What kind of animal is a seal? An updated explanation of its characteristics, ecology, and habitat

What kind of animal is a seal? We will explain the physical characteristics, ecology, and habitats of marine mammals. One of the creatures that attracts a lot of attention at aquariums is seals. You can see seals in any aquarium or zoo, but what kinds of seals are there? Please use this as a reference as we have summarized the types and characteristics.

What is a seal? About basic status

Seals are a group of marine mammals (sea animals, fish) that belong to the pinniped order. Their scientific name is Phocidae, which means they are like seals. Depending on the subspecies, they can be 200-300cm long and weigh 200-400kg. The basic information is as follows. Both young and adults can often be seen moving around and eating on the ice or coasts. In Japan, you can see many of them in zoos from Hokkaido to Kyushu. They catch a variety of prey in the water.

Japanese（和名）	アザラシ
English（英名）	Seal
scientific name(学名)	Phocidae
classification（分類）	Mammalia、  Carnivora、 Phocidae 哺乳綱、食肉目、アザラシ科
IUCN Status(保全状況)	VULNERABLE～ENDANGERED
Length（体長）	200-300cm
Weight（体重）	200-400kg

What are the roots and origins of seals?

Tracing the roots of seals leads us back to a carnivorous mammal that walked on land—a fact hard to imagine given their current appearance. Seals belong to the group known as Pinnipedia (which also includes fur seals and sea lions) and are the descendants of animals that ventured into the ocean approximately 30 million years ago.

Ancestors were land-dwelling carnivores

Between 50 million and 40 million years ago, the lineage leading to modern seals consisted of land-dwelling members of the order Carnivora.

The evolutionary progression:

Land-dwelling carnivorous mammal
↓
Semi-aquatic animal living near the water’s edge
↓
Early pinniped
↓
Evolution into the family Phocidae (true seals)

An early seal ancestor: Puijila

A well-known early pinniped is:

Puijila darwini

It lived approximately 24 million years ago (early Miocene).

Characteristics:

Body length: Approx. 1 meter

Had four legs

Capable of walking on land

Capable of swimming in water

Resembled an otter

It was an “amphibious” animal that existed before evolving into the modern seal.

Unique evolution of seals

The family Phocidae underwent significant physical changes to adapt to life in the ocean.

Forelimbs

Past:

Legs used for walking

Present:

Small, flipper-like forelimbs

Used for steering while swimming

Hind limbs

This is the seal’s most distinctive feature.

Hind flippers extend backward

Propel the body by swinging side-to-side

Cannot rotate forward on land

Consequently, on land, they move by:

“Wriggling the body while lying on the belly”

Body shape

Adapted for life in the ocean by acquiring:

A streamlined body

A thick layer of fat (for insulation)

Dense fur

The ability to store oxygen

About classification

Seals are made up of many different species. There are the following subspecies. It is said that seals branched off from a common ancestor with weasels. It is said that their ancestors are close to bears. There are various species of mammals in some areas.

Name (名前)	Scientific Name (学名)
Hooded seal ズキンアザラシ	Cystophora cristata
Bearded Seal アゴヒゲアザラシ	Erignathus barbatus
Gray Seal ハイイロアザラシ	Halichoerus grypus
Ribbon Seal クラカケアザラシ	Histriophoca fasciata
Leopard seal ヒョウアザラシ	Hydrurga leptonyx
weddell seal ウェッデルアザラシ	Leptonychotes weddellii
Crabeater seal カニクイアザラシ	Lobodon carcinophagus
Northern Elephant Seal キタゾウアザラシ	Mirounga angustirostris
Southern elephant seal ミナミゾウアザラシ	Mirounga leonina
Mediterranean monk seal チチュウカイモンクアザラシ	Monachus monachus
Caribbean Monk Seal カリブモンクアザラシ	Monachus tropicalis
Ross seal ロスアザラシ	Ommatophoca rossii
Harp seal タテゴトアザラシ	Pagophilus groenlandicus
Spotted Seal ゴマフアザラシ	Phoca largha
Harbour Seal ゼニガタアザラシ	Phoca vitulina
Caspian seal カスピカイアザラシ	Pusa caspica
Ringed Seal ワモンアザラシ	Pusa hispida
Baikal seal バイカルアザラシ	Pusa sibirica

Cystophora cristata

Hooded seals are 200-300cm long. Weight 200-400kg. Males are larger than females and have gray fur with irregular dark spots. This seal lives in the North Atlantic and Pacific Ocean, and its meat is eaten, its fat is used for fuel, and its fur is used for leather products, and it is listed as an endangered species.

