Nor were there any signs the sharks had been injured by fishing nets or long-line gear. Mass mortalities in sharks are very unusual. An algae bloom known as red tide has been reported in the area, but it would have killed other fishes and sea life, and no other species was dead, Dr Cortes said. He said the sharks may have died from a low level of oxygen in the shallow waters. Biologists collected tissue samples to send to the Florida Marine Research Institute in St Petersburg to check for signs of red tide.
Red tide occurs when microalgae burst, releasing reddish brown toxins into the water.
It can kill fish and cause respiratory irritations and watery eyes in humans. No plans are being made to remove the carcasses because the area is not heavily frequented by people.