Mammals are a special group of animals with a combination of characteristics that separate them from all others: mammals are warm-blooded, have hair or fur, breathe air through lungs, bear live young, and nurse their young with milk produced by mammary glands.
Marine mammals have the same characteristics as all other mammals, but they have adapted to living all or part of their life in the ocean. To keep warm in the ocean, most of them depend on a thick layer of blubber (or fat). They have streamlined bodies to help them swim faster. Many species can stay under water for a long time, but must come to the surface to breathe. To be able to stay under water for long periods, they store extra oxygen in their muscles and blood. They also have more blood than land mammals in proportion to their body sizes, can direct their blood flow to only their vital organs (such as their heart and lungs), and can slow their heartbeat down so they are using less oxygen in a dive.
All marine mammals are protected in the United States by the Marine Mammal Protection Act of 1972. There are also international laws and treaties that protect marine mammals. Unfortunately, many marine mammals are considered endangered species and there are still threats to most of their populations, such as illegal hunting, pollution, climate change, and habitat loss. Learn more about these issues and tell others, including lawmakers, how you feel about them. Together, we can solve or prevent many of the problems our ocean friends face.
There are five groups of marine mammals: pinnipeds (seals, sea lions, fur seals, and walruses), cetaceans (whales, dolphins, and porpoises), sea otters, sirenians (dugongs and manatees), and polar bears.
For more information about each group and special characteristics of certain marine mammals, see our Marine Mammal Classification page.
To look up the meaning of scientific terms used in this section, please refer to this helpful Biology Dictionary.
Want to learn more about marine mammals?
The Marine Mammal Center website is a great resource for marine mammal information, learning more about conservation and exploring current scientific research. We encourage you to explore and discover on your own before reaching out for further information. Requests often take about two weeks to receive a detailed reply. Student interview requests unfortunately cannot be accommodated due to limited staffing and availability, but we may be able to answer questions via e-mail or sometimes by phone. We also invite you to visit the Center where volunteers, exhibits and signage are available to support your visit and we also offer a variety of tours for different types of groups in which questions can be answered throughout.