Dolphins and porpoises are small toothed whales, or ‘odontocetes’ which means ‘toothed sea-monster’ in Greek. They are grouped into six families; the ocean dolphins are the biggest family with 38 species; there are four river dolphin families each with only one member; and one porpoise family containing all seven porpoise species.
All dolphins and porpoises are highly mobile, powerful predators who hunt fast-moving fish, squid, and other sea creatures. They have super-streamlined bodies, blubber to keep them warm, a single blowhole, and most have a dorsal fin and countershading camouflage which means they are darker on their back than their belly.
The main physical differences between dolphins and porpoises are their size - dolphins are generally larger than porpoises; the shape of their head – dolphins have a bulbous melon and protruding beak, whereas porpoises have blunt heads; and their teeth – dolphins have conical-shaped teeth and porpoises have spade-shaped teeth. Dolphins are more social than porpoises.
Dolphin and porpoise families
The ocean dolphin family is very large and diverse; it has 38 members. The largest ocean dolphins are the orca, pilot whale and false killer whale. The smallest are the Maui’s dolphin, Hector’s dolphin and tucuxi. Other ocean dolphins include Risso’s, striped, spinner, spotted, common, Dusky, hourglass, rough-toothed, white-beaked, Commerson’s and bottlenose dolphins.
Oceanic dolphins are found in all the world’s oceans and seas and from the equator to the ice edges. However, the majority of species live in warm and tropical waters and only orcas live near the polar ice sheets. Many species prefer off-shore, deep-water habitats, and others are more coastal.
The number of teeth they have ranges from 14 (Risso’s dolphin) to 240 (spinner dolphin). The shape, size and even position of their teeth varies depending on their preferred prey. Most ocean dolphins have lots of conical-shaped teeth which are best for grabbing fish. Squid-hunting specialists, such as Risso’s dolphins, have fewer teeth as they suck the squid into their mouths.
Dolphins are sociable creatures and typical group sizes for the different species can range from a few individuals to larger pods, to those numbering hundreds or even thousands in deep water. Dolphins have an array of vocalisations such as clicks, whistles and squeals which they use for their well-developed communication and echolocation skills. Dolphins are intelligent; examples of behaviour seen in the wild which demonstrates their intelligence includes cooperative hunting, play behaviour, and tool use.
Dolphins give birth to one baby at a time after a pregnancy between nine and 16 months. Mothers feed their babies with their own milk and take care of them for a number of years, during which time they teach their youngsters how to thrive independently. The sons and daughters of resident orcas will stay with their mothers throughout her lifetime. Lifespan varies from around 20 years in the smaller dolphin species to 80 years or more for larger dolphins such as orcas.
Ocean dolphin facts
- 38 species currently
- Inhabit all the world's oceans and seas
- Includes the largest dolphin (orca) and some of the smallest (New Zealand dolphin, Franciscana)
There are four dolphin species and four families that are grouped together as the true river dolphins. The South Asian river-dolphin is known as the Ganges river dolphin or susu in India and Nepal, the shushuk in Bangladesh and the Indus river dolphin or bhulan in Pakistan; the Amazon river dolphin, known in South American countries locally as boto, bufeo or Inia; the franciscana; and the Yangtze river dolphin, known as baiji in China but now extinct (this was announced by scientists in 2007).
The vaquita, which in Spanish means ‘little cow’, is the smallest porpoise in the world, and also the most endangered. The vaquita lives only in Mexican coastal waters, in a small area of the northern Gulf of California. The species is in terrible trouble and facing imminent extinction; there are only about 30 individuals left. Accidental capture and death in fishing nets is the cause of their rapid decline in numbers; to put it simply, more vaquitas are killed in fishing nets than are born each year.
Maui's dolphin is also on the brink of extinction. Maui’s dolphin is a sub-species of the New Zealand dolphin that lives only in coastal waters of part of North Island, New Zealand. Maui’s dolphins are facing extinction; there are now less than 50 individuals left living along a 22-mile stretch of coastline. The problem causing this rapid decline and indeed the decline of Hector’s dolphin (the other New Zealand dolphin sub-species) in South Island is entanglement in fishing nets.
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