People have been warned to stay away from basking sharks after one was found dead in a fishing net in Cornwall and another injured.
The drowned basking shark was photographed and measured
One of the sharks drowned after becoming accidentally entangled in a fishing net off Sennan Cove.
Another had its dorsal and tail fins severed, probably as a result of a collision with a boat propeller in Porthcurno, experts said.
The Marine Conservation Society said shark protection laws had been ignored.
The injured shark was photographed by University of Exeter Cornwall Campus biologist Dr Ruth Leeney during a boat-based marine wildlife survey on Saturday.
Dr Leeney said the injured animal appeared to be behaving normally despite its open wounds.
The drowned basking shark was photographed, measured and tissue samples taken for research by the Cornwall Wildlife Trust.
The Marine Conservation Society (MCS), the Wildlife Trust and the Shark Trust have produced a Code of Conduct for boat users and swimmers to observe basking sharks without disturbing them.
An MCS spokesman said: "UK law and the basking shark Code of Conduct has been designed to prevent these animals from disturbance and injury.
"Clearly some people are ignoring the law and sadly it seems this shark has suffered as a result.
"Anyone witnessing boats deliberately approaching sharks too closely with their engines running should report the incident to the local police."
According to the code, vessels must immediately turn their engines to neutral if they are within 100m (328ft) of a shark.
The society is calling for the establishment of marine protected areas to restrict boat use and fishing at basking shark hotspots around the Cornish coast.
They have recorded more than 10,500 public sightings of basking sharks in UK waters over the past 20 years.