Sharks’ Sensory Systems, Research Paper Example

Introduction

The present work is dedicated to sharks – predators living in the seas and being the dangerous encounter for any living being. Sharks feel very comfortable in the water both due to their anatomy and their size, making them equipped with all possible facilities that enable them to hunt and to locate themselves in the marine space very skillfully. Thus, this paper will discuss some of the advantages sharks have in comparison with other marine inhabitants – the topic is sharks’ sensory systems.

No matter how surprising it may sound, but sharks possess the same five sensory systems as people do – they can hear, smell, see, feel the neuro-impulses and distinguish taste. There are organs on their bodies that are responsible for each sensory system, so such sensory systems as vision and hearing will be discussed.

Sharks, as strange as it may seem, are not all so dangerous and aggressive as they may seem – depending on their species, they behave in a different way. They feed not only with large mammals and very often prefer fish (Carrier, 2006). The jaws of sharks are designed in such a way so that to suit any food they choose, and small rows of teeth are created for easy crushing the prey that protects many marine inhabitants – lobsters, crabs or shrimp (Carrier, 2006).

There are many legends about sharks as aggressive, scary creatures that hunt for people and create much drama for them. But in fact sharks are much more peaceful animals and their sensory systems help them in their life in the water and in feeding without human victims. Much fiction has also been dedicated to their ability to smell the food, to predict the approach of predators and to sense human beings and danger (Carrier, Musick, Heithaus, 2004). Hence, it becomes relevant to proceed to the discussion of the sensory systems they possess and the way they help them in their natural habitat. It is possible to find some natural connection between the way sensory systems of sharks are designed and the life style they have – living in harsh, unpredictable environment where there is a huge number of enemies that are not weaker in strength and physical constitution is a hard task to accomplish. This is why all sensory systems of sharks are built up in such a way so that to help them survive and feed themselves in an appropriate way.

The Sense of Vision

The visual system of sharks is represented by eyes, as in humans. The common myth about the poorly developed eyesight of sharks and their heavy dependence on their sense of smell and nose as the main sensory organ was ruined as soon as the importance of sharks’ sense of sight and the measure of its development has been proven. The shark’s visual system can be seen on Figure 1:

As one can see, there are many distinguishing peculiarities of sharks’ eyes that help sharks in their habitat and life style, habits in feeding and behavior towards other marine residents as well as humans. There are several elements in sharks’ vision system that help them protect the eyes while feeding, that help them see in the dim light, in the dirty water etc. These peculiarities have been summarized by Parsons (2006) in his scientific research dedicated to sharks:

“An interesting feature of the shark eye is…called the nictitating membrane…The membrane protects the eye from being damaged by thrashing prey. The shark also has a unique reflective coating behind the retina (the light-sensitive layer) of the eye. Many nocturnal (night-active) animals have a similar layer called a tapetum lucidum”.

Such a complicated system of vision designed by the nature for sharks is especially suited to their position of top predators in the nutrition chain. But it is also important to know that sharks cannot see well in turbid water, but are able to see perfectly well in the dim water because of the reflector layers in their eyes that make the peculiarities of their vision similar to those of cats. However, in contrast to cats, sharks do not see the objects in black and white colors and are able to distinguish colors very well (Carrier, 2006). This fact is also proven by the observations and conclusions at which Carrier (2006) arrives further on in his investigation:

“The eyes of most species of shark seem to be capable of color vision and their vision is thought to be fairly sharp (‘visual acuity’), though only about one-tenth of that in humans. In addition, sharks may be able to tell the difference between object shapes”.

Continuing to discuss the physical construction of the shark’s eye, it is also necessary to discuss the protective membrane that is called nictitative – its main role is to cover the eye as an eyelid during the periods when the shark is feeding and to protect the eye from undesirable effects of prey particles (Carrier, 2006). This part of sharks’ eyes is highly important taking into consideration their life style – they have to violently tear their food, if the fish or mammals they catch are very large. This is why adequate protection is necessary to let sharks preserve their organism despite the actions they take within their life.

