Dall's Porpoise
by Kristina Rinell
Title
Dall's Porpoise
Artist
Kristina Rinell
Medium
Photograph - Photography
Description
This uniquely marked, black and white porpoise was named after the American naturalist W. H. Dall, who collected the first specimen of the type, which is now on display in the U. S. National Museum. It may be the fastest swimmer of all the small cetaceans and has been reported to reach speeds of 30 knots. It delights in bow riding with fast-moving vessels. As the porpoise dashes in at high speed, its head and back produce a bow wave called a "rooster tail", which creates a hollow cone allowing the animal to breathe while still under the surface of the water.
Dall's porpoise has an extremely robust and muscular body, especially through the mid-section, and the male is considerably thicker than the female. Its head is very small and rounded, appearing smaller than it really is because of the powerfully built body. The head slopes steeply to a short poorly defined beak. Its mouth is small and narrow, with 19 to 23 very small spade-shaped teeth in each side of the upper jaw and about 20 to 24 teeth in each side of the lower jaw. The teeth of Dall's porpoise are most unusual. Each tooth is separated by rigid, protruding growths called "gum teeth." Since its teeth are so small, these horny growths might be of help in grasping slippery food such as squid. The lower jaw extends slightly beyond the upper. In addition to a dorsal (upper) hump, there is a large hump located slightly forward of the flukes on the ventral (under) part of the body, which makes the animal look somewhat malformed. This ventral hump is more pronounced in adult males. There are few accounts of eye color in cetaceans, but Dall's porpoise is an exception; its eye has been described as having a black or dark blue iris and a deep, iridescent blue-green pupil.
Dall's porpoise are found only in the North Pacific, ranging from Baja California north to Alaska and the Bering Sea and across into Japanese waters, seemingly confined to colder waters with temperatures of less than 60 degrees F (15 C). Many are year-round residents over much of their range.
These animals usually travel in small groups of 10 to 20, but as many as 200 may congregate while engaged in feeding. They are often found in the company of Pacific white-sided dolphins or pilot whales. Although known to bow ride, this small, fast species can often be elusive.
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Uploaded
October 29th, 2016
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