Steno bredanensis

Names

POR : Caldeirão - ITA : Steno - SPAIN : Delfin de pico largo - GB : Rough-toothed dolphin - GER : Rauhzahndelphin NEDER : Snaveldolfijn - JAP : Shiwaha iruka

Biology

The adult rough-toothed dolphin measures 2.1 to 2.7 m long and weighs 120 to 160 kg. It has 20 to 27 pairs of large semi-conical teeth in each jaw. The teeth are rough with vertical wrinkles and this is the origin of their English common name. Size at birth is about 1 m. The shape the head of these animals is unique, with no crease separating the long and slender beak from the forehead. The dorsal, pectorals and tail have a gray-black coloration covered by white or rose blotches. The beak, the lips and ventral surface to the anus are white. This species feeds on small fish, squids and even pelagic octopus. They emit short clicks in the range of 0.1 to 200 kHz.

Observation

In the summer of 1995, a group of rough-toothed dolphins was observed frequently around the central group of islands in the Azores. During this time, the water temperature was higher than the average registered for this region. In fact, this species is more common in tropical or sub-tropical regions of the world, where the water temperature rarely decreases below 25¼ C. This species is difficult to observe because it can remain submerged for 15 minutes. It is also a fast swimmer, with maximum speeds of 15 knots. Sometimes it is possible to observe them riding the bow waves, but this behaviour is not as regular as in other species such as the spotted dolphin. Rough-toothed dolphins are gregarious, swimming in groups of 10 to 20, and sometimes more. They can associate with the pilot whales, with bottlenose dolphins and spotted dolphins. These animals can be mistaken for these last two species. It is mainly the white lips and the white or rose blotch coloration characteristics that distinguish this species from most of the other beaked dolphins.