Whale shark © Noodlefish, Flickr
Common in the waters off Somaliland, the whale shark Rhincodon typus is the largest living species of fish, measuring up to 12m long, weighing up to 35 tonnes, with a lifespan comparable to a human or elephant. As one of only three filter-feeding shark species, this passive, slow swimming giant is essentially harmless to humans (or anything else much larger than a goldfish), though there is a slight danger of snorkellers or divers who approach one too closely being swiped by its powerful tail fins. In common with whales, this gigantic shark feeds mainly on plankton and other microscopic organisms, which are imbibed together with water through its wide mouth and trapped in a specially adapted gill apparatus when the water is expelled, though it will also occasionally eat small fish. Found throughout the tropical oceans, it is listed as ‘Vulnerable’ by the IUCN, with the main threat to its survival being commercial fishing.
Another common species, often associated with reefs, is the manta Manta birostris, the world’s largest ray, sometimes weighing two tonnes and boasting a wingspan of around 7.5m. Although mantas have a flattened shape and long tails similar to stingrays, they cannot sting and are totally harmless to divers. Indeed, like so many other marine giants, they are filter feeders whose main diet is plankton and other tiny suspended organisms. An intriguing aspect of manta behaviour is the regular gathering of several individuals at cleaning stations, where wrasse and other reef fish feed on the parasites and dead tissue accumulated in their gills. They are also capable of breaching the surface and launching into the air, a rare but spectacular sight.