Ragged-tooth sharks (Carcharias taurus) swallow atmospheric air and retain it in the stomach. The trapped air increases buoyancy, helping the shark hover with less effort.
Sharklife field footage: the video above was recorded off Sodwana Bay and shows this unusual buoyancy behaviour.
Surface air-gulping
Ragged-tooth sharks rise slowly to the surface and break through the water – opening the mouth and taking in air.
Air stored in the stomach
After surfacing, the swallowed air is retained in the stomach, forming an air pocket that helps offset the shark’s natural tendency to sink.
Why this is unusual among sharks
Sharks do not have gas filled swim bladders like bony fish. Most rely heavily on a large oil-rich liver and forward movement to help manage buoyancy and generate lift.
Ragged-tooth sharks add something different. They are currently regarded as the only known shark species to use this mechanism for buoyancy control.
A shark that can hover
The result is one of the most distinctive behaviours seen in this species. Ragged-tooth sharks can hover motionless just above the seabed, or move slowly through the water with relatively little fin movement. This behaviour is especially relevant to Sharklife’s long-term ragged-tooth shark monitoring in the iSimangaliso Marine Protected Area.
Reducing the effort needed to remain suspended may help conserve energy. It may also support the slow movement often seen around reefs and aggregation sites.
How does the air come out?
Ragged-tooth sharks can release excess air underwater. In Sharklife footage, bubbles can be seen leaving the mouth and around the gill openings during descent.
Releasing the air reduces buoyancy, allowing the shark to descend and adjust its position in the water column.
Related Sharklife research
See our ragged-tooth shark monitoring project and learn more about the methods used at the Sharklife Marine Research Station.
Sources and further reading
- Hussain, S.M. Buoyancy mechanism, and density of sand tiger shark (Eugomphodus taurus). Indian Journal of Fisheries, 36(3): 266–268. Read source.
- Aquarium of the Pacific. Sand Tiger Shark. Behavioural overview describing air swallowing, near-neutral buoyancy and virtually motionless hovering. Read source.
Terminology: ragged-tooth shark is the common South African name for Carcharias taurus, also known internationally as the sand tiger shark or grey nurse shark.