Author: Judith van der Wal

Sealcentre Pieterburen rehabilitates first pup of the summer


Sealcentre Pieterburen has taken in the first common seal pup of this summer. The animal had been found by bystanders. They saw no mother around and thought it needed help. The Sealcentre would like to remind everyone that it is forbidden to touch seals except for trained seal guards. This is the only way operational seal centres can pursue the policy according to the Seal Agreement.

See also

On Friday afternoon 19 May, bystanders came across a common seal pup near Sint Jacobiparochie. This one was lying alone in the mud with no mother around. As it was a young animal, the bystanders assumed it could not take care of itself. Therefore, they decided to take the pup with them. They then called Sealcentre Pieterburen to seek professional help.

Acting on Seal Agreement

While the Sealcentre understands the good intentions, this is not the desired course of action. Picking up and helping seals yourself is contrary to the policy set out in the 2020 Seal Agreement . This agreement puts the focus on observing wild seals before deciding whether rehabilitation is needed. Therefore, there are trained seal guards who monitor reported animals and relay all necessary information to the seal centre for which they operate. The centre then decides whether to take a seal to the centre. This way gives the most certainty that rehabilitation was the right choice. If the public decides to intervene themselves, it becomes impossible for seal centres to pursue this policy.

Pup Crista is named after the hooded seal

A seal mother can leave her pup alone for up to eight hours, without anything needing to be wrong. Unfortunately, the pup was too severely disturbed to be returned to the area she came from. It was therefore decided to take the animal in. Once in Pieterburen, she was given the name Crista. This name is derived from the scientific name for the hooded seal, Cystophora cristata. A species of seal not normally found in the Netherlands, but which gave birth to a young on Vlieland in March this year. A unique event and therefore the inspiration for the name of the first pup this summer. She was probably at most six days old and born prematurely. This makes her still very weak and she is therefore closely monitored by the vets and intensively cared for. The pup can currently be admired from a safe distance at the Seal Centre.

Pup season in full swing

The first pup marks the start of the common seal's birthing season. Many pups will be born in the coming period and receive milk from their mothers for about three to four weeks. All seal centres and seal guards therefore continue to appeal to keep as much distance as possible from seals at this time in particular, so that mother and pup can pass this suckling period undisturbed. If people still have doubts about the health of an animal, they should report it via 144 (available 24 hours a day). After being reported, seals are observed for at least 24 hours, as research shows that many seals can handle themselves well - provided they get enough rest during those 24 hours. Seal guards can ensure this by cordoning off areas and informing the public, while staying in touch with seal centres about the animal's condition.

Continue reading

Lees verder

Pox virus in seals

Knowledge repository

The pox virus occurs in seals. A virus in which seals get firm skin nodules on the head, neck and flippers, among other things. The pox usually goes away on its own. At the Sealcentre we do everything we can to prevent any contamination.

See also

  • Zeehond - moeder en pup zogen

Pox virus

The pox virus in seals is a different species than the (chicken)pox virus that occurs in humans and belongs to the parapoxvirus family (1). But seals can transmit this virus to humans (2). To minimize the chance of this, our seal caretakers wear protective clothing, gloves and face masks.

Symptoms of pox

The name of the virus refers to one of its most obvious features: pox. Pox are small firm skin nodules. They are between 1 and 3 centimeters in size and they can be all over the body (3). In seals we often see them on the head, neck and flippers.

How do seals get pox?

Pox is a regular occurrence in seals in our sanctuary. This is because the disease is influenced by stress. It is unclear how seals contract the virus, but the seal already carries the virus before it is taken into care. We will only know this if the virus causes visible symptoms. If the seal is taken care of and gets stressed, the virus can 'express' itself, which means that after a while in the shelter, the seal will develop small firm skin nodules on its skin.


Pox is not contagious until it opens and bleeds out. To prevent a seal with the virus from infecting another seal, seals with pox are staying at the Sealcentre. They should not be released until the pox has disappeared, so that wild seals do not become infected.

Treating pox

Usually no treatment is needed. The pox goes away on its own over time, usually around 4-6 weeks. If a seal suffers from the pox virus, we can only treat the sympotms. If the seal is in pain, we administer painkillers. If the pox is infected with a bacteria, we treat it with antibiotics. In addition, we keep the pool water as clean as possible and it contains salt to keep wounds clean. After the pox has cleared, the seals are sometimes left with bald spots or scar tissue.


