Pacific White-Sided Dolphin

HOW TO SPOT

Pacific white-sided dolphins travel in groups ranging from 10 to hundreds of animals. They are extremely playful and can be seen bow riding and performing acrobatic surface behaviors. Watch for a field of splashes and occasional leaps!

WHEN AND WHERE TO SEE

Pacific white-sided dolphins can be seen year-round along the coast and the upper reaches of the Salish Sea. They are rarely seen in central and south Puget Sound.

RANGE

Pacific white-sided dolphins live primarily in the North Pacific and off the west coast of the United States. They are found in temperate waters in both open-ocean and coastal locations. They are occasional visitors to our inland waters.

BIOLOGY

The coloration of Pacific white-sided dolphins is very unique. These dolphins have a light/grey stripe along their sides that extends from the eyes to the tail, resembling a pair of suspenders. Another key color characteristic is their back, fluke, and lips which are black. They have a large, curved dorsal fin compared to overall body size and are sometimes referred to as “hookfin porpoise”, although they are not porpoises. Their pectoral fins are highly curved, unlike other dolphin species.

BIRTH FACTS

Females reach sexual maturity between 7-10 years of age and around 5.5-6 ft (1.7-1.8m) in length. Males reach sexual maturity around 10 years of age. Mating and calving occurs in late spring to fall. The gestation period is 9 to 12 months and mothers nurse their calves for up to 18 months. Females have a relatively slow calving interval in comparison to other cetaceans and give birth every 3-4.5 years.

SOCIAL STRUCTURE

Pacific white-sided dolphins are highly social and playful animals and are often seen associating with other species. In inland waters they have been seen with resident killer whales, Steller sea lions, Dall’s porpoise, humpback whales. Further offshore they have been reported with northern right whale dolphins, Risso’s dolphins, common dolphins and short-finned pilot whales. The group size generally ranges from 10 to 100 animals and a group of 100-200 dolphins have been increasingly seen in the Strait of Georgia. It is thought the largest group of Pacific white-sided dolphins reported traveling together was around 6,000 individuals.

BEHAVIOR

Pacific white-sided dolphins are opportunistic feeders and eat a variety of prey. They have been known to feed on over 60 species of fish, specifically small schooling fish such as anchovies, herring, sardines and herring. They also feed on over 20 species of cephalopods, including squid. They work cooperatively to forage and herd or corral schools of fish. The dolphins are capable of diving for more than 6 minutes to feed and eat around 20 pounds of food per day. Their teeth are highly specialized for their prey selection. They have small cone shaped teeth that help to catch and hold on to prey. They swallow the fish whole and head first so the fish spins don’t get stuck in their throats.

STATUS

Pacific white-sided dolphins are protected under the Marine Mammal Protection Act, but are not listed as threatened or endangered. In Canada they are listed as “not at risk”. In the U.S. there are three different stocks, two off the coast of Washington, Oregon, and California with population numbers around 21,000 (2014) and one North Pacific stock off the coast of Alaska with an unknown population number. In British Columbia, it is estimated there are around 25,000 (2007) Pacific white-sided dolphins along the coast.

CURRENT AND HISTORICAL THREATS

The most significant threat to Pacific white-sided dolphins are drift and gill net entanglements. This is called incidental catch and it is thought upwards to 90,000 were taken between 1978-1990 in fishery nets, primarily in Japan, Korea and Taiwan. Pacific white-sided dolphins are preyed upon by transient killer whales and occasionally by large sharks. They are also affected by vessel noise.

RESOURCES