Pacific White-sided Dolphin | Oceana Canada

Marine Mammals

Pacific White-sided Dolphin

Lagenorhynchus obliquidens

Also known as

Whitesided dolphin, white-striped dolphin, lag, hook finned porpoise

Distribution

North Pacific Ocean

Ecosystem/Habitat

Open ocean (pelagic)

Feeding Habits

Active predator

Conservation Status

Not at Risk

Taxonomy

Suborder Odontoceti (toothed whales); Family Delphinidae (dolphins

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Pacific white-sided dolphins are a truly acrobatic species of dolphin that love to show off. They are frequently seen riding the bows and wakes of ships, and will even perform spectacular leaps, flips, spins and somersaults at high speeds. Their behavious are not exactly subtle, and all this splashing around, swimming at high speeds and disturbing surface waters can make it easy to spot white-sided dolphins from far away. They travel in groups of tens to hundreds of individuals but in some cases have been documented in herds of over 2,000 individuals. The largest herd size ever reported was estimated at 6,000 individuals!

White-sided dolphins are a robust, strong dolphin that grow to be two to two and a half metres in length. As their name suggests, Pacific white-sided dolphins have a white or light-grey stripe that runs along each side of their body from in front of their eye to the mid-body. This stripe blends in almost artistically with the dark grey colour of the rest of their body, while a stark, black stripe clearly divides this light-grey stripe from their bright white underside. Their tall dorsal fin is curved and bi-coloured, a dark grey that fades into a lighter grey, and they also have a grey-ish stripe that runs from below their dorsal fin towards their tail. They are sometimes confused with common dolphins or Dall’s porpoises due to similar colouration.

 

Pacific white-sided dolphins can live to be over 40 years old. Females reach sexual maturity between seven and ten years of age, while males reach maturity at around ten years of age. Adults will typically mate anytime between the spring and fall and, after a gestation period of nine to 12 months, females will give birth to calves that are around one metre long. Females will typically nurse their calves for eight to ten months, although in some cases may nurse for up to 18 months. They have a slow calving interval and only give birth every three to four years.

Pacific white-sided dolphins are opportunistic feeders and feed on a wide variety of prey including squid and small schooling fish. They often work cooperatively as a group to corral and herd groups of fish together, making them easier to pick off. White-sided dolphins can dive to depths greater than 100 metres and stay underwater for up to six minutes in pursuit of prey. One white-sided dolphin can eat about 10 kilograms of food in one day.

Up until 1993, tens of thousands of Pacific white-sided dolphins were captured by large-scale driftnet fisheries until these types of fisheries were banned by the United Nations. Unfortunately, bycatch still remains one of the greatest threats to this species, as they can get caught and drown in commercial fishing gear such as gillnets, seines, trawls and longlines. Pacific white-sided dolphins are also sometimes captured to be displayed in aquariums and are harvested in small numbers for food in Japan’s coastal fishery.

Pacific white-sided dolphins have been listed by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) as Not at Risk. Their populations appear healthy since the ban of driftnet fisheries in 1993, there are fewer direct threats to the species. Even so, incidental catch of white-sided dolphins in other fisheries is still a threat to this species, as is overfishing of their prey species, noise pollution which hinders their ability to communicate, navigate and hunt, entanglement in and ingestion of plastic pollution, and the ongoing impacts of climate change. 

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