How a Whale Senses the World
Whales and dolphins (known in the scientific world as Cetaceans), have undergone incredible changes to their sensory systems in order to adapt to life in the sea. Ancestors of these remarkable creatures were actually land animals that looked something like this animal to the right. Over many millions of years they began to lose certain abilities that were necessary for land dwelling and replaced them with very unique abilities suited for an aquatic life.
Being able to see underwater requires a special lens shape. Light travels more slowly in water than it does in the air. It also refracts or bends when it passes into the water. So ancient cetaceans originally possessed eyes suited for living on land and were at a disadvantage when trying to hunt fish. As a result they were able to develop an eye that is suited to both air and sea. They did this by evolving to have strong muscles around the eye that can actually change the shape of the lens depending on whether it is exposed to air or water.
There is another problem that was faced by the eyes of ancient cetaceans. The intensity of light at the surface is much higher than it is at lower depths or in murky water. A whale needs to be able to see in both situations. Sperm whales, for example, spend much of their time at great depths where there little or no light can reach. As a result, cetaceans have evolved to have a very large pupil that can open wide to allow a large amount of light in at great depths. They also have what is known as a tapetum lucidum, which is a light reflecting layer that sends light back through the retina a second time, creating a higher quality image. When they rise to the surface, they simply close their pupil to a tiny slit, only allowing a small amount of the light in.
Whales and dolphins usually turn on their sides to focus one eye on a target, however they are capable of binocular vision for a small distance. While underwater, they can usually see about 35 feet in front of them. Above the surface however, they become more nearsighted as a result of the change in pressure and air density.
Whales and dolphins have all but lost their sense of smell. This could be a result of evolution. It is reasonable to assume that as the repositioning of the nostrils to the top of the head was occurring, many changes to the function of the organs associated with the nostrils must have also occurred. Baleen whales have a limited sense of smell, perhaps to help them locate krill or plankton which have distinct smells that can be picked up in the air as the whale takes a breath. Toothed whales appear to have completely lost their olfactory system.
Cetaceans do seem to have the ability to taste. Dolphins have shown the ability to detect sweet, sour, bitter and salty flavors. It is also quite common for whales and dolphins to refuse dead fish, or prefer one type of fish over another. Some even have a small Jacobson's organ which you may know is also found in cats and snakes among others.
Sound travels five times as fast underwater as it does in the air. The difference in density between the air and the sea makes it difficult for sound to pass between them. As a result, a normal air-filled mammal ear is useless. Baleen whales and toothed whales have evolved different ways of dealing with this problem and it is not completely understood in both types. Baleen whales have a waxy plug in their ear canal which is thought to transmit sounds to the inner ear. This means they are most likely deaf above the water. Toothed whales do not have this ear plug. There are several theories for how these whales hear but in my opinion the most logical theory is that the ear canal is closed off in most toothed whales and has become redundant. Instead, toothed whales may be able to receive sounds through their lower jaw which contains oil-filled sinuses that may be able to transmit sounds directly to the inner ear. Or perhaps they can hear some sounds through a water filled ear canal and use their lower jaw only for picking up echolocation clicks.
Although I plan to dedicate a separate hub to this fascinating ability, I thought it would be appropriate to summarize what this sense is and what it does for those who have never heard of it.
Echolocation involves emitting sounds in the form of short clicks and picking up information about the world surrounding the dolphin by analysis of the returning echoes. This ability is only found in toothed whales, dolphins, as well as bats and possibly some bird species. They combine low and high frequency sound emissions along with exceptional directional hearing which has given them an edge over other sea animals.
Cetaceans may not have hands but their sense of touch is still very important to them. Their skin is soft and easily damaged but it also heals quite quickly. It is highly specialized and contains a complex system of nerve endings which are more abundant in certain areas. It is believed that cetaceans can use their sense of touch to achieve “laminar flow” of water over their bodies to swim efficiently at high speeds. If turbulence develops somewhere on the surface of the skin, the pressure should help the dolphin adjust its body to keep the correct shape for laminar flow to occur. These creatures also need their sense of touch to know when their blowhole is above the surface of the water, allowing them to take a breath. They have many more nerve endings around the blowhole to help with this. In addition they possess sensitive nerve endings on the tips of their mouths to help investigate objects, much like our fingertips.
The Magnetic Sense
Of all the senses described here, this is the least understood. Small crystals of magnetite have been found in many species including bacteria, bees, butterflies, fish, birds, bats and reptiles. They have also been found in and around the brains of Cetaceans. Magnetite crystals are thought to continuously orient themselves to the earth's magnetic field, like miniature magnets. Perhaps these animals are able to sense the orientation of these crystals and work out the direction in which it is traveling. Normally the magnetic fields run north to south at an even density. Occasionally however, it will be distorted by certain geographical formations that are rich in metals like iron. These formations are called geomagnetic anomalies. It is possible that this is one of the causes of strandings by whales and dolphins.
In conclusion, cetaceans have adapted to live in a completely alien world compared to ours. Although we are both air breathing mammals, whales and dolphins have been evolving for so long (around 54 million years) that they have become extraordinarily unique animals.
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