The Rough-Toothed Dolphin
Steno bredenensis

The only species in the genus Steno is the rough-toothed dolphin, Steno bredanensis. Although first described in 1828, virtually nothing about this species was known before 1964, when the first specimen was taken into captivity. The rough-toothed dolphin has long been considered an enigma to cetologists. It is approximately 2.5 meters in length, with a somewhat elevated dorsal fin near the middle of the body. On the dorsal side, it is described as sooty black or purplish, while the ventral side has an almost rosy color and has numerous black patches. The demarcation between the two main areas of color is very irregular. On the dark area, there are many white or pinkish blotches, leading to one of the most unusual colorations of any species of cetacean: "pink with purple polka dots." Another characteristically unusual feature is that there is no crease between the forehead and the beak. In this respect the species looks almost like an icthyosaur. The flippers are proportionally large, and the lips are white with crisscrossed scars, possibly resulting from encounters with squid. Older specimens are fat and heavily scarred. Because of these irregularities, some consider this species to be the ugliest dolphin.

The rough-toothed dolphin prefers deeper waters where the temperature is more than 25° C. It is found is nearly all tropical and subtropical waters around the world, although its distribution in the Atlantic is limited to regions north of the equator. In the past it was believed that its appearance in the Mediterranean Sea was rare, but recent sightings near Sicily suggest that there may be a permanent population there.

A somewhat rare animal, very few individuals are actually seen in the wild. It likes remaining under water and will dive for long periods of around 15 minutes when approached. The rough-toothed dolphin is one of the more skillful of the dolphins at diving. In one experiment, an individual named Pono was able to dive to a depth of 30.5 meters without actually nearing its maximum abilities. It was also able to perform 51 dives in 105 minutes without exerting much effort. Although a quick learner, rough-toothed dolphins are known to have hot tempers, and trainer errors such as contradiction and confusion may elicit strong emotional responses. It is not a bow-rider, but it has been known to travel in the stern wake of a vessel. Echolocating abilities have been demonstrated in this species, and the echolocating clicks are remarkably directional.

Bibliography

Baker, Mary L. Whales, Dolphins, and Porpoises of the World. New York: Doubleday & Company, Inc., 1987.

Carwardine, Mark. Eyewitness Handbooks: Whales, Dolphins, and Porpoises. New York: Dorling Kindersley Ltd., 1995.

Ellis, Richard. Dolphins and Porpoises. New York: Alfred & Knopf, Inc., 1982.

Klinowska, Margaret. Dolphins, Porpoises, and Whales of the World: The IUCN Red Data Book. Gland, Switzerland: World Conservation Union, 1991.