Finback  whales mate in winter, when they are in warm waters. After a gestation period of about a year, a 6 m calf weighing 2 tons or more is born. Finbacks mature at around 10 years of age, and may grow 18 to 23 meters in length and weigh as much as 50 tons. Finback whales may live to be 100 years old and are extremely fast swimmers.