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Author: Alexander Eberlei

World Heritage Centre Wadden Sea


We hebben feestelijk nieuws! In 2023 start de bouw van Werelderfgoedcentrum Waddenzee. In 2025 verhuizen we naar Lauwersoog om te werken aan een bredere missie.

See also

  • World Heritage Centre Wadden Sea

  • Werelderfgoedcentrum in haven Lauwersoog

  • Dak Werelderfgoedcentrum Waddenzee

In 2023 begint de bouw van het nieuwe Werelderfgoedcentrum Waddenzee in Lauwersoog, dat we in 2025 feestelijk zullen openen. Een spiksplinternieuw gebouw, waar wij niet alleen ons werk mogen voortzetten, maar ook mogen uitbreiden. In 50 jaar hebben we veel bereikt voor de zeehond. Maar we weten ook zoveel meer over haar leefomgeving, het UNESCO Werelderfgoed de Waddenzee. De Waddenzee zien we als graadmeter voor het totale ecosysteem, waar ook wij als mens deel van uit maken. 

Een inkijkje in Werelderfgoedcentrum Waddenzee

UNESCO World Heritage the Wadden Sea

The Wadden Sea World Heritage Site is the largest continuous tidal area in the world. A unique area that is the only one of our country to have UNESCO Natural World Heritage status. In the Wadden area, you can experience at first hand how valuable, complex and challenging man's relationship with nature is. We will take our unique working method, knowledge and 50 years of experience in seal care and rehabilitation to Lauwersoog. In doing so, we will build a new and better awareness of the relationship between man and nature. And we invite you to work on this relationship with us. Curious? On the World Heritage Centre Wadden Sea project website you can learn more about the new centre and get a taste of the atmosphere.

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UNESCO World Heritage the Wadden Sea

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Common seal

Knowledge repository

Scientific name: Phoca vitulina
Family: Phocidae
Size: male: 1.60 meter; female: 1.50 meter
Weight: male: 87 kilo; female: 65 kilo
Habitat: entire Northern hemisphere
Endangered status: not endangered

See also

  • Gewone zeehond moeder en pups

  • Gewone zeehond moeder en pups

  • Gewone zeehonden in de Waddenzee

  • Zeehonden rusten op zandbank

"The other name of this species reveals where it is common: harbour seal"

External characteristics of the common seal

The common seal has a fairly round head and a blunt snout. The nostrils are a v-shape. Their face looks a bit like a cat. Their fur is very short, smooth and has a light brown or grey colour with dark spots on it. The spot pattern is unique for each seal. You can think of it as a human fingerprint.

The common seal is relatively small compared to other seal species. In the Netherlands, the males can reach an average length of 160 cm and weigh 87 kg. The females are on average 148 cm long and weigh 65 kg. The average size of the common seal varies by region.

In Japan, for example, there is a common seal population that is getting a lot bigger. Namely 186 cm long and between 87 and 170 kg for the males and 169 cm long and between 65 and 142 kg for the females.

In the wild, common seals live about 20-30 years. In captivity, they can grow even older. For example, common seal “Piet” spent his entire life in Ecomare on Texel, until he died in 2009 at the age of 41.

Gender differences

There are few differences between males and females. This is because their coats are the same colour and they are almost the same size.

Did you know...

Harbour seals regularly swim up in rivers and can stay there for a long time before returning to the sea. In 2022, for example, a common seal may have lived for a month in a spur of the Lek in Gelderland.

Distribution and status

The English name of the common seal is "harbour seal". That says a lot about where this species occurs. The common seal lives quite close to the coast and can therefore sometimes be seen in harbours.

The habitat of the common seal is spread throughout the Northern hemisphere, but they always stay close to the coast.

The common seal is not considered to be endangered. According to IUCN, the international conservation organisation, the population worldwide consists of about 600,000 common seals. That number is large enough and ensures that the world population is stable. This means that no intervention is necessary for the species to continue to exist.

The common seal in the Netherlands

Every year, about 8,000 common seals are counted in the Netherlands and scientists estimate that about 10,000 common seals use Dutch waters.

Did you know...

That there are two types of seals living in the Netherlands? The common seal is one of them. Do you know the other? You can find the answer here.

The largest population of seals live in the Wadden area. There they use the sand banks to rest, reproduce and give birth to pups. They hunt and eat in the North Sea. Common seals also live in Zeeland, but a lot less than in the Wadden area. There, they mainly live on sandbanks in the Oosterschelde and along the North Sea coast.

In recent years, the number of seals that are counted annually in the Netherlands and in the entire Wadden Sea has been more or less the same. In the Netherlands, it was quite recently that the population of common seals was in danger. Until 1962 there was still a lot of hunting of the common seal. There have also been outbreaks of the seal virus (Phocine Distemper Virus) in 1988 and 2002 in which half the population died. In both cases, the population quickly recovered. Also with the help of shelters along the entire Wadden Sea coast.

Diet and foraging

The common seal is an opportunistic hunter. It means that this species is flexible when it comes to where and what kind of prey it hunts. This allows them to look for food close to their resting place. But sometimes seals swim miles away from their resting spot, either along the coastline or further out to sea to hunt. They can dive to depths of more than 500 meters for food.

