Marine mammal

Marine mammals are animals that live in the water and need marine ecosystems to survive. They include groups like cetaceans, which are whales and dolphins, pinnipeds such as seals and sea lions, sirenians like manatees, marine otters, sea otters, and polar bears. Even though they are all called marine mammals, these animals have different ways of living in the water. Some, like whales and manatees, can only live in the water, while others, like seals, come to land for activities such as mating, breeding, and molting.

These animals eat many different things, from tiny zooplankton to fish, squid, shellfish, seagrass, and even other animals. Even though there are not as many marine mammals as land animals, they help keep the ocean healthy by controlling the numbers of other sea creatures.

In the past, people hunted marine mammals for food and other resources, which caused many of their populations to drop sharply. Some species, like the gray whale and northern elephant seal, have started to grow in number again, but others, such as the North Atlantic right whale, are still in danger. Today, marine mammals face threats such as getting caught in fishing nets, colliding with ships, losing their homes because of human activities, and dealing with changes in the environment due to the effects of global warming.

Taxonomy

Marine mammals are animals that need the ocean to live. They include whales, seals, manatees, sea otters, and polar bears. These animals are different in size and shape, but they all depend on the sea for food and survival.

Marine mammals are a group of many different species. They all rely on the ocean, but some need it more than others. For example, whales can only live in the water, while seals eat in the ocean but give birth on land. Polar bears need land to hunt.

Whales began living in the water long ago. They are closely related to hippos. Sea cows, like manatees, also started living in the water a long time ago. Seals and their relatives came from land animals. Sea otters came to the ocean more recently. Polar bears evolved from brown bears during cold times.

Distribution and habitat

Marine mammals live all over the world. They are often found where the ocean has lots of food. This is usually around 40° north and south of the equator, near places like America, Africa, Asia, and Australia. Most of these animals live close to the shore, such as seals and sea otters. Some seals also use land, like beaches, rocky shores, and even structures made by people like piers and buoys.

Many marine mammals move to different places each year. For example, polar bears follow their food as the ice changes, and whales travel far to warmer waters to have their babies. The gray whale has the longest journey, traveling thousands of miles from one ocean to another.

Adaptations

Further information: Aquatic locomotion

Marine mammals have special features that help them live in water. They have shapes that help them move easily, like torpedo-shaped bodies. They use their limbs, tail flukes, and dorsal fins to push themselves forward and stay balanced. They also have thick fur or blubber to stay warm.

These animals can stay underwater for long times. They have special blood systems that store extra oxygen in their muscles and spleen. They can also slow their heart rates and send oxygen to the most important parts of their bodies when needed.

Marine mammals use sound in water to talk, find food, and stay safe. Whales and dolphins use a special skill called echolocation, sending out clicks to find their way and locate objects.

Different marine mammals have different ways of eating. Some have teeth made for catching fish, while others, like baleen whales, have special plates to filter tiny plants and small fish from the water. Some, like polar bears and sea otters, have fur that traps air to keep them warm, while others have thick skin and fat to stay insulated and move easily through the water.

Ecology

All cetaceans, which include whales and dolphins, eat only meat. Toothed whales mainly eat fish and squid, along with some crabs and clams. They sometimes hunt with other animals, like other whales or seals. Some whales, like orcas and bottlenose dolphins, may push their prey onto beaches to eat it. Other whales with simpler teeth rely on sucking in water and prey.

Baleen whales, like humpback whales, use special plates in their mouths to filter small animals, such as plankton, from the water. They either lunge into large groups of these animals or swallow big amounts of water and prey at once.

Otters can lift and move rocks with their front paws to find food underneath. Sea otters often eat snails and other sea creatures from kelp forests and dig in mud for clams. They are the only marine mammal that catches fish with their front paws instead of their teeth. Sea otters float on their backs and use rocks to crack open shellfish, which they keep in a special pouch on their chests.

Pinnipeds, such as seals and sea lions, mostly eat fish and squid, along with crabs, clams, and small fish-like animals. Some hunt alone, while others work together in groups. Polar bears, which are a type of bear, mainly eat seals.

Sirenians, also known as sea cows, mainly eat seagrass. They eat the whole plant, including the roots, but will also eat algae when seagrass is hard to find. Manatees eat many types of plants and sometimes small fish and invertebrates.

Sea otters help keep the balance of ocean ecosystems. By eating sea urchins, they help protect kelp forests, which are important homes for many sea creatures.

Polar bears are top hunters in their cold homes. Killer whales are also top hunters and eat many different sea animals, including fish, sharks, and even other whales.

Whales help provide nutrients for the ocean. They bring important nutrients like nitrogen from deep water to the surface, which helps tiny plants called phytoplankton grow. When whales die, their bodies fall to the deep ocean and become homes for many deep-sea creatures.

Interactions with humans

Threats

It can be hard to know how many marine mammals there are, especially near the Antarctic. When numbers of some marine mammals drop, it often goes unnoticed.

Exploitation

Marine mammals have been hunted by people near the coast for food for a very long time. These hunts still happen in places like Canada, Greenland, Indonesia, Russia, the United States, and some islands in the Caribbean. In the past, commercial hunting caused great harm and led to some species going extinct, like the Steller's sea cow, sea mink, Japanese sea lion, and the Caribbean monk seal. Today, some whales have far fewer numbers than before because they were hunted a lot. Some whales are still hunted today, even though there is a rule against it from 1986. Only Norway and Iceland still allow commercial whaling. Japan also hunts whales under the idea that it is for science.

In the past, sea otters were hunted for their fur, especially between the Columbia River and Cook Inlet. Furs were sold to China.

Sealing was also a big industry in the past. After rules were made to protect seals in the 1960s, some seal populations have grown back. But others, like the Mediterranean monk seal, are still in danger.

Polar bears can be hunted in Canada with special permission.

Ocean traffic and fisheries

Fishing nets can sometimes catch animals that are not the target, called by-catch. This can hurt or kill whales and seals. Ships can also hit and hurt whales, especially fast ships. Whales like the North Atlantic right whale are especially at risk. Boats for watching whales and dolphins can also bother these animals.

Fisheries can also affect marine mammals by taking away their food. When fish numbers go down, it can cause problems for marine mammals that eat those fish.

Habitat loss and degradation

Human activities like building near the coast and making noise underwater can hurt the places where marine mammals live. Pollution can also make them sick.

Changes in the climate, like warmer temperatures and melting ice, can change where marine mammals live and find food. For example, polar bears depend on sea ice, which is disappearing.

Protection

There are laws to protect marine mammals. In the United States, the Marine Mammal Protection Act from 1972 helps stop people from harming these animals without permission. There are also international agreements to protect marine mammals.

As food

For thousands of years, people living in the Arctic have eaten whale and seal meat. This is still done today in some places, like the Faroe Islands, where pilot whales are hunted each year. In a few other places, like Japan, dolphin meat is eaten.

In captivity

Some marine mammals, like dolphins and sea lions, are kept in places like aquariums and zoos. People enjoy watching them do tricks, but some believe this is not good for the animals because it does not feel like their natural home.

Dolphins and sea lions are also sometimes used by the military to find underwater mines and protect ships. There is debate about whether this is fair to the animals.