What Mammals Live in the Sea? Comprehensive List

Are you fascinated with the numbers of different living creatures swarming within the oceans as you were on a boat ride? How many of them do you know or are familiar with? Well, it is very amazing to think that marine animals exist underwaters in a number of populations and in various species. If you want to know what mammals live in the sea, we have here a comprehensive list of those various aquatic animals. See which one really fascinates you!

What Mammals Live in the Sea?

Generally, the mammals that live in the sea are well-known as marine mammals. They are generally similar to other mammals in terms of their characteristics. The only difference is that they already adopted all or part of their lives existing in the ocean. Most of them have the ability to be underwater for a longer period of time. Yet, they still need to come to the surface to give them time to breathe.

Here is the list of marine mammals that you may enjoy watching wagging on the sea or underwater.

1. Whales

General Information:

• DIET: Carnivore
• HABITAT: Warm coastal waters
• AVERAGE LIFE SPAN: Unknown
• SIZE: 9 ft to 98 ft in length
• WEIGHT: 500 lbs to 200 tons

The first on the list of mammals that live in the sea is none other than the whales. Compared to fish, the whales encompass a streamlined body that tapered to the supine tail. They generally have wide flippers which are highly modified on their front limbs.

The whales are usually lacking with back limbs and outer ears. However, there is a presence of thickly layered bubbler under their skin. This part of the whales’ body generally supports their way of heat conservation.

Additionally, if you would ask what mammals live in the sea, you would find out that there are different types of whales. Here are three of them:

Whalebone whales

Whalebone whales are also popularly called baleen whales. Generally, this type of mammal that lived in the sea does not have any teeth. Instead, they have plates located on their upper jaw that usually in the form of a V-shape. The basic function of the plates is to sieve or strain plankton.

In the aquatic kingdom of Animalia, the whalebones are the largest animal ever lived. They generally grow up to 100 feet and weigh about 200 tons. Blue whales, California gray whales, Fin whales, and the Greenland right whales all belong to these mammals that lived in the sea.

Toothed whales

Compared to whalebones, this type of whale is generally smaller. Their teeth appear conical and pointed on the lower or on each side of the jaws. In some instances, there is also a presence of one tusk-like tooth located on the upper jaw.

Usually, their main food source is the fish. And there is a broad range of whales grouped under this whale type. These include the beaked whales, killer whales, narwhal, sperm whales, and white whales or beluga. Moreover, the harbor porpoise, Atlantic dolphin, and river dolphin are also included in this group.

2. Beavers

General Information:

• DIET: Herbivore
• HABITAT: Freshwaters like the lakes, streams, and ponds and in heavy woods rivers
• AVERAGE LIFE SPAN: 10 to 20 years
• SIZE: 4 ft average in length
• WEIGHT: 24 lbs to 66 lbs

The beavers are the other mammals that live in the sea. Traversing the rivers and lakes along with Asia, Europe, and North America, you may see one of the mammals that live in the sea. The beavers may also be found enjoying along the southern deserts of Mexico and the US. Generally, this mammal features a coat resistant to water and ears and nostrils that are usually closable.

Averaging from 30 to 50 pounds, the beavers also have paddled tails and webbed feet. With that, they tend to be the world’s second-largest rodent. And, compared to other mammals or all animals within the kingdom Animalia, beavers’ resources are credited to produce its distinct dam. 

3. Dolphins

General Information:

• DIET: Carnivore
• HABITAT: Temperate coastal waters, bays, and harbors
• AVERAGE LIFE SPAN: 20 to 45 years
• SIZE: 6.5 ft to 13 ft in length
• WEIGHT: 220 lbs to 660 lbs

What mammals live in the sea? Well, another great inclusion here is the common dolphin. They are widely found within the Mediterranean Sea. Moreover, the deep off-shore waters and part of the continental shelves or shallow waters are also one of their favorite nesting places.

Some of them may tend to be present all throughout the year, while there are a few that migrates to other parts of the water. Usually, they travel within the sea in groups for about 10-50 members. And when they gather for up to 100 to 2,000 individual dolphins, they generally form schools.

Another interesting fact about dolphins is that they include in the list of the fastest swimming mammals that live in the sea. Their speed can be as fast as 25 mph. Well, this speed of the dolphins and their large group size are the factors that help them in developing various ways of prey hunting.

