The eye of this whale is about the size of a big grapefruit.

Photo courtesy Iain Kerr, Ocean Alliance

Blubber

In order to have much of a life in the ocean, whales had to be able to swim for long periods of time without coming up for air. To do this, they developed highly specialized respiratory systems. A whale's lungs work the same basic way ours do, but they make the most of each breath. In one breath, your body might absorb 15 percent of the oxygen you inhale. The whale, on the other hand, absorbs as much as 90 percent of the oxygen it breathes in. When you consider the immense size of a whale's lungs, that's a lot of oxygen per breath!. As in other mammals, whales store this excess of oxygen in myoglobin, a specialized protein cell found in muscles. Whales have greater amounts of myoglobin than other animals, which allows them to store larger amounts of oxygen at a time.

Whales also make more efficient use of this oxygen. When they dive, their heart beats more slowly and select arteries are constricted. This slows the flow of blood to certain organs without decreasing blood pressure. Essentially, a whale's specialized physiology gives it better "gas mileage" -- they make each breath last. The sperm whale's respiratory system is among the most efficient in the world -- the huge animal can hold its breath for 80 to 90 minutes at a stretch. The beaked whale takes the prize, however. It can swim without a breath for as long as two hours.

Apart from the lack of breathable air, the most inhospitable element of the oceans is the extreme cold. Little sunlight penetrates the water's surface, and the temperature can drop below freezing even at relatively shallow depths. To deal with this biting cold, whales have developed a thick layer of blubber all around their bodies.

Blubber, a layer of stored-up fat beneath the skin and above the muscles, acts as a blanket to hold in the whale's body heat. In colder seasons, this insulating layer is the only thing keeping whales from freezing to death. Whales also use their blubber to store up energy for future use. Some species will feed heavily for half the year, when food is plentiful, and fast the rest of the year, living off their built-up blubber layer.

Next, we'll look at how whales sleep and handle the pressure of the ocean.