Steno bredanensis (G.Cuvier, 1828)

Species Introduction

The rough-toothed dolphin, Steno bredanensis, is a relatively large dolphin species.

Adult Size

Adult length ranges from 2.09 to 2.83 metres (6.9 to 9.3 ft), and adult weight ranges between 90 and 155 kilograms (198 and 342 lb), with males growing larger than females.

Head and Snout Traits

Its most prominent visible traits are a conical head and slender nose; other dolphin species typically have either a shorter snout, or a more noticeably bulging melon on the forehead.

Tooth Structure

As the species' common name suggests, its teeth are also distinctive: they have a roughened surface formed by many narrow, irregular ridges. Individuals have between nineteen and twenty-eight teeth in each quarter of the jaw.

Jaw Appearance

The outer shape of the rough-toothed dolphin's jaw is very distinct, and the lower jaw is usually white, sometimes with a faint pink tint.

Flipper Placement

The species' flippers are positioned further back along the body than those of other similar dolphins, though at sea rough-toothed dolphins may still be confused with spinner, spotted and bottlenose dolphins.

Dorsal Fin Size

The dorsal fin is prominent, with a height between 18 and 28 centimetres (7.1 to 11.0 in).

Body Coloration

The animal's flanks are light gray, while the back and dorsal fin are a much darker gray. Older individuals often develop distinct pinkish, yellow, or white markings around the mouth and along the underside.

Population Knowledge

The distribution and total population of the rough-toothed dolphin are poorly understood.

Global Range

The species inhabits warm temperate to tropical waters of the Pacific, Atlantic, and Indian Oceans, as well as the Mediterranean Sea, with occasional reports of individuals in cooler environments.

Atlantic Occurrence Records

They are regularly sighted in areas stretching from the Windward Islands to Cape Verde, while only a small number of individuals have been recorded in the Azores and Madeira.

Habitat Depth

Almost all live sightings occur far offshore, beyond the continental shelf, in water that is at least 1 kilometre (0.62 mi) deep.

Eastern Pacific Population

Most research on the species has focused on the eastern Pacific, where researchers produced a population estimate of 150,000 in the 1980s.

Fossil Record

Fossils belonging to the genus Steno, dated to the early to mid-Pliocene, have been found in Europe.

Mediterranean Population

In the Mediterranean Sea, the species was once thought to only visit from the North Atlantic, but recent findings confirm there is a small resident population in the eastern part of the sea.

Reproduction Unknowns

Rough-toothed dolphins give birth to a single calf, but the length of their gestation period is unknown, and it is also unclear whether they have a distinct breeding season.

Calf Growth

Newborn young are roughly 100 centimetres (39 in) long at birth, and grow rapidly for their first five years of life.

Sexual Maturity Ages

Females reach sexual maturity between six and ten years of age, and males reach sexual maturity between five and ten years of age.