Seasonal changes in the ovarian structure ofthe Cape fur seal, Arctocephalus pusillus pusillus

Abstract

The annual reproductive cycle of the female Cape fur seal (Arctocephalus pusillus pusillus) was described by noting monthly gross changes in ovaries from 159 females, histological changes in 46 females and placental scars in 119 females. The size and weight of an ovary containing a corpus luteum was significantly greater than that of an ovary containing a corpus albicans for most of the year, the latter only approaching, or exceeding the former during the breeding season. Follicular activity initially increased in ovaries containing either a corpus luteum or a corpus albicans; however, it declined in the ovary containing a corpus luteum after implantation, while in that containing a corpus albicans it increased, reaching a maximum in December of 32.0 ± 10.08 follicles, averaging 5.41 ± 0.73 mm. The corpus luteum increased in size following ovulation, attaining a maximum size of 22.28 ± 3.38 mm in August (eight months after ovulation). Thereafter, it gradually decreased in size, generally becoming invisible to the naked eye by 30–32 months after ovulation. Luteal cells increased until seven months after ovulation, reaching a maximum size of 34.36 ± 1.26 μm before regressing, disappearing from the corpus luteum by 18 months after ovulation. Using placental scarring and CA counts in 119 females, a pregnancy rate of 77.4% was calculated, with 6.5% abortions and 16.1% non-implantations making up the remainder.