Sharks can “throw up,” but their method differs significantly from most creatures. Unlike the muscular contractions associated with vomiting in many animals, sharks employ a unique process involving the physical expulsion of their stomach. This adaptation helps them manage their digestive system and respond to various stimuli.
Gastric Eversion: The Shark’s Unique Process
Sharks push their entire stomach out through their mouths, turning it inside out in a process known as gastric eversion. This action is similar to turning a sock inside out. The stomach is then exposed to the surrounding seawater, which helps to cleanse it of unwanted contents. After expelling the material, the shark retracts its stomach back into its abdominal cavity, returning it to its normal position.
Gastric eversion is rapid, often occurring in less than a second, with some observations recording it in as little as 0.28 to 0.40 seconds. This swift action is believed to involve a combination of muscle contractions and changes in internal pressure within the shark’s body. The shark’s stomach is robust and elastic, allowing for this extreme maneuver without causing damage to the organ. This differs significantly from mammalian vomiting, which primarily involves the forceful expulsion of stomach contents through muscular contractions rather than the eversion of the stomach itself.
Reasons for Stomach Ejection
Sharks engage in gastric eversion for several reasons, primarily to maintain their digestive health and respond to threats. One common motivation is to expel indigestible items that have been accidentally swallowed. Sharks often consume prey whole or in large pieces, and while their stomachs contain highly acidic fluids capable of dissolving many materials, certain objects are too tough to break down. These can include bones, shells, feathers, and human-made debris like fishing hooks or cans.
Another reason for stomach ejection is to cleanse the stomach lining. This cleaning function helps remove accumulated debris, parasites, or excess mucus that might interfere with digestion. By rinsing the stomach in seawater, sharks can maintain a healthy alimentary tract. This periodic self-cleaning is part of their adaptations for efficient digestion in their marine environment.
Gastric eversion can also occur as a response to stress or capture. When sharks are caught in fishing gear or subjected to the stress of being handled, they may evert their stomachs. This behavior might be a reflex triggered by extreme stress or an attempt to lighten their load, potentially aiding escape. Some observations suggest that certain species, like great white sharks, might voluntarily evert their stomachs to make room for more food after a large meal.