A close-run fin

A diver alerts a fellow snorkeller to the dorsal fin of a shark as they swim in waters around the Inner Hebrides archipelago in Scotland. Thankfully, Will Clark, from Somerset, was able to take a photograph under the water (left ) to reveal that their visitor was not a threat, but the mild basking shark. Second only to whale sharks as the biggest in the ocean, basking sharks average 20-25ft in length and migrate to the UK every summer. The slow-moving filter feeders survive on a diet of plankton and small crustaceans and are harmless to humans – to the relief of these divers.