Distemper Kills Thousands of European Seals

By Maarten Bakker

THE HAGUE, Netherlands, September 17, 2002 (ENS) - Phocine distemper, a virus akin to distemper in dogs, has killed 11,000 seals in and around the Wadden Sea, an international wetland on the coast of Denmark, Germany and Holland. More deaths are expected, for the epidemic has not yet reached its peak. Environmentalists say the seals are vulnerable to this virus because they suffer from an immunity defect caused by toxic industrial waste.

The Wadden Sea is an international nature reserve and serves as a breeding ground for the seal population in Northwest Europe. The mammals nurse their offspring on the numerous sandbanks in the tidal area.


Common seals like this one are at greatest risk of phocine distemper. (Photo courtesy NOAA)
Of the 19 types of seals worldwide, two species live in the Wadden Sea - the common seal (Phoca vitulina) and the grey seal (Halichoerus grypus). The common seals, or harbor seals as they are known in Europe, have been hit hardest by the virus. Grey seals, although exposed to the disease, appear to be less susceptible.

In 1988 the Wadden Sea was hit for the first time by the virus phocine distemper. Almost two-thirds of the population of seals in the Wadden Sea was wiped out at that time.

The virus emerged again in May this year, when 200 dead seals were found on the coast of Anholt Island in the Kattegat, the sea between Denmark and Sweden. In June the epidemic reached the Wadden Sea, and in the last few weeks dead seals infected by the virus have been found on the shores of Norway, Great Britain, Belgium and France.

The Dutch government estimates that the virus has killed 11,000 seals in the coastal areas of Northwest Europe. The Common Wadden Sea Secretariat puts that figure at 12,000.

The Sea Mammal Research Unit at the University of St. Andrews, Scotland reports that between September 4 and 10, 209 dead seals were found around the UK, most from the Norfolk coast, bringing the total to 1,005 since the beginning of the outbreak. Post mortem examinations are being carried out to determine if phocine distemper was the cause of these deaths.


Seals on a Wadden Sea beach (Photo courtesy SRRC)
It is expected that the epidemic will last another three months. By then, 50 percent of the Wadden Sea seal population will have fallen victim to phocine distemper.

When it emerged in 1988, the virus was totally new in the European seas. Scientists identified the virus as related to canine distemper, a virus that infects dogs.

Marine mammal scientists found that phocine distemper originated from the coast of Greenland, and was taken to Denmark by migrating seals. The animals had to leave their habitat in the Greenland Sea because human fishing activities left them little food.

Why the virus appeared again this spring in Denmark, in exactly the same area as in 1988, is not yet clear.

The Seal Rehabilitation and Research Centre (SRRC), a nongovernmental organization in the Dutch town of Pieterburen, stresses that the physical condition of the seals in the Wadden Sea was weakened before the virus made its appearance this year. Toxic waste from industries in Northwest Europe has affected the seals' immune systems.


Seals on a Wadden Sea beach close to an industrial area (Photo courtesy SRRC)
Through rivers like the Rhine, the waste is carried to the Wadden Sea, where it gets taken up in the food chain. Scientific research carried out by SRRC virologist Peter S. Ross shows that pollution suppresses the immune system of the Wadden Sea seals.

WWF, the conservation organization, says that oil pollution from shipping and tanker spills, inputs of nutrients and toxics from land-based and offshore sources, impacts from tourism, agriculture, shellfish fisheries and large scale construction all impact the Wadden Sea.

"It is wrong to see the infection merely as a case of natural selection," says SRRC spokesman Frans Duut, who considers the disease to be the result of human activities.


Visitor cars blanket a Wadden Sea beach. (Photo courtesy IRWC)
When phocine distemper infects a seal, its immune system receives another blow and it becomes vulnerable to all kinds of diseases. Ninety percent of the animals have no chance of recovery and die soon after they are infected.

Duut says, "The epidemic in 1988 taught us that it has no use to keep on treating. In most cases we commit euthanasia on the animals brought to us."

Duut doubts if the epidemic will kill only half of the seal population, as the Dutch government thinks. "They say the survival of the seal community itself is not at stake. I think this is wishful thinking."

Duut points out that in 1988 almost two-thirds of the Wadden Sea seals died, and he warns that the virus may not wait another 14 years before it strikes again. "You never know when the next epidemic will take place," he says.

Visit SRRC at: http://www.zeehondencreche.nl

Detailed scientific information is available at the Common Wadden Sea Secretariat: http://cwss.www.de/

See the WWF approach to Wadden Sea conservation at: http://www.ngo.grida.no/wwfneap/Projects/Waddense.htm, and an extensive list of links at: http://www.ngo.grida.no/wwfneap/Projects/waddlink.htm