Rough-Toothed Dolphin

## Description

The rough-toothed dolphin (Steno bredanensis ) is a 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.

## Appearance

The Rough-toothed dolphin’s curious name and difference to other dolphin species refers to its very prehistoric reptile look, having wrinkles and ridges on their teeth. The four sections of the teeth in their upper and lower jaw have between 19 and 28 teeth. Their narrow beak is noticeable, and they have a small head. They are small dolphins, and they do not have a crease in their melon like other dolphins.

## Distribution

Rough-toothed dolphins are found in all of the world’s three major oceans: the Pacific, Atlantic and Indian. In the US there are two recognized populations: in Hawaii and the northern Gulf of Mexico. They inhabit warm temperate and tropical waters, usually over 25 degrees Celsius, and typically occur in deep, offshore waters.

## Behavior

Rough-toothed dolphins are diurnal creatures, most commonly found in groups of 10 to 30, though pods of as many as 160 individuals have been seen, containing eight smaller groups. Sometimes they are seen with Pilot whales, Spotted dolphins, Bottlenose dolphins, and Spinner dolphins. These animals are great divers, staying submerged for up to 15 min. They are fast swimmers, often swimming just below the surface of the water, their dorsal fins being clearly visible. This species enjoys "surfing" or bow-riding, though not as often as other tropical dolphins. Their most commonly observed behaviors are travelling, physical social contact with pod members, resting, feeding, object play, milling and sexual activity. They communicate with each other with echolocation clicks, burst pulse signals, whistles, and synchronous swimming patterns.

## Diet

Rough-toothed dolphins are carnivores (piscivores and molluscivores) and their diet includes silverside, saury, needlefish, squid and mahimahi, their preference being for the latter.

## Reproduction

Little is known about the mating systems of these dolphins in the wild, including whether there is a certain season for mating. The gestation period is about 100 days. A single calf is born, tail first, every 1-4 years. Calves drink their mother’s milk and gain weight fast. Their mother introduces them to fish when they are about 2 months old. Females are sexually mature at 9 to 10 years old, when they measure 212 to 217 cm. Males are sexually mature at 5 to 10 years old when they are about 216 cm long.

## Population

### Population threats

The main threat to this species is likely to be as bycatch in fishing nets. It is also hunted for its meat in several countries including Japan, Indonesia, Sri Lanka, Papua New Guinea and the Solomon Islands. Habitat destruction as a result of human disturbances is another threat to this species.

### Population number

The species is widespread and abundant, and it's current population estimates around 150,000. According to the IUCN Red List resource, an estimated 145,900 Rough-toothed dolphins live in the eastern tropical Pacific, and around 2,746 occur in the northern Gulf of Mexico, with an estimated 1,238 on the continental shelf. The regional population around Hawaii has been estimated by the US NMFS at 19,904 individuals. Overall, Rough-toothed dolphins are classified as Least Concern (LC) on the IUCN Red List.

### Ecological niche

Rough-toothed dolphins help control adult populations of mahimahi, as it's their preferred food.

## Fun Facts for Kids

Rough-toothed dolphins often have bite marks from scarring due to conflicts with sharks. Older individuals sometimes have white scars that can cause complete white patches on their skin.

This species was first described in 1823 by Georges Cuvier. Its genus name steno, of which it is the only member, is from the Greek word for 'narrow', referring to its beak, one of its characteristics. Its specific name is from van Breda, who studied the writings of Cuvier.

A female of this species protects her calf by swimming in close by and positioning herself between her calf and other dolphins.

If a fellow dolphin is injured, a member of this species will support it at the water’s surface so it can breathe. They have also been seen supporting a dead dolphin at the surface for several hours and even for several days.

Rough-toothed dolphins adapt well to being in captivity, which is unusual among oceanic dolphins.

Aquarium trainers who work with this species say it is among the most intelligent of the dolphins.

## References

https://animalia.bio/rough-toothed-dolphin