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Dieren en planten

Predators   Seals   Harbour seal   Grey seal   Ringed seal   Harp seal   Hooded seal   
Seal corpse, Ecomare

Virus epidemics in harbour seals

In 1988 and 2002, the harbour seals in the North Sea and wadden region were infected with a virus. Both times, more than half of the population of harbour seals in the Dutch Wadden Sea were killed. Successive epidemics of viruses are usually caused by a virus that is slightly different from the cause of the previous epidemic. That is why we speak of a family or group of viruses with different strains. This is equivalent to families and species in plants and animals, but new species of viruses form much more quickly. The occurence of different strains makes it difficult to discover which virus is active at the time, making it very difficult to fight. A well known example of this is the various forms of flu epidemics in people.

  • The first epidemic: Mobilli virus

    Because of the virus epidemic in 1988, more than half of the harbour seals in the Dutch Wadden Sea died. In the spring of 1989, there were a little over 400 Dutch seals alive. The situation in Germany and Denmark was even more serious, where approximately 80% had perished.

    Studies showed that the disease in 1988 was caused by a virus from the morbilli virus group. These viruses are very similar to those found in dogs. It was later discovered that several harp seals, which had wandered into the Skagerak and the Danish wadden region, were the carriers of the disease. Therefore, we can assume that they contaminated the harbour seals.

  • Recovery after the first epidemic

    The first recovery from the epidemic began quickly, with the birth of many young pups in the summer of 1989. The number of seals counted in the whole wadden region just after the epidemic was 4500 specimen. In 2002, it had risen to 20,975. All in all, the seal population had recovered much more quickly than we had ever dared to hope. The virus epidemic probably caused a stringent natural selection: only extremely vital animals with a high resistance and a good reproduction could survive. And these animals were the reason that the number of seals quickly grew. Until 2002, when a second epidemic broke out ...

  • Recovery from the second epidemic

    The second epidemic ended in December 2002. In the summer of 2003, 10,800 seals were counted in the entire Wadden Sea, of which 1160 in Denmark, 4235 in Schleswig-Holstein, 3050 in Niedersaksen and 2365 in the Netherlands. Once again, there was a rapid recovery. In 2004, the counted population had grown to 12,803, including 3704 pups. In 2008, the Trilateral Seal Expert Group (TSEG) concluded that the international population had completely recovered from the epidemic of 2002.

  • Third epidemic?

    In 2007, it seemed as if there would be another outbreak when the virus was found in several dozens of dead seals in Denmark. As a precaution, the seals in the sanctuaries were vaccinated. After two months, it was discovered to be a different virus. Fortunately, the disease was limited to about 100 animals in the vicinity of the Kattegat.