  1. Becher P, Konig M, Muller G, Siebert U, Thiel HJ (2002) Characterization of sealpox virus, a separate member of the parapoxviruses. Arch Virol 147: 1133–1140 DOI 10.1007/s00705-002-0804-8
  2. Clark C, McIntyre PG, Evans A, McInnes CJ, Lewis-Jones S (April 2005). “Human sealpox resulting from a seal bite: confirmation that sealpox virus is zoonotic”.  J. Dermatol. 152 (4): 791–3. doi:10.1111/j.1365-2133.2005.06451.xPMID 15840117S2CID 38466772.
  3. Sealpox Virus in Marine Mammal Rehabilitation Facilities, North America, 2007–2009 Amira A. Roess,1 Rebecca S. Levine, Laura Barth, Benjamin P. Monr oe, Darin S. Carroll, Inger K. Damon, and Mary G. Reynolds. Emerging Infectious Diseases • • Vol. 17, No. 12, December 2011

On this page

Continue reading

Lees verder

Herpes in seals

Knowledge repository

The herpes virus that seals can carry is not the same herpes virus that we humans can get. It is a highly contagious virus, which is why we are doing everything we can to prevent any spread in the Sealcentre.

See also

  • Zeehond onder water

Types of herpes

Herpes is a virus that seals carry for the rest of their lives after infection. This virus is not the same herpes virus that humans can get. There are seven variants of this phocine herpesvirus (PhHV).

Did you know...

Our vet Ana, together with other scientists, has discovered the seventh variant of the phocine herpes virus? (1)

We think it is very special that our head veterinarian Ana Rubio García belongs to the group of scientists who discovered this seventh variant in 2014 (1). When seals in our rehabilitation centre carry herpes, it is almost always this seventh species.

Symptoms of herpes

Herpes is not clearly visible by one specific complaint or change in appearance. Seals can have several complaints at the same time. Possible symptoms of herpes viruses are:

  • Runny nose (often with blood)
  • Inflamed oral mucosa
  • Vomiting
  • Diarrhea
  • Fever
  • Cough
  • Pneumonia
  • Hair loss in grey seals (2)

Herpes remains in the seal's body forever. As a result, the complaints can occasionally return. Something similar happens in humans as well. The cold sore, an irritated blister that some people get around the mouth, is a characteristic of the herpes virus (herpes labialis). If you become infected with the cold sore, you will keep this virus with you for the rest of your life (3). In case of stress or fever, you can regularly get a cold sore again, which always disappears over time.

How do seals get herpes?

Herpes is a highly contagious disease. Seals can transmit it to each other through virus particles in the air. That is why it is very important to immediately separate a seal with herpes from the other seals in the sanctuary, by placing them in separate enclosures.

Treating herpes

There is no cure for herpes. We do try to counteract the symptoms of the virus, for example by lowering the fever with medication. We can also treat the inflamed oral mucosa by giving mouthspray. As soon as the seal no longer has any symptoms, it is no longer contagious. The animal can then stay with other seals and eventually be released.


  1. Bodewes R, Contreras GJS, García AR, Hapsari R, van de Bildt MWG, Kuiken T, Osterhaus ADME. Identification of DNA sequences that imply a novel gammaherpesvirus in seals. J Gen Virol. 2015;96(Pt 5):1109–14.
  2. Field, C. L. (2022, 7 juli). Viral diseases of marine mammals. MSD Veterinary Manual. Geraadpleegd op 30 juni 2022, van
  3. Herpes labialis (koortslip) | RIVM

On this page

Continue reading

Lees verder

Influenza in seals

Knowledge repository

There are four types of influenza in total. Types A, B and C cause flu in humans. Influenza types A and B can occur in marine mammals, such as in seals. Influenza can cause a huge wave of disease in wild seals.

See also

  • Zeehondenmoeders en pup

Types of influenza

There are four types of influenza in total. Types A, B and C cause flu in humans. Influenza types A and B can occur in marine mammals, such as in seals. Influenza can cause a huge wave of disease in wild seals.