4. Dugongs

General Information:

• DIET: Herbivore
• HABITAT: Warmer tropical waters and seagrass forest
• AVERAGE LIFE SPAN: 50 to 70 years
• SIZE: 8.9 ft to 9.8 ft in length
• WEIGHT: 330 lbs to 880 lbs

Usually, the dugong is in close relation with that of the manatees. They really love to be underwater and there never comes a time that these mammals that live in the sea leave their habitat. The body of the dugong is generally hairless and their tail is a fluky supine similar to the whales. This is actually their main distinction from the manatees. Moreover, dugong can stay long under the water for around 6 minutes time.

You can often found the dugong swimming alone or in pairs within the warm waters of the western Pacific coast, Red Sea, and the Indian Ocean. They can also come in herds having more than 100 members. Most time of the day until night, dugongs really love to be on water grasses. Moreover, the docile dugong can live longer within the wild. 

5. Hippopotamus

General Information:

• DIET: Herbivore
• HABITAT: Rivers, lakes, wetlands
• AVERAGE LIFE SPAN: 40 to 50 years
• SIZE: 6.5 ft to 16.5 ft in length
• WEIGHT: 2,200 lbs to 9,900 lbs

For as long as 16 hours per day, the hippopotamus has the ability to submerge in it. Being the other mammals that live in the sea, the hippopotamus has eyes and nostrils situated up high within its head. Generally, those body parts are elevated enough to allow them to breathe and stay longer underwater.

Normally, during the period of vegetation, the hippo gets out from the water during the time of dusk for them to feed on land. Most of the time, you can usually see them swarming along the African rivers.

6. Manatees

General Information:

• DIET: Herbivore
• HABITAT: Warm coastal waters, slow-running rivers
• AVERAGE LIFE SPAN: 50 to 70 years
• SIZE: 13 ft in length
• WEIGHT: 800 lbs to 1,212 lbs

If you are still asking what mammals live in the sea and looking for more of them, well, the manatees are the one to include in the list. They are totally aquatic allowing them to submerge below the water for about 15 minutes long. But, to give themselves time to breathe, they swim toward the surface for around three to four minutes.

Generally, this marine mammal is mostly found in Central America, Florida, and West Indies coasts and estuaries. Within a day, these mammals that live in the sea engulf for more than one-tenth of their overall weight.

7. Sea Lions

General Information:

• DIET: Omnivore
• HABITAT: Coastal waters, shorelines with rocks
• AVERAGE LIFE SPAN: 15 to 22 years
• WEIGHT: 660 lbs to 2,200 lbs

Well, their conspicuous outer ear and their limbs that allows for their mobility on land are the unique characteristics of the sea lions. If you are asking what mammals live in the sea, the sea lion is one of them. But they are not just only mammals that live in the sea; they are also a smart marine animal. Amazingly, they have a high capability to comprehend various sign languages.

The sea lions are in close relation with that of the walruses and the seals. And based on history, there are 7 sea lions subspecies enjoying the world’s different water areas. Sadly, because of hunting and commercial fishing, the Japanese sea lions became extinct in the year 1850. All-in-all, there are 6 subspecies of sea lions that exist widely nowadays.

Generally, the sea lion species that is the greatest in population is the California sea lion. You can normally see it over the coast of North America. Moreover, you can also find the other species in other coastal waters of Japan and California. Since there are lots of sea lion species existing; they can live in various climates of the northern and southern regions.

Australian sea lions

Normally, this sea lion species can be found in Australia over the west and south coasts. They are more concentrated within the Houtman Abrolhos Islands located in Western Australia and over the Pages islands. Unfortunately, this sea lion species tend to be endangered now.

California sea lions

Along the perimeter of the Pacific Ocean traversing from Alaska to Mexico, you can find the habitat of the California sea lions. These types of mammals that live in the sea are very comfortable being surrounded by humans. They usually haul out over man-made piers and marinas.

Because of that, the Marine Mammal Protection Act of 1972 was approved to protect this sea lion species. It generally outlaws any harassment act to these sea lions including hunting and capture.

Galapagos sea lions

Obviously, the Galapagos sea lions live in Galapagos Islands and they do not breed in another hemisphere other than that, except for the Isla de la Plata. Usually, this sea lion species loves to attract tourists for their gracefulness and playfulness.

Due to that amazing characteristic of the Galapagos sea lions, they are considered by the locals as the “official welcoming party”. However, the Galapagos sea lions are also considered as one of the endangered species. 

