Calving season has been reported to be summer, but in recent studies calves have been found primarily in early fall (Leatherwood and Reeves 1983).

High seas drift net samples in Central North Pacific (Ferrero and Walker 1996): a calving period preceded sampling during late winter and spring; estimated gestation period 11-12 months; males sexually mature in 10-11 years, females in 8-11 years.