Growth and reproduction of captive Pacific Walrus (Odobenus rosmarus divergens)

Abstract

A pair of pacific walruses were subjected for a long term study for 20 years on their growth and reproduction since 6 months of age, and succeed breeding four times. The body lengths both male and female walruses continued to grow after they have reach the sexual maturity, until the age of 14 years, then growth have reached their plateau. The ages of the male and the female at sexual maturation were 10 and 9 year-old. The body weight markedly increased in the breeding season in the sexually matured male, showing the “fatted male phenomenon”. The copulatory behavior showed a clear seasonal pattern, which was observed for one or two days, during February 26 through March 22. Parturition occurred during May 3 through June 6, and the mean gestation period was 441 ± 2.3 days (n = 4). The urinary estrone conjugate (EC) and pregnanediol-3-glucuronide (PDG) in the pregnant female showed sharp increase in the late September, an approximately 200-day after copulation, as the body weight of pregnant female started to increase. These results may be suggesting that delayed implantation had been completed and fetal development had started. The calf started to wean at approximately 6 months, although the nursing continued throughout the following 3 years until the next parturition. The birth interval was three years.