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In its first year of life, a seal is susceptible to infection by lung worms. After being weaned, young seals will go out and start hunting for prey by themselves. This is when they often contract lung worm infections. A number of them will get so sick, that they would not be able to survive without help. 

See also

  • Longwormpatient

  • Longwormen bij gewone zeehond

  • Longwormen bij zeehonden

Lung worms are parasites that can severely damage the lungs – they eat the tissues in the lungs and reproduce there, causing more and more damage in the process.

The seal will experience shortness of breath and the damaged lungs are more susceptible to pneumonia or other bacterial infections. The shortness of breath also prevents a seal from staying under water long enough to hunt. This leads to starvation, weakness, and possibly death.

Seals are exposed to lung worm through the food they eat. For example, a fish might have been infested with lung worm when it was eaten by a seal. From the stomach, the lung worms will travel through the blood stream to the lungs, where they grow and produce larvae. Infected seals will start coughing, expelling the microscopic larvae from their lungs.

These larvae are then ingested by the seal, thus entering the host’s digestive tract. When the seal defecates, the larvae are released into the sea, where they can infect small sea creatures and grow. The infected sea creatures are eaten by seals, at which point the infection cycle restarts. If an infected animal is found on time, it can be treated. A seal with lung worm infection can be recognised by symptoms such as laboured breathing, a high back, and blood around the mouth from coughing.

Usually a seal with a lung worm infection will need to be rehabilitated for two to three months; once a seal has been cured, it will be resistant to this parasitic infection for the rest of its life.

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History of seals

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Did you know that seals were hunted in the Netherlands*? Seals have been killed for their fur and meat for centuries, but there came a time when bounties were even paid for simply killing these animals. We can hardly imagine it anymore, but it was only after 1962 that seal hunting was officially banned and the seals were given a protected status. On this page you can read more about the history of seals in the Netherlands and how our image of the seal has changed over the centuries.

*Most of this history is about the common seal. The grey seal probably hadn't been seen in the Netherlands for centuries - until their return in the 1980s.

See also

The seal as a source of food

Until the Middle Ages, people caught seals in the Netherlands for their meat. They actually ate seal meat! You could buy the seals at the fish market. The paintings by Frans Snijders from the 17th century give you an idea of what such a fish market may have looked like at that time. In the 16th century, the need to eat seal meat disappeared, although people still occasionally ate the liver.

  • Schilderij Frans Snijders 17e eeuw

    Painting 1

  • Schilderij vismarkt 17e eeuw

    Painting 1.2

  • Schilderij zeehond 17e eeuw

    Painting 1.3

Three paintings by Frans Snijders about the fish market, from the 17th century. Can you find the seal(s) in each painting?

The seal as a fish thief

Bounty yacht in Zeeland

There was a turnaround at the end of the 16th century. Fishermen in Zeeland were of the opinion that seals were their competitor, because according to them seals ate too much fish. To protect the fisheries, Zeeland was the first to start paying a premium in 1591 if you killed a seal. The distribution of the premiums was tracked. For example, this documentation shows that more than 40,000 seal premiums were paid between 1591 and 1801!

Everyone was free to earn money by catching a seal. In Zeeland, there were specialized seal hunters. But if you happened to encounter seals in the rivers or along the coast as a fisherman, you could also hunt them (see image 2). Even islanders from Schiermonnikoog came all the way to Zeeland to hunt for seals. Zeeland finally stopped the seal premiums in 1857.

Prent uit 1582 over zeehonden en tarbotvangst

Print of seals and turbot fishing by Adriaen Collaert from 1582. On the left of the print you see how two seals are caught. Source. 

Seal hunting in other provinces

In 1610, Holland (nowadays North and South Holland) started with a premium to combat seals. Bounty hunting was considerably smaller: in South Holland, 40 seals were caught in the 12 years that the seal premium existed.

Seal hunting also existed in both Friesland and Groningen. No premiums were paid for it. Seal hunters used to live in Westernieland, a village close to Pieterburen. Documentation showed that between 1859 and 1899 they caught between 100 and 250 seals per year.

National seal bounty

In 1900, a national seal bounty started. The cause was again due to complaints from the fishing industry. Fishermen saw the seal as a common tern and destroyer of their fishing nets, although the exact damage caused by seals to the fishery had not been investigated. Despite the lack of evidence, the national seal bounty went ahead anyway. For example, the government gave you 3 florins for a killed female seal and 2.50 florins for a killed male seal.

Criticism of seal hunting

The image that people had of seals and the seal hunt eventually came under discussion during this period. At the end of 1920, the opposing voices became somewhat louder. Some people did not think it wise to spend state money on seal hunting during the general depression.

 Other insights also emerged about nature and that animals can also have an indirect use. Even "harmful" animals - as was thought of the seal - have their role in nature. Nature and animal protection became increasingly important and the method of killing seals also received criticism.

Seal hunt with pens

However, this still had little impact on daily practice. Only the gruesome hunting with pens stopped on Terschelling. This form of hunting went as follows: a beam with sharp pins was placed at the tide line. Seals were frightened from a sandbar and fled into the water. There, they got into the pens and were injured. Hunting with a rifle and bat was still allowed (see image 3).

  • Zeehondenjacht

    Image 3

  • Zeehondenjacht

    Image 3

Image of children clubbing a seal from an early 20th century school book. Photo of pleasure hunters with their shot seals. Source: Seal hunt in the Netherlands 1591-1962

The hunt continued

Despite the criticism, bounty payments continued uninterrupted. In the period from 1900 to 1942 (with a stop for a number of years), between 800 and 1600 seals were killed per year. Seal hunting was abolished by the German occupiers in 1942, but resumed after World War II. In 1954, a new hunting law was even introduced in which all existing rules regarding hunting were canceled: the hunting season applied both throughout the year and throughout the country.


