AGE AT ATTAINMENT OF SEXUAL MATURITY IN HUMPBACK WHALES, MEGAPTERA-NOVAEANGLIAE

Twelve female humpback whales (Megaptera novaeangliae) in the southern Gulf of Maine produced first-observed calves at ages ranging from 5 to 7 years. These data confirm that most females of this species attain sexual maturity at an average age of approximately 5 years. Observations in the West Indies of two males, aged 6 and 7 years, engaged in breeding-related behavior that is characteristic of mature animals suggests that males attain sexual maturity within a similar range of ages to females, although they may not be able to successfully engage in intrasexual competition until later in life. These data imply that the examination of ear plugs to determine the age of dead humpback whales should be based upon an assumed annual growth rate of two growth layer groups, not one.