There are about 100 species of aquatic or marine mammals that depend on fresh water or the ocean for part or all of their life. A marine mammal trainer cares for and trains marine life such as sea lions, dolphins, walruses, porpoises, manatees, killer whales, sea otters and polar bears.

Apart from the training, they are responsible for the animal's mental and physical health, preparation of food, performing maintenance duties, giving trainer tours, interacting with the public, and keeping up-to-date records about the animals. Most marine mammal trainers have a formal education in marine biology or animal behaviour. It is just as important to get hands on experience, learning and becoming familiar with all aspect of the animal's behaviour. Training marine life is a large undertaking and takes a lot of responsibility.