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Do Great White Sharks Sleep? The Truth About Their Sleep

The great white shark (Carcharodon carcharias) is one of the most infamous and feared predators in the ocean. As apex predators, great whites play an important role in maintaining balance in the marine ecosystems they inhabit. Their sleeping habits have long fascinated both scientists and the general public alike.

What Is Sleep?

Before examining whether sharks sleep, it’s important to understand what sleep actually is. Sleep is defined as a natural periodic state of rest during which consciousness of the world is suspended, and the body’s physical activity is decreased. It is distinguished from wakefulness by reduced sensory activity, reduced mobility, and reduced interactions with surroundings.

During sleep, the body alternates between two primary stages – rapid eye movement (REM) sleep and non-REM (NREM) sleep. REM sleep is associated with vivid dreaming, bursts of eye movements, paralysis of voluntary muscles, and irregular heart rhythms. NREM sleep is divided into three stages ranging from light sleep to very deep sleep.

Most terrestrial mammals and birds exhibit clear sleep cycles, usually with periods of sleep and wakefulness corresponding to night and day. Aquatic mammals like dolphins show sleep-like behavioral and brainwave patterns as well. This suggests sleep is essential for basic functioning across the animal kingdom.

Learn more: Great White Shark Upside Down

Do Sharks Sleep Like Other Animals?

For a long time, scientists struggled to determine if sharks actually sleep. After all, these powerful predators never seem to stop moving and lack eyelids to close while asleep.

Initial research focused on whether sharks exhibit sleep-like behavioral changes. However, great white sharks and other shark species swim continuously to ensure a constant flow of oxygenated water over their gills. They also lack features like perches or nests where they can safely exhibit motionless sleep-like behavior.

More recent studies analyzed chemical changes and electrical activity in the brains of captive sharks. This research provides compelling evidence that sharks do, in fact, enter sleep-like states.

Resting and Sleep-Swimming Sharks

The most concrete evidence for shark sleep comes from a 2021 study on Port Jackson sharks. Researchers observed these resting sharks lying motionless on the sea floor for hours. During these periods, the sharks’ brainwaves showed a pattern consistent with NREM sleep.

Scientists also noticed Port Jackson sharks swimming slowly but continuously in a small area at night. Electroencephalogram (EEG) recordings of their brains revealed a sleep-like pattern in the higher brain regions. But signals from the spinal cord suggested the sharks retained some awareness to coordinate swimming motions.

This phenomenon is described as “sleep swimming” – a state where the shark’s forebrain rests while the midbrain remains active to control essential body functions. Some researchers hypothesize great whites and other open ocean sharks maintain slow, sleep-like swimming to perform their version of sleep. The coordination demands of consistent swimming likely prevent sharks from ever achieving deep NREM sleep or REM sleep characterized in humans by complete muscle paralysis.

Why Can’t Sharks Stop Moving?

Sharks lack swim bladders – gas-filled sacs that most bony fish use to control their buoyancy. Without swim bladders, sharks must rely entirely on the lift force of their pectoral fins and the downward thrust produced by tail movement to prevent sinking. Great whites and other large sharks may slowly sink if they stop swimming.

A great white shark that stopped swimming would also begin to suffocate because water would no longer flow over its gills. Great white sharks and other shark species need this constant flow of oxygenated water. Interrupting it can quickly result in death by asphyxiation. Unlike bony fish, a sleeping shark that stops moving its body or tail will sink to ocean depths with dangerously low oxygen levels.

Signs of Sleep Deprivation

Since sharks likely enter more wakeful rest rather than true deep sleep, scientists are still investigating whether sleep deprivation negatively impacts sharks. However, extensive research highlights the consequences of sleep deprivation for humans and other mammals.

Effects of sleep deprivation include:

  • Cognitive impairments – confusion, memory loss, paranoia
  • Physical effects – increased pain sensitivity, tremors, weight gain
  • Increased aggression and impulsivity
  • Suppressed immune system – frequent sickness

While sharks may have adapted to forgo deep sleep, they likely need periods of intentional rest to maintain proper health and function. Monitoring sharks’ brainwaves and stress hormone levels could provide clues on whether interrupted waking rest disturbs their bodily equilibrium.

Do Great Whites Migrate for Sleep?

Great white sharks are apex predators found in cool, coastal regions across the world’s oceans. They display seasonal migrations – traveling huge distances between feeding grounds and suspected breeding sites.

