If you’re a fish owner and you’re observant, you would notice that your fish don’t close their eyes. Fish do not have eyelids; hence, they don’t blink. Now considering that sharks are fish, you may ask “Do sharks blink or close their eyes?” or, are they like other fish?
Sharks can actually blink, unlike other fish. They can do this with the help of the nictitating membranes which serve as the third eyelid. This however does not mean that sharks blink like humans or other land animals. Sharks have nictitating membranes on the lower and upper part of their eyes. The main function of this eyelid is to protect their eyes. Though, not all sharks have nictitating membranes.
Fish don’t have eyelids, but sharks do. Is your next question “Why are sharks exception?”
Let us find out the interesting facts and features of the sharks’ eyelids and why they are important to sharks.
What is the Function of a Shark’s Nictitating Membrane?
The nictitating membrane of a shark serves as a protective eyelid. The main function of this eyelid is to protect the shark’s eyes from external injuries.
When sharks attack their prey, they close the eyelids to protect their eyes. The nictitating membranes of sharks do not hinder their eyesight since they are transparent.
This is unlike humans and many other terrestrial animals whose eyelids serve to also moisturize their eyes. Of course, we tend to blink involuntarily. However, try keeping your eyes open for a while, they will dry out leading to itching and tears coming out in an attempt to add moisture to the eyes.
Sharks are already in the water and their eyes are adapted to sight underwater. Therefore, the nictitating membranes provide protection to their eyes and not really moisturizing them. An obvious reason why other fish kinds that don’t engage in violent prey attacks have no eyelids. Nor, do they need to blink.
You see, while sharks have nictitating membranes serving as eyelids, they do not function exactly like ours.
Do All Sharks Have the Nictitating Membranes?
No! not all shark species possess the nictitating membranes. In fact, out of the over 400 known shark species, about 15 do not have the nictitating membrane.
Does this mean they don’t protect their eyes?
No! sharks that lack nictitating membranes resort to other means of protecting their eyes. For example, the great white shark doesn’t have the nictitating membranes however, it can roll its eyes backward. When this happens, the eyes go into their head to avoid exposure to external harm. These sharks do this especially when attacking prey, mating, or bump into objects.
This is why the great white shark appears to have a ghostly look when attacking prey.
In essence, sharks would protect their eyes by blinking, closing, or rolling it back when the need comes. If they don’t, they may lose their eyesight and would no longer see underwater.
Do Sharks Close Their Eyes When They Sleep?
If you’re hoping to catch a shark sleeping with its eyes closed, then you may stop hoping from this moment. Sharks do not close their eyes while sleeping. In fact, they lack eyelids like most terrestrial animals.
As a result, when sharks sleep, they tend to turn off part of their brain while the other part remains active. Meanwhile, their eyes will always be open.
The nictitating membrane of some shark species is not like our eyelids. Instead, it is a protective clear layer that serves as a covering to the shark’s eyes when they make an impact. They mostly function when the sharks are feeding.
Are Sharks’ Eyes Different from Other Animals?
The eyes of sharks appear similar to many other animals including humans. However, they are particularly efficient for swimming under the water.
The make-up of the shark’s eyes is just like most other animals consisting of the lens, cornea, and retina. They also function similarly compared to other creatures.
There is however a special tissue, tapetum lucidum that sharks have that makes their sight underwater efficient. With the tapetum lucidum, sharks are able to contract and dilate their pupils just like we humans do.
This tissue contains mirrored crystals and is positioned at the back of the retina. On normal comparison, sharks’ vision when in the water is up to 10 times better than that of humans. Source This is because the light that enters the shark’s eyes reflects back to the retina and not absorbed.
Therefore, they have better vision in the deep ocean which is mostly dark. The tapetum lucidum is more prominent in sharks that are more active in the night i.e. nocturnal sharks.
Also, like humans, sharks have rod and cone cells in their eyes. The rod cells help the sharks to differentiate between light and dark, whereby, the cone cells are responsible for color detection. It is not yet certain how much of colors sharks can see, although, scientists are still working toward it.
Normally, researchers believe that sharks have more rod cells than cone cells.
Sharks also can switch from monocular to stereoscopic vision if they wish. Where monocular vision involves the use of one eye, stereoscopic is just like humans combining the two eyes.
You see, sharks’ eyes aren’t as different from most other animals.
Are Sharks Attracted to Light?
For all animals with eyes, they see as a result of the reflection of light. Hence, as light bounces off an object, it becomes visible. Therefore, light is an important element to the sight of animals.
Sharks can see in the deep ocean known to be dark. However, this does not mean they do not require light. It is basically possible that bright light may attract a shark. From what we know, bright lights would catch their attention.
Most shark species have sharp sight; therefore, they respond to light quickly. If light reflects off an object, chances are they would mistake the object for prey.
Note that not all shark species have sharp eyesight. Thus, bull sharks for instance barely have a good sight. In fact, they find their prey using their sense of smell and not vision. Bull sharks hunt their prey by first bumping it before attacking. Since they have quite poor sight, this method of hunting compensates for it.
The tapetum lucidum tissue in sharks helps them reflect the light back into their eyes.
We can conclusively say that sharks respond actively to light. However, whether they will follow the light is not certain. Of course, sharks have very many rod cells in their eyes, these cells help we humans to see the light.
How Does Sharks’ Sharp Eyesight Help Them?
Considering that sharks live in the ocean depth where the water is dark, it is important that they develop sharp eyesight. This is because they need to see what is around them to either take advantage or protect themselves.
With their adept vision, sharks are much likely to see you first when you enter the water. This may not look good to you, but hey, it is an advantage to the sharks. Of course, the ocean is their habitat, so they should navigate it better.
More so, that sharks would see you first doesn’t mean they would launch an attack. While some may come close to you as a result of curiosity, others would remain indifferent and might even swim away.
Can Sharks See Clearly Outside the Water?
It is not clear yet how well sharks can see outside the water. Scientists and divers alike speculate that some shark species would often swim to the water surface to take a look at boats.
If sharks lift their head outside the water, considering the build of their eyes, lights will fill their retina. The shark will now be forced to adjust its pupils so rapidly to be comfortable.
An example of the shark species that would usually raise its head above the water to take a peep is the great white shark.
If this shark is able to see clearly outside the water is still a subject of scientific discussion. Certainly, sharks in recent times have been part of several scientific and biological research initiatives.
Do Sharks Close Their Eyes When They Attack?
Sharks certainly protect their eyes when attacking their prey. However, you wouldn’t say they do this by closing their eyes. Sharks don’t have eyelids as we do, so they wouldn’t be closing their eyes the way you think.
There are two ways sharks protect their eyes when they attack. The first is using the third eyelid known as the nictitating membrane to cover their eyeballs. This nictitating membrane is however clear that you may not notice the difference when it is covering the eyes and when not.
For sharks that do not have the nictitating membrane, they resort to other means of protecting their eyes during an attack. An example is the great white shark which rolls its eyes into their head to protect the eyes during an attack. This gives the shark an eerie look as the eyes turn all white.
These sharks obviously negotiate their eyesight during such attacks.
Conclusion
Sharks are amazing creatures with many fascinating features. On this page, we discussed the ability of sharks to close their eyes and extended it to the strength of their eyesight.
Now, you know sharks don’t have eyelids like humans do, however, they are able to protect their eyes during an attack. More so, these creatures though not all species, have adept sight underwater.