Just as people used to heat whale blubber to make whale oil, this used to be done with seals. By heating the fat layer of a seal, a tear was created that people could use in different ways. After the Second World War, the demand for tear quickly declined again. Petroleum then became increasingly popular and took the place of seal tear.

Sealant was used for:

  • Fuel in lamps
  • A kind of oil for frying food
  • Grease to keep leather supple
  • Raw material for margerine and soap

The seal as a fashion trend

Before World War II, hunters shot young and older seals. This changed after the war. Back then, young seals were mainly hunted. The fur industry paid much better for a seal than the government did. According to Groninger Hendrik Teerling from the documentary Other Times you got 30 to 45 guilders for the fur of a young seal. People started to hunt seals for the fur industry.

Seal fur was fashionable. The sealskin has been used for clothing and shoes for centuries. But the demand for seal fur grew when the Groningen fur trader Van Daal & Meijer (1938 – 1973) came into the picture. The big breakthrough came after the war: the company had devised a processing process in which the seal skins did not become stiff, but remained flexible and soft. This lead made them one of the largest seal fur traders in the world.


Image caption: Lady in seal fur coat, designed by Jacques Fath from the collection of Bonthandel Van Daal & Meijer (1950-1954). Source: Groninger Archieven.

The supply of sealskin from the Netherlands was not enough. Van Daal & Meijer expanded into seal hunting in Canada, Greenland and Iceland (see figure 5). There they hunted the hooded seal and the harp seal. After the seal hunting ban in the Netherlands after 1962, they continued to hunt seals abroad until the 1970s.

Vangplekken van zeehonden bij Canada, Groenland en IJsland

Map with trapping locations of various species of seals near Canada, Greenland and Iceland, from Bonthandel Van Daal & Meijer (1950-1954). Source: Groninger Archieven.

The seal as a protected species

People started to work to help the seal. Before the seal hunt stopped, seal rehabilitation had already started. Gerrit de Haan and Annie de Haan-Langeveld were the pioneers and were the first in Europe to set up a seal rehabilitation center (see video). This started in 1952 on the Wadden Island of Texel at the Texel Museum, which is now called Ecomare .

Video from Ecomare with video footage of founder Annie de Haan. Source: Youtube channel Ecomare Texel – De Koog.

In In 1961, the Wentzel family also started saving seals. They lived in the village of Uithuizen in the province of Groningen. After the death of Mrs. Wentzel, Lenie ’t Hart was asked to take over the seal sanctuary in 1971. That was the start of Sealcentre Pieterburen. You can read more about the history of Sealcentre Pieterburen here .

Zeehondenopvang in Uithuizen

René and Anneke Wentzel in their backyard where they rescued seals in Uithuizen. Source: Peter Wentzel.

Things went badly for the seals

Things went very badly for the seals when the seal rehabilitation centers on Texel and Uithuizen started. This can be clearly seen with a graph of the counts of seals in the Dutch Wadden Sea. From the year 1900 it can be seen that the number of seals has decreased enormously: from about 15,000 seals to about 2,000 seals in 1960. The fact that the seals were doing so badly was taken seriously by the government in the 1960s. In the end, the government decided to ban seal hunting in the whole of the Netherlands after 1962. 

Grafiek zeehondenpopulatie 20e eeuw in Nederlandse Waddenzee

Graph showing the number of seals in the Dutch Wadden Sea. The light blue line represents the harbor seal and arises from the dark blue line; the orange line represents the number of gray seals that returned in the 1980s.

Serious pollution of sea water

The number of seals in the Wadden Sea remained low. The seawater was seriously polluted and commercial shipping and water tourism caused a lot of disruption. The harmful substances PCBs in the water in particular had a negative influence on the reproduction of the seals.

After an outbreak of a virus in which half of the seals died in 1988 and in 2002, seals were given the opportunity to grow in numbers again – and they succeeded. There was more good news: grey seal re-established itself in the Wadden Sea in the 1980s. Conclusion: the seal has made a comeback!

The relationship between humans and seals has changed a lot over the past few centuries. It's actually amazing how differently we thought about seals compared to now. By changing our image of the seal and by committing ourselves to its protection, we as people ensured that we did not lose the seal in the Netherlands. One thing is clear from a look at history: we must ensure that the seals have a future. We will therefore continue to work for a healthy seal in a healthy sea. Day in day out. Are you in?


  1. Zeehondenjacht in Nederland 1591 – 1962. Pieter ’t Hart.
  2. Aflevering Zeehondenjacht van het programma Andere Tijden (2004).
  3. Het begin van de zeehondenopvang op Texel.
  4. Reijnders, P. J. H. 1986. Reproductive failure in common seals feeding on fish from polluted coastal waters. Nature 324:456-457
  5. Gewone en grijze zeehond in Waddenzee en Deltagebied, 1960 – 2020.

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Sea lions (Otariidae)

Knowledge repository

A family very close to seals (Phocidae) is the sea lion family. They may look very similar to seals at first glance, but there are big differences. Do you know the difference? On this page, you will get to know the sea lion family a little better.

See also

  • Zeeleeuwen

  • Zeeleeuw op strand

  • Zeeleeuwenpopulatie


The sea lion family is also known as eared seals. They derive this name from their auricles. In the scientific world, we call this family Otariidae. Like seals , sea lions belong to the order Carnivora, or carnivorous mammals. Bears, lions, wolves and walruses are also members of this order. Sea lions are carnivores. They hunt fish, crustaceans and shellfish in shallow coastal waters.

Sea lions, seals and walruses are often placed in a special group of marine mammals. This group is called the pinnepeds (Pinnipedia). You might have guessed it: this group gets their name from the shape of the legs. In these animals, the legs are very short, but with very long toes and fingers. This makes them look like they have fins.

