Saturday, February 1, 2014

Blue whales-Mirissa


Blue whales are the largest animals ever known to have lived on Earth. These magnificent marine mammals rule the oceans at up to 100 feet (30 meters) long and upwards of 200 tons (181 metric tons). Their tongues alone can weigh as much as an elephant. Their hearts, as much as an automobile. Blue whales reach these mind-boggling dimensions on a diet composed nearly exclusively of tiny shrimplike animals called krill. During certain times of the year, a single adult blue whale consumes about 4 tons (3.6 metric tons) of krill a day. 

Blue whales are baleen whales, which means they have fringed plates of fingernail-like material, called baleen, attached to their upper jaws. The giant animals feed by first gulping an enormous mouthful of water, expanding the pleated skin on their throat and belly to take it in. Then the whale's massive tongue forces the water out through the thin, overlapping baleen plates. Thousands of krill are left behind—and then swallowed. Blue whales look true blue underwater, but on the surface their coloring is more a mottled blue-gray. Their underbellies take on a yellowish hue from the millions of microorganisms that take up residence in their skin. The blue whale has a broad, flat head and a long, tapered body that ends in wide, triangular flukes.

Blue whales live in all the world's oceans occasionally swimming in small groups but usually alone or in pairs. They often spend summers feeding in polar waters and undertake lengthy migrations towards the Equator as winter arrives. These graceful swimmers cruise the ocean at more than five miles an hour (eight kilometers an hour), but accelerate to more than 20 miles an hour (32 kilometers an hour) when they are agitated. Blue whales are among the loudest animals on the planet. They emit a series of pulses, groans, and moans, and it’s thought that, in good conditions, blue whales can hear each other up to 1,000 miles (1,600 kilometers) away. Scientists think they use these vocalizations not only to communicate, but, along with their excellent hearing, to sonar-navigate the lightless ocean depths.

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