Before reaching adulthood, baleen whales grow at an extraordinary rate. In the blue whale, the largest species, the fetus grows by some per day just before delivery, and by per day during suckling. Before weaning, the calf increases its body weight by and grows from at birth to long. When it reaches sexual maturity after 5–10 years, it will be long and possibly live as long as 80–90 years. Calves are born precocial, needing to be able to swim to the surface at the moment of their birth.