The bodies of five basking sharks have been discovered in one week washed up on the coast of Cornwall.
They were found on the Roseland Peninsula, on The Lizard, in the Fal Estuary and at Perran Sands on the north coast.
The Marine Conservation Society says the toll is unusual and worrying.
Environmentalists fear they may have been the victims of fishing nets. Fishermen deny being the cause of any large animals' deaths.
Doctor David Sims, a research fellow with the Marine Biological Association, said: "We've been studying shark movements for about 10 years around the south-west coast and in UK waters.
"Anecdotally, there does seem to be a higher incidence of strandings this year compared to the previous ten."
Fishermen have already been blamed for dolphin deaths around the south-west coast.
Environmentalists say the deaths are because of fishing boats engaged in pair trawling.
The practice involves two boats dragging a net that can be the size of several football pitches.
Animals, the environmentalists claim, become caught up in the massive nets used to catch bass mainly by French and Scottish boats.