught 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.
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.
Pacific white-sided dolphins are protected under the Marine Mammal Protection Act. They are not considered endangered or threatened under the Endangered Species Act. NOAA Fisheries and our partners work to conserve and protect this species in many ways.
Dolphin-Safe/Tuna Tracking and Verification Program
Dolphins, like other marine mammals, may become bycatch in fisheries. Some species of tuna are known to aggregate beneath schools of certain dolphin stocks. In some parts of the world, this close association led to the fishing practice of encircling a dolphin school to capture the tuna concentrated below. The Dolphin Protection Consumer Information Act established a national tuna tracking program to ensure that tuna imported into the United States meets certain requirements to ensure the safety of dolphins during tuna fishing operations.
Reducing Interactions with Fishing Gear
Bycatch in fishing gear is a leading cause of Pacific white-sided dolphin deaths and injuries. To reduce deaths and serious injuries from drift gillnet commercial fishing gear off the coast of California and Oregon, NOAA Fisheries implemented the Pacific Offshore Cetacean Take Reduction Plan in 1997. Representatives from NOAA, the fishing industry, regional fishery management councils, state and federal resource management agencies, the scientific community, and conservation organizations worked together to develop the plan. The plan included skipper education workshops and required the use of pingers and minimum 6-fathom extenders. As a result, overall entanglement rates in the drift gillnet fishery dropped considerably.
Minimizing Harassment and Illegal Feeding
As human interactions with wild dolphins increase, so does the risk of disturbing or injuring these animals. NOAA Fisheries provides guidance on how to safely and responsibly view dolphins, including the following initiatives:
Addressing Ocean Noise
Underwater noise threatens marine mammal populations, interrupting their normal behavior and driving them away from areas important to their survival. Increasing evidence suggests that exposure to intense underwater sound in some settings may cause some cetaceans to strand and ultimately die. NOAA Fisheries researches aspects of acoustic communication and hearing in marine animals, as well as the effects of sound on marine mammal behavior and hearing. In 2016, we issued technical guidance for assessing the effects of anthropogenic (human-caused) sound on marine mammal hearing.
Overseeing Marine Mammal Health and Stranding Response
We work with volunteer networks in all coastal states to respond to marine mammal strandings. When stranded animals are found alive, NOAA Fisheries and our partners assess the animal’s health. When stranded animals are found dead, our scientists work to understand and investigate the cause of death. Although the cause often remains unknown, scientists can sometimes confirm the cause of strandings, such as disease, harmful algal blooms, vessel strikes, fishing gear entanglements, pollution exposure, or underwater noise. Some strandings can serve as indicators of ocean health, giving insight into larger environmental issues that may also have implications for human health and welfare.
All Pacific white-sided dolphins are protected under the MMPA.
Before the United Nations issued a moratorium that banned large-scale drift nets in 1933, Japanese fisheries often captured Pacific white-sided dolphins. The MMPA was later enacted in 1972 to protect all marine mammals, severely reducing the amount of “taken” animals. This species is now no longer commercially hunted in the United States, though some Pacific white-sided dolphins are still harvested for food in Japan's coastal fisheries.
In 1999, the United States signed on as a Party to the Agreement on the International Dolphin Conservation Program (AIDCP). In addition to other requirements, the AIDCP’s main objective is to reduce incidental dolphin mortalities in the tuna purse-seine fishery.
The International Dolphin Conservation Program Act amended the MMPA to make AIDCP objectives and requirements legally effective in the United States.
NOAA Fisheries conducts research on the biology, behavior, and ecology of the Pacific white-sided dolphin. The results of this research are used to inform management decisions and conservation efforts for this species and other marine life.
Determining the size of Pacific white-sided dolphin populations helps resource managers determine the success of our conservation measures. NOAA Fisheries scientists collect population information from various sources and present the data in an annual stock assessment report.
Aerial and Shipboard Surveys
Scientists use small aircraft and research vessels to spot Pacific white-sided dolphins and photograph them to identify individuals and record their seasonal distribution. Understanding this species’ distribution patterns helps managers establish measures to limit the overlap between fisheries and dolphins. This research can be used to inform management actions that protect the Pacific white-sided dolphin.
NOAA Fisheries scientists conduct guided research projects to answer questions about a particular ecosystem or ecology. For example, the Cetacean Assessment and Ecology Program conducts studies to assess the status of cetaceans in Alaskan waters under the Endangered Species Act and the Marine Mammal Protection Act, which includes the Pacific white-sided dolphin. The program uses the results of stock assessments, surveys, and studies to provide the scientific advice necessary to manage cetaceans in Alaskan waters.
Other research focuses on the acoustic environment of cetaceans, including the Pacific white-sided dolphin. Acoustics is the science of how sound is transmitted. This research involves increasing our understanding of the basic acoustic behavior of whales, dolphins, and fish; mapping the acoustic environment; and developing better methods to locate cetaceans using autonomous gliders and passive acoustic arrays.