Reproductive Biology of Steller Sea Lions in the Gulf of Alaska

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Abstract
Reproductive biology of Steller sea lions (Eumetopias jubatus) in the Gulf of Alaska was studied between 1975 and 1979 by examination of reproductive tracts, estimation of ages from dental annuli, and observations at rookeries and hauling areas. Timing of key reproductive events was: 1) birth, mid-May to mid-July; 2) breeding, late-May to mid- or late-July; and 3) implantation, late-September and October. The female-pup bond usually was 1 year, however, 1-, 2-, and 3-year-old animals occasionally were seen to suckle females. Some males became sexually mature by 3 years and all were sexually mature by 8 years. Mature males had seasonal spermatogenic activity with abundant epididymal spermatozoa from late April through July. Initial ovulations and pregnancies occurred between 2 and 8 years of age. The average age at first ovulation was 4.6 ±0.8 years (95% confidence limits) and first pregnancy 4.9 ± 1.2 years. Ovulation rates ranged from 26% at 3 years to 100% for animals ≤6 years. Incidence of pregnancy ranged from 20% at 3 years to 87% for females 8 to 20 years. Prenatal mortality between implantation and birth was estimated at 4.7% per month. The annual birth rate of full-term pups was estimated to be about 63% for sexually mature females.

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