Symptoms of influenza in seals

Influenza is not clearly visible by one specific complaint or change in appearance. Seals can have several complaints at the same time. The characteristics of influenza B are unknown. Possible features of influenza A are:

  • Weakness
  • Bad coordination
  • Short of breath
  • Swollen neck
  • White or bloody runny nose
  • Pneumonia

How do seals get influenza?

The virus droplets are spread by, among other things, coughing and sneezing, and are then inhaled again. Influenza is extremely contagious. Not only for seals, but also for humans. That is why it is very important to protect both the seals and ourselves if someone is carrying the virus.

Common seals

Common and grey seals can be sick with influenza. It is shown that mainly common seals suffer from the influenza virus. In several major outbreaks of the virus, mainly common seals died. The last outbreak of influenza was in 2014, when thousands of common seals washed up dead on the coasts of the Netherlands, Germany, Denmark and Sweden (1).

Avian flu in seals

Seals can also get influenza from birds. In October 2015, the avian flu virus (H10N7) was the cause of major deaths among harbor seals (2). Seals probably contracted the virus through direct or indirect contact with wild birds or their faeces.

In June 2022, researchers found the avian flu virus in three seals in Germany, but it hasn't sparked a massive outbreak. The fact that the virus is transferred from a bird to a marine mammal means that there is a chance that humans can also be infected.

Treating influenza

It is not possible to cure influenza. There is no medicine for this virus. We can only try to reduce the symptoms and wait until the seal gets better.


  1. Bodewes R, Rubio García A, Brasseur SM, Sanchez Conteras GJ, van de Bildt MWG, Koopmans MPG, et al. (2015) Seroprevalence of Antibodies against Seal Influenza A(H10N7) Virus in Harbor Seals and Gray Seals from the Netherlands. PLoS ONE 10(12): e0144899. doi:10.1371/journal. pone.0144899
  1. Zohari S, Neimanis A, Härkönen T, Moraeus C, Valarcher JF. Avian influenza A(H10N7) virus involvement in mass mortality of harbour seals (Phoca vitulina) in Sweden, March through October 2014. Euro Surveill. 2014;19(46):pii=20967. Available online: 

On this page

Continue reading

Lees verder

Adult grey seal Cornelia


Last Sunday, Cornelia was released! This adult grey seal came to us weakened on 21 February. And now she is strong enough again to return to the Wadden Sea. Together with other grey seals, she was released. It was a beautiful release at sunset.

Het gebeurt niet vaak dat we een volwassen grijze zeehond in de opvang hebben. Vrijwilliger Martina Zilian heeft mooie foto’s van haar gemaakt. 

See also

Continue reading

Lees verder

Collega Sander op tv programma Tijd voor Max


De geboorte van een klapmuts op Vlieland was bijzonder nieuws. Onze collega Sander van Dijk was uitgenodigd bij het tv programma Tijd voor Max om meer te vertellen over de deze zeehondensoort. Hij had onder andere een schedel van klapmuts meegenomen om te laten zien aan de kijkers. Ook was Gerard Koster Joenje van erbij om wat mooie beelden te laten zien. De onderstaande afbeeldingen zijn ook van Gerard. 

Bekijk here het fragment.

See also

Continue reading

Lees verder

Hooded seal

Knowledge repository

Scientific name: Cystophora cristata
Family: Phocidae
Size:: 3.50 meter; vrouw: 2.00 meter
Weight: male: 400 kilo; female: 300 kilo
Habitat: Northwest Atlantic Ocean and the Arctic
Endangered status: vulnerable

See also

“A male hooded seal makes tries to attract females in an extraordinary way: they have an inflatable, stretchy, red cavity in their nose (also called hood).”

External features of the hooded seal

Hooded seals can reach a weight of about 145 to 352 kilograms and a length of 2 to 2.6 metres. Large animals can even reach more than 400 kilograms. Hooded seals have a large and broad but relatively short head with large nostrils. The head and flippers are usually coloured completely black. The rest of the body is white in both males and females with black spots of all sizes and shapes1,2. In contrast to their robust body, their flippers are relatively short.

Gender differences

Imagine this: you inflate a red balloon bigger than your head. You would stand out in an audience. So does a male hooded seal, but with a hood coming from their nose! This is where the species gets its name from. They do this to attract the attention of females, but also to threaten other males (and compete when mating with females)1,6.

