Dolphin

A dolphin is any one of the many aquatic mammal species from several cetacean families. These include oceanic dolphins, river dolphins, and brackish dolphins. Dolphins belong to the group of toothed whales, which also includes belugas, narwhals, and porpoises.

Dolphins vary in size, from small ones to larger ones like the orca. They have streamlined bodies with flippers and a tail fluke that help them swim quickly through the water. Dolphins use their teeth to catch prey like fish and shrimp, and they have very good hearing that works in both air and water.

Dolphins live in many parts of the world, mostly in warm ocean waters but also in some rivers. They are social animals that live in groups called pods and talk to each other using clicks and whistles. Because of their intelligence and graceful movements, dolphins are popular in many cultures and are sometimes kept in special facilities called dolphinariums. However, dolphins face threats from getting caught in fishing nets and pollution in their habitats.

Etymology

The word "dolphin" comes from the Greek word delphís, meaning "dolphin." This word is linked to delphus, meaning "womb." It gives the idea of a "fish with a womb." The word traveled through Latin and French before it became the English word we use today.

Today, "dolphin" refers to many species, including oceanic dolphins and river dolphins. Sometimes people also call the mahi-mahi fish a "dolphinfish," which can be confusing. A group of dolphins is called a school or a pod. Male dolphins are called bulls, females are cows, and their babies are calves.

Evolution

Main article: Evolution of cetaceans

Dolphins started as land mammals that walked on four legs. About 48 million years ago, they moved into the water. Over time, their bodies changed to help them swim. They grew fins and a tail to move faster, and their ears changed so they could hear underwater. Today, dolphins are most closely related to hippos, who also have a shared ancestor that lived in water long ago.

Anatomy

Dolphins have bodies shaped like torpedoes. They have necks that can't bend, limbs changed into flippers, and a tail fin. Dolphins range in size from the 1.7-metre-long Maui's dolphin to the 9.5-metre orca. Their skulls have small eye openings and long noses.

Dolphins breathe by blowing out old air from their blowhole and taking in fresh air. They have a thick layer of blubber to keep warm, protect themselves, and store energy. Their teeth are cone-shaped and used for catching fast prey like fish and squid.

Dolphins have two pectoral flippers, a dorsal fin for balance, and a fluke for moving forward. They swim by moving their fluke and back body up and down, using their flippers mostly for steering. Some dolphins can swim very fast and dive deep, slowing their heart rate to save oxygen.

Dolphins use echolocation to find their way and locate things. They make sounds using recycled air and special organs. Even though they have good eyesight, their vision is different from humans, with eyes on the sides of their heads. They cannot smell or taste.

Intelligence

Further information: Cetacean intelligence and Cetacean surfacing behaviour

Dolphins are very smart animals. They can learn, work together, and show feelings. Some parts of their brains are like those in humans, which may help them think in complex ways.

Scientists study animal intelligence by looking at brain size compared to body size. Orcas have very large brains for their body size, similar to humans. One way to test if an animal knows itself is by using a mirror. When dolphins see their own reflection and notice a mark, they act in ways that suggest they recognize themselves, though some scientists discuss these results.

Behavior

Dolphins are very social animals. They often live in groups called pods. These pods can change size and sometimes join together into bigger groups when there is lots of food. Dolphins form strong bonds and help injured or sick members stay near the surface to breathe. They talk to each other using clicks, whistles, and body language.

Dolphins do many interesting things. Some dolphins in Australia use sponges to protect their noses while looking for food. They also help other animals, like a stranded whale, and can protect people from sharks. Dolphins are playful. They jump out of the water and play with objects or other animals. Sometimes they chase small animals, perhaps just to be curious.

Threats

Dolphins have few natural enemies. Many are at the top of the food chain. Smaller dolphins may be at risk from larger sharks, such as bull, dusky, tiger, and great white sharks, especially when young. Larger dolphins, like orcas, might occasionally prey on smaller dolphins, though this is rare. Dolphins can suffer from diseases and parasites.

Dolphins face dangers from humans. Some species are critically endangered. Pollution from pesticides, heavy metals, and plastics can harm dolphins. Collisions with boats are also common dangers. Fishing practices, such as seine fishing for tuna and the use of gill nets, often result in dolphins being caught accidentally. In some places, dolphins are hunted for their meat. Efforts to make fishing "dolphin-safe" have helped reduce some of these risks.

Climate change also affects dolphins. Warmer waters force many dolphin species to move to new areas. This change can reduce their food supplies and lead to population declines. River dolphins are especially vulnerable to changes in water temperature and quality, which can threaten their survival.

Relationships with humans

In history and religion

Dolphins have been important in human culture for a long time. In Greek myths, they were seen as helpers. They were also important to the Minoans, as shown by art from the palace at Knossos. Ancient Greeks liked dolphins and thought seeing them was a good sign. Dolphins appear in many stories and artworks, including ones with Cupid and the poet Arion.

In Hindu mythology, the Ganges river dolphin is linked to the goddess Ganga. In Amazon River cultures, dolphins are thought to change shape.

In captivity

Dolphins became very popular in the 1960s, so many places were built where people could see them. Today, many places still keep dolphins, with bottlenose dolphins being the most common. These dolphins are kept in places like SeaWorld and are often trained to do tricks.

Some groups work to help sick or injured dolphins, while others work to protect them. India has made the dolphin its national aquatic animal and created a safe place for them.

Military

Some militaries have used dolphins for tasks like finding mines or helping lost people. The United States Navy has trained dolphins for different jobs, though they say the dolphins were never trained to hurt anyone.

Therapy

Dolphins are sometimes used to help people with mental or development issues. However, it’s not clear if this works better than other types of therapy.

Controversy

There is debate about keeping dolphins in places where people can see them. Some think it’s stressful for the dolphins and doesn’t feel like their natural home. There have been rare cases where dolphins have hurt people, both in places where they are kept and in the wild. Some scientists think dolphins should have special rights because they are very smart.

Consumption

In some places, like Taiji, Japan and the Faroe Islands, dolphins are caught for food. The meat can contain harmful substances like mercury, which can be dangerous to health.

Main article: Military dolphin

See also: Captive orca