Dolphin

Dolphins are aquatic mammals of the infraorder Cetacea that constitutes five families, including oceanic dolphins, the Indian river dolphins, brackish dolphins, the New World river dolphins, and the extinct Chinese river dolphins. Research has shown that the ancestors of today’s dolphins were land-dwelling mammals, which became fully aquatic approximately 39-44 million years ago.

List of Common Types of Dolphin Species

There are about 40 species of dolphins living today, divided into four extant families, including Platanistidae, Delphinidae, Iniidae, and Pontoporiidae. Some of the commonly found dolphin species are listed below:

• Common bottlenose dolphin
• La Plata dolphin
• Short-beaked common dolphin
• Long-beaked common dolphin
• Burrunan dolphin
• Indo-Pacific bottlenose dolphin
• Southern right whale dolphin
• Northern right whale dolphin
• Guiana dolphin
• Indo-Pacific humpbacked dolphin
• Australian humpback dolphin
• Atlantic humpback dolphin
• Clymene dolphin
• Atlantic spotted dolphin
• Spinner dolphin
• Pantropical spotted dolphin
• Striped dolphin
• Chilean dolphin
• Rough-toothed dolphin
• Fraser’s dolphin
• Commerson’s dolphin
• Hector’s dolphin
• Risso’s dolphin
• Atlantic white-sided dolphin
• Hourglass dolphin
• Dusky dolphin
• Pacific white-sided dolphin
• Peale’s dolphin
• White-beaked dolphin
• Australian snubfin dolphin
• Irrawaddy dolphin
• Killer whale
• Melon-headed whale
• False killer whale
• Pygmy killer whale
• Long-finned pilot whale
• Short-finned pilot whale
• Araguaian river dolphin
• Amazon river dolphin
• South Asian river dolphin
• Tucuxi
• Bolivian river dolphin

Physical Description and Appearance

Size: Dolphin species exhibit various sizes, ranging from the smallest Maui’s dolphin with a length of 5.6 ft (1.7 m) to the largest killer whales or orcas, measuring 31 ft (9.5 m). Several species like the long-beaked common dolphins display sexual dimorphism, with the males being more robust and longer than females.

Weight: The weight of dolphins varies depending on the species, with the Maui’s dolphin weighing 50 kg (110 lb) and killer whales having a weight of 10 tons (22,046 lb).

Color: They can have diverse color combinations. The Amazon river dolphin, for example, is grayish-pink or bright pink, while the killer whale and Commerson’s dolphins have a mix of black and white. Common dolphins come with a shade of dark gray and white.

Body: Dolphins have streamlined bodies, along with non-flexible necks, modified flippers, a tail fin, non-existent ear flaps, and bulbous heads.

Teeth: Unlike porpoises, dolphins possess conical teeth for catching quick-moving prey, including fish, squid, and seal. The number of teeth varies widely across species, with the orcas carrying 40-56 teeth, bottlenose dolphins having 72-116 teeth, and the common dolphins possessing 188-268 teeth.

Genitals: The reproductive organs occur inside their bodies, with the genital slits being located on the side of their belly. Males possess two genital slits, while the females have one.

Distribution

Dolphins are widely distributed and found in all of the world’s oceans and some rivers. Although these aquatic mammals can inhabit the cold sub-Antarctic and Antarctic waters, most species prefer living in warm tropical areas.

What kind of habitats are dolphins found in

Their habitat varies depending on food accessibility and environmental factors. While most of them are found in saltwater, some species of dolphins thrive in freshwater. Dolphins are usually seen in bays, creeks, rivers, inlets, shallow waters along the coast, and at great depths in oceans.

How long do they live

In captivity, the average lifespan of dolphins is only about 20-25 years, although there have been instances of killer whales living more than 30 years with two orcas, Lolita and Corky II, surviving up to their mid-40s. Wild dolphins have higher life expectancies, with the females living roughly 45 years on average, and sometimes up to 75-80 years. The males live for 31 years on average but can survive up to 55-60 years.

What do they eat

Dolphins typically feed on fish and squid, although the orcas and false killer whales also eat other sea mammals, such as dugongs and seals. Occasionally, orcas also hunt whales bigger than themselves.

