Cetacean

Cetaceans are marine mammals that include whales, dolphins, and porpoises. They belong to a group called Cetacea and live mostly in the ocean. Some can also be found in rivers and other water bodies. These animals move through water using their tails and flippers, and they need to come up to breathe air.

All living cetaceans can use a special sense called echolocation to find their way and locate food. They have large brains and are known for their intelligence and complex social lives. They communicate through sounds that can sound like songs. The blue whale, one of the largest cetaceans, can grow up to almost 30 meters long and weigh as much as 173 tonnes. It is the largest animal known to have ever lived.

There are about 90 different species of cetaceans, split into two main groups. One group, called toothed whales, includes dolphins, porpoises, and whales like the sperm whale. They hunt fish and other sea animals. The other group, called baleen whales, includes large whales like the blue whale and humpback whale. They feed on tiny animals like krill by using special plates in their mouths called baleen.

Many cetaceans face dangers from human activities. They have been hunted for their meat, blubber, and oil, though rules now limit commercial hunting. They also face risks from pollution, getting caught in fishing nets, and changes in their environment due to climate change. Some species have been greatly affected by these dangers, while others remain more common.

Etymology

The scientific name Cetacea comes from the Latin word cetus, which means "whale". This word comes from an Ancient Greek word κῆτος (kêtos), meaning "huge fish" or "sea monster".

Baleen whales and toothed whales

Baleen whales and toothed whales separated from each other long ago. Today, there are ninety kinds of whales alive. Fifteen of these are baleen whales, and seventy-five are toothed whales.

Baleen whales do not have teeth. Instead, they have special bristles made of a material called keratin. For example, gray whales eat small creatures that live on the ocean floor. Some baleen whales, called rorquals, can stretch their mouths wide to catch tiny animals like krill. Other baleen whales, such as right whales and bowhead whales, have very large heads.

Toothed whales include sperm whales, dolphins, porpoises, and others. They have teeth for catching fish, squid, or other sea animals. Their teeth come in many shapes. Toothed whales can see and hear well both in water and in air. They also use sounds to find their way, a skill called echolocation. Some toothed whales, like sperm whales, can dive very deep.

Anatomy

Cetacean bodies look like fish bodies because they live in water and swim the same way. Their bodies are built for swimming, with a smooth shape and flippers for steering. Most have a dorsal fin on their backs, though some, like the beluga whale, do not. Their bodies are covered in a thick layer of fat called blubber, which keeps them warm and helps them stay smooth and sleek. In big whales, this blubber can be very thick.

Whales have long heads, especially baleen whales. Their mouths contain either teeth or baleen. Baleen looks like a fringe and helps them catch food by filtering water. Their nostrils, called blowholes, sit on top of their heads so they can breathe while most of their body stays underwater. Many toothed whales have a special fat pad called a melon in the front of their heads, which helps them use sound to navigate and find food.

The skeleton of a cetacean is strong and special, made to help them stay stable in the water. Their bones are dense and in some places replaced by cartilage or fat, which makes them lighter. Their spines have between 40 to 93 vertebrae, and their necks are made of just seven fused vertebrae. Their front limbs are shaped like paddles, with shortened arms and long finger bones that help them swim. The only moving joint in their bodies is at the shoulder, except for the Amazon river dolphin.

Cetaceans have a tail fin, called a fluke, made of cartilage. This fluke moves up and down to help them swim fast, unlike fish tails which move side to side.

Physiology

Brain

Cetaceans have brains that look different from land mammals because they live in water. Their brains fold around a part called the insula and expand to the sides. Many cetaceans have special cells in their brains called spindle neurons, which are also found in humans and may help with social behavior and emotions.

Some cetaceans, like belugas and narwhals, have brains that are very large compared to their body size, almost as large as humans. Sperm whales have the largest brains of any animal, averaging about 8,000 cubic centimeters. Brain size used to be thought of as a sign of intelligence, but scientists now know that the ratio of brain size to body size may be more important.

Senses

Vision

Cetacean eyes are on the sides of their heads, which means only some species, like dolphins, have good vision straight ahead and down. Their eyes make special oily tears to protect them from saltwater. Their eyes are shaped to focus light well in deep water.

Chemical senses

Toothed whales have very little ability to taste or smell, while baleen whales may have some ability to smell.

Electroreception

At least one species, the tucuxi or Guiana dolphin, can sense prey using electroreception.

Echolocation

Toothed whales can use echolocation to find and catch prey even in total darkness. They make clicks that bounce off objects, helping them determine the size, shape, and movement of what they encounter. Each whale’s clicks are unique, possibly allowing them to tell their own clicks apart from others.

