Rough-toothed Dolphin
Encyclopedia
The Rough-toothed dolphin (Steno bredanensis) is species of dolphin that can be found in deep warm and tropical waters around the world.
The species was first described by Georges Cuvier
in 1823. The genus name Steno, of which this species is the only member, comes from the Greek
for 'narrow', referring to the animal's beak - which is a diagnostic characteristic of the species. The specific name honours van Breda, who studied Cuvier's writings. There are no recognised subspecies.
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 flippers are set back further along the body than in other similar dolphins, although, at sea this dolphin may be confused with spinner
, spotted
and bottlenose dolphin
s. The dorsal fin
is pronounced, being from 18 to 28 cm (7.1 to 11 ) in height. The animal's flanks are a light gray, while the back and dorsal fin are a much darker gray. Older individuals often have distinctive pinkish, yellow, or white markings around the mouth and along the underside.
, Atlantic
, and Indian Ocean
s, and in the Mediterranean Sea
, in warm temperate to tropical waters, with occasional reports from cooler environments. Live sightings are almost universally made far off-shore, beyond the continental shelf
, in water at least 1 kilometre (0.621372736649807 mi) deep.
Most of the research activity concerning the dolphin has been directed in the eastern Pacific, where a population estimate of 150,000 has been obtained. Fossils belonging to the genus Steno are known from Europe and date to the early to mid Pliocene
.
s, false killer whale
s, and humpback whale
s.
Rough-toothed dolphins have been reported to bow-ride on a number of occasions, although apparently they do not do so as frequently as many other dolphin species. They do, however, commonly "skim", by swimming with their heads and chin above the surface of the water. They are known to be able to dive to at least 50 metres (164 ft) and be able to stay underwater for at least fifteen minutes. Their echolocation
clicks are unusually brief, lasting no more than 0.2 seconds, and have a relatively low frequency, ranging from 2.7 to 256 kHz, with a maximum peak frequency of 25 kHz. They also make longer whistles with a frequency between 3 and 12 kHz.
Although details of their diet are sketchy, the stomach contents of stranded
dolphins have included such fish such as silversides
, sauries
, houndfish
, smelts, cutlassfish
, and various squid
and octopus
es. Predators on rough-toothed dolphins are thought to include killer whales and shark
s.
ed by Japanese whalers
. Others have been caught in seine nets by trawlers fishing for tuna
. They adapt well to captivity and have proven to be intelligent and creative. Less than a dozen rough-toothed dolphins live in dolphinaria around the world.
The species was first described by Georges Cuvier
Georges Cuvier
Georges Chrétien Léopold Dagobert Cuvier or Jean Léopold Nicolas Frédéric Cuvier , known as Georges Cuvier, was a French naturalist and zoologist...
in 1823. The genus name Steno, of which this species is the only member, comes from the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
for 'narrow', referring to the animal's beak - which is a diagnostic characteristic of the species. The specific name honours van Breda, who studied Cuvier's writings. There are no recognised subspecies.
Physical description
The rough-toothed dolphin is a relatively large species, with adults ranging from 209 to 283 cm (6.9 to 9.3 ft) in length, and weighing between 90 and 155 kg (198.4 and 341.7 ); 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 melonMelon (whale)
The melon is an ovoid-shaped, fatty organ found in the forehead of all toothed whales , including dolphins and porpoises and believed to be used in echolocation....
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 flippers are set back further along the body than in other similar dolphins, although, at sea this dolphin may be confused with spinner
Spinner Dolphin
The Spinner Dolphin is a small dolphin found in off-shore tropical waters around the world. It is famous for its acrobatic displays in which they spin longitudinally along their axis as they leap through the air.-Taxonomy:...
, spotted
Pantropical Spotted Dolphin
The Pantropical Spotted Dolphin is a species of dolphin found in all the world's temperate and tropical oceans. The species was beginning to come under threat due to the killing of millions of individuals in tuna purse seines...
and bottlenose dolphin
Bottlenose Dolphin
Bottlenose dolphins, the genus Tursiops, are the most common and well-known members of the family Delphinidae, the family of oceanic dolphins. Recent molecular studies show the genus contains two species, the common bottlenose dolphin and the Indo-Pacific bottlenose dolphin , instead of one...
s. The dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
is pronounced, being from 18 to 28 cm (7.1 to 11 ) in height. The animal's flanks are a light gray, while the back and dorsal fin are a much darker gray. Older individuals often have distinctive pinkish, yellow, or white markings around the mouth and along the underside.
Population and distribution
The distribution and population of the Rough-toothed Dolphin is poorly understood. They inhabit the PacificPacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
, Atlantic
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
, and Indian Ocean
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
s, and in the Mediterranean Sea
Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...
