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 , except the Arctic, 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 , but accelerate to more than 20 miles an hour when they are agitated.
Blue whales are among the loudest animals on the planet. Scientists think they use these vocalizations not only to communicate, but, along with their excellent hearing, to sonar-navigate the lightless ocean depths. Calves enter the world already ranking among the planet's largest creatures. After about a year inside its mother's womb, a baby blue whale emerges weighing up to 3 tons and stretching to 25 feet.
It gorges on nothing but mother's milk and gains about pounds every day for its first year. Blue whales are among Earth's longest-lived animals. Scientists have discovered that by counting the layers of a deceased whale's waxlike earplugs, they can get a close estimate of the animal's age. The oldest blue whale found using this method was determined to be around years old.
Average lifespan is estimated at around 80 to 90 years. Aggressive hunting in the s by whalers seeking whale oil drove them to the brink of extinction. Between and the mids, some , blue whales were slaughtered. They finally came under protection with the International Whaling Commission , but they've managed only a minor recovery since then.
Blue whales have few predators but are known to fall victim to attacks by sharks and killer whales, and many are injured or die each year from impacts with large ships. These whales have strong sphincter muscles surrounding their blowhole to prevent water from coming in and filling their lungs, which could cause these marine mammals to drown.
During deep dives, the blue whale can hold its breath for up to 90 minutes before resurfacing for air; however, most dives usually last less than 30 minutes. Interestingly, unlike most land animals, the blue whale actually all cetaceans have separate breathing and eating passages. One possible reason for this may be preventing the blue whale from accidentally taking water into its lungs when consuming food underwater. The blue whale can freely consume prey without inhaling water by completely separating the esophagus and lung passages.
The other half of the brain stays awake at a low level of alertness. This attentive side is used to watch for predators, obstacles and other animals. It also signals when to rise to the surface for a fresh breath of air. After approximately two hours, the animal will reverse this process, resting the active side of the brain and awaking the rested half. This pattern is often called cat-napping.
Dolphins generally sleep at night, but only for a couple hours at a time; they are often active late at night, possibly matching this alert period to feed on fish or squid, which then rise from the depths.
Bottlenose dolphins, based on electroencephalogram EEG readings, spend an average of It is not clear whether cetaceans undergo dream sleep. But a pilot whale was noted as having six minutes of REM in a single night. To avoid drowning during sleep, it is crucial that marine mammals retain control of their blowhole. The blowhole is a flap of skin that is thought to open and close under the voluntary control of the animal.
Although still a matter of discussion, most researchers feel that in order to breathe, a dolphin or whale must be conscious and alert to recognize that its blowhole is at the surface. Humans, of course, can breathe while the conscious mind is asleep; our subconscious mechanisms have control of this involuntary system. But equipped with a voluntary respiratory system, whales and dolphins must keep part of the brain alert to trigger each breath. Other methods help marine mammals to hold their breath longer than other types of mammals can.
Marine mammals can take in more air with each breath, as their lungs are proportionately larger than those in humans. In addition, they exchange more air with each inhalation and exhalation. Their red blood cells also carry more oxygen. And when diving, marine mammals' blood travels only to the parts of the body that need oxygen--the heart, the brain and the swimming muscles.
Digestion and any other processes have to wait.
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