Steller sea lions range along the North Pacific Rim from northern Japan to California. Pupping and breeding occur late May to early July throughout their range. Males set up territories on rookeries in late May, females arrive shortly thereafter and give birth to a single pup. They alternate between nursing their pup and feeding trips; most pups are weaned by the end of their first year. The species is not known to migrate, but individuals disperse widely outside of the breeding season, particularly adult males and juveniles. Adult males are up to 3.25 m long and weigh up to 1120 kg; females are considerably smaller at up to 2.9 m and 350 kg. Pups weigh about 23 kg at birth. Two separate stocks of Steller sea lions are recognized within U. S. waters: an eastern and western stock. As a result of a precipitous decline in numbers beginning in the 1970s, the western stock is presently listed as Endangered under the ESA.