Protracted breeding season, reportedly with no fixed breeding or calving season, though a peak in calving in March was found off Japan. Gestation lasts about 15-16 months. Lactation lasts apparently about 18 months. Sexually mature at about 3.2-3.8 m (Leatherwood and Reeves 1983), probably at a minimum age of 8 years (IUCN 1991, Stacey et al. 1994). Off Japan, the average interval between births has been estimated at about 7 years, with females over 45 years old post-reproductive (see Stacey et al. 1994). May live several decades.