How do you recognize sea lions

Sea lions are often confused with seals. Do you have any idea how you can actually distinguish a sea lion very easily? Their name (eared seals and Otariidae) kind of gives it away: the ears. You can see little auricles protruding from the side of their heads. Seals and walruses do not have these; they have holes as ears.

De lichaamsbouw van zeeleeuwen lijkt wel wat op dat van zeehonden. Ze hebben een lang lichaam met een grote borstkas. Ze zijn over het algemeen wat slanker gebouwd dan zeehonden, met een spitsere kop. De voorpoten van zeeleeuwen zijn een stuk langer dan die van zeehonden.

Sea lions can move a lot more smoothly over land than seals. This is because they can fold their rear flippers forward. By leaning on their front and rear flippers, they can simply walk on land. And when needed, for example to flee, they can even run quite fast!

You can usually clearly see the difference between males and females in adult sea lions. Males are a lot bigger, with a very large chest, thick neck and larger head. This distinct difference between males and females is called sexual dimorphism.

Did you know...

Sexual dimorphism can look very different in different animal species? In many birds, males are very colourful, while females have more camouflage colours. Also, it is not always the males that are bigger or more colourful than the females. In fact, many insect and spider species have larger, more colourful, or more venomous females.

Flying over the seabed

Sea lions are incredibly good swimmers. Just like other pinnipeds, for that matter. They just take a slightly different approach from seals and walruses. Seals and walruses use their hind flippers to gain speed and their front flippers to steer. Sea lions do the opposite.

Sea lions have very long front flippers. Instead of their rear flippers, they use these long front flippers to gain speed. They move their front flippers up and down, like wings. By doing this, they push themselves forward through the water. They then use their rear flippers to steer.

Because they swim this way, sea lions are a lot more agile than seals. But, they cannot swim as long and deep as seals.

Together in big groups

Sea lions are social animals: they often live together in huge groups. These groups are also called colonies. During the mating season, an entire colony often lies together on the coast. Within a colony, there are smaller groups consisting of a male and his harem. These harems can sometimes consist of dozens of females!

Especially when hunting, sea lions are a lot more social than seals. Sea lions often hunt schools of fish in groups. By working together, they can easily catch fish from schools. This is much more difficult for seals, which hunt alone.

Did you know...

Some sea lions are so good at hunting together that other animals take advantage of it too? Galápagos Sea Lions (Zalophus wollebaeki) go after whole schools of fish while hunting. Then birds, sharks and other sea lions often lurk as well. Once the Galápagos Sea Lions have chased the fish together, the other predators quickly snatch a few!

Where do sea lions live?

In the Pacific, sea lions are fairly widespread. They live mostly in tropical and subtropical seas (California and Galápagos, for example), but also in the more temperate and sub-Antarctic regions (such as South America and New Zealand).

Sea lions always mate and have their pups on land. Therefore, there are no species found in the Arctic. The only places in the Atlantic where sea lions live are the southern tip of the African continent, and along the South American coasts. So here in Europe, you cannot see sea lions in the wild.

How many sea lion species are there?

The family of sea lions (Otariidae) consists of 14 species in total. These are often divided into 2 groups based on their appearance. The fur seals or sea bears (Arctocephalinae) are slightly smaller and get their name from the longer fur around the chest and neck. In these animals, you can see an extreme size difference between males and females (sexual dimorphism). This group consists of eight species. The sea lions (Otariinae) are a bit larger, have smoother fur and have a somewhat smaller difference between males and females. This group consists of 6 species.

Did you know...

At the time of writing, there is an ongoing debate in science about the classification and designation within the sea lion family (Otariidae)? New analyses have shown that the division between fur seals (Arctocephalinae) and sea lions (Otariinae) is no longer correct.

However, this outdated division is still often used, as it is convenient to divide the sea lion family based on their external characteristics. Once a scientific consensus is reached, this article will be updated.

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Northern fur seal (Callorhinus ursinus)
South American fur seal (Arctocephalus australis)
New Zealand fur seal (Arctocephalus forsteri)
Antarctic fur seal (Arctocephalus gazella)
Galápagos fur seal (Arctocephalus galapogoensis)
Juan Fernández fur seal (Arctocephalus philippi)
Cape fur seal (Arctocephalus pusillus)
Subantarctic fur seal (Arctocephalus tropicalis)


Steller sea lion (Eumetopias jubatus)
Australian seal ion (Neophoca cinerea)
South American sea lion (Otaria flavescens)
California seal ion (Zalophus californianus)
Galápagos sea lion (Zalophus wollebaeki)
New Zealand sea lion (Phocarctos hookeri)

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Walruses (Odobenidae)

Knowledge repository

A family close to seals (Phocidae) is the walrus family. In terms of behaviour and body shape, they are very similar to seals and sea lions. Yet many walruses have one very recognisable feature: their tusks. Read on to get to know walruses a little better.

See also

  • Walrus

  • Walrussen op ijs

  • Walrus op sneeuw


The family of walruses is also known in science as the Odobenidae . Like seals, walruses belong to the order Carnivora, the carnivorous mammals. This order also includes animals such as wolves, bears and lions.

Walruses are one of the three members of the Pinnipedia (pinnipeds). This group of mammals is special because they spend much of their lives in the water. Their front and hind legs have turned into fins after millions of years of evolution, allowing them to move very well in water. The other two members of this group are sea lions (Otariidae) and seals (Phocidae).

This family is a bit special because it only has one relative! It might be a bit confusing, but the only species in the walrus family (i.e. the Odobenidae) is the walrus (Odobenus rosmarus). All other species have unfortunately been extinct for a long time.

How do you recognize walruses?

Walruses, like other pinnipeds, have a large, rounded thorax. Their abdomen is relatively small, giving them a cone-shaped body. They have shorter front flippers than sea lions. Nevertheless, walruses can lean on these, allowing them to lift their head and thorax off the ground.