Differences in skull shape also relate to echolocation abilities. Toothed whales have asymmetrical skulls that help produce echolocation sounds, while baleen whales, who cannot echolocate, have more symmetrical skulls.

Ears

Cetaceans have excellent hearing. They lack visible outer ears but still have ear canals and small, dense bones that help transmit sound. Their ear structures are adapted to protect their hearing from sounds traveling through their skulls. Baleen whales have special ear structures that allow them to hear very low frequencies.

Cetaceans use sound to communicate, making sounds like groans, moans, whistles, clicks, or the singing of humpback whales.

Circulation

Cetaceans have strong hearts and are warm-blooded, keeping a steady internal temperature. Their blood distributes oxygen efficiently throughout their bodies.

Respiration

Cetaceans breathe air using lungs. They can hold their breath for minutes to over two hours, depending on the species. Whales must be awake to breathe in and out. When they exhale, the warm, moist air creates a visible “spout.” This spout can help identify different whale species from a distance.

Their lungs absorb oxygen very efficiently—about twice as much as land mammals. Oxygen is stored not just in the blood and lungs but also in muscles, thanks to a substance called myoglobin. This extra oxygen storage is crucial for deep diving, as water pressure compresses the lungs at depths greater than about 100 meters.

Abdominal organs

Cetacean stomachs have three parts: a loose gland area, a muscular forestomach, and a main stomach, all equipped with digestion-helping glands. Their livers are large and separate from their gallbladders. Their kidneys are long and flat, helping them manage salt from seawater. The testes are internal, and the uterus has a special bicornuate shape.

Chromosomes

Cetaceans typically have 44 chromosomes in their cells. However, sperm whales and pygmy sperm whales have 42 chromosomes. Their chromosomes come in various shapes and sizes, with some having centromeres near one end and others near the middle.

Ecology

Range and habitat

See also: Cetaceans of the Caribbean

Cetaceans live in many different water places. Big ocean animals, like the blue whale, the humpback whale, and the orca, can be found almost everywhere in the ocean. But some animals live only in small areas. For example, the vaquita lives in just a small part of the Gulf of California, and Hector's dolphin lives near the coast of New Zealand. Most river dolphin kinds live only in fresh water, not salt water.

Many cetaceans like warm areas, such as Bryde's whale or Risso's dolphin. Others live in just one special place. The southern right whale dolphin and the hourglass dolphin are only in the Southern Ocean. The narwhal and the beluga live only in the Arctic Ocean. Sowerby's beaked whale and the Clymene dolphin are found only in the Atlantic, and the Pacific white-sided dolphin and the northern straight dolphin live only in the North Pacific.

Some animals can be found in the Pacific, Atlantic, and Indian Oceans. Whales that move long distances often go to warm places to have babies and to cold places to find food.

Thirty-two kinds of these animals live in the waters around Europe, including twenty-five with teeth and seven without teeth.

Behaviour

Sleep

Cetaceans need to breathe while they sleep, so they can't be unconscious for long or they might drown. Some cetaceans can sleep with just one side of their brain at a time. This lets them stay aware of their surroundings while resting.

Diving

When cetaceans dive, they lower their heart rate and blood flow to save oxygen. Some can dive for up to two hours and reach depths of almost 4,000 meters, though most dives are much shorter.

Social relations

Most cetaceans live in groups called pods, usually with ten to fifty members, though they can sometimes be much larger. These groups have a clear order, but they are usually peaceful unless there is not enough food. Cetaceans often swim close to each other, touch, and play, especially smaller ones like dolphins and porpoises.

Whale song

Some male whales make long, complex sounds called songs that can travel for hundreds of kilometers. Each group has its own song, which changes over time. These songs might help attract mates.

Hunting

Cetaceans often hunt together. Dolphins sometimes follow schools of fish, while orcas hunt in groups and target larger whales. Some whales, like humpbacks, work together to trap small fish in bubbles before catching them.

Intelligence

Cetaceans are very intelligent. They can teach, learn, work together, and show emotions. Dolphins and porpoises play complex games with bubbles, such as creating rings of air underwater. Whales also seem to enjoy playing, such as lifting their tails out of the water.

Cetaceans may understand themselves and their surroundings. Dolphins have shown signs of recognizing themselves in mirrors, which suggests they might think in more complex ways.

Decision-making

Living in groups is important for many cetaceans, and they need to make decisions together. Scientists are still learning how these decisions are made, but they know that some groups work together to reach a consensus, while others follow leaders.

