Whales evolved from land mammals many years ego and share many of their senses with modern-day land mammals. However, some of their senses are unique to allow them to survive in the oceans.
Whales, dolphins and other marine mammals have the same senses as land mammals. They have vision, touch, hearing, taste and smell. Toothed whales are also able to use echolocation.
In this article we look at the different senses that marine mammals use. If you want to know more then please read on.
Marine mammals are unique. Although they breathe air as other mammals do, they need to see both in air and underwater.
As marine mammals evolved from land mammals, their eyes were originally only adapted for sight on land. Evolution of the eye was essential to allow them to see not only on land but underwater.
Eyes that are adapted to being able to see in air lose their focus in water. This is because light travels slower in water than it does in air. In water, the light bends when it passes into the water.
Marine mammals have strong muscles around their eyes. These muscles allow the lens to change shape in the eye. The changes in shape allow them to see in air or underwater.
Land mammals have spherical eyes whereas marine mammals have an elliptical eye when underwater. The muscles around the eye allow the lens to change from a spherical shape to the elliptical shape.
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Light levels whilst deep in the ocean are very low but at the surface, they are very strong. The light intensity and the differences between depths can cause problems.
Marine mammals have adapted to the differences in light intensity between shallow and deep depths. Cetaceans have a very large pupil. The large pupil can bring in large amounts of light, helping them to see in low light situations.
Marine mammals can contract their eyes to a narrow slit, allowing them to use their eyes at the surface of the water.
Many species of whales and dolphins often turn on their side and use just one eye. This can be seen not only at the surface but at depth. The single eye can move around giving them a wide vision.
Whales and dolphins can also use both eyes together and can see objects that are close to the front of their mouth.
Scientists have suggested that marine mammals may be able to see a limited amount of colors like red and yellow light is absorbed by water. This makes most objects underwater appear as bluish-green.
Some species of dolphins do have a preference for red and yellow objects when tested so do have a more varied color vision.
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The further down into the ocean you travel the darker it gets and light levels get very low. Many species of toothed whales do swim down past depths of 200 meters and feed at these depths.
Many of the food items that they catch at these depths have a chemical process that gives them light. The light is at certain frequencies and it is thought that the toothed whales have eyes that are adapted to detect the chemical light.
The sense of touch to a marine mammal is very important but without hands, they can no longer get the same information from an object as humans can.
The skin of a cetacean is highly specialized and is very complex. The skin contains a system of organized nerve endings. The number of nerve endings in some areas is greater than in other areas giving them greater sensitivity in these areas.
Many whales have a scarred look which is due to the soft skin tearing and ripping. The skin heals fast but leaves scars and scratches.
The skin of a whale helps them to swim much more efficiently. Laminar flow is when each layer of fluid moves smoothly past the adjacent layers. Due to their size cetaceans need to achieve this over the body to allow them to be able to swim at high speeds and efficiently.
Due to the need for laminar flow when a large whale is swimming, the body shape needs to be able to adjust all the time. If there is any turbulence then the laminar flow does not work and the whale will not be able to swim efficiently.
Whales use their skin to act as a sensor to the pressure of the water. By using the highly sensitive skin they can stretch parts of their skin keeping their bodies in the correct shape for efficiency.
Areas of the skin can also tell them how fast they are swimming by sensing a build-up of pressure around the jaws. These same areas can also be used to detect low-frequency vibrations.
Marine mammals are air-breathing mammals and cannot breathe underwater. Proper co-ordination of breathing is needed so that only air is taken into the lungs and not a mixture of both air and water.
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Cetaceans have their nostrils on top of their heads. These nostrils are also known as blowholes. The nostrils have muscles that are powerful enough to close them whilst underwater.
Although the nostrils are on top of the head, they still need to be clear of the water to breathe in air. Cetaceans have many nerve endings in an area of skin around the blowhole.
The skin around the blowhole senses changes in pressure. This allows them to open when in the air and not underwater.
Dolphins will blow the water out when 5-10mm close to the surface before breathing in the air once they breach the surface. The complex arrangement of nerve endings picks up the changes in pressure of the water allowing them to know when they are near to the surface.
The hearing of a cetacean has adapted from hearing in the air to hearing in water and air. As water is denser than air, sound moves about five times as fast in water as it does in air. The difference in density between the water and air makes it more difficult for sound waves to pass between the two.
Between air and water, there is an acoustic impedance mismatch, which is why an air-filled ear is not good underwater.
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Cetaceans do not have external ears and this is due to the streamlined shape and their need for laminar flow through the water.
