Western Atlantic: single pups are born during late December-early February, with a peak in mid-January. In the British Isles, most births occur in fall. Young are weaned in 2-3 weeks. Weaned pups may fast on land or ice for 1-4 weeks before beginning to feed at sea. Mates around time of weaning. Bulls may monopolize 4-6 cows if cows are not widely dispersed. Gestation lasts about 1 year, including delayed implantation period of 3-4 months. Most females are sexually mature at 5 years (Can. J. Zool. 70:1604), sometimes a year or two sooner. Males become sexually mature at 4-8 years but, because of social interactions with dominant older males, are not likely to breed successfully until at least 10 years old. Few live longer than 30-35 years. Recent genetic data from North Rona Island off Scotland indicate a surprisingly high level of mate fidelity (in 30% of cases, pups born in consecutive years to a particular female were full siblings); resident dominant males sired relatively few of the pups (Amos et al., 1995, Science 268:1897-1899).
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