New Zealand sea lions

Generally, within Auckland and Campbell Islands together with the South and Stewart Islands, you can find a congregation of these sea lions species. Another endangered sea lion species, the system for population classification recognizes the New Zealand sea lions as “nationally critical”.

Steller sea lions

The North Pacific Ocean is the normal habitat of the Steller sea lions. In terms of the off coasts, they are commonly seen along with Alaska, Central California, and Russia. Among the other sea lion species, this one prefers to be in isolated locales.

South American sea lions

This mammal that lives in the sea usually loves to dwell within the west coast of South America. Aside from that, they can also be found frequently within the off-shores of Argentina, Chile, Ecuador, Falkland Island, Peru, Southern Brazil, and Uruguay.

8. Sea Otters

General information:

• DIET: Omnivore
• HABITAT: Close to seashore
• AVERAGE LIFE SPAN: 12 to 15 years
• SIZE: 4 feet in length
• WEIGHT: 30 lbs to 100 lbs

Unlike the other mammals that live in the sea, the sea otters are semiaquatic. But, same as the other mammals with amphibious personalities, the sea otters have fur that is thick and dense with streamlined bodies. You may also find various species of sea otters including the North American river otter. This sea otter generally weighs about 18 pounds and can be as long as 4 feet.

The sea otters basically belong to the weasel family and they tend to be the largest member of it. Aside from that, among the other members, they are the one that lives their day all throughout the water. Most of their activities involve hunting within the ocean beddings, going into the surface for eating and resting, and mingle with other otters.

Their numbers are seemingly stable and tend to be increasing within the areas of British Columbia, Southeast Alaska, and Washington. Unfortunately, within southwest Alaska, the population of sea otters is actually declining due to killer whale predation.

9. Seals

General information:

• DIET: Carnivore
• HABITAT: Coastal waters and shores with rocks
• AVERAGE LIFE SPAN: 15 to 25 years
• SIZE: 20 feet in length
• WEIGHT: 230 lbs to 6,000 lbs

Primarily, these mammals that live in the sea stay within the oceans of the Southern and Northern hemispheres. Most of them usually found their way home in the polar, subpolar, and temperate regions except for the tropical monk type of seals. They generally have flippers and webbed feet. Yet, their ears are not actually visible externally.

It generally took the seals millions of years in adapting to the sea life. And, due to that, they became experts in swimming and diving. However, getting into the land becomes too awkward for them. The oily fat thick layer that grows up to 3 inches thick basically insulates the seals. That thick layer works as insulation by keeping their body temperature about 100 degrees Fahrenheit.

Widely, there are about 18 species of seals existing. All-in-all, these include the Baikal seal, common or harbor seal, gray seal, harp seal, leopard seal, ringed seal, spotted seal, and Weddell seal, to name a few.

10. Walrus

General information:

• DIET: Carnivore
• HABITAT: Coastlines with presence of ice floes and rocky
• AVERAGE LIFE SPAN: 40 to 50 years
• SIZE: 7.5 ft to 11.5 ft in length
• WEIGHT: 880 lbs to 3,740 lbs

When you cross along the subarctic seas of the Arctic Ocean, you will generally found the walrus. They are exceptionally graceful in water making them exceptional mammals that live in the sea. However, most of their time is spent all throughout the land. They also have the ability to dive deep down waters up to 180 feet and look for clams and shellfish within the ocean beddings. With that, they can stay longer underwater for as long as 30 minutes.

Generally, there are two distinct species of Walrus but the variations only come slightly in their appearance. Yet, they were highly distinguishable based on their geographical locations. The one is the main inhabitants of the Atlantic Walrus, whereas the other one will be found on the Pacific Walrus. But, the Laptev Walrus which is the third species is under debate because more of its population is believed to be a type of Pacific Walrus. 

Although the data is very vague, there is an increasing rate in terms of the vulnerability of this aquatic creature. Nowadays, these mammals that live in the sea are already in their “near threatened” status within their natural environment. Their population count as of these days is already declining since the 18th century. This is highly accountable for natural ice reduction because of global warming. 

Final Thoughts

It is very interesting to know that there is a long list of mammals that live in the sea. Most of them have good numbers populations and are still found to exist abundantly in various bodies of water around the globe. Unfortunately, there are some that are already on the list of endangered or near critical status.

Good to know that the government is taking its part in protecting these marine animals by implementing laws and treaties. Basically, these laws aim to cover the natural habitat of aquatic animals as well as taking good care of them. Knowing that it is time to take and make our part as caretaker of Mother Nature.