Perrin, W.F.; Würsig, B.; Thewissen, J.G.M. (2009). Encyclopedia of marine mammals. Second edition. Academic Press: London. ISBN 978-0-12-373553-9. xxix, 1316 pp. (look up in IMIS) [details]
Females are larger than males throughout life, by about 2 ft (0,5-0,6 m) at full maturity. It is believed they reach 15,5 m, but most are much smaller. Southern Hemisphere animals are also larger than Northern Hemisphere animals.