What Is A Marine Mammal? | Definition and Characteristics

Marine mammal is a mammal adapted to aquatic life and relies on the ocean to maintain a healthy, livable existence.

These amazing animals can be found living in all of the world’s major oceans, from the tropical environments in and around the equator to the northern and southern polar hemispheres in and around the Arctic and Antarctic oceans.

Marine mammals share several common characteristics among all mammals, such as the need to breathe air, being warm-blooded, having mammary glands that produce milk to feed their young, giving birth to live young (pregnancy/gestation periods) and in some cases having hair.

Here are several common characteristics found in marine mammals:

  • Marine mammals breathe air – Although marine mammals live in and around the water, they must come to the surface to breathe; otherwise, they’ll drown.
  • Marine mammals are warm-blooded – To maintain their body heat, marine mammals consume large quantities of calories and develop a thick layer of fat or blubber to keep their vital organs from freezing in cold environments.
  • Marine mammals give birth to their offspring – Unlike fish and other aquatic animals, whales do not lay eggs; instead, they carry their children in their womb until they are born.
  • Marine mammals produce milk – Marine mammals have mammary glands that produce milk, which they use to feed their children. The milk is often full of fat and nutrients to help the child develop.

Marine mammal characteristics

While land mammals are similar in many ways, marine mammals have adapted to deal with living in environments that are generally surrounded by water rather than being elusively surrounded by land, and the way marine mammals live, hunt for food, and navigate the world is largely dependent upon their oceanic environment and physical characteristics.

For example, marine mammals such as whales, dolphins, and porpoises have streamlined bodies designed to reduce water resistance when swimming, they also have specialized lungs and muscles designed to store oxygen, thick blubber or fat to help maintain body heat in cold environments, large veins to help transfer blood to vital organs in cold water or when in deep waters where compression can become an issue and fins, flukes, and flippers to assist with swimming.

Other species such as polar bears have thick layers of fat and fur to help them maintain their body heat in cold climates, a large body to help keep them warm and disperse their body heat, thick curved claws for gripping the ice and predators, sharp teeth and strong jaws for tearing apart prey and powerful muscles for fighting and attacking.

Seals have thick layers of fat/blubber to help keep them warm, rounded bodies to help disperse their body heat, limbs designed for walking/waddling on land with webbed feet/flippers to help them swim, and teeth which they use to grip onto their prey.

Seals, sea lions, and walruses have several similar characteristics among the separate species and share a few distinct differences.

For example, walruses tend to have a stockier build than seals and sea lions, and they also possess two large teeth that protrude from their mouth, similar to a saber toothed tiger only larger.

Seals also have separate, distinct characteristics from sea lions, such as having shorter limbs with long claws, which requires them to waddle on land rather than walk. Their strong rare flippers allow them to propel themselves through the water more effectively than sea lions.

While not all marine mammals share the same biological characteristics, (a clear example would be to compare polar bears to whales), they all live near or in the ocean. They need the ocean for its supply of food and water to survive.

The distinct types of marine mammals

In terms of the various marine mammal species, there are several distinct groups of marine mammals; sirenians (manatees and dugongs), cetaceans (whales, dolphins, and porpoises),  fissipeds, sea otters, pinnipeds (seals, fur seals, sea lions, and walruses) and (as considered by some researchers and biologists) polar bears.

Both cetaceans and sirenians live in the ocean, while polar bears, pinnipeds, and fissipeds are land dwellers, but rely on the ocean to supply them with food and water.

As a whole, there are over 125 recorded species of marine mammals inhabiting the ocean and native aquatic environments of the world.

Here is a list of the individual subgroups within the marine mammal family:

  • Cetaceans (whales, dolphins, and porpoises)
  • Fissipeds
  • Pinnipeds (seals, fur seals, sea lions, and walruses)
  • Ursidae (polar bears)
  • Sea otters
  • Sirenians (manatees and dugongs)

Although these animals can be found throughout the world, the highest concentration of marine mammals (about 40%) is found at or around 40° north and south of the equator.

Marine mammals and the ecosystem

When it comes to survival and the food chain, marine mammals play a large role in maintaining a healthy marine ecosystem; however, since around 20% – 30% are considered endangered and/or threatened, it raises some concerns on the impact of aquatic life and the impact humans have played in contributing to its condition.

The elimination of one species could significantly decrease the chances of survival for another species, especially among species that rely on their prey for survival.

If their prey were to become extinct, then the predators also face the possibility of extinction.

On the other hand, if a predator were to become extinct, its prey could overpopulate and quickly consume their food supply, leading to starvation.

Although these are extreme examples, they are important to point out as it is a possibility.

To better protect these animals, all marine mammals in the United States are protected by the Marine Mammal Protection Act created in 1972.

In addition to the Marine Mammal Protection Act, other countries have also created laws designed to protect these animals, and organizations have been created to bring awareness about the importance of protecting the endangered marine mammals and implementing programs designed to aid in the recovery of certain species.