Walruses have a lot less fur than seals and sea lions. Adult males sometimes look as if they have no fur at all. To stay warm, walruses have a thick layer of blubber. It often looks like walruses have extremely many small rolls of fat, especially the adults.

The only species still alive today (Odobenus rosmarus) has very recognisable tusks protruding down from the upper jaw. Fossils of very old walrus species show that many of their extinct relatives also had tusks.

Walking and swimming

Walruses on land

Walruses, like sea lions, can fold their rear flippers forward. This allows sea lions to lift their entire body off the ground to walk. Walruses cannot do that: they are too heavy for that.

Walruses move over land by dragging themselves forward with their front flippers. In the process, they push off with their rear flippers. The belly does not come off the ground in the process, so it slides over the ground. On land, they are somewhat more clumsy than sea lions.

Walruses in water

The way walruses move in the water is very similar to how seals do. They use their rear flippers to gain speed, but do not hold them flat against each other. They paddle alternately with their rear flippers while moving the abdomen back and forth.

Happily together

Walruses are social animals. On land, they lie down together in very close groups to rest. They also like to swim in groups in the water. Outside the mating season, males and females will usually live separately from each other. Walruses are pregnant longer and take care of their pups a lot longer than seals and sea lions.

During the mating season, different groups of males and females come together in a large group. The males then fight each other for a piece of territory. These fights can be fierce.

Where do walruses live?

The only walrus species alive today is found around the Arctic. They need shallow water with a soft seabed to hunt well. Therefore, they usually do not go very far from the shore. Walruses often rest in groups on sandy or rocky shorelines, as well as on the ice.

Walruses also used to occur a lot further south. Archaeodobenus, a primordial walrus, lived around Japan about 6 million years ago. At the same time, species also lived around California, such as the Gomphotaria. It seems they all lived in the northern hemisphere, as did the only surviving species.

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True seals (Phocidae)

Knowledge repository

What is a seal? What do seals look like and do you know how they differ from sea lions? How many species of seals are there and where do they live? On this page you will learn more about the seal family.

See also

  • Gewone zeehond - Moeder zoogt pup

  • Gewone zeehond in de Waddenzee

  • Seals


The group of animals that we call true seals are all members of the family Phocidae .

Pinnipedia (pinnipeds)

Seals are mammals that live in the ocean, also known as marine mammals. Together with the family of sea lions and the family of walruses they are placed in a special clade of marine mammals. This clade consists of so called pinnepeds (Pinnipedia).

Pinnipeds got their name from the shape of their flippers. These animals have very short flippers, but with very long fingers and toes. This makes it look as if they have fins.


Seals belong to the order of mammals that mostly eat meat: CarnivoraThis order also includes animals such as bears, lions, wolves, sea lions and walruses .

Did you know...

Seals do not spend all their life in the water? The land is where they rest, warm up, mate and birth their pups. That is why we call them semi-aquatic: spending a part of their lives on land and in the sea!

Seals are carnivores, which means that they must eat other living animals to survive. They often eat fish, crustaceans and shellfish. Some species can eat very small animals such as krill. Others hunt for even bigger prey such as birds and other mammals.

How do you recognise seals?

You can partially recognize seals by their special physique. They have a long body with a broad chest and a small lower body. This gives them a streamlined, cone-shaped body. Their flippers are very short and wide and they have five digits which are webbed. This makes them perfectly suited for aquatic life.

How do seals differ from sea lions and walruses?

Sea lions and walruses have similar physiques and adaptations, so what makes seals stand out? First of all, seals’ hind flippers cannot be folded underneath their body to walk on. Sea lions and walruses are able do this, which it easier for them to "walk" on land.

Seals have to hobble on their bellies to move on land. The way in which seals move is also referred to as caterpillar-like motion.

Another difference are their ears. Sea lions have small external ear flaps. Seals don't have such visible ears, they have ear holes on the side of the head.

Did you know...

That most seal species are larger than sea lions and walruses? The largest seal is the southern elephant seal (Mirounga leonina). Male southern elephants can weigh up to two tons!

Like a duck takes to water

Seals are strong swimmers. They have to be, as seals spend a lot of time in the water. In general seals can stay underwater for a longer period of time than sea lions and walruses. To hunt for food, some seal species must be able to dive very deep.

A seal has a special way of swimming. To speed up, seals swim with their hind flippers by holding them flat against each other and moving them quickly side to side. You could compare this to how fish swim. Fish also whip their tail to the side to move through the water. The front flippers are a lot smaller than the back flippers. They also don't use it to move forward, but to steer.  

Did you know...

The northern elephant seal (Mirounga angustirostrisis a champion in deep diving? They have reached depths as great as 1500 meters. In these depths they hunt for prey such as squid and other deep sea animals. Northern elephant seals can hold their breath for a very long time: almost 2 hours!


Most seal species live a solitary lifestyle. This means that they prefer to do almost everything on their own. The only exception is during the mating season, because then the animals congregate in large numbers to birth pups and mate. When mating season is over, the seals moult together, after which they each go their separate ways.

You can see seals resting in groups on beaches and sandbars, but that does not mean that they like to be together. Because seals are less agile on land, they cannot run away from large predators. Therefore, when the seals are on land it is safer for them to be with other seals. Additionally, often times there is not enough space to lie far apart so they are “forced” to be closer than they would want to.

Where do seals live?

Seals can be found in every ocean of the world. They often live along the coasts or on the ice of the North or South Pole. There is even a species of seal that does not live in the sea, but in the freshwater Lake Baikal in Russia! Each species is adapted to live in certain areas and not one seal species can be found all over the world.

Did you know...

There are two seal species living in the Netherlands? The common seal (Phoca vitulina) and the grey seal (Halichoerus grypus).

How many seal species are there?