Erignathus barbatus

Bearded seals belong to the genus Bearded Seal and live from the Arctic to the Bering Sea. The body length is 200-260cm, the weight is 200-360kg, and the body color is light gray to dark brown. Populations are very stable and are classified as Least Concern.

Halichoerus grypus

Gray seals live in the North Atlantic Ocean and can grow up to 1.6m to 2m in length and 100kg in weight. In recent years, the population of gray seals has increased so much on the western side of the North Atlantic that there are calls for their removal in Canada.

Histriophoca fasciata

The black seal is a subspecies with distinctive band-like patterns around its neck, waist, and legs, and it lives near the Sea of Okhotsk. The body length is 170cm and the weight is 70-130kg. They are very solitary, usually traveling in groups of one or two, and their population is very stable.

Hydrurga leptonyx

Leopard seals live in Antarctica and are 2.8 to 3.3 meters long and weigh 300 to 500 kg. The body shape is elongated. The head is large and the tip of the snout is pointed. Seals do not form groups and live alone, have few natural predators, have a stable population, and are classified as low concern.

Leptonychotes weddellii

Weddell seals live in Antarctica and are approximately 2.9 meters long for males and 3.3 meters for females. Weight is 400-450 kg. This species is distributed in the waters near Antarctica and often appears at Antarctic bases, so many photographs have been taken of it. The population is stable and it is classified as low concern.

Lobodon carcinophagus

The crabeater seal lives in Antarctica and is 220-230cm long and weighs 200-300kg. The body shape is elongated. Their whole body is covered with pale gray hair, and they live mainly on drift ice. The population is stable and it is classified as low concern.

Mirounga angustirostris

Northern elephant seals belong to the genus Elephant Seal. Male seals are very large, weighing 1,500 to 2,300 kg and reaching 4 to 5 meters in length. They are polygamous, and the elephant seal’s distinctive feature is its elephant trunk. The population is stable and it is classified as low concern.

Mirounga leonina

Southern elephant seals live on islands in the sub-Antarctic and can be seen in large numbers in areas such as South Georgia. The body length is 4.2 to 5.8 m and the weight is 1,500 to 3,700 kg. The elephant seal, which is polygamous and is characteristic of elephant seals, is larger in northern elephant seals. The population is stable and it is classified as low concern.

Monachus monachus

Testudo monk seals live in the Atlantic Ocean and the Mediterranean Sea, and are 230-280 cm long and weigh 200-300 kg. The fur on the back is black or brown, and there are white markings on the abdomen. Due to overfishing and competition with fishing, their population has declined dramatically, and they are designated as an endangered species.

Monachus tropicalis

Caribbean monk seals live in the Caribbean Sea and can be over 2m long and weigh 160kg. Caribbean monk seals were overhunted and became completely extinct in 1952.

Ommatophoca rossii

Ross seals live in Antarctica and have a body length of 1.68-2.09m and a weight of 129-216kg. The snout is short and wide, and the fur is the shortest of all seals. Populations are very stable and are classified as Least Concern.

Pagophilus groenlandicus

Harp seals are widely distributed in the North Atlantic Ocean, and can reach a length of 190 cm and a weight of about 135 kg. The fur is gray and has markings. Harp seals live in the ocean and on glaciers, and sometimes live in groups. Populations are very stable and are classified as Least Concern.

Phoca largha

Harbor seals live in the Bering Sea and the Sea of Okhotsk, and their body length is between 160 and 170 cm, and their weight is between 70 and 130 kg. The back is gray with scattered black markings. Populations are very stable and are classified as Least Concern.

Phoca vitulina

Harbor seals are widely distributed from the Atlantic Ocean to the Pacific Ocean. Harbor seals are 120-170cm long and weigh 50-150kg. There are two types of body color: dark and light. Populations are very stable and are classified as Least Concern.

Pusa caspica

The Caspian seal is a seal that lives in the Caspian Sea and other areas.In the summer, it lives in the southern part of the Caspian Sea, and in the winter, it moves north to the northern part of the Caspian Sea. The body length is 180cm, the weight is 90kg, and it is endemic to the Caspian Sea, so it is designated as an endangered species because its population is small.

Pusa hispida

Ringed seals are small seals that are widely distributed in the northern part of the Northern Hemisphere, with a body length of 120 to 130 cm and a weight of 50 kg. The back side is gray with gray-brown to black markings, and it is smaller than other seals. Populations are stable and classified as low concern.

Pusa sibirica

Baikal seals live around Lake Baikal in Russia. The body length is 100-110cm and the weight is 50-90kg. The flanks are yellowish gray and the overall color is dark grayish brown. It is the only seal in the world that lives exclusively in freshwater, and its population is stable and classified as low concern.

