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Reproduction

A. Sexual maturity.

1. Most male walruses are sexually mature at about eight to ten years. Successful reproduction, however, probably doesn't occur until 15 years of age, when the male attains full physical growth and is able to compete for females.

2. Most females are sexually mature at about five to six years. Successful reproduction probably begins at about ten years.

B. Mating activity.

1. Only a portion of the female population mates each year, as some are pregnant from the year before. Nonpregnant females may go into estrus some time between December and June, and most ovulate in February.

2. In the Pacific, female herds meet male herds as they move south into the central and south Bering Sea in January. Estrous females gather at traditional places separate from pregnant females.

3. Most mating probably occurs from December through March, when most sexually mature males produce viable sperm. Mating takes place off the pack ice, remote from shore; breeding locations are thus largely inaccessible for observation.

4. Each herd of estrous females is attended to by one or more large adult males. According to one study, the ratio of males to females averaged 1 to 23.

a. The males display visually and vocally from the water while the females rest. A display occurs both at and below the surface and lasts about two to three minutes. It includes teeth-clacking, clanging bell-like sounds, and whistles.

b. Bulls either maintain a distance of about 7 to 10 m (23-33 ft.) or fight violently with each other.

c. When displaying males are present, subadult males are scarce or absent. Those present remain on the fringes of the group and do not display.

d. Females leave the ice to join a male in the water, where copulation takes place.

5. After the mating season, mature bulls return to all-male herds.

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