Behavior

• They are highly social mammals, usually living in groups (or pods) consisting of up to 12 individuals, though the size and structure of these groups can vary depending on the species and locations. Groups can merge temporarily in places with an abundance of food. These superpods may comprise more than 1,000 dolphins.
• These aquatic mammals form strong social bonds, as they stay with individuals that are ill or injured, often bringing them to the surface to help them breathe.
• Dolphins can produce a wide range of sounds, including frequency-modulated whistles and burst-pulsed sounds for communication. They also use touch and posturing for nonverbal communication.
• They display cultural behavior, something that is exhibited by humans and primate species. In 2005, Indo-Pacific bottlenose dolphins were found teaching their babies to cover their snouts using sponges for protecting them while foraging.
• Dolphins often jump above the water surface while traveling. This activity, called porpoising, is done for social displays, orientation, entertainment, nonverbal communication, dislodging parasites, and saving energy.

Adaptations

• Their skin can adapt to harsh climate because of a thick layer of fat or blubber that provide insulation from cold. It is also used for obtaining energy when food is scarce.
• They have limbs that are modified into flippers, comprising four digits, which they use for steering. Their boneless dorsal fin is used for stability while the tail fin helps them to swim and propel forward.
• Some dolphins are capable of slowing down their heart rate for conserving oxygen, helping them to dive deep in the ocean. They can also re-direct blood from the tissues (that can tolerate water pressure) to the brain, heart, and other organs.
• The forehead of dolphins has a specialized organ, called melon, made of fat for sending out clicks, which is a high-frequency sound used for communication.
• Dolphins usually have slightly flattened corneas, enlarged pupils, and moderately flat eyeballs to enable large amounts of light pass through their eyes, giving a clear image of their surroundings.

How do they Reproduce and Mate

Dolphins are polygynous, meaning the males mate with more than one female every year, while the females mate every 2-3 years. Copulation is generally brief, occurring belly to belly, often happening quite a few times within a short interval. The gestation period varies among dolphin species, ranging from 11-12 months in the tucuxis to roughly 17 months in the orcas. They typically give birth to one offspring in the spring or summer months, with the calf born tail first. Young dolphins usually become sexually active before reaching sexual maturity, which occurs at about 8-13 years of age.

Conservation

Several organizations, such as the Hong Kong Dolphin Conservation Society (HKDCS) and the Whale and Dolphin Conservation (WDC), have been set up for their protection and welfare. The Mote Marine Laboratory, a Florida-based research organization, work on rescue and rehabilitation of wounded, sick, or orphaned dolphins. Countries like India have declared it as the national aquatic animal to save the Ganges river dolphin from extinction. The Vikramshila Dolphin Sanctuary has been established for their protection.

Dolphin-FAQs

1. Are orcas dolphins?

Yes. Orcas are the largest dolphin species.

2. How do dolphins sleep?

Dolphins usually sleep with one of their brain hemispheres in a deep sleep at a particular moment, remaining conscious enough to breathe and be wary of the presence of predators or other threats. Captive dolphins enter a state of deep sleep with both eyes closed, automatic respiration, and no response to a mild stimulus.

3. How smart are dolphins?

Scientists have shown that dolphins have a high level of intelligence, demonstrating self-awareness, empathy, innovation, problem-solving ability, playfulness, teaching skills, grief, and joy. They are also known for their fantastic mimicry skills and quick learning ability.

4. Is a dolphin a fish?

No

5. Do dolphins have hair?

Baby dolphins have whiskers on their snout, but they lose them soon after birth.

6. Are dolphins endangered?

Some dolphin species, such as the Indus river dolphin, Ganges river dolphin, and Hector’s dolphin, are endangered.

7. How fast can a dolphin swim?

These aquatic mammals are fast swimmers. The orcas, for example, can swim with a top speed of 55.5 kph (34.5 mph).

8. What is a group of dolphins called?

A pod or school

9. How long can dolphins hold their breath?

On average, dolphins can remain submerged, holding their breath for 8-10 minutes. However, individuals have been observed to stay underwater for approximately 15 minutes.

10. What is a baby dolphin called?

A calf or pup

Interesting Facts

• Their sense of hearing is extraordinarily well developed, and they can hear both in air and under the surface of water. Some dolphins stay alive even after becoming blind.
• Dolphins are often held captive and trained to obey commands and perform tricks. Common dolphin species kept in captivity include bottlenose dolphins and killer whales.
• These fascinating aquatic mammals have also appeared in literature and movies like Free Willy.
• In the Faroe Islands and some parts of Japan, dolphins are traditionally eaten and killed in drive hunts.
• The coat of arms of Romania, Anguilla, and Barbados feature dolphins.
• Dolphins sometimes exhibit non-reproductive sexual behavior, including masturbation or stimulation of the genitals of other individuals with the flippers or rostrum, and homosexual contact.
• Male dolphins may show aggressive behavior towards both males and females, resorting to violent sexual encounters or ‘rape’ for asserting authority. Dolphins have also been observed to behave sexually towards humans.