Population structure of a non-breeding colony of the cape fur seal arctocephalus pusillus pusillus at Cape Frio, Namibia

Abstract

The age and sex composition at a large non-breeding colony of the Cape fur seal Arctocephalus pusillus pusillus at Cape Frio, Namibia, are described. A ground estimate indicated that there were approximately 20 000 seals of all age groups and of both sexes at the colony during September 1989, around two months before the pupping season. The sex ratio of seals sampled was 1.61 : 1 (n = 107, 61.7% male). Most of the males were immature, 2- and 3-year-olds, although some older, mature bulls were present at the colony. In contrast, only 9.8% of females were sexually immature and 80.5% were older than 13 years. None of the young females was reproductively active and older females had reduced reproductive rates. Reproductive status of females differed from that of seals at other breeding colonies.