Nonetheless, the possession of such a membrane that protects the eyes of a shark during their nutrition procedures is not present with all species, and such sharks as the white shark and the whale shark have to find some alternative ways to save their eyes from prey particles. Thus, they have the special muscles, extraocular ones, that are applied to rotate the eye orbits to the direction opposite to their usual position and make them protected while they are hidden (Carrier, Musick and Heithaus, 2004).

While discussing the visual system of sharks it is necessary to mention that the physical location of sharks’ eyes provides practically unlimited scope of vision for the animals, with the 360⁰ of grasped area. However, as Carrier, Musick and Heithaus (2004) note, there are some species that have some limits of their vision – it usually occurs right in front of their head and behind it in the steady position of the shark. The authors also mention that the limits of their vision are denominated by the character of their sinusoidal movement in the water (Carrier, Musick and Heithaus, 2004).

The last section to be discussed in the context of speaking about the capabilities of shark eyesight is the inner characteristics of the shark’s eye. At first the opinion existed that sharks have only rods as the building element of their eyes. But further on the hypothesis about cones also being present in the eye tissue was proven, and even those sharks that do not possess clear cones in their eye tissues have the cone-like rods that constitute their eyes (Carrier, Musick and Heithaus, 2004).

Drawing up a conclusion on the sharks’ visual ability it is important to note the conclusions at which scientists most commonly arrive studying the visual system of sharks and tying it to the daily necessities of the discussed predators:

“The importance of vision in the daily lives of elasmobranchs certainly finds support in the complexity of their anatomical and physiological adaptations, many of which appear to be correlated with species behavior and ecology” (Carrier, Musick and Heithaus, 2004).

Thus, it becomes possible to conclude that the eyesight of sharks fits their life style perfectly well – sharks are often urged to act in the dim light, in the dirty water where they are not able to see that well if they are unable to apply all additional functions of their eyes. The matter is that sharks hunt wonderfully in the dim light due to their reflective membranes in the eyes, which helps them to retain the leading position among other hazardous predators living in the same habitat with them. In addition, the specificity of their prey defined the evolutional emergence of a protective membrane that helps them avoid injuries while feeding etc. It is clear that the evolutional structure of sharks’ bodies allows them perform all their feeding and protective functions without excessive risk and hardship.

The Hearing System of Sharks

The hearing system of sharks is also very acute and plays a crucial role in the feeding process. The reason for this is that a shark is able to hear not only normal sounds, which is not that important in the water, but low frequency sounds as well: “it is able to detect sounds in the low-frequency range, the same sounds that are produced by wounded fish or struggling swimmers” (Carrier, 2006).

The reason for such comparison of the two different cases, with a wounded fish and a struggling swimmer, proves to be true on the biological level for the sharks as the frequency of sounds is highly similar and may attract a shark from a considerable large distance. This is why all swimmers who dive in the region of possible existence of sharks are strongly recommended to behave calmly and not perform any violent, quick or aggressive movements when coming across a shark in the water.

Carrier (2006) outlines the main purposes that suggest the evolution of the shark’s system of hearing in the way that it represents at the present moment of time as follows:

“The sense of hearing in sharks is remarkable well adapted for aiding in the detection and location of food…This would be useful for any predator and might help to locate food that requires less energy to capture because of its injuries”.

The inner ear of sharks consists of saccule, lagena and utricule as they are the three sensory areas that are considered responsible for the balance and sound perception of sharks. Their constitution is represented by a set of sensory hair cells on the epithelium covered by an otoconial mass. It acts as the inertial mass and is considered responsive to accelerations produced by a sound field (Carrier, Musick, Heithaus, 2004).

Sharks are also thought to have a sensor that is used to measure the distance and the water depth as well as respond to the changes of pressure. Among other studies connected with sharks’ hearing are the tests run at the present period of time that are aimed at finding out the range of possible ways to attract sharks by sound. Some considerable achievements have been made in the present sphere which can be supported by the opinion of Carrier, Musick and Heithaus (2004).