The true seal family (Phocidae) is often divided into two subfamilies: northern seals (Phocinae) and southern seals (Monachinae). The group of northern seals consists of ten species. The southern seal group is made up of eight species. Worldwide there are a total of eighteen different seal species.

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Northern hemisphere seal species

Bearded seal (Erignathus barbatus)
Hooded seal (Cystophora cristata)
Harp seal (Pagophilus groenlandicus)
Ribbon seal (Histriophoca fasciata)
Baikal seal (Pusa sibirica)
Ringed seal (Pusa hispida)
Caspian seal (Pusa caspica)
Largha seal (Phoca largha)
Common seal (Phoca vitulina)
Grey seal (Halichoerus grypus)

Southern hemisphere seal species

Leopard seal (Hydrurga leptonyx)
Weddell seal (Leptonychotes weddellii)
Crabeater seal (Lobodon carcinophaga)
Ross seal (Ommatophoca rossii)
Northern elephant seal (Mirounga angustirostris)
Southern elephant seal (Mirounga leonina)
Hawaiian monk seal (Neomonachus schauinslandi) Mediterranean monk seal (Monachus monachus)

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Knowledge repository

Seals belong to the order Carnivora. This is a special group of animals within the class Mammalia (mammals). Carnivora are mammals that are specialized in eating other animals, better known as carnivores.

See also

  • Zeeleeuw

  • Wasbeer

  • Sneeuwluipaard

Did you know...

When scientists study the evolution of certain species, it helps to divide them into categories. This categorization is called classification or taxonomy. For example, the scientific classification of the common seal (Phoca vitulina) is this:

Domain (Eukarya) -> Kingdom (Animalia) -> Phylum (Chordata) -> Class (Mammalia) -> Order (Carnivora) -> Family (Phocidae) -> Genus (Phoca) -> Species (Phoca vitulina)

Ancestors of the Carnivora

Millions of years ago, dinosaurs were the dominant animals on Earth. During that time there were mammals, but their fossil records showed that they were the size of tiny shrews. They specialized in living nocturnal lives, a feature that mammals still have to this day.

The first mammals ate insects in order to survive. After the massive extinction of the dinosaurs there was room for mammals to expand and evolve. This resulted in various mammals with all kinds of specializations. This gave rise to the specialization of eating meat; the birth of the order Carnivora.

Miacis Congitus

The oldest Carnivora fossils that have been found are from the Miacis congnitus. These predators somewhat resembled modern civets with their long, agile bodies and long tails. Miacis most likely lived in trees and ate small invertebrates, reptiles and birds. They lived during the late Paleocene and early Eocene epoch (62 – 34 million years ago). All modern Carnivora descend from these prehistoric animals, including seals.

Phocidae: the pinnipeds

Do you want to learn more about the evolution of the seal family? Check out our page on the evolutionary history of the Phocidae.

How do you recognize Carnivora?

They are mammals

All the Carnivora are mammals (Mammalia). This means that they nourish their offspring with milk.

They are viviparous

All Carnivora are 'viviparous’. This means that they develop their offspring in the placenta inside the uterus of their mother and give birth to "living” young.

Large skull

Carnivora have a relatively large skull with a large cranium. They have large brains and are considered to be intelligent animals. In general Carnivora have somewhat rounder heads than other mammals. These rounder heads ensure that their eyes are well positioned for hunting other animals.

Position of the eyes

The shape and position of their eyes are striking. Carnivora have relatively large eyes that are close together. Because both their eyes face forward, Carnivora such as seals have a very good depth perception. This is extremely important for carnivores. After all, in order to hunt other animals they must be able to see exactly how far away their prey is.

Sharp teeth

But the easiest way to recognize Carnivora is by their teeth. Because Carnivora eat meat, their teeth have been adapted to killing and eating animals. They have large, pointed canine teeth and sharp, serrated molars. This helps carnivores to cut muscles and tendons and even crack bones.

Zelfs zeehondenpups hebben al scherpe tanden

Foto: Martina Zilian

Did you know...

That Carnivora does not have the same meaning as carnivores?

Carnivora and carnivores

Thes two words can be confusing, because they seem very similar. They do not have the same definition.

The Carnivora are an order of mammals that are adapted to eating meat. To survive, they must kill animals or find carcasses. When talking about Carnivora we are talking about the classification of carnivores in relation to other mammals. Examples are wolves, lions and seals.

But these mammals are not the only animals that eat meat. If an animal's diet consists mainly of meat, we are talking about a carnivore diet. Birds of prey, crocodiles, Tyrannosaurus rex and seals are therefore all carnivores.

How can you live on meat alone?

To eat and digest high-fiber plants (such as grass) you need an extremely long and complex digestive system. This is because plants are very difficult to digest and that take a lot of time. They also have very few nutrients, therefore herbivores are almost constantly eating.

Meat, on the other hand, is easier to digest. Carnivora therefore have very short, simple digestive systems. Meat is also very rich in energy and protein, so they can spend less time eating compared to herbivores.

But depending on energy alone is not enough to survive. As you may know, animals also need vitamins, fats and minerals. Therefore, Carnivora not only eat the meat from their prey, but also their organs, fat, skin and sometimes even their bones. It contains all the nutrients an animal could wish for. Seals, for example, swallow many of their prey whole. Skeleton and everything else.

Did you know...

That the seal is the largest predator of the Netherlands?

Do Carnivora only eat meat?

Not always. There are species that eat almost exclusively meat, but there are also Carnivora with a mixed diet. Yet we still call them carnivores, because their bodies are mainly specialized in eating and digesting meat.


If the diet of a Carnivora consists of at least 70 percent meat, we call them hypercarnivores. They cannot digest other foods properly or at all. Seals and the other Pinnipedia are hypercarnivores. They only eat meat, so no plant materials.


