Marine experts are calling on the public to report sightings of basking sharks in UK waters this summer.
The sharks are drawn to warm, plankton-rich surface waters off the west coast of Great Britain and Ireland.
These huge sharks are harmless, but experts are also asking people to "keep a respectful distance and enjoy the spectacle".
Basking sharks are protected under European and UK law, so it is illegal to disturb or harass them.
"They're here for most of the summer," said Dr David Gibson, managing director of the National Marine Aquarium in Plymouth. "We're asking people to let us know whenever they see one of these fantastic animals.
Basking sharks are the ocean's second biggest fish, measuring up to seven metres in length.
A large adult male can have a dorsal fin up to 1.5m high, which protrudes from the water when the fish are feeding at the surface.
"We'd also like people to take photographs if they can," said Dr Gibson.
"These animals live for between 30 and 40 years, so [with photos] we might be able to identify individuals that are returning to UK waters."
Researchers at the aquarium also use photographs to spot any signs of damage to sharks' fins that could indicate where the fish might be "coming into conflict" with fisheries.
Read more: http://www.bbc.co.uk/nature/17846524