Life history

Most cetaceans grow up and become adults between seven to 10 years old. One exception is the La Plata dolphin, which becomes an adult at just two years old but lives only up to about 20 years. Sperm whales take about 20 years to become adults and can live between 50 and 100 years.

For most cetaceans, having babies happens at certain times of the year. Females often choose more than one partner during the season. Gestation, the time from when a baby is conceived until it is born, lasts from 9 to 16 months. Cetaceans usually have one baby at a time, and the mother carries the newborn to the surface for its first breath of air. At birth, baby cetaceans are about one-third the size of an adult.

Cetaceans feed their babies milk produced by the mother. The milk is rich in fat, which helps the baby grow quickly. In smaller cetaceans, this feeding lasts about four months, while in larger species it can last over a year.

Some cetaceans, like the bowhead whale, can live over 200 years. When these animals die, their bodies fall to the deep ocean and become a home for many sea creatures.

Disease

Some diseases can affect whales, dolphins, and porpoises. One such disease is called brucellosis, found all over the world. It can cause health problems, like trouble having babies and sickness, in these animals. It was mostly seen in dolphins before, but some porpoise groups are now at risk too.

Evolution

Main article: Evolution of cetaceans

The ancestors of today's cetaceans, like whales, dolphins, and porpoises, likely lived on land. Over many years, they changed to live in water. Their hind legs got smaller, and their front legs became flippers. They grew special ways to hear underwater, and their bodies became smooth for swimming.

Scientists think cetaceans are related to animals like hippos. Evidence from fossils and science helps us understand this. Cetaceans left land about 55 million years ago. Today, they are in two groups: baleen whales, which have baleen plates instead of teeth, and toothed whales, which have teeth and use echolocation to find their way and food.

Threats

The main dangers to cetaceans come from human activities. These include hunting, fishing, and pollution.

Whaling

Main articles: Whaling, History of Whaling, and Dolphin drive hunting

Whaling is the hunting of whales for food, oil, and bones. People have hunted whales for a very long time. Over time, better tools made whaling easier, and more whales were killed. This greatly reduced many whale populations.

Today, rules help protect many whales. Some countries still hunt whales under special permits. Some groups still hunt whales in traditional ways. Dolphins and smaller cetaceans are also sometimes hunted by driving them into shallow water.

Fishing

See also: Cetacean bycatch

Fishing can accidentally harm cetaceans. Dolphins often swim near fish that fishermen catch. Sometimes, fishermen pull their nets around dolphins, accidentally catching and hurting them. River dolphins face similar risks.

Strandings

Sometimes cetaceans end up on beaches far from the ocean. This is called stranding. These animals usually cannot survive out of water. The reasons for strandings are not fully known but may include illness or loud underwater noise.

Environmental hazards

See also: Marine mammals and sonar

Pollution and changes in the ocean also threaten cetaceans. Harmful substances like heavy metals and plastic can harm their health. Changes in the ocean from climate change, such as warmer waters, reduce the food for many whales. Loud noises from ships and other activities can disturb cetaceans.

Relationship to humans

Research history

See also: Cryptid whale and Whale § In myth, literature and art

Long ago, people thought whales were fish because they looked similar. But smart thinkers like Aristotle saw that whales had blood and lungs, like land animals. Later, Carl Linnaeus showed that whales are mammals, not fish.

Culture

Whales and dolphins have been in stories and art for thousands of years. Ancient people used whale bones for tools. In myths, dolphins helped heroes and were loved by gods. Today, many people enjoy stories and movies about these clever sea animals.

Middle Ages to the 19th century

See also: History of Whaling and Cryptid whales

For many years, people hunted whales for their oil and bone. Books and paintings showed whales as big sea monsters. Famous stories like Moby Dick made whales well-known.

Modern culture

Further information: Whale § Interactions with humans

In recent times, people began to see whales as wonderful, intelligent friends. Today, many people enjoy watching whales in movies, TV shows, and even in special places where they live. Songs made from whale calls became popular too.

Captivity

Whales and dolphins have lived in special places for learning, studying, and showing people since the 1800s.

Belugas

Main article: Beluga whale § Captivity

Beluga whales were the first to live in these special places. They are popular because of their white color and friendly looks.

Orcas

Main article: Captive killer whales

See also: SeaWorld § Criticism and resulting impact, and Incidents at SeaWorld parks

Orcas, also called killer whales, are smart and can learn many tricks. Many places show them, but some people worry about keeping them in small spaces.

Others

Many kinds of dolphins live in special places too. Some are easy to train and make great friends for people.