There are also Carnivora with a mixed diet. If they consume meat for less than 30 percent of their diet, we call them hypocarnivores. They often eat mushrooms and fruit in addition to meat. These contain little fiber and a lot of sugars and proteins, so they are quite easy to digest for Carnivora. Brown bears (Ursus arctos) are known hypocarnivores. For their hibernation they have to build up a lot of reserves. That is the reason why they eat everything they come across.


In between the hyper- and hypocarnivores you have so-called mesocarnivores. Their diet consists of 50-70 percent meat. Many canids are mesocarnivores. They mainly eat meat, but they can also digest certain plants as long as they don't contain too much fiber.

Did you know...

The giant panda (Ailuropoda melanoleuca) is a bear species from the order Carnivora that eats almost exclusively high-fiber bamboo? If you look closely at the teeth of a giant panda, you will see that the serrated molars are a lot flatter than those of other Carnivora. This helps the panda to crush these woody plants.

Families in the order Carnivora

Within the order Carnivora there are 16 families and 296 species. The families are divided into two suborders : the Caniformia and the Feliformia.


The suborder Caniformia consists of nine families:


The suborder Feliformia consists of seven families:

  • Felidae (felines)
  • Eupleridae (Madagascarian carnivorians)
  • Herpestidae (mongooses)
  • Hyaenidae (hyenas)
  • Nandiniidae (African palm civets)
  • Prionodontidae (Asiatic linsangs)
  • Viverridae (civets and genets)

Did you know...

That the largest species within the order of Carnivora is the southern elephant seal (Mirounga leonina)? These seals can be more than 6 meters long and weigh 3,700 kilos!

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Seals in fresh water

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As the name suggests, seals live in salt water. Nevertheless, it sometimes happens that we receive a report of a seal in an area with fresh water. Such a report often comes in with the question: "Isn't that a bad thing?"

Luckily, that is not the case. A seal mainly needs fish to survive and they are also in fresh water. There are reports of seals in the Utrecht canal, the Schildmeer and in the major rivers. Seals are smart. They usually find their way back. 

See also

  • Zeehond in zoet water

  • Zeehonden in De Onlanden, Drenthe

Influence of fresh water on health

Seals don't necessarily need to be in salt water to survive. Unlike other marine animals, they are not very sensitive to the salinity of water. It is true that after a while their eyes can get irritated. Apart from that, seals can survive in fresh water for a while. As long as there's plenty of fish to hunt.

Reports of seals in fresh water

The two most recent cases reported to us are seals Hulcky and Thor. We took Hulcky from the Veluwemeer when it turned out that she was suffering from a lungworm infection. She was taken in at the Sealcentre and eventually released back into the sea.

Seal Thor was just seen in the fresh water of De Onlanden after we had caught and released him. Thanks to its tag and its spots on fur, we were able to recognize that it was this specific seal. After a while he found his way back on his own.

Since March 2012 we have had more reports:

  • March 2012: common seal near Goudswaard, South Holland.
  • December 2012: common seal in the Biesbosch.
  • December 2012: common seal in the Schildmeer, Groningen. The animal seemed to swim back and forth between the Schildmeer and Farmsum.
  • January 2013: common seal in the Meuse near Dreumel.
  • April 2013: common seal in river Hunze in Drenthe, moved on by itself.
  • December 2013: common seal in the Schildmeer, Groningen. Unknown if it was the same seal. The animal was seen with fish in its mouth.
  • August 2015: ringed seal in Utrecht canals, collected at seal sanctuary A Seal in Stellendam.
  • October 2015: common seal in Biesbosch.
  • March 2016: common seal in the Maasplassen near the Weerd in Roermond.
  • November 2016: common seal “Hulcky” spotted in Veluwemeer.
  • August 2021: common seal Thor spotted first in Peizerdiep, later in De Onlanden.

Seal species in freshwater

The seal species that occur in the Netherlands all live in salt water. But there are seal species in the world that actually live in fresh water. There are five in total. These populations probably became separated from the sea long ago.

It concerns the following five species:

Lake Iliamna, Alaska Phoca vitulina mellonaea freshwater subspecies of the common seal.
Lake Baikal, Siberiia Pusa sibirica, Baikal seal , a separate species. Also the smallest seal species.
Lake Ladoga, Russia Pusa hispida ladogensis, freshwater subspecies of the ringed seal.
Lake Saimaa, Finland Pusa hispida saimensis, freshwater subspecies of the ringed seal.
Lac des loups marins, Quebec Phoca vitulina mellonae, a freshwater subspecies of the common seal.

Bron: Van Lanen, 2012

Were there more seals in fresh water in the past?

It is believed that more seals visited the Dutch inland waterways in the past, but that has decreased in the last century.

The construction of flood defenses in all major rivers in the Netherlands has probably contributed to this. Because of all the locks, dikes and scuppers, it is quite difficult for a seal to find an easy way to inland. Sometimes seals find a way, but they get lost along the way and can't find their way back. If those animals do not receive enough food, then action must be taken to help them return to the sea. In other cases, seals seem to know very well how to move between sea and lake.

The seal that has already been seen a number of times in the Schildmeer, for example. It was first seen at Farmsum, then at Schildmeer. To get to that lake, the seal first had to swim through a channel to the south, and then swim into a small drainage channel. When the animal was later spotted again at Farmsum, it seemed that the animal knew what it was doing. A year later another seal was seen in the Schildmeer.

It has been said by several people that the seals may be able to learn how locks work.

Water quality deteriorating: less fish means fewer seals?

Due to industry, agriculture and waste water from households, the water quality has deteriorated rapidly in the last century. Due to the deteriorating quality of the freshwater ecosystem, many freshwater bodies became uninhabitable for certain fish species. As a result, diversity in many freshwater bodies also declined sharply. As mentioned before, seals need a lot of fish to survive. If that fish is not there, a seal will not easily choose to hang out in such an area.

