Unwitting bodyguards

Reef white-tip sharks can be found just about everywhere at Cocos Island, a pelagic metropolis located 350 miles off Costa Rica’ s Pacific coast. You often find them resting on the seabed in little groups while they wait for darkness and the evening hunt. Less well known is the behaviour of tiny blackfin cardinalfish, which seem to use the sharks as a place of safety. They have also been known to use moray eels in a similar fashion. After all, the cardinalfish are much too small to interest a sizeable predator, but would otherwise be an attractive mouthful for mid-sized fish, of which Cocos has no shortage. Photo: Simon Rogerson