What Is a Whale Fluke?

A whale's tail is made of two lobes separated by a deep notch. Unlike fish, which have vertical tails, the whale's tail is on a horizontal plane when his body's upright. Another difference between flukes and fish tails is that flukes don't contain bones. They are made up of dense, fibrous connective tissue surrounded by a network of arteries and veins. Long muscles that run above and below the backbone move the flukes up and down.

The development of flukes was the last step in the whale's evolution from land animal to water animal. The first whales to have flukes lived about 38 million years ago. Before this time, whales paddled around using two feet at the base of their spine. Flukes allow whales to travel further and move through water faster and with greater agility.

A whale uses his flukes to propel himself forward in the water and the flippers at his sides to steer and brake. As he swims, he moves the fluke up and down like a paddle, pushing himself forward with each stroke. Whales also use their flukes to get food into their mouths. When flick-feeding, a whale uses his fluke to direct a wave of small animals toward his mouth. Kick-feeding is similar to flick-feeding: The whale slaps its pray to move it toward his mouth. Another role of flukes is body temperature control. The flukes' arteries and veins can manipulate blood flow to conserve or release heat.

When a large whale prepares for a deep dive, he arches his back, moving the central part of his body above water to get a better downward angle. The arching gives the whale a humpbacked appearance. With his head in position, he moves downward. The last thing you see of him before he disappears into the depths is his fluke sticking straight up above the water. Called fluking, this diving posture gives researchers a good look at the tail markings, which can be distinct enough to identify individual whales. Some whales, notably fin whales and minke whales, don't fluke.