Pacific white-sided dolphins (Lagenorhynchus obliquidens) are a social species that may be found in pods of thousands of dolphins. They are found in the Pacific Ocean. These dolphins may also be called white-striped dolphins, hookfin porpoise or lags (a reference to their genus, Lagenorhynchus). The Pacific white-sided dolphin's species obliquidens means "slanting tooth" in a reference to its teeth, which are slightly curved.

Description:

Pacific white-sided dolphins have a short, dark beak, black back, white underside and a white or gray stripe that extends from their forehead, over their head and up and over their flank, where it runs into a light gray patch. They also have a black stripe from their mouth to their flippers, and then from their flippers to flank. They have a strongly hooked, tall dorsal fin that is dark in front and gray on the sides and back.

Pacific white-sided dolphins can grow to about 8 feet in length, and males are slightly larger than females. These dolphins weigh about 300-400 pounds on average.

The average pod size for Pacific white-sided dolphins is 10-100 (Source: NOAA), but they can be found gathered in pods of thousands of individuals.

These dolphins commonly leap (breach) and somersault. They may also ride the bow and stern waves created by ships, and they commonly associate with other cetacean species, including Risso's dolphins.

Like other toothed whales, Pacific white-sided dolphins find their food using echolocation, which involves emitting high frequency pulses of sound from an organ in their head, called the melon.

These sounds waves bounce off objects around them and are received back into the dolphin's lower jaw, transmitted to the inner ear and interpreted to determine the size, shape, location and distance of prey.

These dolphins have large, 2.5-pound brains that are more than 4 times the size of what would be expected for a terrestrial mammal of similar size (Source: Field Guide to Marine Mammals of the Pacific Coast)

Classification:

• Kingdom:Animalia
• Phylum:Chordata
• Subphylum:Vertebrata
• Superclass:Gnathostomata, Tetrapoda
• Class: Mammalia
• Subclass:Theria
• Order:Cetartiodactyla
• Suborder:Cetancodonta
• Infraorder: Cetacea
• Suborder: Odontoceti
• Superfamily: Odontoceti
• Family: Delphinidae
• Genus: Lagenorhynchus
• Species: obliquidens

Habitat and Distribution:

Pacific white-sided dolphins are found in the Pacific Ocean in the U.S. from the Aleutian Islands and Gulf of Alaska to Baja California, and in the western Pacific Ocean north of 20 degrees North. Pacific white-sided dolphins inhabit the open ocean (pelagic zone) in deep waters of about 3,000 feet. They may also travel inshore in areas where there are submarine canyons. Click here for a distribution map.

Feeding:

Pacific white-sided dolphins feed on fish (such as as herring, sardines and capelin) and cephalopods. They may work cooperatively to herd schools of fish, and can dive for up to 6 minutes when feeding. Although these dolphins have teeth, the teeth are used for grasping prey, rather than chewing.

Reproduction:

Pacific white-sided dolphins are sexually mature when they reach a length of about 5.5-6 feet, which occurs at 7-10 years of age. Mating occurs in the summer, and the gestation period is about 12 months, after which a calf about 2.5-4 feet long and weighing about 30 pounds is born. Calves nurse for about a year. Females give birth to a single calf every 1.5-5 years.

The lifespan for Pacific white-sided dolphins is estimated to be over 40 years.

Conservation:

The Pacific white-sided dolphin is listed as of least concern on the IUCN Red List, and the species is protected under the Marine Mammal Protection Act. NOAA estimates the population size of Pacific white-sided dolphins at more than 900,000 animals.

Pacific white-sided dolphins may be affected by pollution, noise pollution and entanglement or bycatch in fishing gear.

Pacific white-sided dolphin predators include great white sharks and orcas (killer whales). They may also be exhibited in aquariums (e.g., you can see them at the Shedd Aquarium and Vancouver Aquarium (which has 3 rescued dolphins).

References and Further Information:

• Allen, S.G. and J. Mortenson. Field Guide to Marine Mammals of the Pacific Coast: Baja, California, Oregon, Washington, British Columbia. 2011. University of California Press: Berkeley and Los Angeles, California.
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• Gill, P. (ed.) 2000. Whales, Dolphins and Porpoises. Fog City Press: California.
• Hammond, P.S., Bearzi, G., Bjørge, A., Forney, K., Karczmarski, L., Kasuya, T., Perrin, W.F., Scott, M.D., Wang, J.Y., Wells, R.S. & Wilson, B. 2008. Lagenorhynchus obliquidens. IUCN 2011. IUCN Red List of Threatened Species. Version 2011.2. Accessed April 30, 2012.
• NOAA Fisheries: Office of Protected Resources. Pacific White-Sided Dolphin (Lagenorhynchus obliquidens). Accessed April 30, 2012.
• OBIS SEAMAP. Pacific White-Sided Dolphin (Lagenorhynchus obliquidens). Accessed April 30, 2012.
• Perrin, W. 2010. Lagenorhynchus obliquidens Gill, 1865. In: Perrin, W.F. World Cetacea Database. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=254981 on 2012-04-30 Accessed through: World Register of Marine Species on April 30, 2012.