Single pup is born mid-March to mid-April (peak in second half of March). Breeds near end of lactation period, which lasts only about 4 days. In any given area, breeding season spans only 2-2.5 weeks. One to several males may be on ice floe with female and pup; these groupings are widely scattered (loose aggregations). Females sexually mature usually in 3-4 years; more than 90% of adult females are pregnant each year. Males sexually mature in 4-6 years but do not do much breeding until several years older. Few live beyond their late 20s. Polygynous mating system.