Newborn are most commonly reported in winter or early spring; sexually mature at length of about 2 m (Leatherwood and Reeves 1983, Jefferson and Newcomer 1993). Based on samples caught in squid driftnets in the central North Pacific, about half of females were mature; among mature females, 16% were pregnant, 3% were pregnant and lactating, 33% were post partum, 24% were lactating (no recent pregnancy), 10% were resting, and 14% were of unknown condition; gestation period was 12.1-12.3 months; calving appeared to peak in July and August; average of sexual maturity was 10 years; the oldest male was 27 years old, the oldest female 42 years old; minimum calving interval was 2 years (Ferrero and Walker 1993).