A snorkeller is believed to have been snatched by a shark as he swam last weekend with his son at a beach south of Perth. Witnesses reported seeing a dorsal fin and thrashing in the water before the sea turned red and the man vanished at the scene on Australia's west coast.

Father-of three Brian Guest, 51, who had campaigned for many years for the protection of sharks, had been looking for crabs on yesterday morning with his 24-year-old son when he was attacked about 30 metres from the shore.

Daniel Guest, who was swimming six metres away at the Port Kennedy beach, heard his father's screams but did not see the attack. He raced to shore when he saw blood in the water. His father's shredded wetsuit was found later, and aerial searches spotted a five-metre great white shark swimming in the area.