WHALE SENSES – SIGHT
Like just about every land and sea animal on the planet, cetaceans (of which whales are members) have eyes and a degree of eyesight. Some animals rely heavily on this faculty and, therefore, have well-developed sight organs to enable them to perceive things of various distances from themselves.
However, because of the watery habitat of a whale, eyesight is not as important as some of its other senses.
Water is denser than air and is always in a state of motion (in the case of the oceans and bodies in which these animals live). In addition, the rays of the sun do not permeate very deep into the water. This is partly because light travels extremely slowly in water) and because the water refracts it to such a degree that it is almost imperceptible (both factors are due to the density of the water).
And, although whales do surface quite regularly for a breath of fresh air; they feed, mate and interact with one another in the murky depths far below. Therefore, it is here that they need to be able to perceive other whales as well as threats and, where applicable, prey.
Whales tend to rely more on their senses of hearing, touch and echolocation, since their sight is compromised. Still, they do have eyes and are certainly able to use them.
Whales have slightly flattened eyeballs with an enlarged pupil. Both of these adaptations allow the eye to let in as much light as possible. The cornea is less curved than in land mammals, which has the same effect of allowing more light in without causing as much refraction. The tapetum lucidum is a reflective layer within the eye that redirects incoming light back through the retina so that it is reflected twice. The result is an image that is clearer.
When under the ocean’s surface, whales can see about 35 feet (or 10.7 metres) ahead. They have a shorter range of vision when they are out of the water.
When whales rise to the surface of the water, they are subject to the sunlight that we enjoy. If their pupils were to remain as large as they need to be in the dark waters, their eyes would be damaged by the harsh rays. Therefore, as they surface, their pupil naturally shrinks so that only a small proportion of the light is allowed inside.
Over shorter distances, cetaceans are able to use both of their eyes to focus on an object. Usually, though, they will tilt onto their sides and only use one eye to focus on the object. This can be seen when they surface alongside a boat and angle their heads to peep at its occupants with just one eye out of the water.
In any animal, the rod cells are mainly for perceiving light, while the cone cells are more for colour perception. Therefore, whales have far more rod cells than cone cells, as seeing light is more important than having a good perception of colour (which is more important for animals like birds, who will be warned off by a red beetle, for example).
In order to safeguard their eyeballs, there are glands at the outer corneal layer and eyelids, which secrete a substance that lubricates and flushes the eye of any impurities.
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