MARINE MAMMALS – AN INTRODUCTION
The fascinating world of marine mammals is enormously varied. Although they are warm-blooded and breathe by means of lungs (as opposed to gills), these animals have adaptations that enable them to live within a marine environment. For some, this means that they are under the water for the vast majority of the time, coming up only for air. Others may laze about, feed and find mates on the warm rocks or polar ice caps, but enter the water to hunt or breed. Thus, they are defined as being marine mammals.
Sea Lion on the beach.
Seal under water.
There are five main types of marine mammals:
Whales, dolphins and porpoises make up this group. Within this class, there are about 86 species; ranging from the world’s biggest animal in existence, the blue whale, to the smallest dolphin, the Hector’s dolphin, which measures only 39 inches (or just under one metre) in length.
This refers to fin-footed animals like seals, walruses and sea lions. These are carnivores and are found all over the world. There are 33 species within this class.
3. Polar bears
These webbed-feet bears live in the Arctic and are renowned for their hunting abilities. They are fantastic swimmers.
This group is not limited to marine mammals, but does include the sea otter and the sea cat (or marine otter) under its umbrella. Other members of the class include badgers and weasels.
Manatees and dugongs are categorised as Sirenians. This category of marine mammal is limited to the coastlines and inland waterways of North and South America, West Africa, Asia and Australia.
Because of the sheer diversity of these marine mammals, there are few defining characteristics that they share. However, it can, generally, be said that they have holes instead of external ears, streamlined bodies that enable far easier swimming, internal mammary glands and reproductive organs, and no hind legs (of course, there are some exceptions to these “rules”). They are also particularly well adapted to maintaining their warm body temperature. Their small appendages and fusiform bodies reduce heat loss and many marine mammals have a layer of blubber just below the skin, which acts as an effective insulator.
Accomplished swimmers, marine mammals have various swimming mechanisms. Dolphins, whales and porpoises have flippers and tails, while others have webbed feet, for example.
Interestingly, marine mammals tend to share a friendly disposition. They are social amongst themselves and have been known to help one another, as well as other animals and even human beings when threatened. They are known for approaching boats, inquisitively keen to explore them and their passengers. They are also particularly trainable, which has led to the capture and taming of so many of them for zoos and aquariums.
This group of mammals is adept at communicating with one another, usually using sound as their main medium. Whales are known for composing and singing songs, even teaching certain melodies to their young. Dolphins use sonar to communicate with other dolphins and to find their way (as the sound bounces off objects around them). The young often recognise the voice of their parent in different species.
Marine mammals carry their young in their womb until they are fully matured. They are then born live and fed on the nutritious breast milk of the mother. A weaning period takes place, after which the offspring will reach sexual maturity.
Many marine mammals are currently threatened. Because they are forced to surface or spend some of their lives out of the protection of the deep ocean, they are susceptible to dangers that other marine animals are not. Many are hunted for their meat, blubber, skin or fur. Others succumb to pollution or fishing nets (in which they become tangled and soon drown).
It is our responsibility, as human beings, to protect and conserve these animals to the best of our ability. This can only be accomplished if we understand them more fully, necessitating research and investigation.