Some researchers hypothesize great whites may also migrate to locate ideal safe spaces for intentional waking rest. Massive great white sharks up to 20 feet long have difficulty finding sheltered spots to idle. And they tend to avoid areas near humans and shipping lanes.

Tagging data reveals great whites repeatedly return to specific ocean regions along migration paths. These sites generally have few predators, ample prey availability and strong ocean currents that require minimal swimming efforts. Researchers speculate such areas may allow great whites respite to achieve more substantial rest.

Deep Dives and Deep Sleep?

Great whites also make occasional deep dives down to nearly 1,200 meters. These long, deep dives seem to serve purposes beyond simply chasing prey. Instead, great whites may take these plunges to enter cooler waters that reduce their metabolisms and facilitate restful states.

At mesopelagic depths reached during deep dives, the chilly waters match great whites’ body temperature. This eliminates the need to burn energy on heat generation, allowing sharks to reach a state of torpor resembling hibernation in other animals. Though they retain some awareness of oxygen intake, the shark’s bodily functions significantly slow down during these dives – perhaps the closest great whites come to deep NREM sleep.

Rest Requirements Still Uncertain

There is still much to uncover about sharks’ sensory capabilities, swimming efficiency and sleep requirements. Advances in underwater tracking technology and EEG testing on captive sharks provide expanding insight. Still, the constraints of laboratory tests make it difficult to observe sharks’ rhythms under natural conditions.

Perhaps future monitoring of different shark species in their native habitats will reveal distinct sleep-related behaviors adapted to their particular environments. Determining baseline sleep needs could also help assess sharks’ health during encounters with environmental disturbances – like noise pollution, habitat destruction, and climate change. There remains extensive research required to truly define and understand how sharks meet their rest requirements in the wild.

So in Summary

Scientific evidence suggests great white sharks do not sleep in the same manner most mammals exhibit with extended intervals of deep sleep. Due to physiological constraints, great whites likely enter more wakeful resting states that may involve continuous slow swimming or periodic deep dives. But ongoing research is still required to better define shark sleep requirements and behaviors meeting those needs. One thing remains clear – these apex ocean predators seem uniquely adapted to largely forgo extended unconscious deep sleep common in land mammals.

Frequently Asked Questions

Do sharks sleep with their eyes open?

Yes, sharks sleep with their eyes open. Sharks have no eyelids to close while asleep. To rest their vision, sharks shift to monocular vision during sleep – closing one eye at a time. Scientists believe this allows each eye some recovery from constant use while the opposite eye maintains vigilance against threats.

Why don’t sharks drown if they never stop moving?

Sharks extract oxygen from water flowing over their gills using ram ventilation. Without swim bladders, sharks rely on consistent tail movements to prevent sinking. Interrupting bodily motion causes sharks to asphyxiate from lack of water flow or possibly drown from sinking away from well-oxygenated surface water.

Do great white sharks migrate just to sleep?

While great white sharks do undertake long seasonal migrations, their movements likely serve several purposes. Migration allows them to access dispersed food resources in different regions. Their return to specific sites along migration routes may provide safer spots to enter intentional waking rest. But feeding, breeding, and other functions also impact great whites’ migratory habits.

Can sharks sleep if they stop swimming?

Some sharks can sleep while resting motionless on the sea floor. Port Jackson sharks exhibit this sleep-like behavior. However, great white sharks and other open ocean sharks lack the same ability to stop swimming and settle on the seabed. Though they can enter waking rest, pelagic sharks may never reach stages of deep NREM sleep characterized by a complete lack of bodily movement.

Do sharks sleep together in groups?

There is little evidence of coordinated sleep behaviors between sharks. While some shark species form social groups, sleeping sharks have only been observed alone, resting on the ocean bottom. Pelagic sharks that sleep while continuously swimming are unlikely to synchronize such activities. However, future tracking may reveal the shared use of safe habitats that provide space for open ocean shark species to enter restful states.

Are great white sharks safe to swim near while sleeping?

Absolutely not! Approaching a great white shark under any circumstances is extremely dangerous. While sharks may enter sleep-like states, they remain large, powerful predators. Great whites can be provoked to attack with little warning if they sense a potential threat. Given their ability to inflict lethal wounds, swimmers should never seek proximity to a great white – whether the shark appears awake, resting, or asleep.

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