Delphinidae: Dolphin Family
There are 32 species in this, the largest, most diverse cetacean family, which is found in all oceans and some tropical rivers. Most have beaked snouts and slender streamlined bodies and they are among the smallest whales. Typically, the dolphin has a bulging forehead, housing the melon, a lens-shaped pad of fat thought. A few species, notably the killer whale, are much larger and do not have beaks. Male dolphins are usually larger than females, and in some species the sexes differ in the shape of their flippers and dorsal fins. Dolphins swim fast and feed by making shallow dives and surfacing several times a minute. They are extremely gregarious and establish hierarchies within their social groups.
Atlantic Humpback Dolphin
Atlantic humpbacks are shy dolphins, making them a difficult species for scientists to observe and study. Political instability in many West African countries along the coasts of which this dolphin lives has also compounded the problems of studying these animals. They inhabit tropical coastal waters, preferring to stay in shallow water. Typical school sizes range from between three and seven individuals, but groups of up to 25 have been observed. As these dolphins get older, they become more and more solitary, and eventually hardly ever associate with other individuals.
The humpback dolphin gets its name from its distinctive method of surfacing and its slightly bulbous dorsal fin.
The humpback dolphin has a unique way of surfacing: the beak and head break the surface before the body arches tightly, making the dorsal fin more prominent. Orcas are a major threat to this species. They locate the dolphins by listening in to their calls. By staying close to land, the dolphins are able to disrupt their calls and thwart the killers.
Distribution: Eastern Atlantic Ocean off West Africa.
Habitat: Tropical coastal waters, usually less than 20 m (65 ft) deep, and tidal zones of rivers.
Size: 1.2 - 2.5 m (4 - 8.25 ft); 75 - 150 kg (165 - 330 lb).
Maturity: Between 4 and 8 years.
Breeding: Single calf born every 1 - 2 years.
Life span: Unknown.
Status: Declining because of habitat loss.
Heaviside's dolphin is a relatively common species that can often be seen from the shore among the waves. However, it is found only off the remote coasts of Angola, Namibia and the Cape Province of South Africa, and therefore is not particularly well understood.
The dolphins swim from just beyond the breakers to about 80 km (50 miles) off shore. They prefer water that is less than 180 m (590 ft) deep. Heaviside's dolphins prey mainly on fish and other animals, such as octopuses and lobsters, that live on or near to the sea floor. The long lower jaw may aid them in scooping prey from the bottom.
Heaviside's dolphin is a sturdy, rounded species. Its girth is about two-thirds of the total body length. It has a cone-shaped snout and lacks the beak of other dolphins. The lower jaw sticks out past the upper jaw. The back is a dark blue with a grey "cape" over the head. A fork-shaped white mark runs along the belly.
They are found mainly in pairs, probably a mother with her calf. Little is known about their reproductive habits, but most births occur in the summer months.
The dolphins often display by tail-flipping. This is a half somersault that ends in a splash with the tail. They are also often seen escorting boats. Heaviside's dolphins are thought to be common in their range, but there are reports that they are increasingly being hunted for their meat and killed by accident by fishing craft.
Distribution: South-western Africa.
Habitat: Shallow coastal waters. Often seen in the breaker zone.
Food: Fish and squid and other swimming animals, as well as octopus and other animals that live on the seabed.
Size: 1.7 m (5.5 ft); 70 kg (154 lb).
Breeding: Young are born in summer and newborns are large, about half the length of adults.
Life span: Unknown.
Status: Common, although increasingly at risk.
Short-beaked Saddleback Dolphin
Size: 1.5 - 2.4 m (5 - 8 ft); 70 - 110 kg (154 - 242 lb).
Often called the common dolphin, this species is one of the smallest dolphins. It is common in European waters, but it also swims in coastal areas of the Atlantic and Pacific oceans, including along the shores of the Americas, where it is most often seen in the Gulf of Mexico. Common dolphins prefer to swim in warmer water near the surface. They have many small, curved teeth, with which they snatch herrings and other small, slippery fish. Common dolphins live in small family groups, or pods. Sometimes many pods join together to form vast clans up to 100,000 strong. Most of the time these dolphins swim at about 8kmh (5mph), but their top speed is around 46 kmh (29 mph).
Southern Right Whale Dolphin
Size: 1.8 - 2.3 m (6 - 7.5 ft); 60 kg (132 lb).
This species lives in the southern hemisphere. It is found around the edge of the Southern Ocean surrounding Antarctica. It also swims further north along the cold-water currents that flow from the polar region. The northern limit of the dolphin's range is in the subtropical zones where these cold currents meet warmer water heading south - for example, off the coasts of Chile and Peru, along which the Humboldt Current flows. Like the right whale, this dolphin species is largely black, with white patches on the belly and under the mouth, and it lacks a dorsal fin. The southern right whale dolphin also has a very slender body - unlike its giant namesake, which is known for its enormous girth.
Size: 2.1m (7 ft); 90 kg (198 lb).
Striped dolphins are found in the world's warm seas, including the Caribbean and Gulf of Mexico. They keep to areas where the water temperature is above 20°C (68°F), and they are just as at home in open water as they are in the shallows near the coast. They get their name from the blue stripe that runs along the entire length of the body. There are also black stripes running down to the flippers. Being inshore dolphins, they eat a range of foods, from free-swimming fish to bottom dwelling crabs and octopuses. Striped dolphins are very active swimmers. They also perform an unusual manoeuvre called roto-tailing, in which they leap out of the water in a high arc and spin around their tail.
Chinese River Dolphin
Size: 1.4 - 2.5 m (4.75 - 8.25 ft); 42 - 167 kg (92 - 334 lb).
This freshwater dolphin lives in the Yangtze River in China from its estuary to around 1,900 km (1,200 miles) upriver. Like the Ganges river dolphin, it has small eyes, a long, thin snout and a reduced dorsal fin. This species has suffered extensively from boat traffic strikes, hunting and the decline of its prey brought about by the construction of dams and pollution. It is probably the most endangered of all the dolphins.
Size: 1.6 m (5.25 ft); 50 kg (110 lb).
This small dolphin lives off the coast of Chile. Mineral-rich currents from Antarctica make the continental shelf here a fertile feeding ground for black dolphins, which feed on fish and sea-floor animals. To help them get at their prey, the dolphins have a relatively flat snout, more like that of a porpoise than the beak-like snout of other dolphins. Black dolphins live in small schools and communicate with clicks. Similar noises are used to locate prey by echolocation.
Size: 1.6 m (5.25 ft); 83 - 100 kg (183 - 220 lb).
These dolphins are found in the colder waters of the southern hemisphere. These shy animals live in small groups and travel huge distances in their lifetime. In general, hourglass dolphins keep to the waters around Antarctica, but they occasionally follow cold-water currents moving north, such as the Humboldt Current that flows along the coast of Chile.
Range: China: Yangzte River; formerly Lake Tungting.
Habitat: Muddy-bottomed rivers.
Size: 6 1/2 - 8 ft (2 - 2.4 m).
Since 1975 this species has been protected by law in China, but although the total numbers are not known, population still seems to be low. The whitefin dolphin has a slender beak, which turns up slightly at the tip, and a total of 130 to 140 teeth. With little or no vision, it relies on sonar for hunting prey, mainly fish, but may also probe in the mud with its beak for shrimps.
Groups of 2 to 6 dolphins move together, sometimes gathering into larger groups for feeding. In the rainy summer season, they migrate up small swollen streams to breed, but no further details are known of their reproductive behavior.