The blue whale (Balaenoptera musculus) is a marine mammal belonging to the baleen whales. At up to 30 meters (98 ft) 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.
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.
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.
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.