REPRODUCTIVE-PERFORMANCE OF FEMALE ANTARCTIC FUR SEALS - THE INFLUENCE OF AGE, BREEDING EXPERIENCE, ENVIRONMENTAL VARIATION AND INDIVIDUAL QUALITY

1. The reproductive performance of female Antarctic fur seals was exam ined in relation to age, reproductive experience and environmental var iation over 10 consecutive years (1983-92) at Bird Island, South Georg ia. 2. The age at which females first gave birth varied from 3 to 6 ye ars; over 90% of these females were 3 or 4 years of age. We found no e vidence to suggest that age at primiparity had significant effects on subsequent reproduction; however, 3-year-old primiparae were less like ly to be seen in subsequent years than 4-year-old primparae which may indicate a cost, in terms of survival, for females that first give bir th at an early age. 3. Age-specific reproductive rates increased rapid ly from ages 2 to 6 years, reached a peak of 0.80 at 7-9 years, remain ed above 0.75 until 11 years and then began to decline with increasing age. 4. The mean duration of foraging trips in the current year (whic h was used as a measure of the availability of food resources) consist ently improved models of the likelihood of pupping and of weaning succ ess. When these trips were long (indicating reduced local food resourc es), females returned to the breeding beaches later, fewer females pup ped, they gave birth to lighter pups and weaning success was reduced. 5. The reproductive performance of older, experienced Antarctic fur se als was greater than that of younger, inexperienced animals because th ey had higher natality rates, gave birth to heavier pups earlier in th e season, had greater weaning success and were more likely to pup the next season.