Improving water quality + opening rivers for more fish: more seals in the future?

In the past few years, a lot of work has been done to improve the water quality. And that will continue. Various projects are also being developed to increase the species richness in Dutch waters. For example, by leaving the sea locks ajar and creating fish passages in dikes, it is hoped that migrating fish species will return to the Dutch interior. With this return, they hope that the ecosystem will improve.

Perhaps with this improvement we will encounter more seals in Lake Veluwe in a few years? 

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Zeehond met melanisme


Knowledge repository

Have you ever seen a black seal? That would be very special because black coloured seals are quite rare. These seals have melanism, which makes them completely black from head to toe. In this article you can read all about what melanism is and learn what a melanistic seal looks like.

See also

  • Melanism

  • Melanistische zeehond

  • Zwarte zeehond

  • Melanisme is het tegenovergestelde van albinisme

What is melanism?

Having melanism means too much of the pigment melanin is produced. This is caused by an abnormality in genes. The pigment melanin is found in humans and animals in the skin, eyes and hair. The more melanin you have, the darker your skin color, eyes and hair are.

The amount of melanin you naturally have can vary per person/animal, but it is quite unique to produce both an excess of melanin (melanism) and no melanin at all (albinism).

Black seals in the Netherlands

Seals that are completely black are called melanistic. These seals have completely black fur and black nails. As far as we know, we have taken care of at least 10 melanistic seals in Pieterburen.

The most recent one came to us in January ,2016. We see that seals with melanism behave the same as all other seals and are no more sensitive or weaker than the rest. We, therefore release seals with melanism back into the sea with confidence.

Watch this video

Curious what a melanistic seal looks like? Then watch the short video below of seal Pepper at our Sealcentre:

Melanism is rare

It is almost never the case that you see a completely black seal. It is difficult to say exactly how little melanism occurs in the seals in the sea. We have only seen melanism in grey seals, not in common seals (yet).

Zwarte zeehond - melanisme

Melanism in other animals

Melanism does not only occur in seals. There are also melanistic foxes, chickens, frogs, guinea pigs and house cats. A very well-known example of a melanistic animal is the black panther.

Did you know...

The black panther is not a separate animal species, but is a collective name for all melanistic felines?

In most cases, the completely black animals are in the minority in felines, but in the feline jaguarundi about 80 percent are melanistic animals [1].

Advantages or disadvantages of melanism

Melanism can be beneficial and/or disadvantageous for animal species and individual. For scientists, melanism is an interesting topic. If animals can differ in appearance, does black fur have certain advantages or disadvantages? It often happens that the colour and/or pattern of the coat matches the colours of the environment.

White pups

Think, for example, of a seal pup with a white coat lying on the ice in the North Pole. This way he is less noticeable to predators who would love to eat the pup. On the other hand, it also works to their advantage for predators. A polar bear is colored white for the same reason, so that seals are less likely to see it coming when it goes to hunt them. If you have the color of your environment, it works like a protective color: you stand out less which increases your chance of survival.

For that reason, melanism should not occur in the North Pole. According to this theory, black animals would stand out in such a snow-white environment. The result: they are eaten earlier and therefore even rarer. The fewer black animals there are, the less likely they are to reproduce and pass on their genes that provide the black coat.

Melanistic advantage in the Netherlands

For a seal in the Netherlands, a black fur has no advantage or disadvantage in any case. This is because the seal is at the very top of the Wadden Sea food chain. That is so because there is no other animal that eats the seal.

Also, there are no other reasons that can cause melanistic seals to increase or decrease. The number of black seals in the seal population depends entirely on how many of these melanistic seals reproduce.

Did you know...

Animals can change colour when their environment changes? A special and well-known example of this is the pepper-and-salt butterfly [2].

Adapt to the environment

The name says it all: the pepper-and-salt butterfly was white with black. But in the 19th century (1800-1899) completely black specimens of this species suddenly appeared in England. These black butterflies are very noticeable when they were on a light tree trunk. Why did more black butterflies appear at that time if that seems to be a disadvantage?

In this century, the Industrial Revolution was in full swing. Due to the large spread of factories and machines, there was a lot of air pollution. The black soot in the air precipitated, turning buildings and trees black. Suddenly you didn't stand out as a black butterfly. In cities, the ratio turned around. Black butterflies of the pepper-and-salt butterfly were mainly found there, while the light variant occurred in nature reserves.

Depending on various factors, such as your environment, melanism can therefore work in your favor! Can you think of in which nature reserves a black seal has an advantage compared to a grey seal?


  2. Majerus, Michael E. N. (2008). “Industrial Melanism in the Peppered Moth, Biston betularia: An Excellent Teaching Example of Darwinian Evolution in Action”.Evolution: Education and Outreach 2 (1): 63–74. doi:10.1007/s12052-008-0107-y

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You have probably heard of the word 'albino'. Most likely, you think of white rats or white rabbits with red eyes. There are also people with albinism. But did you know that there are also albino seals? In this article you can read about what albinism means and what it looks like in seals.

See also

What is albinism?

Albinism, the opposite of melanis , is a rare disorder in which little or no pigment melanin is made at all [1]. Without pigment, the skin color, hair and eyes look different. Usually, albino animals have red eyes and white fur, but that is not always the case. There are multiple forms of albinism with differences in hair, skin and eye color.

As far as we know, we have treated at least seven albino seals in our Sealcentre. Seal Sealas the most recent case of this (2017). 

Partially albino?

We have had different forms of albino seals in the sanctuary. One of the variations is called ocular albinism. Seal Sealas is a good example of this. In ocular albinism, it is mainly the eyes that lack the pigment melanin. That is why these albino seals have red eyes, but no white fur, for example. The fur is lighter in color than that of the congeners.

