Lovely Day for a Walk
Named for the conspicuous large dark patch on the 'shoulder', the Epaulette Shark (Hemiscyllium ocellatum) uses its rounded, highly mobile pectoral and pelvic fins to clamber over the substrate with an endearing clumsiness — resembling a salamander with ping-pong paddles for legs. This delicately slender, prettily-marked shark actively hunts inside the cramped and convoluted passageways within coral reefs. It is one of the few fishes that, when startled or frightened, will try to 'walk' away rather than swim. The co-ordinated limb motion that the Epaulette Shark uses to 'walk' over the bottom is being studied by Australian biologist P.A. Pridmore as a model for that employed by the first terrestrial vertebrates — tetrapod pioneers, which clambered out of the ocean some 350 million years ago.
Not to be outdone by its orectloboid cousin, the Nurse Shark (Ginglymostoma cirratum) has devised another clever use of its pectoral fins. Young Nurse Sharks have been observed resting with the snout pointed upward and the forward part of the body raised off the bottom, propped up by curled-under pectoral fins. In a short 1972 paper, Sanford Moss suggested that this behavior may provide a false shelter for crabs and small fishes, which the shark then ambushes and eats. In the Florida Keys, I once observed a 4-foot (1.2-metre) that had been resting in this position for some time suddenly perform a rapid, rather comical 'push up' and hoover up a small xanthid crab that had taken up shelter between its pectorals.