Marine Scientists Fear for Future as European Seal Plague Subsides

John Pickrell
for National Geographic News
December 31, 2002

As many as 30,000 harbor seals in Europe may have died this summer from a devastating epidemic of distemper. Though the current outbreak is now subsiding, a new report suggests that if the disease strikes again within the next few years, it could reduce European harbor seal populations to near extinction levels.

The risk of catastrophic population collapses are increased by the scale of the mortality and the close proximity to the previous distemper epidemic in 1988, said Karin Harding, a biologist at Gothenburg University in Sweden.

Harding, along with colleagues at Gothenburg and the Woods Hole Oceanographic Institution in Massachusetts, are behind a report in the November issue of the journal Ecology Letters, which predicts that frequent recurrences of epidemics could threaten the long term survival of European colonies of harbor seals, (Phoca vitulina).

Researchers were alerted to this year's epidemic of phocine distemper virus (PDV) in May when dead seals washed up on Denmark's Anholt Island. By mid-September the disease had spread along the coastlines of Scandinavia and the Wadden Sea and as far as the eastern coast of England and Scotland. PDV is a virus related to both distemper in dogs and measles in people.

Shocking Death Toll

Current data suggests that around 22,000 animals have been found dead, but the real death toll may be up to 30,000 said Harding. The total harbor seal population in Europe was thought to number around 88,000 prior to the epidemic.

Scientists know of no simple way to stop the spread of the disease, which attacks both the respiratory and immune systems of seals.

"Harbor seals develop pneumonia that gets so bad that air is pushed out in the lung tissue," said Harding. "They get more and more air in the tissue and finally become inflated and can't dive anymore."

Reduced immunity leads to secondary viral and bacterial infections, she said.

Harding and her team were concerned about the relatively recent recurrence of the disease—just 14 years after the catastrophic 1988 epidemic in harbor seals. Using mathematical models and data from Swedish seal populations affected in both epidemics, the researchers plotted the course of this year's epidemic.

They also used the data to explore how the frequency and severity of PDV epidemics might impact future populations in Sweden and other areas.

Continued on Next Page >>




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