In addition, seals do not hunt one particular type of fish, squid or shrimp. Their diet varies greatly depending on the region and season. In the Netherlands they mainly hunt small to medium-sized fish species, such as cod, hake, mackerel, herring, sardines, allis shad, capelin, sculpin, various sandeels, flatfish and salmon species. In addition to those fish species, the common seal also often hunts squid and crustaceans such as shrimps and crabs.

Did you know...

That the common can hunt effectively in poor visual conditions, for example in dark murky waters?

The common seal, like many other seal species, uses its whiskers to find prey. Their specially shaped whiskers are super sensitive and can detect the smallest vibrations. Due to their irregularity and wavy shape (unlike the smooth whiskers you've probably seen on a cat or dog), the whiskers are so streamlined that they glide smoothly through the water.

Thanks to research we know that the common seal can still feel the vibrations in the water of a fish that swam away a while before. So they use their whiskers in a similar way that whales and dolphins use echolocation: by picking up vibrations of sound waves in the water. With seals it is all about movements in the water.

Common seal behavior

Common seals are solitary animals. That means that they prefer to be alone. On land, seals may lie in groups, because then it is more likely that one of the seals will see predators approaching. They also want to remain close to the water's edge, so that they can quickly flee when disturbed. They often do this at the slightest threat.

Have you ever seen a seal 'wave'? They are not doing this to say hello. On the contrary: it is a threat. With this waving, the seal means that if the threat approaches, it risks being scratched with the long nails on the front flipper.

Towards the end of summer/beginning of autumn, common seals are more often found on land. They lie together in larger groups. Seals moult two to three months after the mating season: then they shed their old fur for a new coat.

Reproduction in common seals

Mating behaviour

Common seals mate in the water, around the time the pups are weaned (late summer). Males will compete with each other for females. They do this by making noise, diving and fighting with each other. Males often mate with multiple females.

Diapause and pregnancy

As with all seal species, the fertilization is followed with an embryonic diapause. A diapause means that there is a time between fertilization and the actual pregnancy. In the common seal, the diapause lasts up to 2.5 months. After this, the fertilized egg implants in the uterus. The total pregnancy (including diapause) lasts 10.5 months.

In most seal species, more than 85% of females become pregnant each year. Once the common seals reach sexual maturity, they remain reproductive throughout their entire lives.

Birth and nursing period

Common seal pups are born on land in the summer. These pups can go into the water almost immediately after birth, which is often necessary when the tide comes in. In the water, pups often hang onto their mother’s back to hitch a ride. Common seal birthing season in the Netherlands usually lasts from June to July.

Did you know...

That pups from the common seals grow 17 kilos in the first 4 weeks of their life?

The pup are nursed by their mother for 4 weeks with milk containing approximately 40% fat. The puppies then gain weight quickly. They grow from 8 kg at birth to 25 kg in 4 weeks. After this they are completely abandoned and they have to learn to hunt on their own. Fortunately the instinct of young seals to learn this on their own is very strong.

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Knowledge repository

If you take a close look at a particular natural area and want to know how everything in it lives together, we talk about an ecosystem. The Wadden Sea is an example of one. What an ecosystem is, what lives in it and what unmistakable elements such as a food web and balance are; you can find out on this page.

See also

  • zeekraal is ook onderdeel van het ecosysteem van de Waddenzee

What is a ecosystem?

An ecosystem is a natural system with all the organisms living in it. This can be as big as a forest. Or you zoom in on something small like the pond in your garden. Everything inside is interrelated in some way. 

What lives inside an ecosystem?

An ecosystem consists of all living and non-living parts in that area. In biology, we call these the biotic and abiotic factors. The biotic factors are all the living things in that area and what influence they have on each other. This includes all organisms such as animals, plants, fungi and bacteria found in that particular ecosystem.

So, besides everything that is alive, an ecosystem also consists of non-living parts. They affect all those living things. These are the abiotic factors. Here you can think of:

  • water
  • sunlight
  • air
  • soil
  • temperature

The Wadden Sea

You can think of the Wadden Sea as an ecosystem! The Wadden Sea refers to the sea between the coast of the Netherlands, Germany and Denmark and its Wadden Islands. Among other things, sea life , the seabed, seawater and sea air are related to each other.

Eat or be eaten

Everything that lives needs energy to stay alive. To get energy, you need to eat. That can be plants, animals or a combination of them. In the Wadden Sea, there are hundreds of species eating or being eaten by each other. You are either the prey or the prey animal. To visualise this, you can make a food web maken.


Everything within such a food web is directly or indirectly related to each other. If one of the species disappears then it affects the whole ecosystem. Take plankton, for example. Plankton is not food for a seal. But if the plankton goes bad, eventually the seal will also go bad. Here's the thing: the seal eats fish, the fish eat shrimps and the shrimps eat plankton. So the presence of plankton has an impact on the entire food chain. If plankton goes bad, the entire food chain can collapse. It is important to keep an ecosystem in balance.

De Waddenzee heeft een complex maar ook kwetsbaar ecosysteem. Er zijn verschillende bedreigingen waar de Waddenzee mee te maken heeft. Veel van die bedreigingen komen door de mens.

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Pinnipeds (pinnipedia)

Knowledge repository

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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