The ocean waters are, by their very nature, dark and murky. The sunlight penetrates only the top of the water. Therefore whales (and other fish and cetaceans) do not rely heavily on their sense of sight. Their eyes are adapted to these conditions, though. They are generally flatter with less of a corneal curve to allow as much light as possible to enter into them. In addition, the light is reflected twice for maximum vision to be achieved. Because the focus is on light, there are far fewer cone cells, which enable the perception of colours.
It remains to be seen whether or not baleen whales actually make use of the very limited smelling capabilities that they have. There are some olfactory structures in place, but they are reduced in size. They do not exist at all in toothed whales, which means that these animals are not capable of sensing smell.
Whales have an advanced sense of hearing, which is aided by the fact that sound waves travel better (and are, therefore, more readily heard) through the dense water than through air. Whales are, generally, more adept at hearing low-frequency sounds. In fact, some whale species have been shown not to detect high-frequency sounds at all, but this is not a rule. This sense of hearing is especially useful because whales are known to communicate with one another in an audible way. They emit sounds, even sing. This is an essential part of their interpersonal dynamics, defining the way that these cetaceans relate with one another. When they make a sound, they may emit anything from 20 to 200 000 Hertz. Human beings only have the ability to hear up to about 2 000 Hertz.
Whales are, naturally, able to sense touch all over their bodies, no matter how big they are. However, there are regions that are more sensitive than others, for a variety of reasons. These areas are the head, flippers, genitals and belly. The skin of the whale is actually very thin. It may appear thick because of the layer of blubber directly beneath it, but this is misleading. It is rich in nerves and the blood vessels necessary to feed them. Dermal sensors may be visible on the head and snout of baleen whales. These are small lumps that aid in their being able to feel external stimuli.
When examining the whale with the aim of determining the effectiveness of its senses, scientists have found there to be taste buds on the tongue. However, in most cases, they have atrophied (or wasted away). Therefore, it is fairly safe to assume that they do not taste much, if anything at all.
This sense is a fascinating one and is an ability that only the toothed whales have. The whale emits a high-pitched sound (which often sounds like a click). This sound then travels through the water until it hits an object, bounces back (or echoes) and returns to the whale. The whale is then able to assimilate and interpret the echo to ascertain the shape, distance, direction and even the texture of the object off which the sound bounced.