What is even more important about the sharks’ hearing system is the substantial difference from other mammals in not only hearing the sound, but localizing it as well. As it has been proven by field tests, the sharks are able to localize the sound very distinctly, up to several degrees. Nonetheless, this sphere is still under-researched and the peculiarities of localizing sounds by sharks, as well as the organs responsible for that function, are not fully found out yet. Further research is suggested by Carrier, Musick and Heithaus (2004) in the spheres of diagnosing “hearing sensitivity, masking the noise, frequency discrimination, intensity discrimination, and temporal activity”. According to their opinion, investigation of these peculiarities shown by sharks will open up the new scope of possibilities in shark hearing studies.

Consequently, it is possible to say that the whole hearing system of sharks is directed at locating food, which may be extremely hard in the living conditions of these animals. The sharks’ hearing is very acute and functions very well in the alliance with other systems. The intricate way of its construction and the multiple purposes for its application can be seen from its complexity – according to the laws of nature, those biological systems that are not heavily used do not need to be developed strongly. Sharks represent an opposite example – their hearing system is very complicated, which implies its importance and wide application. It is surely hard to believe that the hearing system may play such a decisive role in the life of a marine inhabitant, but the life style and habits of sharks prove the opposite.

Overview of Other Sensory Systems of Sharks

One of the most interesting and at the same time unknown sensory abilities of sharks is to detect weak electric voltages. It is considered that all living beings emit the electric voltages that not everyone is able to detect and feel, but for sharks the present ability turns out to be highly helpful and useful.

This unique possibility of sharks was thoroughly tested to prove its presence and not to mix it with any other possibilities of this animal. The conditions of the experiment presupposed blocking all sensory systems of a shark and finding out whether it was able to locate its victim. In fact, every shark was able to find it, even taking into consideration the full isolation of senses of smell, taste, hearing and vision. However, as soon as another test, under the same conditions but with the blocked electric signals of the victim, was conducted, the result was substantially different. The results were astounding – the shark was not able to locate the victim and felt absolutely lost without the ability to feel the victim’s electrical signals (Carrier, 2006).

Other systems, the one of taste and smell, are also well-developed and help the shark allocate food in the water. Under the conditions of all sensory systems being well-developed, these ones perform the complementary functions that are solely directed at one purpose – finding prey and feeding, detecting the danger etc. So it goes without saying that sharks indisputably feel the taste and smell of blood in the water, which leads to their unmistakable captures of their victims, but also helps fishers catch sharks when they disseminate blood in the place where they are planning their catch.

Conclusion

As it can be seen from the observation of sharks, the nature has created an ideal set of sensory systems for those predators in order for them to achieve the goals that are prescribed by the style of living to them. Sharks are at the top of aggressive and dangerous predators’ rating, so it is essential to understand what systems of their body help them in their nutrition, finding the prey and predicting the danger that may exist for them. In addition to the strongest jaws in the world and the ability to move fast , sharks also possess the sensory systems that make their hunting ideal – they can localize their victims by sound; they may not only hear them but also locate their place in space and follow them without any mistake; they can feel the neuro-impulses and low-frequency signals that help them detect whether the fish is wounded or not, or whether there is a careless swimmer nearby; they also possess the perfect smell and taste of blood in the water that helps them detect the wounded victim.

Thus, it becomes possible to assume that sharks are really wonderfully adjusted to the natural habitat in which they reside, and they have learned to accommodate to it by various means. This way, for example, they know how to protect the vulnerable tissue of eyes while feeding, or how to detect the wounded victims, how to respond to the changing characteristics of the water like vision, pressure etc. They have become highly responsive to negative conditions they may face and in which they have to operate, so they manage to function successfully and remain the most dangerous encounters for the majority of fish and mammals. The sensory systems of sharks together with their ideally designed anatomy to fit the need of fast swimming, locating themselves and other organisms in the water, together with some other functions, perform the whole range of functions needed for a shark and reduce the risk of being caught or killed by other marine inhabitants to minimum.

References

Carrier, J.C. (2006). Discovering Sharks. Voyageur Press.

Carrier, J.C., Musick, J.A., and Heithaus, M.R. (2004). Biology of sharks and their relatives. CRC Press.

Parsons, G.R. (2006). Sharks, skates, and rays of the Gulf of Mexico: a field guide. Univ. Press of Mississippi.

Shark Sensory System (2009). Retrieved December 7, 2009, from http://static.howstuffworks.com