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Circumstantial evidence is mounting that pollution contributed to the
European seal epidemic of 1988, when tens of thousands of animals died from
viral infection in the North Sea and the Baltic.

Mark Simmonds, of the University of Greenwich, and his colleagues Paul
Johnston and Mike French, have made a fresh analysis of tissue samples from
eight grey seals which died in the Dee estuary, 15 harbour seals that had
died off the Norfolk coast, and nine harbour seals that died in northeast
Scotland.

Their results, published in the Veterinary Record, show that concentrations
of pollutants – mercury and organochlorine compounds, including DDT and
PCBs – were much lower in samples from the Scottish seals. This colony got
off lightly during the epidemic. ‘There’s a clear correlation between contamination
of tissue and mortality,’ says Simmonds.

Simmonds and his colleagues argue that their findings support the hotly
disputed claim that pollution lowered the seals’ resistance to the distemper
virus that swept through the population.

‘Many factors come into play, and we are not trying to be overly simplistic,’
says Simmonds. But ‘the circumstantial evidence is amassing, and keeps getting
heavier all the time’.

John Harwood of the Sea Mammal Research Unit in Cambridge believes pollutants
were probably insignificant in the European seal epidemic because the virus
itself had such a devastating impact. ‘It’s more worrying what effects pollution
might have on the everyday resistance of seals,’ he said.