Blue Whale

Balaenoptera musculus

The largest animal known to have existed — confirmed to 30 m and close to 200 tonnes. The body is long and slender, various shades of grey-blue above and lighter below, and the pale flanks read as turquoise when an animal rises under a boat. It is a rorqual, and it feeds by lunging into a krill swarm with the mouth gaping as wide as 80 degrees, engulfing a mass of water comparable to its own body and then squeezing it back out through the baleen; an adult works through roughly a tonne of krill a day and eats almost nothing else. Four subspecies are recognised across the North Atlantic and North Pacific, the Southern Ocean, and the Indian and South Pacific oceans, most of them shifting between polar summer feeding grounds and warmer winter breeding waters — though some populations stay put year-round, and some feed on the breeding grounds. Blue whales travel alone or in pairs, gathering in numbers only where food is exceptional, and call at fundamental frequencies of 8–25 Hz, at or below the floor of human hearing. Whaling cut a population of at least 140,000 mature animals in 1926 down to a few thousand before the International Whaling Commission banned the hunt in 1966; the IUCN listed the species as endangered in 2018, with ship strikes, pollution, ocean noise and climate change the threats that remain.