Rough-Toothed Dolphin

The rough-toothed dolphin is a relatively large species, with adults ranging from 2.09 to 2.83 metres (6.9 to 9.3 ft) in length, and weighing between 90 and 155 kilograms (198 and 342 lb); males are larger than females. Its most visible characteristic feature is its conical head and slender nose; other dolphins either have a shorter snout or a more visibly bulging melon on the forehead. As the common name for the species implies, the teeth are also distinctive, having a roughened surface formed by numerous narrow irregular ridges. They have been reported to have between nineteen and twenty-eight teeth in each quarter of the jaw. The rough-toothed dolphins jaw on the outside is very distinct. The color of the lower jaw is usually white, but can have a hint of pink mixed in.

The distribution and population of the rough-toothed dolphin is poorly understood. They inhabit the Pacific, Atlantic, and Indian Oceans, and in the Mediterranean Sea, in warm temperate to tropical waters, with occasional reports from cooler environments. Rough-toothed dolphins can also be seen regularly in locations stretching from the Windward Islands to Cape Verde, but only a small handful have been seen in Azores and Madeira. Live sightings are almost universally made far off-shore, beyond the continental shelf, in water at least 1 kilometre (0.62 mi) deep.

Most of the research activity concerning the dolphin has been directed in the eastern Pacific, where a population estimate of 150,000 was obtained by researchers in the 1980s. Fossils belonging to the genus Steno are known from Europe and date to the early to mid-Pliocene.

Rough-toothed dolphins are typically social animals, although solitary individuals are also sighted. An average group has between ten and twenty members, but they can vary from as few as two to as many as ninety. Such groups are thought to be temporary assemblages, composed of smaller, more permanent groups of two to eight closely related individuals that occasionally join with others. They have also been reported to school together with other species of dolphin, and with pilot whales, false killer whales, and humpback whales.

Rough-toothed dolphins give birth to a single young, after an unknown period of gestation; it is also unknown whether or not they have a distinct breeding season. The young are about 100 centimetres (39 in) long at birth, and grow rapidly for the first five years of life. Females reach sexual maturity somewhere between six and ten years of age, and males between five and ten years.

The population is not believed to be threatened by human activities. A small number of individuals have been harpooned by Japanese whalers and pods are also slaughtered in the Taiji drive hunts. Others have been caught in seine nets by trawlers fishing for tuna. Less than a dozen rough-toothed dolphins live in dolphinaria around the world. The rough-toothed dolphin is covered by the Agreement on the Conservation of Small Cetaceans of the Baltic, North East Atlantic, Irish and North Seas (ASCOBANS) and the Agreement on the Conservation of Cetaceans in the Black Sea, Mediterranean Sea and Contiguous Atlantic Area (ACCOBAMS).