Blue Whale - biology.

Blue Whale - biology. I INTRODUCTION Blue Whale, largest whale, and the largest living creature on Earth, exceeding 30 m (100 ft) in length. Blue whales belong to a fast-swimming group of baleen whales called rorquals and are found in all oceans of the world. They mainly feed on tiny shrimplike invertebrates called krill. Blue whales were hunted nearly to extinction by the 1960s and remain endangered, with only a small recovery in numbers since official protection began in 1966. The blue whale is also known as the sulfur-bottom whale and the great northern rorqual. II HABITAT AND RANGE Blue whales are mainly found in deep water along the edges of continental shelves and along ice packs. Scientists generally recognize three subspecies of blue whales found in three geographic regions: a subspecies that lives in the Northern Hemisphere, a subspecies that lives mainly in Antarctic waters, and a subspecies sometimes called the "pygmy blue whale" that lives in a zone in the southern Indian Ocean and western South Pacific. Most populations of blue whales migrate extensively, traveling from the tropics or near tropics in winter to the edges of the pack ice in the northern and southern hemispheres in summer. III PHYSICAL DESCRIPTION Blue whales may reach over 24 m (80 ft) in length; mature females are usually slightly longer than mature males. Blue whales in the Antarctic region of the Southern Hemisphere grow somewhat larger than those in the Northern Hemisphere. The longest blue whale recorded by whalers measured 33.6 m (110 ft). As adults, blue whales can weigh more than 100 tons. Females are larger than males of the same age, the largest sometimes weighing as much as 150 tons. The heaviest blue whale caught by whalers weighed 190 tons. Blue whales are likely the most massive creatures to ever live on Earth, exceeding the largest dinosaurs that lived on land. Some giant plant-eating dinosaurs known as sauropods may have grown up to 39 m (130 ft) long and may have weighed up to 100 tons. The internal organs of blue whales are also enormous. The tongue can weigh more than two tons. The heart is the size of a small car and beats about eight times a minute, compared to about 70 times a minute in humans. The blue whale has a small dorsal fin set far back on the body. The powerful flukes (tail fins) can measure 7.6 m (25 ft) across. The flippers are about 2.4 m (8 ft) long. The whale's blowhole has a large raised "splash guard" in front. The skin has a light-gray-and-white mottled pattern, which appears light blue when the whale is just below the surface of the water on a sunny day. The mottled pattern, which is unique to each animal, has been used by researchers to identify individual whales. Microscopic algae called diatoms sometimes coat the underbelly, resulting in a yellowish appearance that led to the old name "sulfur-bottom whale." Studies of yearly growth rings in waxy inner ear plugs found in blue whales indicate some individuals may live more than 100 years. Average life spans are estimated to be between 40 and 90 years. IV BEHAVIOR A Swimming and Diving Blue whales can swim at up to 35 km/h (22 mph) and can dive for periods as long as 35 minutes. When feeding, however, they swim much more slowly and generally dive for periods lasting less than 20 minutes. Like all marine mammals, they must come to the surface to breathe. They produce a spout of moist, exhaled air that can reach 10 to 12 m (34 to 40 ft) high, the highest spout of any whale. Blue whales usually swim alone or in pairs. They are sometimes found in small pods (groups) and may occur in pods as large as 50 when feeding on swarms of krill or other prey. B Vocal Sounds Blue whales produce loud, low-frequency, moanlike calls that can travel over thousands of kilometers underwater. Most of these sounds are below the range of human hearing but can exceed 180 decibels--the loudest sound made by any animal and louder than the noise of a jet aircraft taking off. Blue whales likely use these calls to communicate, enabling the members of a group to remain in contact across a vast expanse of ocean. Males also produce special calls that may help them find mates. Like other baleen whales, blue whales are not thought to use high-pitched sounds to echolocate prey the way toothed whales do. However, some scientists think blue whales may navigate using the underwater echoes from their low-pitched calls, which could reveal the shapes of land forms and other features on the seafloor. V DIET AND FEEDING Blue whales feed by lunging open-mouthed into dense groups of small sea creatures such as krill, zooplankton, or fish. As water and food rush into the whale's mouth, more than 60 throat pleats expand so that the whale's throat, or gular pouch, forms a huge bag that extends from the front of the whale's snout to its navel. The whale then partially closes its mouth, leaving a small gap, and forces water past 270 to 390 pairs of wide, black, fringed baleen plates that hang from the roof of the mouth. The plates act as a sieve, catching food inside the fringes. Blue whales often lunge through their prey side by side, apparently using each other to block the escape of their prey. Blue whales commonly feed in Arctic and Antarctic waters during the summer, when krill is plentiful and found in large swarms. Blue whales may also feed on krill or plankton where there are upwellings of cold currents. The whales can live off stored blubber when they migrate into warmer regions where krill is less available. The only natural predators on blue whales are killer whales. Pods of killer whales have been seen attacking blue whales, although how common or how successful such attacks are is not known. VI REPRODUCTION Blue whales generally reach sexual maturity between the ages of eight and ten years. Mating occurs in the summer season, but not much is known about courtship behavior. Male and female blue whale pairs have been seen together for periods of up to three weeks. If a third whale approaches the pair, the whales may engage in vigorous splashing displays. Mature females may give birth once every two or three years. The gestation period lasts about 11 months. A single young is usually born the following spring; twins are rare. The females migrate to warm regions to give birth. The young nurse for seven or eight months, gaining as much as 90 kg (200 lb) per day. VII CONSERVATION STATUS Blue whales were not targeted by the whaling industry until the late 1800s after faster steam-powered ships were developed. The peak slaughter of blue whales occurred in the 1930s when explosive harpoons and factory ships that could process enormous whale carcasses became available. Blue whales were heavily hunted for oil, baleen, meat, and other products from the 1930s to the 1960s. The largest numbers of blue whales were taken in the Southern Ocean around Antarctica. This intensive hunting of blue whales nearly caused the extinction of the species, which may have had a population before whaling of more than 200,000. The International Whaling Commission imposed a ban on killing blue whales in 1966. Blue whales are now protected and may be gradually returning in several areas of their range. Since 1985, blue whales feeding in Monterey Bay, California, have become a familiar sight in late summer. Scientists estimate a global population of blue whales of up to 15,000. The blue whale is classified as an endangered species. It is protected under the United States Endangered Species Act and the Marine Mammal Protection Act (MMPA). The blue whale is listed as endangered on the World Conservation Union (IUCN) Red List. It is also listed as threatened with extinction on Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), which prohibits international trade in specimens for commercial purposes. Reduced populations of krill could affect blue whales as well as other marine animals that depend on the tiny crustaceans as a primary food source. In the Antarctic, krill feed on algae released by melting sea ice in summer. Shrinking sea ice from global warming means less algae as food for krill. By some estimates, krill populations in the Antarctic may have dropped by 80 percent since the 1970s. In addition, the fishing industry has developed new technologies designed for the large-scale harvesting of krill. If humans take significant amounts of krill from the Antarctic and other regions, blue whales may have difficulty finding food. Other threats to blue whales include collisions with ships and effects of pollutants in the marine food chain, which may interfere with the animals' reproduction and immune systems. Scientific classification: The blue whale belongs to the family Balaenopteridae of the suborder Mysticeti, order Cetacea. It is classified as Balaenoptera musculus. The Northern Hemisphere subspecies is classified as Balaenoptera musculus musculus and the large Southern Hemisphere subspecies as Balaenoptera musculus intermedia. The pygmy blue whale is classified as Balaenoptera musculus brevicauda. Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.