Young are born in warm, low latitude waters in the winter months after the adults return from their high latitude feeding grounds. At birth the young are 7-8 m long. While nursing, blue whales can gain up to 90 kg in body weight a day. Young are weaned after seven or eight months, usually after attaining a length of 16 m. Sexual maturity occurs as young as 8 or 9 years and young are produced every 2 or 3 years.
Twins are rare but do occur occassionally.
Behavior Most populations of blue whales are migratory, though some animals do not migrate. Migrators typically spend the winter in low latitude waters, move towards the poles during the spring, feed in high latitude waters during the summer and head back toward the equator during the fall. There are northern and souther ocean populations that remain distinct. Habitat Blue whales live in the open ocean. Because of the immensity of the blue whale, only the sperm whale approached it in economic importance.