Sharks are typically an ocean-going species. It may come as a shock that some can spend up to an hour outside their natural watery habitat. Of course, not every shark species can survive this long out of water; some can only survive mere minutes.
However, through the incredible process of evolution, some sharks have dared to defy science.
In the tropical waters off Australasia, one shark has learned how to use the terrestrial environment to its advantage. How is this possible? To understand that, first, we need to determine whether sharks can survive on land in the first place.
Can sharks breathe on land?
The short answer is no. To the relief of some, sharks cannot breathe on land.
While some sharks can survive extended periods in terrestrial environments, they cannot exclusively live in this dry realm.
Terrestrial animals breathe in air, acquiring oxygen that gets sent around the body.
This is the work of the lungs. Unfortunately for sharks, they lack this vital organ. Consequently, they cannot acquire oxygen the way terrestrial animals would.
However, they do need to breathe in oxygen to survive. But without lungs, how do they do this?
Like most fish, sharks have gills. They need a constant flow of water passing over specialized organs, or gills, that take in oxygen from the surrounding water. So, without water, the survival of sharks is exponentially decreased.
Sharks are obligate ram ventilation breathers. This means a constant supply of water needs to pass over the gills in order for sharks to survive.
However, this isn’t to say they will die instantly if they were to be exposed to air.
Sharks can survive out of the water for as long as it takes for their gills to dry out completely. Moreover, the larger the shark, the larger the gills, and therefore the longer it takes for the gills to dry out.
Other factors that affect the survival of sharks outside of water
Oxygen acquisition is not the only issue sharks face when exposed to air.
There are two other factors that pose a risk to the survival of sharks outside of water: dehydration and internal bleeding.
Essentially, this is the loss of fluids within the body.
Sharks are specifically adapted to the environment they have evolved to. Any deviations from this norm, and a shark could suffer fatal consequences. In ocean environments, the internal conditions of a shark are in balance with the outside ambient salt levels.
Sharks have specialized chemicals within their bodies, called urea. This ensures the species is in equilibrium while swimming – there are equal quantities of urea and other chemicals within the water inside sharks, as there is salt in the external sea. Consequently, water doesn’t continuously flow out.
Unfortunately, when a shark is out of the water, balance is lost, and water escapes at a much higher rate. This causes dehydration.
Another rather gristly problem sharks face out of water is the risk of internal bleeding.
Sharks belong to a group of fish, along with rays, known as cartilaginous fish. This means they lack a bony skeleton.
With no skeleton, for example, a rib cage or other strong bones, there is no support when pressure changes.
With no support, organs are crushed, and mass internal bleeding occurs. Lovely.
Are there any shark species that can be found on land?
Sharks cannot be found naturally on land, as they cannot breathe here. However, and it is a big however, there are some rare exceptions.
In the Western Pacific Ocean, a small shark species inhabit reef systems and tide pools.
Meet the epaulette shark.
Incredibly, this bottom-dwelling shark has found fame from its walking abilities! Yes, you heard that right. These sharks have been known to “walk”.
The habitats in which epaulette sharks are found tend to be cut off from one another with the changing tides. In these small, isolated “islands”, oxygen levels drop to near hypoxic levels; a low oxygen level that can cause irreversible damage to many species.
To overcome this, the epaulette shark can perform a strange behavioural response: a crawling-walking motion along reefs and rocks to find larger bodies of water. They warp their bodies while wiggling their pelvic and pectoral fins to create this movement.
But how can they survive extended periods outside of the ocean?
Overtime, this species has adapted to survive in a habitat with severe oxygen depletion. To do this, they can increase blood supply to the brain and shut down other, not-so-essential organs. They can also keep their gills moist enough, preventing the collapse of these organs.
It has been found that epaulette sharks can withstand complete hypoxia without causing harm to themselves. Now, that’s a real-life superpower!
So, while sharks cannot exclusively be found on land, one species braves the air to move between its salty home.
Sharks are almost exclusively water-based animals. Due to the lack of lungs, which are found in terrestrial animals, sharks cannot breathe on land.
Instead, they have adapted to absorb oxygen from the water using specialized organs: the gills.
Similarly to how humans would not survive submerged in water for too long, sharks cannot spend an extended period on land or in the air.
Most species can tolerate just a few minutes exposed outside of water. Unless it’s an epaulette shark – those little guys have defied the laws of sharks and have adapted to walk on land.