REPRODUCTION IN THE FEMALE SUB-ANTARCTIC FUR-SEAL, ARCTOCEPHALUS-TROPICALIS

The reproductive tracts of 89 female subantarctic fur seals, taken at Cough Island between November 1977 and October 1978, were examined. Females started ovulating at age 4 yr and all 6-yr-old females were sexually mature. They are mono-ovulatory, alternating between ovaries, and only single embryos were found. Females older than 13 yr (n = 11) showed poor follicular development and some failed to ovulate. The gestation period (first recorded ovulation to first recorded birth) was 360 d, while delayed implantation (first recorded ovulation to first recorded implantation) lasted for 139 days. Follicle numbers in the functional ovary declined sharply after ovulation while the corpus luteum increased in size until at least 1 mo prior to parturition. The number of follicles in the contralateral ovary increased after midwinter (June/July), and the mean size of the largest follicles peaked prior to ovulation in December. The mean size of the largest follicles increased in both ovaries near implantation time, after reaching a low subsequent to ovulation. The regressing corpus albicans, conspicuous for approximately 3 mo after parturition, could not be detected macroscopically within one year postpartum. Subantarctic fur seals at Cough Island have a distinct postreproductive class of older females. The pregnancy rate for all females greater than or equal to 4 yr of age was 79%, and it was 84.5% for the sexually mature group of greater than or equal to 6 yr of age, while the mean age at puberty was 4.80 yr.