In fact, males have a rather large nose, the skin of which they can inflate into a black "balloon". This one can be bigger than their own head! But that's not all, as they can additionally inflate a sheet on the inside of their nose into a red "balloon". They inflate these different air sacs to show how big they are. The nose of females has no other notable modifications and they remain somewhat smaller than males.

Distribution and status

Hooded seals are found in the North Atlantic and the Arctic Ocean. They are native to Canada, Greenland, Iceland and Norway. It is estimated that there are about 600,000 hooded seals in the North Atlantic and another 100,000 or so in the Arctic Ocean. The hooded can swim in water from -1.9°C to 10.7°C9

Did you know...

The habitat of the hooded seal is decreasing due to climate change?

Decreasing habitat

This gives? the hooded seal the "vulnerable" status on the IUCN Red List, meaning that the species may be endangered in the future2,3The habitat of the hooded seal, like other Arctic or ice dependent species, is threatened by habitat loss - due to climate change. Therefore, it could be the case that the hooded seal will be listed as an "endangered" species2. Because of its vulnerable status, the hooded seal is protected by the Marine Mammal Protection Act1.

Humans hunting hooded seals

In the past, there was intensive and unsustainable commercial hunting of hooded seal mothers for oil and leather or the pups' fur. Usually, when pups were hunted for their fur, the mothers were also killed because they would try to defend their pup. In Greenland today, people still hunt hooded seals for meat or fur1,2,5,8.

Further threats to the hooded seal population include entanglement or bycatch, competition for food with commercial fisheries or other predators, climate change and, as usual, typical diseases1,2.

Diet and foraging

The diet of hooded seals consists mainly of squid, starfish, mussels and some fish species such as Arctic and Atlantic cod and herring. Young hooded seals eat pelagic crustaceans, such as krill 

Did you know...

Hooded seals can dive as deep as 1 kilometre?

While foraging, hooded seals dive as deep as 100 to 600 metres. They then do so for about 13 to 15 minutes. However, it is known that they can even reach a depth of 1,000 metres! Hooded seals can stay underwater for 1 hour and can travel as fast as 27 kilometres per hour 1,2,7.

Behavior of the hooded seals

Hooded seals are solitary animals. That means they prefer to go their own way. In general, hooded seals show aggressive and territorial behaviour. Males are known to patrol along the ice edge and often stay close to females. There is considerable fighting between males, with often bloody results, whilst showing off vocally their inflated red 'hood'1,5

The only social contact with other hooded males occurs during the mating and moulting season 1,10. The males then appear together in small groups. But: even then they will avoid lying close together2.

Did you know...

Hooded seals can stay at sea for weeks without resting?

The hooded seal is a migratory species: they migrate. Sometimes they spend weeks at sea without resting. When they do rest, they prefer to do so on floating pack ice 6,8. Their annual migration cycle begins when they are sexually mature1. Males are sexually mature at 6 years of age, females at 3 to 6 years of age7. The molting period is annual in July, after the young are born 1,2

Voortplanting bij de klapmuts

From April to June, the hooded seals have only 2.5 weeks to mate6. Hooded seals are polygamous: males mate with several females. Mating takes place under water2,4.

Diapause and pregnancy

As with all seal species, there is a diapause after fertilization. A diapause means that there is a time between fertilization and the actual pregnancy, so implantation is delayed. This delayed implantation of the fertilized egg takes about 3 to 4 months. After these months, gestation lasts about 8 to 11 months7,8

Birth and nursing period

A hooded seal gives birth to one single pup. The pup is born and suckled on the sea ice1,2. The mother will aggressively defend her pup. Usually, the mother will not forage while lactating. Usually, a male will assist the mother and her pup and stay nearby. When the mother will suckle her pup, the male can mate with her directly in the water5,8

The birthing season usually takes place around March and April5. The pups are also known as "bluebacks" because their fur appears blue-grey. Unlike their backs, the pups have a whitish belly. The fur falls out during the molt when they are 14 months old1

Did you know...

Pups of hooded seals have the shortest lactation time of all mammals? Suckling lasts only 3-5 days after birth.

