Marine mammal

Marine mammals are animals that live in the water and depend on 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 play an important role in keeping the ocean healthy by helping control 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 129 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 about 50 million years ago. They are closely related to hippos. Sea cows, like manatees and dugongs, started living in the water about 40 million years ago. Seals and their relatives split from land animals about 50 million years ago. Sea otters came to the ocean more recently, about 2 million years ago. Polar bears evolved from brown bears during the ice ages.

Distribution and habitat

Marine mammals are found all over the world, but they are more common in areas where the ocean produces a lot of food. These areas are usually around 40° north and south of the equator, near places like America, Africa, Asia, and Australia. Most marine mammals live near the coast, such as seals and sea otters. Some seals also use land areas, like beaches, rocky shores, and even man-made structures 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 very long distances to warmer waters to have their babies. The gray whale has the longest migration, 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, and 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 have also learned to 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, are animals that 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. One way they hunt is by herding fish into a small area and then taking turns catching them. Some whales, like orcas and bottlenose dolphins, may even 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. They hunt seals by waiting near breathing holes in the ice or sneaking up on seals resting on the ice.

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 play a big role in keeping the balance of ocean ecosystems. By eating sea urchins, they help protect kelp forests, which are important homes for many sea creatures. Without sea otters, some areas can become filled with sea urchins and lose their kelp forests.

Polar bears are top hunters in their cold homes. They affect the numbers and behavior of animals like seals. Killer whales are also top hunters and eat many different sea animals, including fish, sharks, and even other whales. Their hunting can influence where some whales travel to have their babies.

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

Because it is hard to count how many marine mammals there are, about 38% of them are known to scientists only through guesses, especially around the Antarctic Polar Front. When populations of marine mammals that live only in the water drop, it often goes unnoticed around 70% of the time.

Exploitation

Marine mammals have been hunted by people living near the coast for food and other resources for a very long time. These hunts still happen today in places like Canada, Greenland, Indonesia, Russia, the United States, and some islands in the Caribbean. These hunts affect only small areas because they have been done on a small scale. But when commercial hunting began, it caused much more harm. This led to some species going extinct, like the Steller's sea cow, sea mink, Japanese sea lion, and the Caribbean monk seal. Today, animals like blue whales and North Pacific right whales, which were hunted a lot in the past, have far fewer numbers than before. Because whales grow and have babies slowly, it takes them a long time to recover.

Some whales are still hunted today, even though there is a rule against it from 1986. Only two countries still allow commercial whaling: Norway and Iceland. Japan also hunts whales under the idea that it is for science, but many believe this is not true.

In the past, sea otters were hunted a lot for their fur, especially in areas between the Columbia River and Cook Inlet. After they were almost gone, hunters turned to other sea otters in California. Furs were sold to China through special trading places.

Sealing was also a big industry in the past. Many different kinds of seals were hunted. After rules were made to protect them 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. This can be important for making money in small communities.

Ocean traffic and fisheries

Sometimes, fishing nets catch animals that are not the target, which is called by-catch. This happens a lot with whales and seals. Small whales and seals often cannot escape and drown. Bigger whales can sometimes pull nets with them, which can stop them from eating and lead to starvation. Lost nets can also hurt marine mammals.

Ships can hit and hurt or kill whales, especially fast ships like container 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 hurt marine mammals by taking away their food. When fish numbers go down because of fishing, it can cause problems for marine mammals that eat those fish. Sometimes, this leads to fights between people and marine mammals over food. In some places, people have killed marine mammals to protect their fish.

Habitat loss and degradation

Human activities like building things near the coast, dumping waste, and making noise underwater can hurt the places where marine mammals live. Pollution from things like heavy metals and plastic can build up in their bodies and make them sick.

Changes in the climate, like warmer temperatures and melting ice, can also 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, like ones to stop whaling and protect seals.

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, though this can be unhealthy because it contains high levels of harmful substances.

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 and can be stressful.

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.