Author: Alexander Eberlei

Werelderfgoedcentrum Waddenzee

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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

  • Werelderfgoedcentrum Waddenzee

  • 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 Werelderfgoed de Waddenzee

Het Werelderfgoed Waddenzee is het grootste aaneengesloten getijdengebied van de wereld. Een uniek gebied dat als enige van ons land de status van UNESCO Natuurlijk Werelderfgoed heeft. In het Waddengebied kun je bij uitstek ervaren hoe waardevol, complex en uitdagend de relatie van de mens met de natuur is. Onze unieke werkwijze, kennis en 50 jaar aan ervaring in de zeehondenopvang en -zorg nemen we mee naar Lauwersoog. Daarmee gaan we bouwen aan een nieuwe en betere bewustwording van de relatie tussen mens en natuur. En we nodigen je uit om samen met ons aan deze relatie te werken. Nieuwsgierig? Op de projectwebsite van het Werelderfgoedcentrum Waddenzee leer je meer over het nieuwe centrum en kun je alvast een beetje van de sfeer proeven.


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UNESCO Werelderfgoed de Waddenzee

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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 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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Ecosystem

Knowledge repository

Als je een bepaald natuurgebied onder de loep neemt en wilt weten hoe alles daarin samenleeft, dan spreken we over een ecosysteem. De Waddenzee is een voorbeeld van een ecosysteem. Wat een ecosysteem is, wat erin leeft en wat onmiskenbare elementen zijn zoals een voedselweb en balans; dat lees je op deze pagina.

See also

Wat is een ecosysteem?

Een ecosysteem is een natuurlijk systeem met alle organismen die in dat systeem leven. Zo’n ecosysteem kan zo groot zijn als een bos. Of je zoomt in op iets kleins zoals de vijver in jouw tuin. Alles binnenin zo’n ecosysteem hangt op een bepaalde manier met elkaar samen. 

Wat leeft er in een ecosysteem?

Een ecosysteem bestaat uit alle levende en niet-levende onderdelen in dat gebied. In de biologie noemen we dat de biotische and abiotische factoren. De biotische factoren zijn alle levende wezens in dat gebied en welke invloed ze op elkaar hebben. Daar horen alle organismen zoals dieren, planten, schimmels en bacteriën bij die in dat specifieke ecosysteem voorkomen.

Naast alles dat leeft bestaat een ecosysteem dus ook uit niet-levende onderdelen. Zij hebben invloed op al die de levende wezens. Dit zijn de abiotische factoren. Hierbij kun je denken aan:

  • water
  • zonlicht
  • lucht
  • bodem
  • temperatuur

De Waddenzee is een ecosysteem

De Waddenzee kun je beschouwen als een ecosysteem! Met de Waddenzee wordt de zee tussen de kust van Nederland, Duitsland en Denemarken en de bijbehorende Waddeneilanden bedoeld. Zo staan onder andere alle zeebewoners , de zeebodem, het zeewater en de zeelucht in relatie met elkaar.

Eten en gegeten worden

Alles wat leeft heeft energie nodig om in leven te blijven. Om aan energie te komen moet je eten. Dat kunnen planten, dieren of een combinatie ervan zijn. In de Waddenzee zijn honderden soorten die elkaar opeten of opgegeten worden. Je bent of de prooi of het prooidier. Om dit in beeld te brengen kun je een voedselweb  maken.

Balans in een ecosysteem

Alles binnen zo’n voedselweb heeft direct of indirect met elkaar te maken.  Als een van de soorten wegvalt dan heeft dat invloed op het hele ecosysteem. Neem bijvoorbeeld plankton. Plankton is geen voedsel voor een zeehond. Maar als het slecht gaat met het plankton, dan zal het uiteindelijk ook slecht gaan met de zeehond. Dat zit zo: de zeehond eet vissen op, de vissen eten garnalen op en de garnalen eten plankton op. De aanwezigheid van plankton heeft dus impact op de gehele voedselketen. Als het slecht gaat met plankton, kan de volledige voedselketen instorten. Het is belangrijk dat een ecosysteem in balans blijft.

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. Wij vertellen je hier meer over op deze pagina. 


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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?

Diet

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.

Pups

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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