Albino zeehond in Pieterburen

Albino seals are sensitive to light

Albino seals are more sensitive to light and therefore behave differently. We saw the seal Sealas close her eyes above water to protect her eyes from the sun (see photo 4). The sun is dangerous for the sensitive skin and eyes of albino animals. It doesn't matter much for a seal to hunt, because seals hunt underwater and their whiskers are more important than their eyes. But above water, they are more at risk of sun damage.


There is also leucism. In leucism, the pigment melanin is produced, but it is not expressed in the coat or skin. This means that only the coat is lighter in color and the eyes are normally colored. The eyes of these seals are in any case less sensitive to the sun than those of albino seals. In 2009, we captured a leucistic seal, appropriately named Golden Queen.

Leucisme bij zeehonden

Watch this video

Would you like to see what an albino seal looks like? Then watch the video below of seal Sealas at our centre:

1. Fertl, D., & Rosel, P. E. (2009). Albinism. Encyclopedia of Marine Mammals, 24–26. doi:10.1016/b978-0-12-373553-9.00006-7 

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Pinnipeds (pinnipedia)

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The pinnipeds (Pinnipedia) are a group of marine mammals comprising of three families: the seals (Phocidae), the sea lions (Otariidae) and the walrus (Odobenidae). They are all members of the order Carnivora, the carnivorous mammals. 

This order can be divided into two sub-orders: the felines (Feliformia) and the canids (Caniformia). Pinnipeds belong to the latter group: the canids. They share an ancestor with the marten families (Mustelidae). This ancestor will have looked a bit like an otter.

See also

  • Zeehond in zee

  • Zeeleeuw op het strand

  • Grijze zeehonden op het strand

Did you know...

The paws of seals are called flippers?

What do pinnipeds look like?

Pinnipeds all have a long body with large chest and narrow flared abdomen. Their main characteristic is the shape of the legs. This is also where they get their name from. The legs of pinnipeds are short with very long fingers and toes. The space between the fingers and toes are webbed, making their legs look more like fins. We also call their legs flippers.

Because they spend much of their lives in cold seas. Their skin is also covered with a short, dense fur. This keeps pinnipeds warm. They can put that to good use in cold water or in the icy areas where they sometimes live. 

How do pinnipeds move?

Some marine mammals, such as whales, only live in the water. Pinnipeds are different. They live (largely) partly in the water and partly on land. They all have their own way of moving around, both on land and in the water.

Mostly pinnipeds use the land to rest, shed hair, mate, and raise pups. But their life mainly takes place in the water. Most pinnipeds can spend days in the water to hunt and eat. They can even sleep in the water. Some species also mate in the water.

Because they live this way, we call pinnipeds semi-aquatic. Literally it means half in the water.

Under water

All pinnipeds are most agile underwater. Their build allows them to move much faster there. This does come in handy, as their food is all found in the water!

Seals (Phocidae) keep their back flippers against each other while swimming . They then move their abdomen back and forth to push through the water. When you see a seal swimming, they make a bit of the same movement as a fish. Their front flippers are mainly for steering, not for speed.

Walruses under water
Walruses (Odobenidae) swim in the same way as seals, so by moving their back flippers back and forth. They use their front flippers to steer and paddle.

Sea lions under water
Sea lions (Otariidae) have a different way to swim. They have much longer and stronger front flippers than seals, and use them to gain speed. They move the front flippers up and down, pushing themselves through the water. It resembles the way a bird flies through the sky. Sea lions are a lot more agile than seals and walruses, but can swim for less time.

On land

Because their bodies are well adapted for life in the water, pinnipeds on land are much less agile. But there is a difference between the families in how easily they move on land.

Seals on land
Seals cannot fold their rear flippers forward. Due to the construction of their bodies, they always point backwards. Instead of walking, they move more like a caterpillar. They lift their backs up, making their rears stick out a bit. Then they push themselves off with the back of their body. By doing this often and in quick succession, it looks like the seal is bouncing a bit. 

Walruses on land
The walrus (Odobenidae) can fold the back flippers forward. But their bodies are too big and heavy to lift off the ground. Instead of actually walking, they slide across the land on their stomachs by leaning on their flippers.

Sea lions on land
Sea lions (Otariidae) are the most mobile of the three families on land. Their front and rear flippers lift their entire body off the ground (folding the rear flippers forward under their bodies). For example, sea lions can walk on all fours, and even gallop!

How do pinnipeds live?


The sea is where pinnipeds get their food from. They hunt all kinds of animals there. Most pinnipeds are opportunistic hunters.. This means they will eat pretty much anything they can get their hands on. Generally, they go for fish, squid, shellfish that they can swallow whole. But sometimes there will be a few that will also go after larger animals such as seabirds and small marine mammals.

In groups or alone?

Most pinnipeds are very social. Outside the mating season, walruses and sea lions often lie together in huge groups on land. Large groups of the same species are called colonies. Sea lions also sometimes hunt in smaller groups. They then work together to herd schools of fish together.

Walruses mainly eat shellfish that live in the seabed. They will stick together in groups while feeding, but do not need each other to hunt.

Seals vary by species whether they live in groups or alone, but most seal species hunt alone.

Mating season

Pinnipeds gather in large numbers on land or ice during the mating season to mate. They usually do this with several partners. Pinnipeds are therefore polygamous. In sea lions, walruses and some seal species, a male will have a group of several females around him. Such a group is called a harem. The male defends his harem against other males and then has the right to mate with all those females.


Pinnipeds have one pup at a time. Twins are extremely rare. If they did, twins would in most cases not survive. How pinnipeds give birth and care for their pups varies by family and by species, but it is always the females who raise the pups. Males have nothing to do with this.

Sea lions and seals get a pup almost every year. Walruses care for their pups much longer. They get one pup every 4-5 years.

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