Where is its habitat?

Seals are distributed in the world’s oceans, including the Atlantic, Pacific, and Caribbean.

1. Geographic Distribution

Seals can be broadly divided into “species that live in cold regions such as the Arctic and Antarctic” and “coastal species that live in temperate and subtropical regions.”

Arctic and Cold Region Seals

Arctic Seals: Northern Canada, Greenland, and the Arctic Ocean coast

Harp Seals: North Atlantic coast, Greenland, Iceland, and Norway

Antarctic and Cold Region Seals

Ringed Seals and Bearded Seals: Sea ice around Antarctica

Temperate and Coastal Seals

Spotted Seals: North Pacific coast, Hokkaido, the Kuril Islands, and the Aleutian Islands

California Seals: West Coast of North America

2. Habitat Characteristics

Marine: Spends most of its time in the water

Coastal and Ice Resting: Comes onto the shore or ice for breeding and molting

Ice and Beach Use: Spawning (birth) and raising children are limited to safe areas

3. Migration and Range

Migrates in response to seasonal changes in ice and water temperature

Travels widely across the ocean in search of food (fish, squid, and crustaceans)

feature is? What kind of creature is it?

Seals are marine mammals that belong to the family Sealidae. Seals have very sensitive whiskers to detect prey. The neck is short and the limbs have five fingers, with webs between them. Seals are known for their excellent diving ability, and some subspecies can dive more than 1,000 meters. The nasal passages can be closed and most of the air in the lungs can be exhaled.

1. Appearance and Physical Characteristics

Body Shape: Streamlined and rounded, making them easy swimmers.

Body Length and Weight: Varies by species.

Small species (spotted seal): Body length 1.2-1.5m, weight 50-100kg.

Large species (ringed seal): Body length 2.5-3m, weight 400-500kg.

Skin and Fur: Hair is short and dense, with spots or stripes depending on the species.

Flipper-like Limbs: Forelimbs for direction control, hind limbs for propulsion.

2. Behavior and Personality

Excellent Swimmers: Capable of high-speed underwater movement and diving.

Rests on land or ice: Spends time on the coast or ice during breeding and molting seasons.

Sociality: Many species live in groups, congregating in large numbers at breeding grounds.

3. Diet

Carnivorous (piscivorous)

Preys primarily on fish, squid, and crustaceans

Hunts underwater

Highly diving ability, allowing them to catch prey in the deep sea

4. Special Characteristics

Thick subcutaneous fat (blubber layer): Maintains body heat even in cold climates

Well-developed sensory organs: Uses whiskers to detect the location of underwater prey

Diving ability: Can dive for several minutes to 10 minutes, with some species even longer

What is your personality like?

Seals have a curious personality. You can clearly see this when you are in an aquarium. They will probably approach the person in front of the aquarium and make a gesture as if they are looking into your face. One of their characteristics is that they are highly social and tend to live in groups.

1. Basic Personality

Timid and cautious

Sensitive to natural predators (wolf seals, polar bears, humans, etc.)

Especially cautious on land, they will immediately flee to the sea at the first sound or human presence

Curious

Once accustomed to their environment, they may approach and observe others.

2. Sociality

Many species live in groups

They gather in dense groups at breeding and resting areas

They are not aggressive when in contact with other individuals, but fights between males can occur during the breeding season.

Communication Skills

They communicate with each other through vocalizations and body movements

3. Relationship between Behavioral Patterns and Personality

Highly adapted to swimming and diving, they behave calmly in the water.

They are cautious on land and ice, and often suddenly flee in groups.

What is the ecology like?

Seals make a living by eating fish, squid, and crustaceans. Most seal couples are polygamous, and they give birth on land or on the sea ice. The lifespan of a seal is said to be 25 to 30 years.

1. Diet

Carnivorous: Feeds primarily on fish, squid, and crustaceans.

Hunting Method: Dive underwater to pursue and capture prey.

Some species are capable of deep-sea prey.

2. Reproduction and Growth

Breeding Season: Varies by species, but generally breeds on land or ice in winter and spring.

Gestation Period: Approximately 9-11 months (depending on species).

Birth: Usually gives birth to a single calf on ice or shore.

Calves: Fed by their mother’s milk, they learn to swim within a few weeks to a few months.

Sexual Maturity: Varies by species, but they are capable of breeding at around 2-6 years of age.

3. Behavior and Lifestyle

Aquatic Lifestyle: Spends most of their time underwater.

