How fast does a blue whale calf grow?

About ninety kilograms a day - a newborn putting on the weight of an adult human every twenty-four hours. It is born at around 2,700 kilograms and seven metres, already among the largest animals alive, and roughly doubles in length in its first year.

It runs on milk with a fat content around forty per cent, closer to a thick paste than to a liquid, delivered under pressure because a calf cannot form a seal and suckle underwater the way a land mammal does - the mother contracts muscles around the mammary gland and effectively injects it. The calf drinks something like 200 litres a day.

All of that comes out of the mother, who is often feeding hard on krill while nursing and loses an enormous share of her body reserves doing it. Reproduction is therefore slow: one calf every two or three years, a long gestation, and sexual maturity around ten. That is why commercial whaling was able to reduce blue whales from perhaps 250,000 to a few hundred within a few decades, and why the recovery since protection in 1966 has been so slow - the animal simply cannot replace itself quickly.