Sharks have been swimming in the oceans for millions of years and are, in many cases, their main predators. These cartilaginous fish are fascinating from multiple points of view. One of them is the one corresponding to their senses, which allow them to be very efficient hunters.
Among these senses is vision, about which several hypotheses have been formulated. To learn about them and answer any questions about them, we invite you to read this article on our site in which we discover if sharks are blind.
What are sharks' eyes like?
For some time it was speculated that sharks relied more on other senses than vision, so they probably couldn't see well. However, it is known that this is not entirely true, since the eyes of sharks are like those of other vertebrates both anatomically and physiological. What happens is that they present some differences related, mainly, to the type of ecosystem in which they live, in addition to others linked to the perception of colors.
Thus, vision in sharks is an important aspect. Through their sight they manage to identify their prey or possible attackers. Sharks' eyes are two structures located on each side of the head and, like ours, they have a cornea, iris, lens and retina:
- Cornea: is the tissue that externally covers the eyes of sharks and other living beings. Sharks use this structure to focus after light enters the eye.
- Iris: is a muscular sheet with the ability to contract. It is perforated by another structure known as the pupil When the shark is in low-light areas, the iris contracts, dilating the pupil and allowing more to be captured luminosity efficiently. This is very common in sharks found in deep areas. Conversely, when there is enough sunlight, the iris then relaxes, so the pupil constricts.
- Crystalline: it is a transparent lens with an almost spherical shape, which allows these sharks a high capacity to refract light.
- Retina: is the tissue that covers the inside of the eyeball and whose function is to send signals to the brain for image processing. This occurs through various physiological processes and from the incidence of light.
In addition, sharks have two more structures associated with the visual organs. On the one hand, they present a layer behind the retina that has the ability to retroreflect light. It is known as tapetum lucidum. The other structure is present in some sharks and is called nictitating membrane Its function is to protect the animal's eye during hunting or attacks it may receive. However, some species, such as the great white shark (Carcharodon carcharias), lack this and instead are capable of turning the eye backwards so that it is protected, exposing a fibrous layer to the outside.
Are sharks blind?
As we have seen, sharks are not blind On the contrary, they have a complex visual system that indicates their high development. Although these animals use, in principle, other sensory systems to perceive chemical, thermal, mechanical and even electromagnetic changes produced by their possible prey, vision is ultimately the sense they use to clearly identify their target or distinguish whether it is an attacker. Therefore, sight is not only present, but plays an extremely important role in these animals.
If you want to know more about how sharks capture their prey, don't miss our article How do sharks hunt?
How do sharks see?
Sharks, in principle, as occurs in vertebrates in general, depend on light stimuli to be able to see, so vision begins focusing through the cornea and, just like in humans, the iris regulates the amount of light entering the eye. The pupil dilates or contracts depending on the availability of light, but in the case of sharks that live in very deep areas, the pupils are constantly dilated in order to capture the little light that arrives.
Some species of sharks, when their eyes are relaxed, can rotate them within their orbits, thereby managing to follow an object or individual with their gaze. The refraction of light in the eyes of these sharks is extraordinary, thanks to the fact that the lens is almost completely spherical. Unlike humans, focus is not achieved by changing the shape of this structure, but by changing its position by relaxing or contracting the muscles associated with this lens. This means that at distances of less than 15 meters vision is the sense that sharks primarily use.
On the other hand, these animals are capable of distinguishing different levels of luminosity, as well as intensities of tones. The vision of sharks, without a doubt, is closely related to the type of habitat in which they live. Unlike the terrestrial environment, where colors play an important role, in the marine environment this is secondary, mainly in the areas where the luminosity begins to lose its presence. Shapes and tones are more important than color for both hunting and defense, so it is not unreasonable to think that evolution has focused more on favoring other important aspects of vision before color differentiation.
Can sharks see colors?
In sharks' eyes there are two types of photoreceptor cells, known as rods and cones. The former are useful for detecting colors, while the latter appreciate contrasts and brightness, but do not distinguish small details of the captured image. For some time it was thought that sharks could not perceive colors and had limited vision because they were reported to lack cones.
However, the study [1] of various species revealed that, indeed, some did not have cones, but others did they had them, only they were of only one type, specifically the sensitive ones to perceive the color green, so these sharks would be colorblind.
