Melon, baleen, echolocation—what do all those complicated words mean? Check out our glossary for lots of easy-to-understand definitions.

Abundance means the number of dolphins, whales and porpoises in our oceans. The abundance for many species has decreased dramatically in recent years, which means that not many of them are left in our oceans compared to previously.

Adaptation means the ability of a type of animal to change so that it can improve its chance of surviving in a particular environment. Changes in the shape, behaviour or function of an animal and its body parts, all developed and changed over time to try and make an animal perfectly suited for its environment.

A whale skeleton with baleen hanging from the upper jawbones  © Thesupermat/Wikimedia Commons

A whale skeleton with baleen hanging from the upper jawbones
© Thesupermat/Wikimedia Commons


Baleen is what gives baleen whales their name. Baleen is made up of keratin, the same material as your hair and fingernails. Baleen hangs from the roof of their mouths and filters and acts as a sieve to sieve out the tiny animals that whales eat. Baleen is made up of 200 to 600 single “plates” which overlap a little to keep the prey trapped inside the whale’s mouth.





The thick layer of fat that protects all marine mammals from injuries and the cold is called blubber. Blubber can also provide a source of energy when food is scarce. Because fat is lighter than water, the blubber helps the animals to stay afloat. The layer of blubber on a whale can be up to 30cm (1ft) thick.

“Cetaceans” is the collective term that scientists use to refer to all whales, dolphins and porpoises. The word is derived from the Greek ketos, which means “whale”. Cetaceans are perfectly adapted to live underwater but they are not fish, they are air-breathing mammals which spend all their lives in water. They breathe through blowholes located on the top of their heads.

Dorsal Fin
“Dorsal” means towards the back. A dorsal fin sits on a cetacean’s back. It is made of tissue and not supported by any bones. Scientists believe that it helps the animals to maintain their balance, aid making sharp turns and regulate the body temperature. Most polar species (beluga, narwhals, right whale and bowhead whale) and gray whales do not have a visible dorsal fin.

Echolocation is when cetaceans produce a sound, listening to its echo, which helps them to detect and identify the speed, location and size of other objects in the water (for example their favorite fish to eat). They produce a series of sound signals and listen to the echoes, which bounce off various objects near them. This allows dolphins and whales to “see” things that are far away, which is why it’s an amazing adaption to hunting and navigating underwater.

When a cetacean is said to be endemic, it can only be found in that one place and nowhere else in the entire world. For example the Northern Bottlenose Whale is endemic to the North Atlantic, which means it can only be found in the North Atlantic.

When whales, dolphins and porpoises are threatened to go extinct, they are at risk of dying out and will no longer be found alive anywhere on our planet. The Yangtze River dolphin has been one of the world’s rarest and most threatened cetacean species and has sadly gone extinct now.

Flippers are the front “paddles” of dolphins and are also called pectoral fins. They have evolved from front limbs, much like our arms and now help dolphins to balance and steer.

Instead of hind limbs, or legs, cetaceans have a big paddle-like tail called a fluke. They use it in an up-and-down movement to swim.

The habitat of an animal is the area where an animal normally lives in. For example your habitat is on land but a whale’s habitat is the ocean.

Hemisphere (Northern-/Southern-)
The word Hemisphere comes from the Greek word hemisphairion which literally translated means half of a sphere or ball. In this case a hemisphere refers to half of the earth. Halfway between the South Pole and the North Pole there is an invisible line called the Equator. This line divides the Northern Hemisphere and the Southern Hemisphere.

Krill are small shrimp-like animals that live in cold polar seas. They are a whale’s favourite food and an adult blue whale can eat up to 3600 kilogram of krill a day!


The melon is the blue part. The vocal cords of dolphins are located beneath their blowholes (red). In green you see the bones of the skull. All parts are important for sending out sounds and hearing them © Petwoe/Wikimedia Commons

Toothed whales have a special organ at the top of their heads: the melon. It is an oil-filled sack which is connected to the vocal cords of the animals. The melon acts as an acoustical lens which focuses sound waves, much like the lenses in your eyes. Toothed whales rely on it when they hunt for their prey. They use sound like bats to “see” their surroundings during echolocation. Being able to focus the sound waves is very helpful for cetaceans, just like being able to focus your eyes on a certain object is helpful for you.




Mysticetes (pronounced ‘miss-tee-seats’) are a family of cetaceans with baleen instead of teeth. Blue whales are the largest mysticetes growing up to 25 meters.

Odontocetes (pronounced ‘oh-dohn-toh-seats’) are a family of cetaceans with teeth. Odontocetes are also known as toothed whales, although they also include dolphins and porpoises. If you want to learn more about some of these species, have a look at our species guide!

An opportunist is an animal that will feed on whatever suitable food is available to them at any given time. Many dolphins are opportunist and love to eat many different types of fish and squid.

Plankton are very small animals and plants that float in our seas. Plankton cannot swim so they are dependent on ocean currents to transport them through our oceans.

A species is a group of animals or plants which look and act alike. Their young can breed to produce more young. There are around 90 different species of cetaceans swimming in our rivers and oceans: can you name a few? Why not check out our species guide!

White-sided dolphins stranded on a beach © IFAW

White-sided dolphins stranded on a beach © IFAW

Stranding (Beaching)

When marine mammals, such as cetaceans, are found on the beach or ashore, either alive or dead, we say that they have stranded or beached themselves. Sadly, many individuals or big groups of species beach themselves and we don’t always understand why. Some scientists think it is the underwater noise that disturbs their orientation or they were too sick to swim on.


Temperate waters
Temperate waters are generally areas without any extremes in temperature or weather (either very hot like at the equator or very cold like at the pole). Those areas lay between tropic regions (around the equator) and the Polar Regions. Most of Europe is considered temperate.

Vestigial Bone
A “vestigial” body part has lost some or all of its function during evolution. It is therefore smaller or has a simpler structure than in related species. Whales, dolphins and porpoises have no hind limbs anymore, only one vestigial bone remains hidden inside of the body that proof that their ancestors once had legs.

In the red circle you can see the remains of the hind limbs of cetaceans © Azcolvin429/Wikimedia Commons