Rough-toothed Dolphin (Steno bredanensis)
Suborder: Odonticeti Family: Delphinidae
Common in Hawaiian waters.
Other known names:
Slopehead
Identity Keys to use in the field:
Streamlined body, Narrow head, Smooth sloping forehead, no teeth visible, White "lips", Blue-gray skin color, Pale blotches, Dark cape area around the dorsal fin), White underside, Tall dorsal fin, Black patch around eye, Fast active swimmer, May float motionless at the surface, Normally in small groups, Long, slender beak
General description and habits:
Rough-toothed dolphins get their name from the vertical ridges or wrinkles found on their teeth. However, as these are impossible to see, other features must be relied on when identifying them. They can be mistaken for bottlenoses but unlike other dolphins, rough-toothed dolphins do not have prominent beaks with a crease between their beak and forehead. Their long narrow beak blends smoothly into the forehead and some people have described them as looking like reptiles. Their skin is dark gray or blue-gray, sometimes with a hint of purple. The area around their mouths is often white or pinkish white especially on the underside where the whiteness covers the throat too. They have large eyes that are surrounded by a dark patch of skin. Rough-toothed dolphins have quite slim bodies, especially behind the dorsal fin that has a wide base and curves backwards. Their flippers are large and set quite far back on their body. The flukes have pointed tips and a notch in the middle. Rough-toothed dolphins often have spots or blotches on their lower body and they are often scarred. They have between 38 and 52 teeth in the upper jaw and between 38 and 56 in the lower jaw. Male rough-toothed dolphins are between 2.2 and 2.6 meters (7ft-8ft 6in) in length. The females are between 2.3 and 2.4 meters (7ft 6in and 8 ft). When they are born, the calves are about 1m (39in) long. We do not know how heavy newborn rough-toothed dolphins are, but adults weigh between 100 and 150 kg (200-330lb). Rough-toothed dolphins are fast swimmers and often swim just under the surface with the dorsal fin and part of the back showing above the water. Sometimes they swim with only their head showing above the water. They can stay under water for up to 15 minutes. They can be seen to bow ride, though not as often as other dolphins. They do not tend to do full breaches. Sometimes they are seen resting on the surface of the water. Rough-toothed dolphins live in groups of about 10-20, though they have been seen in groups numbering up to 50 individuals, and, occasionally, in groups of several hundred. They are sometimes seen with bottlenose dolphins, pilot whales, spinner dolphins and spotted dolphins.
Diet:
Fish, Squid, Octopus
Distribution:
Rough-toothed dolphins prefer deep, warm waters away from the shore and avoid places with cold currents. They have been seen near Hawaii, the Bahamas and Ogasawara in Japan. There is a population living in the Mediterranean and they have also been spotted off the coast of Brazil.
Population estimates:
Unknown
Threats:
Hunting/Whaling, Entanglement in fishing nets
