The reproductive tracts of 89 female subantarctic fur seals, taken at
Cough Island between November 1977 and October 1978, were examined. Fe
males started ovulating at age 4 yr and all 6-yr-old females were sexu
ally mature. They are mono-ovulatory, alternating between ovaries, and
only single embryos were found. Females older than 13 yr (n = 11) sho
wed poor follicular development and some failed to ovulate. The gestat
ion period (first recorded ovulation to first recorded birth) was 360
d, while delayed implantation (first recorded ovulation to first recor
ded implantation) lasted for 139 days. Follicle numbers in the functio
nal ovary declined sharply after ovulation while the corpus luteum inc
reased 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 ovul
ation 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 approxim
ately 3 mo after parturition, could not be detected macroscopically wi
thin 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.