Fish
Epaulette Shark
Hemiscyllium ocellatum · also called epaulette shark, walking shark
The epaulette shark is a small, patient, spotted shark of the Great Barrier Reef, and it does two things most sharks cannot. It walks — clambering over coral and hauling itself across exposed reef at low tide on its paddle-like fins — and it survives being almost completely starved of oxygen by shutting down parts of its own brain.
Overview
Epaulette sharks live on shallow reefs, reef flats, and tide pools in northern Australia and southern New Guinea. They are small and slender, 70–90 cm, sandy brown with dark spots and a large black white-ringed patch behind each pectoral fin — the “epaulette.” They hunt crabs, shrimp, worms, and small fish on the reef at night.
Walking
The epaulette shark uses its paired fins as limbs, moving them in an alternating, lizard-like gait to clamber over the reef. At low tide it will cross exposed rock and coral from one tide pool to the next rather than wait for the water to return, and it can survive out of the water for an hour or more.
Shutting down
When a warm pool runs low on oxygen, the shark slows its heart, lowers its blood pressure, and idles non-essential brain activity, surviving about two hours of near-total oxygen loss and then recovering with no damage. Because a human brain dies within minutes of losing oxygen, researchers study the epaulette shark for clues to protecting the brain and heart during strokes and heart attacks.
Status
The epaulette shark is Least Concern, common and stable. It is little fished and copes with warm, low-oxygen water better than most sharks, though long-term reef degradation remains a concern. It is one of about nine species of small “walking sharks.”
Epaulette Shark: common questions
Can the epaulette shark really walk?
Yes, in a meaningful sense. It does not have legs, but it uses its paired pectoral and pelvic fins as limbs, moving them in an alternating, lizard-like pattern to push and pull its body along the seabed and over obstacles. It can also use this gait to travel short distances across coral, rock, and even air-exposed reef at low tide, working its way between tide pools. The movement is slow and deliberate rather than fast, and it is one of the clearest examples of a fish using fins for something close to terrestrial locomotion.
How does the epaulette shark survive without oxygen?
Its home is shallow reef-top pools that, on a hot still night at low tide, can lose almost all their dissolved oxygen. Rather than dying or fleeing, the epaulette shark goes into a kind of controlled shutdown. It drops its heart rate and blood pressure, diverts the limited oxygen to the organs that need it most, and reduces activity in the parts of the brain that are not essential, effectively idling until fresh, oxygenated water returns. It can keep this up for around two hours and then resume normal life without brain damage, an ability very few backboned animals have.
Is the epaulette shark dangerous to people?
No. It is small, slow, and feeds on invertebrates and tiny fish, and it has flattened crushing teeth rather than cutting ones. It is not aggressive and poses no threat to swimmers or divers. If handled it may struggle or give a weak nip, and it is a popular and hardy species in public aquariums precisely because it is so undemanding and harmless. As with any wild animal, the sensible approach on a reef is to look and not touch.
Why do scientists study the epaulette shark?
Mainly for its brain. A human brain starved of oxygen for even a few minutes suffers permanent damage, which is what makes strokes and cardiac arrests so devastating. The epaulette shark routinely survives two hours of near-total oxygen loss with no ill effects, so understanding the biochemical and physiological tricks it uses, such as how it protects nerve cells and manages energy, could point toward treatments that buy time for a human brain or heart during a medical emergency.