Blue whale
The blue whale (Balaenoptera musculus) is a marine mammal belonging to the baleen whales. At up to 30 meters (98 ft)[5] in length and with a maximum recorded weight of 173 tonnes (190 short tons) and probably reaching over 181 tonnes (200 short tons), it is the largest animal known to have ever existed.
Long and slender, the blue whale's body can be various shades of bluish-grey dorsally and somewhat lighter underneath. There are at least three distinct subspecies: B. m. musculus of the North Atlantic and North Pacific, B. m. intermedia of the Southern Ocean and B. m. brevicauda (also known as the pygmy blue whale) found in the Indian Ocean and South Pacific Ocean. B. m. indica, found in the Indian Ocean, may be another subspecies. As with other baleen whales, its diet consists almost exclusively of small crustaceans known as krill.
Blue whales were abundant in nearly all the oceans on Earth until the beginning of the twentieth century. For over a century, they were hunted almost to extinction by whalers until protected by the international community in 1966. A 2002 report estimated there were 5,000 to 12,000 blue whales worldwide, in at least five groups. The IUCN estimates that there are probably between 10,000 and 25,000 blue whales worldwide today. Before whaling, the largest population was in the Antarctic, numbering approximately 239,000 (range 202,000 to 311,000). There remain only much smaller (around 2,000) concentrations in each of the eastern North Pacific, Antarctic, and Indian Ocean groups. There are two more groups in the North Atlantic, and at least two in the Southern Hemisphere. As of 2014, the Eastern North Pacific blue whale population had rebounded to nearly its pre-hunting population.
Taxonomy
Blue whales are rorquals (family Balaenopteridae), a family that includes the humpback whale, the fin whale, Bryde's whale, the sei whale, and the minke whale. The family Balaenopteridae is believed to have diverged from the other families of the suborder Mysticeti as long ago as the middle Oligocene (28 Ma ago). The blue whale lineage diverged from the other rorquals during the Miocene, between 7.5 and 10.5 million years ago. However, gene flow between the species appears to have continued beyond that date. The blue whale has the greatest genetic diversity of any baleen whale, and a higher than average diversity among mammals.
Description
The blue whale has a long tapering body that appears stretched in comparison with the stockier build of other whales.[26] The head is flat, U-shaped and has a prominent ridge running from the blowhole to the top of the upper lip. The front part of the mouth is thick with baleen plates; around 300 plates, each around one meter (3.3 feet) long, hang from the upper jaw, running 0.5 m (20 in) back into the mouth. Between 70 and 118 grooves (called ventral pleats) run along the throat parallel to the body length. These pleats assist with evacuating water from the mouth after lunge feeding.
The flippers are 3–4 meters (9.8–13.1 ft) long. The upper sides are grey with a thin white border; the lower sides are white. The head and tail fluke are generally uniformly grey. The whale's upper parts, and sometimes the flippers, are usually mottled. The degree of mottling varies substantially from individual to individual. Some may have a uniform slate-grey color, but others demonstrate a considerable variation of dark blues, greys and blacks, all tightly mottled.
Blue whales can reach speeds of 50 kilometers per hour (31 mph) over short bursts, usually when interacting with other whales, but 20 kilometers per hour (12 mph) is a more typical traveling speed.[4] Satellite telemetry of Australian pygmy blue whales migrating to Indonesia has shown that they cover between 0.09 and 455.8 kilometers (0.056 and 283.221 miles) per day.[28] When feeding, they slow down to 5 kilometers per hour (3.1 mph). They typically swim at a depth of about 13 meters (43 feet) when migrating in order to eliminate drag from surface waves. The deepest confirmed dive is 506 meters (1,660 feet).
Blue whales most commonly live alone or with one other individual. It is not known how long traveling pairs stay together. In locations where there is a high concentration of food, as many as 50 blue whales have been seen scattered over a small area. They do not form the large, close-knit groups seen in other baleen species.
Behavior
Blue whales feed almost exclusively on krill, though they also take small numbers of copepods. The species of this zooplankton eaten by blue whales varies from ocean to ocean.
An adult blue whale can eat up to 40 million krill in a day. The whales always feed in the areas with the highest concentration of krill, sometimes eating up to 3,600 kilograms (7,900 lb) of krill in a single day. The daily energy requirement of an adult blue whale is in the region of 1.5 million kilocalories. Their feeding habits are seasonal. Blue whales gorge on krill in the rich waters of the Antarctic before migrating to their breeding grounds in the warmer, less-rich waters nearer the equator. The blue whale can take in up to 90 times as much energy as it expends, allowing it to build up considerable energy reserves.
Because krill move, blue whales typically feed at depths of more than 100 meters (330 ft) during the day and only surface-feed at night. Dive times are typically 10 minutes when feeding, though dives of up to 21 minutes are possible. The whale feeds by lunging forward at groups of krill, taking the animals and a large quantity of water into its mouth. The water is then squeezed out through the baleen plates by pressure from the ventral pouch and tongue. Once the mouth is clear of water, the remaining krill, unable to pass through the plates, are swallowed. The blue whale also incidentally consumes small fish, crustaceans and squid caught up with krill.
The weight of individual blue whales varies significantly according to fat condition. Antarctic blue whales gain 50% of their lean body weight in the summer feeding season, i.e. a blue whale entering the Antarctic weighing 100 tons would leave weighing 150 tons. Pregnant females probably gain 60–65%. The fattened weight is 120% the average weight and the lean weight is 80%.
Scientists estimate that blue whales can live for at least 80 years, but since individual records do not date back into the whaling era, this will not be known with certainty for many years. The longest recorded study of a single individual is 34 years, in the eastern North Pacific.
The whales' only natural predator is the orca. Studies report that as many as 25% of mature blue whales have scars resulting from orca attacks. The mortality rate of such attacks is unknown.
Conservation
Blue whales are not easy to catch or kill. Their speed and power meant that they were rarely pursued by early whalers, who instead targeted sperm and right whales. In 1864, the Norwegian Svend Foyn equipped a steamboat with harpoons specifically designed for catching large whales. The harpoon gun was initially cumbersome and had a low success rate, but Foyn perfected it, and soon several whaling stations were established on the coast of Finnmark in northern Norway. Because of disputes with the local fishermen, the last whaling station in Finnmark was closed down in 1904.
Blue whale hunting was banned in 1966 by the International Whaling Commission, and illegal whaling by the Soviet Union finally halted in the 1970s, by which time 330,000 blue whales had been caught in the Antarctic, 33,000 in the rest of the Southern Hemisphere, 8,200 in the North Pacific, and 7,000 in the North Atlantic. The largest original population, in the Antarctic, had been reduced to a mere 360 individuals, about 0.15% of their initial numbers.
Since the introduction of the whaling ban, studies have examined whether the conservation reliant global blue whale population is increasing or remaining stable. In the Antarctic, best estimates show an increase of 7.3% per year since the end of illegal Soviet whaling, but numbers remain at under 1% of their original levels. Recovery varies regionally, and the Eastern North Pacific blue whale population (historically a relatively small proportion of the global total) has rebounded to about 2,200 individuals, an estimated 97% of its pre-hunting population.
The total world population was estimated to be between 5,000 and 12,000 in 2002; there are high levels of uncertainty in available estimates for many areas. A more recent estimate by the IUCN puts the global population at 10,000–25,000. The IUCN Red List counts the blue whale as "endangered", as it has since the list's inception.