Although the ears are not external they do have ears. They can be seen as a small hole behind the eyes. Some species have extremely small ear holes just a couple of millimeters wide.
The science of how whales hear is still hotly debated by scientists. Baleen whales have a wax plug which builds up over time that transmits sounds heard underwater to the inner ear. The impedance of the waxy build-up matches seawater. This leads scientists to believe that although they can hear underwater, they are deaf when their ears are above water in the air.
The other type of whales, toothed whales, do not have the same wax build-up. Some scientists believe that dolphins can hear in the air which means that the ear channel is filled with air when above the surface of the water. The ear channel would then fill up with seawater when below the surface to allow them to hear underwater.
Some scientists believe that hearing does not work in the same way as our ears and doesn’t occur through the ear canal. Some species of dolphin are believed to have closed ear channels. With these species, they believe that sounds are transmitted through bone conduction or tissue conduction.
Bone conduction works by the bones of the skull or teeth transmitting sounds to the inner ear. Tissue conduction allows sound to filter through deposits of fat from the lower jaw to the inner ear.
In some species of toothed whales, there is a thin bone found in the fatty deposits which scientists believe may help to conduct sound to the inner ear.
Taste And Smell
Taste and smell are less distinguishable underwater than it is on land. Smell determines the source of chemical substances in the air, whereas taste occurs when chemical substances are dissolved in water that is taken into the mouth.
Whereas tasting can still take place underwater as it needs the chemical substances to be dissolved in water, smell takes place in the air. However, marine mammals can still smell underwater.
Whales, dolphins and other marine mammals can smell both predators and prey and this is done at a distance. Taste gives the marine mammals information once the object is close to or in the mouth.
Many marine mammals use chemoreception (chemical sensing) to find food as water is a good carrier for dissolved materials.
Whales can smell underwater and in the air but are not particularly efficient. Whales have their nostrils (blowholes) on top of their head and it is thought that through evolution there must have been many changes to how their noses work.
With their nostrils positioned to allow them to survive, it seems that the number of olfactory receptors decreased. Toothed whales have fewer olfactory receptors than baleen whales.
The blowholes are closed underwater and only open when they breathe in air. Baleen whales use their limited smell to find water with plenty of plankton.
Toothed whales do have taste buds and dolphins can distinguish between bitter, sweet, sour, and salty food.
The sense of taste allows the cetaceans to feed on healthy fish and to keep away from decomposing or dead fish. Wild dolphins will not eat dead fish if you try to feed it to them.
Cetaceans will use their waste to provide cues to others that they are ready to mate or to help others follow the herd when migrating.
It is believed that the range of a cetaceans taste and smell is much more limited than that of a shark.
Baleen whales evolved in several ways to stop sharks from attacking them. First, they grew to huge sizes and adapted to eating a diet of krill which took them away from the same feeding grounds as sharks.
Dolphins and toothed whales did not adapt in the same ways. To survive against their natural predators, toothed whales had to develop another sense to stop being preyed upon by sharks.
Most toothed whales have developed echolocation. This acts as an echo sounder on a ship and provides information to the animal on water depth and profiles of the coastline and seafloor.
Echolocation is a way of emitting clicks which the whale interprets when it returns. This provides information on what the sounds bounced back from.
Clicks are sent out from the animal and the interval between the sounds, along with the strength of the clicks sent back provides them with information.
The interval between clicks sent back provides information on the range of the object, with clicks thought to be able to travel up to 800 meters underwater.
The first click determines the range of the object, and subsequent clicks can show the toothed whale the bearing of the target.
Further clicks are sent out to determine the type of object. Higher frequencies are sent when they get closer to give them a more detailed ‘map’ of what the clicks are rebounding from.
Sound waves carry more information back to the whale than their vision can as vision relies on light sources.
Toothed whales and dolphins have fat deposits in their heads and lower jaws. These deposits have a different chemical composition from other fat in their bodies.
Dolphins have large melons on top of their heads. The melon contains the largest fat deposit which they use for echolocation. They also have another special fat deposit on their lower jaw.
The special fat deposits allow the dolphin to echolocate. They make a sound from their nasal region which is then transferred through the fat in the melon which focuses the nasal sound into a beam.
The beam of sound is sent into the water and they wait for the echoes to be received.
If you want to know more information on how dolphins use echolocation, I have written an article which you can find here.
As you can see, most marine mammals have the same senses that we use. However, some use echolocation as a means of exploring their environment, and it is these adaptations that make whales unique among mammals.