Rest on Land and Ice: Comes ashore to rest, molt, and breed.

Diving Ability: Able to dive for a few minutes to 10 minutes, longer depending on species.

4. Migration/Habitat

Seasonal Migration: They move according to water temperature, ice conditions, and food availability.

Many species live in groups: They gather in dense groups at resting and breeding areas.

Are there any natural enemies?

In the natural world, killer whales are our natural enemies. Seals have very large bodies, so they don’t have many enemies.

Seal Diving

Seals possess exceptional diving capabilities among marine mammals. While abilities vary by species, the Weddell seal of the Antarctic and elephant seals, in particular, are specialists capable of diving to great depths for extended periods.

Dive Duration

This varies significantly by species.

Species	Approximate Dive Duration
Spotted seal	Approx. 10–20 minutes
Harbor seal	Approx. 5–15 minutes
Weddell seal	Approx. 20–30 minutes
Elephant seal	Approx. 1–2 hours

Elephant seals, in particular, possess some of the best diving capabilities of any mammal.

Dive Depth

Species	Maximum Dive Depth
Spotted seal	Approx. 200m range
Harbor seal	Approx. 300m range
Weddell seal	Over 600m
Elephant seal	2,000m range

Weddell seals swim beneath Antarctic ice, hunting for fish and squid in the deep ocean.

How can they dive for so long?

Seal bodies are structured to conserve oxygen.

① Storing large amounts of oxygen in the blood

Compared to humans, they have:

Higher hemoglobin concentration

Greater blood volume

…allowing them to transport more oxygen.

② Oxygen tanks in the muscles

They have very high levels of myoglobin in their muscles,

supplying oxygen to muscles during dives

and enabling them to keep swimming for long periods.

Seal muscles are so rich in myoglobin that they appear dark in color.

③ Diving reflex

Upon entering the water:

Heart rate slows

Blood flow concentrates on the brain and heart

Oxygen consumption decreases

…triggering these specialized physiological responses.

Vocalizations

Seal vocalizations vary significantly depending on the species and the situation. They produce not only “barks”—like those of fur seals or sea lions—but also specialized sounds for communicating underwater.

“Coo-coo” or “kyu-kyu” calls

These are frequently made by seal pups.

Functions:

Calling the mother

Signaling their location

Checking in with others

Since pups can become separated from their mothers, they use these sounds to locate one another.

Low “goh” or “goo” sounds made by adults

Adult seals produce:

Low growls

Deep, rumbling growls

Short barks

Purposes:

Asserting territory

Attracting a mate

Warning other individuals

Males, in particular, use vocalizations to compete with one another.

Underwater vocalizations

Seals are very vocal underwater as well.

Typical sounds include:

“Clicking” sounds

Whistling sounds

“Pew” sounds

Low-frequency “rumbling” or “purring” sounds

Because sound travels farther underwater than in the air, seals use these vocalizations to communicate with others.

Seasonal Activities

While seal activities vary by species and habitat (Arctic, Antarctic, or temperate zones), they generally follow a repeating seasonal cycle of breeding, giving birth, molting, foraging, and migration.

🌸 Spring (March–May)

“Season for Giving Birth and Rearing Pups”

Spring is a crucial time for many seal species.

Key Activities

Giving birth

Rearing pups

Nursing

Resting in groups

Pups (Young Seals)

Newborn pups:

Have whitish natal fur (depending on the species)

Practice swimming

Grow rapidly on mother’s milk

Mothers provide high-fat milk, allowing the pups to grow quickly over a short period.

☀️ Summer (June–August)

“Season for Foraging and Molting”

Summer is a time of active foraging in the ocean.

Key Activities

Hunting fish and squid

Long-duration diving

Recovering physical strength

Molting (shedding and regrowing fur)

Seals consume large amounts of food to…

Withstand the winter cold

Prepare for the breeding season

…and build up fat reserves.

🍂 Autumn (September–November)

“Migration and Preparation for Winter”

As autumn arrives, seals adapt to changing environmental conditions.

Key Activities

Increasing food intake

Migrating to different habitats

Seeking winter feeding grounds

Arctic species migrate in response to changes in sea ice.

❄️ Winter (December–February)

“Season of Sea-Ice Life and Hunting”

This is a critical season for seals living in cold regions.

Key Activities

Diving beneath the ice

Hunting fish and squid

Using breathing holes

Weddell seals in the Antarctic, in particular:

Swim beneath the ice

Dive to depths of several hundred meters

Hunt for extended periods

…as part of their daily lives.

