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article imageWhat’s killing the seals of western Sweden?

By Martin Laine     Oct 4, 2014 in Science
A surge in deaths among harbors seals in the waters of western Sweden has mystified scientists who have thus far been unable to identify a single cause. Officials in neighboring Denmark are also reporting an increase in seal deaths.
So far this year, 388 seal deaths have been reported, 10 times the annual average or 30 to 40, according to an article in the Swedish edition of The Local. Most of the deaths have taken place in the archipelago off the coast of Göteborg.
At least two of the dead seals tested positive for bird flu, but scientists are not yet ready to identify the virus as the cause of the other deaths.
“So far we have not had a sufficient amount of samples in order to establish the causes of death,” said Siamak Zohari of the National Veterinary Institute.
While scientists are running tests for many different kinds of diseases, they are focusing on some type of influenza. Bird flu recently killed two seals in Denmark.
No specific number was given, but the Fisheries and Maritime Museum has reported a “large number” of seal deaths on the island of Fano, in the waters between Sweden and Denmark. About 100 seals were found dead on the island of Anholt in July, according to an article in the Danish edition of The Local.
At first it was thought that the deaths might be caused by a virus known as PDV, which attacks the seals’ immune system. Between 17,000 and 20,000 seals were killed by the virus in 1988, and again in 2002. PDV has thus far been ruled out as a cause of this year’s deaths.
“So far the animals that have been tested have not been shown to have PDV,” said Charlotte Moraeus of the Swedish Museum of Natural History in Stockholm. “This is not as worrying as what happened in 1988. But we do need to do more tests to see if the deaths are connected to something bigger that we don’t yet understand.”
One problem so far this year has been that the samples that have been tested are from seals that have been dead for some time.
“We would like to have fresher samples, as this will make it easier for us to determine what was wrong with the animals before they died,” she said.
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