Whales swim by making powerful up-and-down movements of the tail flukes, which provide thrust. The power comes from body muscles that flex the lower spine up and down in a wavelike motion. The whale’s flippers help the animal steer. In some species, such as humpbacks, the flippers are large and powerful and may be used for fighting among males or, more rarely, for warding off attacks by killer whales.
Most whales remain near the surface of the ocean, but some dive to great depths and remain underwater for long periods ranging from 50 to 80 minutes. Whales possess interesting adaptations for diving, some of which are shared with other aquatic mammals such as seals. For example, whale lungs and adjoining air passages collapse under the pressure of a dive, forcing air into central parts of the lungs and thereby reducing the amount of nitrogen absorbed into the bloodstream. Too much nitrogen in the bloodstream can cause decompression sickness and a disorienting condition known as nitrogen narcosis. At the same time the whale’s blood and muscles contain high concentrations of the oxygen-storing pigments hemoglobin and myoglobin. During prolonged dives these pigments supply 80 to 90 percent of the whale’s oxygen.
Also during a dive, the whale’s heart rate slows to as low as three to five beats per minute. Arteries constrict, greatly reducing blood flow to many of the animal’s organs. This conserves oxygen and maintains blood pressure in the life-supporting structures, such as the brain and heart.
During a dive, the lack of oxygen in the whale’s body triggers the buildup of lactic acid, a chemical produced when body tissues obtain energy by metabolizing sugar in the absence of oxygen. In most animals the buildup of lactic acid in muscle leads to fatigue and can cause cramps. For reasons not well understood, whales can tolerate the pain and fatigue caused by lactic acid accumulation in muscle tissue, enabling them to remain underwater for long periods. Baleen whales can hold their breath up to 50 minutes when diving, and of the toothed whales, sperm whales can hold their breath up to 80 minutes.
Some whales, such as killer whales, regularly jump clear of the water and land on their back or side in a behavior known as breaching. Scientists are unsure why whales breach. Some theorize that this behavior may be a display of dominance used in courtship or may enable the whales to view their surrounding area. The loud sound that breaching makes as the whale lands in the water suggests to some scientists that it is used as a form of long-distance communication.
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