Daily Activity Rhythm

Daytime

Diving to search for food

Hunting fish and squid

Moving through the water

Nighttime

Resting on the water’s surface or on the ice

Communicating with others

*Activity patterns during the day and night vary by species.

Walking Speed

Seals do not move quickly on land. Unlike fur seals and sea lions, seals have evolved bodies specialized for life in the water rather than for movement on land.

Normal movement

Approx. 1–3 km/h

Short, hurried bursts

Approx. 5–8 km/h

Speeds vary depending on the species and the terrain (e.g., sandy beaches vs. ice).

Why are they slow?

The primary reason is the structure of their hind flippers (hind limbs).

Physical characteristics of seals

Hind flippers

Extend backward

Developed for swimming by swaying side-to-side

Cannot rotate forward

Consequently, on land, their movement is not

“walking”

but rather

“moving by wriggling their bodies side-to-side while lying on their bellies.”

This method of movement is also known as galumphing.

About Seal Pups

The following summarizes the appearance, growth, behavior, and mother-pup relationship of seal pups.

1. Appearance and Physical Characteristics

Body Color: Varies depending on species, but most are covered in white or pale gray fur immediately after birth (e.g., ringed seals have white fur for several weeks after birth).

Body Length and Weight:

Small Species: Approximately 50-70 cm, 5-10 kg

Large Species: Approximately 1-1.5 m, 20-30 kg

Body Shape: Round and soft body; flipper-like limbs are underdeveloped; mothers help them move in the water.

2. Growth and Development

Lactation Period: Breastfed for approximately 4-6 weeks

Weaning: After lactation, they gradually begin to eat solid foods such as fish.

Independence: Depending on species, they acquire swimming and diving skills within a few months and become independent.

Sexual Maturity: Depending on species, they are capable of breeding at age 2-6.

3. Behavior and Mother-Child Relationships

Cubs spend time closely with their mothers.

Mothers not only nurse their young but also teach them how to swim, dive, and avoid danger.

Cubs acquire motor skills and group behavioral skills through play with other animals.

4. Threats and Survival

Cubs are vulnerable to predators (wolf seals, polar bears, killer whales, etc.).

If their birthplace (on the ice or on the beach) is unsafe, their survival rate decreases.

Are seals an endangered species?

Unfortunately, seals are listed as an endangered species. The meat is edible, the fat can be used as fuel, and the fur can be used to make coats. Therefore, some subspecies are endangered. Conservation efforts are underway around the world.

1. IUCN Red List Assessment (Selected Representative Species)

Arctic Seal (Phoca hispida)

Distribution: Arctic

Assessment: Least Concern

Ringed Seal (Leptonychotes weddellii)

Distribution: Circum-Antarctic

Assessment: Least Concern

Bearded Seal (Ommatophoca rossii)

Distribution: Circum-Antarctic

Assessment: Least Concern

Monk Seals (Monachus spp.)

Distribution: Mediterranean, Hawaii, California

Assessment: Endangered or Critically Endangered

2. Seals Around Japan

Spotted Seal (Phoca largha)

Distribution: North Pacific coast, Hokkaido, and the Kuril Islands

Assessment: Least Concern

3. Threats

Bycatch in fishing activities

Marine pollution (chemicals, plastics)

Decreased sea ice (Arctic and Antarctic species)

Habitat destruction and tourism pressure

Difference between seal and sea lion

Seals are often mistaken for sea lions. There is a decisive difference that can be determined by appearance. Sea lions have pinnae, but seals do not. Furthermore, sea lions walk on four legs, but seals cannot lift their bodies and move by crawling.

Can seals be kept?

Seals will need a large swimming pool. You also need a space where you can rest, so it’s not always easy. The main food is raw fish. They eat a lot of fish, so it’s quite expensive. Some species are highly protected and may require permission, so be sure to check carefully. It is realistic to obtain seals from zoos or aquariums.

1. The Reality of Breeding

Breeding is generally done in specialized facilities such as aquariums and marine parks.

Keeping seals on your own is extremely difficult, requiring large aquariums, pools, filtration systems, water temperature control, and food (fish, squid, etc.).

Even young seals need swimming and hunting skills learned from their mothers, making it difficult to fully develop them in an artificial environment alone.

2. Ecological Constraints

They primarily live underwater and require ample swimming space.

If an environment does not allow them to fully utilize their swimming and diving abilities, they will suffer from stress and health problems.

Highly social species require social life in groups, and keeping seals alone can be psychologically stressful.

3. Laws and Regulations

In Japan, seals are subject to the Wildlife Protection Act, and individuals are prohibited from capturing and breeding wild seals.

Breeding is only permitted in licensed aquariums and research facilities.