, in warm temperate to tropical waters, with occasional reports from cooler environments. Live sightings are almost universally made far off-shore, beyond the continental shelf
Continental shelf
The continental shelf is the extended perimeter of each continent and associated coastal plain. Much of the shelf was exposed during glacial periods, but is now submerged under relatively shallow seas and gulfs, and was similarly submerged during other interglacial periods. The continental margin,...
, in water at least 1 kilometre (0.621372736649807 mi) deep.
Most of the research activity concerning the dolphin has been directed in the eastern Pacific, where a population estimate of 150,000 has been obtained. Fossils belonging to the genus Steno are known from Europe and date to the early to mid Pliocene
Pliocene
The Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...
.
Behaviour and diet
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 together with others. They have also been reported to school together with other species of dolphin, and with pilot whalePilot whale
Pilot whales are cetaceans belonging to the genus Globicephala. There are two extant species, the long-finned pilot whale and the short-finned pilot whale . The two are not readily distinguished at sea and analysis of the skulls is the best way to tell the difference between them...
s, false killer whale
False Killer Whale
The False Killer Whale is a cetacean, and the third largest member of the oceanic dolphin family . It lives in temperate and tropical waters throughout the world. As its name implies, the False Killer Whale shares characteristics, such as appearance, with the more widely known Orca...
s, and humpback whale
Humpback Whale
The humpback whale is a species of baleen whale. One of the larger rorqual species, adults range in length from and weigh approximately . The humpback has a distinctive body shape, with unusually long pectoral fins and a knobbly head. It is an acrobatic animal, often breaching and slapping the...
s.
Rough-toothed dolphins have been reported to bow-ride on a number of occasions, although apparently they do not do so as frequently as many other dolphin species. They do, however, commonly "skim", by swimming with their heads and chin above the surface of the water. They are known to be able to dive to at least 50 metres (164 ft) and be able to stay underwater for at least fifteen minutes. Their echolocation
Animal echolocation
Echolocation, also called biosonar, is the biological sonar used by several kinds of animals.Echolocating animals emit calls out to the environment and listen to the echoes of those calls that return from various objects near them. They use these echoes to locate and identify the objects...
clicks are unusually brief, lasting no more than 0.2 seconds, and have a relatively low frequency, ranging from 2.7 to 256 kHz, with a maximum peak frequency of 25 kHz. They also make longer whistles with a frequency between 3 and 12 kHz.
Although details of their diet are sketchy, the stomach contents of stranded
Beached whale
A beached whale is a whale that has stranded itself on land, usually on a beach. Beached whales often die due to dehydration, the body collapsing under its own weight, or drowning when high tide covers the blowhole.-Species:...
dolphins have included such fish such as silversides
Atheriniformes
Atheriniformes, also known as the silversides, is an order of ray-finned fish that includes the Old World silversides and several less-familiar families, including the unusual Phallostethidae...
, sauries
Saury
Sauries are fish of the family Scomberesocidae. There are two genera, each containing two species. The name Scomberesocidae is derived from the Greek, skombros = tuna/mackerel, and esox = nursery of salmon....
, houndfish
Houndfish
The houndfish, Tylosurus crocodilus, is a gamefish of the family Belonidae. It is the largest member of its family, able to grow up to and reach . It is also often called the Crocodile Needlefish.-Description:...
, smelts, cutlassfish
Cutlassfish
The cutlassfishes are about 40 species of predatory fish in the family Trichiuridae found in seas throughout the world. Fish of this family are long, slender, and generally steely blue or silver in colour, giving rise to their name...
, and various squid
Squid
Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...
and octopus
Octopus
The octopus is a cephalopod mollusc of the order Octopoda. Octopuses have two eyes and four pairs of arms, and like other cephalopods they are bilaterally symmetric. An octopus has a hard beak, with its mouth at the center point of the arms...
es. Predators on rough-toothed dolphins are thought to include killer whales and shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....
s.
Reproduction
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 (39.4 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.Conservation
The population is not believed to be threatened by human activities. A small number of individuals have been harpoonHarpoon
A harpoon is a long spear-like instrument used in fishing to catch fish or large marine mammals such as whales. It accomplishes this task by impaling the target animal, allowing the fishermen to use a rope or chain attached to the butt of the projectile to catch the animal...
ed by Japanese whalers
Whaling
Whaling is the hunting of whales mainly for meat and oil. Its earliest forms date to at least 3000 BC. Various coastal communities have long histories of sustenance whaling and harvesting beached whales...
. Others have been caught in seine nets by trawlers fishing for tuna
Tuna
Tuna is a salt water fish from the family Scombridae, mostly in the genus Thunnus. Tuna are fast swimmers, and some species are capable of speeds of . Unlike most fish, which have white flesh, the muscle tissue of tuna ranges from pink to dark red. The red coloration derives from myoglobin, an...
. They adapt well to captivity and have proven to be intelligent and creative. Less than a dozen rough-toothed dolphins live in dolphinaria around the world.