Campaigners are expecting more dead dolphins to be found on the South West coast this year.
Since the New Year, nine dead dolphins have been found in Devon, and 30 dead dolphins and porpoises have been washed up in Cornwall.
Skin missing from their fins and other parts of their bodies indicates they have been caught in trawlers' nets.
Figures for 2002-2003 show 250 cetaceans were found dead on Cornwall's beaches while 80 were found on Devon's shores.
Conservationists say that audible "pingers" and escape hatches in nets, introduced to reduce the number of cetacean deaths off the UK coastline, are not working.
Marine expert Nick Tregenza said: "If the dolphins found good feeding here last year, you might get even more animals this year.
"And if it turns out that the dolphins and the fishermen are targeting the same shoals of fish we are in for a heavy mortality again."
Torbay Liberal Democrat MP Adrian Sanders said: "We are going to have to do something dramatic to stop the deaths.
"We are seeing the deaths of hundreds of dolphins off our shoreline every fishing season.
"I think we have to have a moratorium on pair trawling. It is having the effect of destroying the numbers of dolphins and porpoises and small whales and we have to stop it as soon as possible."