All About Dolphins

Why are sharks afraid of dolphins?

How smart are dolphins?

Discovering Dolphins

Dolphin Facts (optional reading materials)

(Note: Italic and bold words in the below article are vocabulary words for elementary students. For example, in this sentence: The solar system orbits around the center of the galaxy… You should pay attention to the word “center” and it may show up in the quiz .)

Introduction

Most of us may know that dolphins are aquatic mammals, not fish. Dolphins have a playful and friendly nature, which makes them very popular with humans. They are members of the cetacea family, which also includes whales and porpoises.

An easy way to tell the difference between a cetacean and a fish is by observing the orientation of their tails. A cetacean’s tail fins, often called flukes, are horizontal and move up and down. Fish have vertical tails which move from side to side.

There are over 40 different species of dolphins in the world. This includes marine dolphins that live in the sea as well as river dolphins. The most common type of dolphin is the bottlenose dolphin. The bottlenose dolphin gets its name from its short and stubby beak. They measure around 6-12 feet (2-4 metres) long and can weigh anywhere between 300 and 1400 pounds (135 – 650 kg). Male dolphins are larger than females.

Dolphin behaviour
Dolphins are very sociable and like to spend time together. They usually live in groups of 5-30 members. These groups are called pods. The female members of the family are called cows, the males are called bulls and young dolphins are known as calves. Pods help dolphins to form bonds and protect each other when facing predators.

Dolphins are also very playful creatures. They have been spotted chasing each other and tossing around objects such as seaweed. They often leap out of the water, ride waves and pop their heads above the surface to look around (this is known as spy-hopping).

Dolphins’ Echolocation and communication
Dolphins and other animals such as bats and whales share a unique way of “seeing” the world through echolocation, also known as sonar. Echolocation works when a dolphin sends and bounces a high pitched sound off an object and then listens for the echo to come back. Echolocation allows dolphins to “see” by interpreting the echoes of sound waves that bounce off of objects near them in the water. It is a very useful way for dolphins to find food and navigate. Dolphins don’t have vocal cords, so they use their nasal cavities to produce high-pitch clicks and other sounds to echolocate. Scientists believe this ability probably evolved slowly over a very long time.

Dolphins communicate with each other through clicks, squeaks and whistles. They use these special sounds to greet each other and to indicate if they are in distress.

Dolphins’ intelligence
Intelligence is the ability to think, to learn from experience, to solve problems, and to adapt to new situations. Dolphins demonstrate the ability to do all of these things and most scientists think that dolphins are one of the world’s most intelligent animals. Dolphins are the third smartest animal on earth, after humans and chimpanzees (other smart animals include elephants, African grey parrots, rats, crows, dogs, pigeons, and octopus). Dolphins have large brains. They have a brain to body ratio second only to humans. Large-brained creatures generally have a few things in common: they live long lives; they are sociable; their behaviour is complicated. Dolphins’ brains have an entire area dedicated to echolocation, which is an obvious difference from humans’ brains. Dolphin brains contain specialized brain cells called spindle neurons. These are associated with advanced abilities such as recognising, remembering, reasoning, communicating, perceiving, adapting to change, problem-solving and understanding. So it seems they are deep thinkers!

How do dolphins breathe?
Like whales, dolphins live in the sea, but they cannot breathe underwater. They breathe through a nostril, called a blowhole, located right on top of their heads. Dolphins are able to hold their breath for several minutes but typically they breathe about 4 or 5 times every minute. Some dolphin species can even remain underwater for up to 15 minutes!

Where do dolphins live?

Most dolphins live in the sea. They can be found in oceans all over the world. Dolphins usually stick to shallow areas of water along coastlines.

There are also some species of dolphins that live in rivers and they are called river dolphins. River dolphins can be found in locations such as the Ganges River and the Amazon River.

What do dolphins eat?

Dolphins are carnivores. Some dolphins eat fishes like herring, cod or mackerel, some others eat squids or other cephalopods. Large dolphins like killer whales, eat marine mammals like seals or sea lions and sometimes even turtles. They usually work together in their pods to find food using their echolocation skills. They trap large groups of fish and take turns to hunt and eat as many as they can. Although they have teeth, dolphins usually swallow their food whole. In a normal day, an adult dolphin eats 22-55 lb (10-25 kg) of fish on average.

Dolphins in captivity and performing dolphins

If you have seen a dolphin in real life, it was probably in captivity. Many zoos, aquariums and waterparks keep dolphins and train them to perform in shows.

Dolphins kept in captivity for this purpose are usually treated very well, and seem to enjoy entertaining people. Many people who would otherwise never have seen a dolphin are able to get close to them and learn more about them. This may in turn help raise awareness of dolphin conservation efforts.

However, many people think that dolphins should not be kept in captivity, and argue that an intelligent animal would prefer life in the wild and should not be contained in a small area. It is impossible for us to know what a dolphin is really thinking. Although they may seem to be enjoying performing, we don’t know what the effect of being in captivity really has on a dolphin.

What do you think? Is it right to keep dolphins in captivity? Both sides have valid arguments and there is no real right or wrong answer.

Are dolphins endangered?

Some species of dolphins are becoming endangered because of human behaviour.

The biggest threat to the dolphin population is fishing. Nets from fishing boats are very dangerous to dolphins because they can get accidentally caught up in them and drown. In some countries, dolphins are even illegally hunted as a source of food.

Human pollution is another big threat to dolphins. Waste and chemicals poured into the ocean can make dolphins sick and reduce their ability to fight infections and diseases.

How can we help dolphins?

Learning about dolphins is a great start. If more people know about dolphins, there will be more awareness of their threats. There are many groups around the world that are dedicated to protecting wild dolphins by reducing hunting and pollution.

Other fun facts about dolphins

• • • Dolphins have 2 stomachs: One is used for storage of food and the other is used for digestion.
    • Dolphins can dive as deep as 3000 feet (915 metres).
    • They can reach swimming speeds of up to 22 miles (35 kilometres) an hour.
    • They can live up to 50 years.
    • The largest member of the dolphin family is the orca, also known as the killer whale, which can grow up to a length of 30 feet.
    • Whilst sleeping, only half of a dolphin’s brain switches off. The other half stays awake to help them breathe and prevent them from drowning.
    • It has been proved by scientists that dolphins give themselves “names”. They develop their own individual whistles and they recognize theirs and other dolphins’ names.
    • Dolphins have no sense of smell!
    • Dolphins don’t need to drink to stay alive. The fish that they eat contain enough water to keep them hydrated.
    • Dolphins have a thick layer of fat called blubber beneath their skin to keep warm.