Suckling lasts only three to five days after birth. This makes the pup of the hooded seal the fastest suckling mammal compared to other mammals. During the suckling period, the pup drinks up to 10 litres of the high-fat content milk per day1,8

At birth, the pup weighs around 24 kilograms and is about 1 metre long1,2. After the suckling period, the pup will weigh about 48 kilograms. In other words, within five days, the pup doubles its weight (and gains about 7 kilograms a day)2,11. The pup first stays in the ‘nursing area’ for a while, but then starts learning to swim, dive and forage independently8. They do this based on their instincts.

Natural enemies of the hooded seal

Hooded seals are on the menu of polar bears. Killer whales could also be possible predators of the hooded seal, but this has not yet been observed. Greenland sharks can feed on young hooded seals2,11.

1. ( Hooded Seal; NOAA Fisheries; 2022)

2. (Hooded Seal; IUCN RedList; 2015)

3. (Vulnerable species; dictionary; 2012)

4. (Polygyn, dictionary; 2012)

5. (Hooded Seal;Marine Species Identification Portal; n.d.)

6. (Hooded Seal; Discovery of the Sound in the Sea; n.d.)

7. (Hooded Seal; Oceanwide; n.d.)

8. (Hooded Seal: Cystophora cristata; 2009)

9. (Hooded seal Cystophora cristata foraging areas in the Northeast Atlantic Ocean-Investigated using three complementary methods; 2017)

10. (Cystophora cristata hooded seal; Animal Diversity Web; 2010)

11. (Hooded Seal; Norwegian Polar Institute; n.d.)

12. Thomas A. Jefferson, Marc A. Webber and Robert L. Pitman, in Marine Mammals of the World  (Second Edition), 2015

On this page

Continue reading

Lees verder

Hooded seal births pup on Vlieland


On the morning of Monday 27 March, a hooded seal gave birth to a pup on the beach of Vlieland. The hooded seal is a seal species that occurs naturally around the polar region, so that makes this very exceptional and special. After consultation with Sealcentre Pieterburen and the local seal guard, police and army have closed the area to the public for the time being. However, this is of limited duration and the centre is concerned about long-term conditions for the pup. Therefore, the centre calls for the animals to rest.

See also

On Monday 27 March, seal guard Willem made a very special discovery on the beach of Vlieland: a hooded seal that had recently given birth to a pup on the beach of Vlieland. Never before had this occurred. Hooded seals are native to the polar region and have one of the shortest nursing periods of all seal species: only four days on average. Therefore, the we are so gratefull that the local police and the army closed off the area around the mother and pup for the time being. Hopefully, the two will be able to get through the suckling period undisturbed.

The short suckling period will be followed by a period of fasting for the young animal, during which it will occasionally ingest some fluids through the ice it normally lies on. Then the animal goes hunting in the open waters of the polar region. These conditions are obviously lacking here. The centre is therefore concerned about how the pup will fare afterwards. Either way, it will be important to give the animals rest, and the centre makes the appeal to do so. Moreover, it is working with police and army to find a solution to keep the area closed for longer.

The hooded seal is a seal species listed as "vulnerable" on the IUCN red list. They live mainly around Greenland. Every now and then, young animals sometimes end up elsewhere. Several hooded seals have also been taken in the Netherlands, but 3 times in the past 10 years. In 2013, a young hooded seal came into Sealcentre Pieterburen and in 2014 and 2018 at A Seal in Stellendam.

Photo credit: Gerard Koster Joenje,

Continue reading

Lees verder

European Association for Aquatic Mammals


Ana, onze Hoofd Dierengeneeskunde, Zorg & Wetenschap en Sara, Stagiare Dierenarts woonden deze week de conferentie van de European Association of Aquatic Mammals (EAAM) bij. Beiden gaven een presentatie over hun onderzoek, gebruikte methoden en eerste bevindingen. Dat Ana en Sara het Zeehondencentrum vertegenwoordigen op de conferentie voor het welzijn en behoud van zeezoogdieren door middel van onderzoek, medische zorg, opleiding, onderwijs, behoud, beheer en activiteiten – dáár zijn we erg trots op!

