Age distribution of breeding female Antarctic fur seals in relation to changes in population growth rate

• Published in: Canadian Journal of Zoology
• Main Authors: Boyd, I. L., Lunn, N. J., Rothery, P., Croxall, J. P.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1990
• Subjects: Animal Science and Zoology; Ecology, Evolution, Behavior and Systematics; Antarctic; Bird Island; Antarc*; Antarctic Fur Seals
• Online Access: http://dx.doi.org/10.1139/z90-307; http://www.nrcresearchpress.com/doi/pdf/10.1139/z90-307

The age distribution of breeding female Antarctic fur seals at Bird Island, South Georgia, in 1988 was compared with the age distribution of a sample obtained in 1971–1973. The mean age in 1971–1973 was 7.41 (SE = 0.26) years and in 1988 it was 6.93 (SE = 0.20) years. After correction for age-dependent arrival time at the pupping beach in 1988, the mean age was 6.22 (SE = 0.14 years), which was significantly lower than in 1971–1973. Indicators of population size suggested that population growth at Bird Island had declined to below 3% annually by 1988 compared with rapid growth (17%) in 1958–1972. Exponential models fitted to the frequency distribution of age-classes greater than age 5 years and corrected for the rate of increase of the population gave adult survival rates of 0.66 (SE = 0.03) and 0.88 (SE = 0.02) for the 1988 and 1971–1973 samples, respectively. The reduced apparent adult survival rate in the 1988 sample was probably caused by emigration brought about by high densities of females on the pupping beaches. There are few signs from this analysis that the fur seal population at South Georgia is close to carrying capacity.