The only way to save marine mammals from unacceptably high death rates may be temporary fishing bans, UK conservationists say.
By Alex Kirby
BBC News Online environment correspondent
They say there has been "an incredible increase" this year in the numbers of dead animals found on British beaches.
They believe many more are dying out at sea where their bodies vanish without trace.
And they say death rates in France are even higher than in the UK.
The warning comes from Jenny Granville, of the Devon Wildlife Trust, and Richard Sabin, coordinator of the national whale stranding recording scheme at the Natural History Museum in London.
Speaking at the museum's new Darwin Centre, Mr Sabin said the increase in strandings of dolphins and porpoises in south-west England in the first weeks of 2003 had been "incredible compared with previous years".
Most appeared to have been caught in fishing nets, mainly in those used in the sea bass fishery, which runs from October to April.
Over the last 10 years that has switched from single nets to pair trawls towed by two vessels, three or four times larger than the old nets.
Mr Sabin said 217 small cetaceans had been washed up so far this year. There were 128 common dolphins, but the rest were too decomposed to identify.
The numbers stranded in Devon so far this year are 72, compared with 42 in the whole of last year.
Ms Granville said the numbers found were a small fraction of the animals dying in the nets, probably no more than 10%.
The worst time for strandings was usually between January and March, and this year there had been much more fishing effort.
This dolphin had suffered skin damage
Reports from France in recent years have suggested the death rate there may be seven times higher than in UK waters.
Trapped animals panic as they try to fight their way to the surface for air. They bite the nets, sometimes breaking their jaws as they do so.
Mr Sabin said the numbers dying were far above the 1.7% of the population which is accepted by scientists as the maximum sustainable annual loss.
More action needed
But he told BBC News Online the baseline data did not exist to say whether any of the cetaceans faced extinction in the UK.
Ms Granville said the recent UK Government consultation paper, UK Small Cetacean Bycatch Response Strategy, was "a step in the right direction", but not the action plan conservationists wanted.
Some cetaceans break their jaws in the nets
She doubted whether pingers, acoustic warning devices the government wants fixed to nets, would work.
"They work very well on static nets", she said. "But the forces on a net being towed at six knots an hour are overwhelming.
"The animals get used to the pingers, and regard them almost like dinner bells.
"Escape grids in nets have worked with sealions in New Zealand - but there's evidence they can be damaged as they swim up through the net."
She told BBC News Online: "We think the answer is localised fisheries closures when there's a problem - and we want the crews to receive compensation for their loss of livelihood.
"But it would be pointless for the UK to go it alone - it would have to be done at the European level."
Images courtesy of the Natural History Museum