Anatomy Senses

Great White Shark Eyes | Sharks Info

great white shark eyes

The great white shark eyes are one of many extremely interesting aspects of this species. It is the largest predator in the world’s oceans, both in temperate and subtropical waters. Many scientists believe that they are a highly intelligent and curious creature. When great whites congregate, they seem to exhibit different behaviours: some are more open and gaping, while others are more assertive and physical. Great white sharks can travel great distances. On the voyage from the Hawaiian islands to California, a shark swam from South Africa to Australia, setting a record for the migration of a fish.

Great White Shark Eyes

Great white shark eyes provide great vision. Like humans, shark eyes are equipped with mirror layers and crystals on the retina. The retina of their eyes is divided into two areas, one for daytime vision and the other for dim light at night.

To protect them, the Great white shark eyes roll back into its eye sockets when threatened. This provides light that can be detected a second time. When the light is defused, sharpness decreases and sensitivity is increased. These adaptations allow sharks to be seen in dim light and dark, murky water, up to ten times larger than humans.

In contrast to humans, shark eyelids are used to protect the eyes from attacks by prey. Sharks have a clear membrane that covers the eyes and protects them when the shark bites its prey. Great White sharks lack this membrane and have to roll their pupils back on their heads for protection when feeding.

great white shark blue eyes
Image of a smiling Great White Shark

Great White Shark Eyes Can Be Misleading

The Great White shark eyes do not see any difference between its typical prey and humans swimming, paddling or surfing. This suggests shark attacks are often cases of mistaken identity, according to a new study. White sharks also don’t have black, beady killer eyes. Instead, they have beautiful blue eyes. The iris of a great white shark is not black, but dark blue.

Researchers filmed seals and people in the water and edited the footage to match the vision of young Great White Sharks, the Great White Sharks that pose the biggest threat to humans and surfers. They found that the shape and movement of humans looked the same from both the seal and shark’s perspective.

The study was published on October 26 2021 in the Journal of the Royal Society, is the first to test the theory that sharks attack humans because they believe humans are prey. The Great White Shark (Carcharodon carcharias) is responsible for more deaths than any other shark species and have killed six people in 2020, but the relative risk of human bites by sharks is low, according to the International Shark Attack File from the University of Florida. Great white sharks are often portrayed as mindless killers who love human flesh but that doesn’t seem to be the case.

Young sharks evolve by looking for images of their prey and combining them with other sensory information such as smell to know what to eat. Sharks started hunting seals when they were 25 metres long. It’s a learning process and sharks are often prone to mistakes. Great white sharks also lack colour vision and cannot see fine details as well as the human eye.

Mature great white sharks rarely bite humans because they are older and more experienced hunters and make fewer mistakes. This could be applied to great white sharks and other sharks such as bull sharks and tigers that bite humans.

great white shark eyes roll back
Image of a Great White with a school of fish

Structure And Function

Although the structure and function of the eyes of big white sharks and other sharks are similar to ours, there are some interesting and important differences. So, while they dominate creatures, their eyesight is the least studied and understood of the sharks’ senses. The great white shark’s eyes are large, suggesting that vision is important for their way of life.

We know next to nothing about the visual abilities of great white sharks. Little of what we know can be gleaned from studies of other species.

Shark eyes are hollow spheres with characteristics that are expected of typical vertebrates: cornea, iris, lens and retina. The cornea is the clear outer shell of a vertebrate eye.

In humans, the cornea is responsible for 81 percent of the total focal power of the eyes, which is why small irregularities in the cornea lead to such severe visual disturbances in humans. Like humans, the amount of light that reaches the eye is controlled by the iris in sharks. In seawater, the optical density is identical to that of corneal tissue, so that sharks rely on a spherical lens to focus the light into the eye.

The iris is a contractile muscle layer with a perforated opening called the pupil. In low light, the iridescent muscles contract to dilate the pupil, which is why many deep-sea sharks dilate to capture the small light flickering in and out of their realm of eternal darkness as they relax in strong light and contract the pupil. As impressive as this may seem, people are accustomed to our pupils widening and contracting without realising.

The contraction of the pupils increases the visual depth of field of the sharks or the depth of field range, just as we extend our focus range in harsh light conditions by squinting.

Many shark eyes have slit-like pupils, but the great white appears to have a dark button-like onyx. The pupil is circular, and the iris has a dark ring with spectral echoes of midnight blue. Looking at the eyes of living individuals up close, the inner structure is easy to see. The great white relaxes its eye sockets and does not follow any objects, so that the white shark eye seems to orient straight ahead.

The shark lens is crystalline and spherical, giving it enormous refractive power. Just as amphibians and snakes (but not other reptiles) focus in the opposite direction, teleosts shift the lens from focusing on a distant object to a nearby one. This orientation explains why animals that cross near a caged diver are better at eye level when inspecting. Focusing on distant objects relaxes the muscles that control the shark lens and allows the lens to distance itself from the cornea, while focusing on the nearby object causes the lens muscles to contract and pull the lens closer to the cornea. Just as human lenses change focal length and shape, sharks “focus changes.

The retina is a light-sensitive layer of tissue that covers the inside of the eyeball. It detects light energy due to a vitamin A-based pigment called rhodopsin. When the pigment is hit by a photon (a packet of visible light), it undergoes a temporary change of conformation. This generates an electrical signal that is sent to the optic nerve in the brain, where stimulus is interpreted as vision.

This adjustment is necessary because the time and speed of nerve transmission are finite and sharp, and there is a limit to the frequency with which images can be separated in the eyes. The persistence of the images on the human retina allows the film to give us the illusion of movement, because each successive image projects the frequency that our eyes transmit to them.

The minimum frequency at which a blinking image in the eye can no longer separate is called the flicker or fusion frequency. A shark vision study by Gruber showed that juvenile lemon sharks (Negaprion brevirostris) exhibit a flicker / fusion frequency of 45% of the flash frequency, at which humans no longer see single flashes.

The visual pigment rhodopsin reacts to green light, which is the greenish light that floods shallow coastal waters. In deep water where blue is the dominant color of ambient light, sharks have a secondary visual pigment, gold, a light-sensitive compound that also responds to light from the blue end of the spectrum. An analogous mixture of rhodopins and secondary pigments gives us color vision.

why are great white sharks eyes black
Image of sunlight reflection on a Great White

Conservation

Sharks play an important role in ocean ecosystems by hunting other animals, keeping prey populations healthy and supporting the size of their habitat and resources. But not knowing when and where sharks attack humans makes public concern and calls people to action to reduce shark populations. This can have harmful effects on other marine life.

The International Union for Conservation of Nature (IUCN) hopes that a better understanding of how sharks bite people will lead to improved solutions to prevent shark attacks and damage to marine life. Great white sharks are at risk of extinction if killed by humans, but under beach conservation programmes in Australia and South Africa they can be caught and released alive.

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