Who doesn't love to sleep? We all know the struggle is real when getting out of bed in the mornings — sleep is just too lovely to leave. But for animals in the ocean who need to keep breathing even while under the sea, sleeping is a little different.
For example, how sharks sleep is so different from the way we do.
Because sharks need to keep water flowing over their gills to breathe, it was previously believed by scientists that they could simply never stop swimming. But, as more research has been conducted, that stance has changed slightly.
According to LiveScience, certain species of shark, like nurse sharks and bullhead sharks, use their mouth muscles to draw in water while remaining still on the ocean floor.
This is called buccal pumping and is further enhanced by the sharks' spiracles. LiveScience defines it as "respiratory openings behind the eyes that allow the fish to pull in water while buried under sand."
As for larger shark species, like great whites, they do need to keep swimming to bring oxygen to their gills. But, according to Discovery, a study conducted on the spiny dogfish shark found that the spinal cord controlled the shark's swimming — not necessarily the brain.
So, while a shark's spinal cord could keep them moving forward, the brain could essentially take a nap.
While filming for Shark Week 2016, Discovery filmed what they believe could be a great white shark "napping."
They captured the shark cruising slowly into a current, allowing water to pass through its mouth and over its gills, while it appeared to be in a catatonic state.
This isn't the only time a shark has been caught possibly sleeping, though. In August 2017, National Geographic reported on video footage of dozens of resting whitetip reef sharks. According to NatGeo, "Sharks will also rest in parts of the ocean floor with strong currents that allow water to easily flow over their gills."
This can be seen in the video below, with all the sharks' tails moving in unison as the current flows by them.
Gathering in piles is just one way the animals can rest. Another behavior sharks have exhibited is called "yo-yo diving." According to Huffington Post, this is when a shark will start at the surface and then slowly glide downward. This allows their brain to disengage, but for the animal to still get air as the shark drifts downward.
Then the shark wakes up as it gets closer to the ocean floor and swims back up to do it again.
But, while all of this gives new insight into how sharks rest, National Aquarium curator Jay Bradley noted to NatGeo that sharks don't really "sleep" at all. "They don't go into an unconscious state," he said. "We still don't fully understand what they do during rest periods."
So, while a shark's brain doesn't necessarily ever turn off, they do experience periods of rest. Whether their swimming slows down or comes to a halt completely, these behaviors allow them to conserve energy, rest and recharge.