The oil spill was catastrophic for wildlife

The reason for the ailments - which include blindness and bone complaints - have not been established.

Possible causes range from food shortages to vulnerable breeding areas.

But staff at the sanctuary are also keen to investigate exactly how the Sea Empress oil disaster in 1996 affected the local seal population.

Teeth drop out

Of 30 seals taken in by the sanctuary since September, more than half have died -whereas normally 80% are returned to health.

"Some are born with milky white eyes where they should be black," said Terry Leadbetter, who runs the Welsh Marine Life Centre.

Terry Leadbetter wants the oil theory looked at

"Their teeth start dropping out and we have found their lower jaws crumbling away.

"They are also suffering from coughs and colds and are generally weak and lethargic."

Similar problems have also been reported at the Irish Seal Sanctuary where biologists are worried about the poor health of pups along the Wexford coast.

Ran aground

While some have dismissed jumping to "a rather large conclusion", Terry Leadbetter said it was worth investigating any possible links to the Sea Empress.

The environmental disaster happened on February 15, 1996, when the Sea Empress tanker ran aground.

Pups are also suffering eye and bone problems

Around 72,000 tonnes of light crude oil and 480 tonnes of heavy fuel oil spilled into the sea, polluting around 200km of coastline internationally recognised for its wildlife and beauty.

"We have a theory that some of the pups that we have had this year could be the offspring of pups born during the Sea Empress year," Mr Leadbetter said.

"It's a localised problem because from different areas further up the coast the seals are bouncing and as healthy as they should be.

"We are not pressing the alarm bells yet, but if we find the same thing next year then I think we need to start looking into it and seeing what the problem is."