See also

Onderzoek Sara

Congenital disorders in harbour (Phoca vitulina) and grey seals (Halichoerus grypus) admitted into rehabilitation from the Dutch Wadden sea 

Congenital disorders are functional or structural defects that are present at birth. Monitoring of birth defects in wildlife can provide conservationists with information about the status of that population and can help with the detection of emerging teratogens. In marine mammals, there are few reports on congenital abnormalities, which are mostly found during postmortem examinations. 

Harbour (Phoca vitulina) and grey seal (Halichoerus grypus) populations of the Dutch Wadden sea are stable and considered healthy. The current study summarizes information on sporadically appearing congenital or potentially congenital abnormalities in harbour and grey seals between 2014 and 2022. All animals were admitted into rehabilitation at Sealcentre, Pieterburen, in The Netherlands. We focused on the diagnostic methods and outcomes of each individual. The diagnoses were based on physical examination, clinical symptoms, and diagnostic imaging. These cases included melanism, albinism, microphthalmia, esophageal stenosis, impaired swallowing reflex, vestibular disease, dwarfism, hiatal hernia, cleft lip, arthrogryposis, and megaesophagus. During the study period, a total of 2739 seals were admitted into rehabilitation. The prevalence of congenital disease in our study was 0.62%. 

Onderzoek Ana

Gut microbiome of stranded harbour seals (Phoca vitulina) admitted for rehabilitation. 

In the Netherlands, the Sealcentre Pieterburen rehabilitates an average of 250 grey seals (Halichoerus grypus) and harbour seals (Phoca vitulina) per year. Being held in temporal captivity for rehabilitation might have an effect on the seals microbiome, and our study aimed to understand this effect in the gut microbiome of stranded harbour seals and the main factors contributing to it. We investigated the distal gut microbiome of two large cohorts (pups and weaners) of stranded harbour seals that were admitted for rehabilitation at the Sealcentre. The gut microbiome of young harbour seals stranded in the Netherlands is composed of Proteobacteria, Firmicutes, Bacteroidota, Fusobacteriota, Campylobacterota, and Actinobacteriota, and corresponds with the main core phyla described for this species in other parts of the world. The alpha diversity (richness and Shannon diversity) of the pup’s microbiome increased significantly during rehabilitation, while there were no significant changes in the weaners. Beta diversity of both pups’ and weaners’ gut microbiome was different before and after rehabilitation, with age and sex as main factors. We conclude that there was an important change in the microbiome of stranded harbour seals that were admitted to the Sealcentre.

Ana Rubio-Garcia1*, Aldert L. Zomer2 , Ruoshui Guo2, John W.A. Rossen3,4,5, Jan H. van Zeijl6, Jaap A. Wagenaar 2,7 , and Roosmarijn E.C. Luiken 2 

1. Veterinary and Research Department, Sealcentre Pieterburen, Pieterburen, The Netherlands 

2. Division of Infectious Diseases and Immunology, Utrecht University Faculty of Veterinary Medicine, Utrecht, The Netherlands 

3. Department of Medical Microbiology and Infection Prevention, University Medical Center Groningen, Groningen, The Netherlands 

4. Department of Pathology, University of Utah School of Medicine, Salt Lake City, UT, USA. 

5. Laboratory of Clinical Microbiology and Infectious Disease, Isala hospital, Zwolle, The Netherlands. 

6. Department of Medical Microbiology Friesland and Noordoostpolder, Certe, Leeuwarden, The Netherlands 

7. Wageningen Bioveterinary Research, Lelystad, The Netherlands 

On this page

  • Onderzoek Sara

  • Onderzoek Ana

Continue reading

Lees verder

Studio Ditte


Wat is ie leuk geworden: de zeehondenprint die Studio Ditte speciaal voor ons heeft ontwikkeld. En nog leuker, het kan bij jou thuis aan de muur hangen! Studio Ditte is een bewust merk dat onder andere behang ontwikkelt. Speciaal voor ons hebben ze dit zeehondenbehang ontworpen. En per rol gaat er €5,- naar ons centrum. Daar zijn we natuurlijk erg blij mee, ontzettend bedankt! Het zeehondenbehang is vanaf nu te koop via de webshop van Studio Ditte en via verschillende winkels.

Lees meer over onze samenwerking op het blog van Studio Ditte here

See also

Continue reading

Lees verder

Report a seal. Seen a seal in need? Call 144 (24 hours a day available) Read more.