Just like humans, seals can get sick from viruses. Some viruses only make seals temporarily ill, but some can be fatal. In the centre, we conduct research into the viruses that seals can carry with them, and — wherever possible — try to fight them.

One of the deadliest viruses is the Phoca Distemper Virus (PDV)This virus, also called the seal virus, is very contagious. It is transmitted when animals come into contact with each other or by virus droplets floating in the air.  

When seals are infected, they develop symptoms such as heavy breathing, coughing, fever, and problems with their nervous system. The virus also makes them more sensitive to other infections. Ultimately, PDV can result in death.

The seal virus caused a massive number of deaths among seals in 1988, and again in 2002. In 1988, more than half of the Dutch seal population died. Back then, the cause of the deaths was still unknown, so Lenie 't Hart asked virologist Ab Osterhaus to investigate it. That was when he discovered the phocine distemper virus (currently known as the phocine morbillivirus).

In 2002, the virus struck again. And again, almost half of the seals in the Netherlands died. The seals that washed ashore were taken from the beach to a research laboratory in Groningen. More than 1200 dead seals were investigated for the cause of death on behalf of the Seal Centre. After fifteen years, the phocine distemper virus had returned. This means that there is a chance that another outbreak will occur in the future.

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We think it is important to keep an eye on the seals in the wild. One way we do this, is by taking blood and saliva from every seal we rehabilitate. These samples are analysed by our veterinarians to check for virus particles. This way, we keep an eye on the health of the seal population in the Wadden Sea. It also aids us preparing for a possible new virus outbreak. 

Watch a mini documentary below about how we monitor a virus outbreak in the Wadden Sea:

When you get sick from a bacterial infection, you can treat it with antibiotics. These are drugs that can kill bacteria. If antibiotics are used too often, bacteria can become resistant to them, making them less effective against infections. Our veterinarian Ana Rubio Garcia tests rescued seals for bacteria that have become resistant to antibiotics. This research can tell us more about antibiotic resistance in the Wadden Sea.

If people use antibiotics too often, the bacteria they are supposed to treat can become resistant. This means that the bacteria are no longer sensitive to the drug—they won’t be killed by it anymore. This is very problematic. If it keeps happening, the chance of healing a bacterial infection becomes smaller and smaller. New medicines would have to be developed to fight these bacteria. That is why it is important to only use antibiotics when necessary.

There is a chance that antibiotic-resistant bacteria end up in the Wadden Sea. When these bacteria leave our body, they get into the sewers through the water we use. From there, they can find their way into rivers and eventually the sea. For example, seals might come into contact with this type of bacteria and ingest them. By examining these seals, we can demonstrate that there are antibiotic-resistant bacteria in the Wadden Sea.

Ana wants to know if seals have bacteria in their bodies that are not sensitive to antibiotics. Her doctoral research (PhD) concerns all microscopic organisms that can occur in a seal, such as bacteria, viruses, and fungi. As a part of her research, Ana investigates whether antibiotic-resistant bacteria are common in seals.

We carry out this research on the seals that we have in rehabilitation. With each intake, we take a sample from the seal’s anus with a cotton swab. The cells in this sample are then grown in our laboratory. By multiplying cell samples in the lab, we can see which types of organisms there are.

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Ana's research shows various results. For example, seals have many of the same types of bacteria in their bodies as humans. She also found very few bacteria that were no longer sensitive to antibiotics. In other words: there are not a lot of antibiotic-resistant bacteria in seals. That is good news! For now, things seem to be going well with antibiotic resistance in the Wadden Sea.

We also looked at what happens to a seal in rehabilitation if it needs antibiotics to treat an infection. It appears that there is no difference between the bacteria of seals that received the treatment and seals that didn’t. This means that the seals’ gut bacteria returned to normal after treatment. This is very striking, since the recovery of natural gut bacteria in humans can sometimes take months or years. This implies that the use of antibiotics in rehabilitated seals will have no effect on the Wadden Sea when they are released.

Seals are an important bio-indicator for antibiotic resistance in the Wadden Sea—they show us how things are going with their environment. By continuing this research, we can keep an eye on whether or not the situation changes.

Watch a mini-documentary below about how the centre monitors antibiotic resistance in seals:  

Every year, we receive dozens of reports of entangled seals. They get trapped in litter floating around in the sea. This could be a fishing net, balloon ribbon or a frisbee. We unfortunately come across the craziest things. The waste can cause deep wounds, or worse: it can kill the seal.  

Trash floating around in the sea is often plastic floating around on the water or underwater. Seals (and other animals) swim through it due to their curious nature. Or they mistake it for prey and get stuck that way. 

Since 2010, we have been tracking the number of reports of entangled seals. Veterinarian and researcher Anna Salazar Casals conducted research into the numbers and types of entanglements in the Netherlands. The data comes from a joint study by seal sanctuaries Zeehondencentrum Pieterburen, Aseal and Ecomare in collaboration with the Max Planck Institute. 

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In the graph below, you can see that this number of reports has increased on average: in 2010, there were 'only' 8 reports, while in 2019, it totalled 38. They came to the startling conclusion that the number of reports has increased four times over the past 11 years.  

Interestingly, 88 per cent of entanglements among seals are caused by material from fishing, such as fishing nets, fishing lines and fish hooks. The remaining 12 per cent comes from other material. We have caught entangled seals at the centre that were even caught in a t-shirt or a frisbee. 

Seals can become entangled in different ways, as the picture shows. Most of these seals are trapped with their necks. These are mainly grey seals (Halichoerus grypus). They can also swallow litter such as fish hooks - with disastrous consequences for the animal. The danger of these entanglements is the damage it causes. A fishing line can cut through the seal's skin and damage its muscles, blood vessels and organs. As long as the depth of the wound is limited to their fat layer, seals can survive an entanglement. 

The majority of entangled seals are young seals (juvenile). Due to their curiosity or playfulness, they probably put their head through plastic or rope or they want to play with it. As a result, the animal becomes so entangled that they are unable to free themselves. Because these are often young animals, they are also still growing. As a result, the entanglement gets tighter and tighter. And the wounds become much worse. 

If we find an entangled seal, we can usually help. In 3 out of 10 cases, we can help the seal on site and release it immediately. We prefer this, of course, because then the animal does not have to go to the shelter.

For 4 out of 10 entangled seals, shelter and further care are needed. We cannot help the remaining 30 per cent of entangled seals: in 20 per cent of cases, we cannot catch the animal and in 10 per cent of cases, the animal has already died.   

Seal guards look at an entangled seal on the beach to see what help is needed. For example, if the fishing net has not yet caused injuries, then the person can immediately cut the fishing net loose and release the seal. If the seal needs medical attention for the injuries, the seal will be taken to a shelter.  

At the centre, our veterinarians check and take care of wounds on entry. Seals usually have a deep fat layer of a few centimetres; this means that the wound can sometimes be quite deep without the seal being injured inside the body. Once the wound is clean and grown closed, the seal can sometimes be released after a few weeks. The only thing the seal is left with is a scar, as you can see in the photo of seal Tefiti.