Sharks are intricately tied to their aquatic environment for survival. Their existence outside of water is severely limited, raising questions about how long they can last when stranded on land.
Shark Respiration and Water Dependency
Sharks breathe by extracting dissolved oxygen from seawater as it passes over their gills. Their gills consist of multiple slits and lack the bony covers found in many other fish. Water enters through the shark’s mouth or specialized openings called spiracles, then flows over gill filaments where gas exchange occurs. Oxygen is absorbed into tiny blood vessels, while carbon dioxide is released back into the water.
Most sharks employ one of two primary methods to ensure continuous water flow: ram ventilation or buccal pumping. Ram ventilation requires the shark to swim forward with its mouth open, forcing water over the gills. Species like great whites and mako sharks are obligate ram ventilators, meaning they must constantly move to breathe. Other species use buccal pumping, actively drawing water into their mouths to pump it over their gills, allowing them to breathe even when stationary. Without water, these processes cease, leading to suffocation.
Factors Determining Survival Time
A shark’s survival time out of water varies significantly, ranging from mere minutes to a few hours under specific conditions. Species plays a substantial role; smaller, more tolerant species, such as the epaulette shark, have adaptations allowing them to survive for up to two hours by tolerating low oxygen levels and even “walking” across exposed reef flats to find water. Larger, pelagic sharks, which rely on constant movement for ram ventilation, typically have much shorter survival times, sometimes only 15-30 minutes.
Several environmental and physiological factors influence this duration. Colder temperatures generally extend survival by reducing metabolic rate and oxygen demand. Conversely, direct sun exposure rapidly increases a shark’s body temperature, leading to overheating and accelerated dehydration of their gills. A shark’s physical condition, including any prior injuries or stress, also impacts its resilience. If a shark thrashes vigorously out of water, it depletes its limited oxygen reserves much faster than if it remains still.
Physiological Impact of Stranding
When a shark is removed from water, its body experiences physiological effects beyond the initial lack of oxygen. The delicate gill structures, designed to be buoyant in water, can collapse under their own weight in air, significantly reducing the surface area for gas exchange. This collapse is often coupled with rapid desiccation, as the gills dry out without constant water flow, rendering them ineffective.
The immense weight of a shark’s body, no longer supported by water, can compress internal organs, potentially causing damage. Overheating is another immediate threat, as sharks are ectothermic and rely on water for thermoregulation; exposure to air and sun can quickly raise their internal temperature to dangerous levels. The stress of stranding triggers a physiological response involving the buildup of lactic acid in their blood, which can compromise organ function and overall health. The shark’s rough skin can also suffer abrasive damage from contact with hard or uneven surfaces, leading to further injury.
Assisting a Stranded Shark
Encountering a stranded shark requires caution to ensure safety. The primary rule is to maintain a safe distance and never attempt to handle or move the shark independently. Sharks are wild animals, and even a seemingly incapacitated one can inflict serious injury. It is also illegal in many places to interfere with marine wildlife without proper authorization.
The most effective step is to immediately contact local marine animal stranding networks, wildlife agencies, or emergency services. Providing precise details, such as the shark’s size, species if known, its condition, and the exact location, is crucial for responders to assess the situation and dispatch appropriate help. While awaiting expert arrival, if advised by professionals, some basic measures might include gently keeping the shark’s gills wet using buckets of water from a safe distance, or covering the shark with a wet sheet to prevent desiccation and sunburn. It is paramount to avoid pushing the shark back into the water without expert guidance, as this can cause further injury to the animal or pose a risk to rescuers.