| Summary: | Progress Code: completed Statement: These estimates are derived from models based on the Arnason-Schwarz method, and account for the probability of females surviving between samples; being resighted (and thus included in the sample); and being in breeding or non-breeding state. In the base model, breeding probability follows a first-order Markov process in that the probability of breeding at time i+1 depends on breeding state at time i. Therefore, reproductive rate can be defined as the probability of being in breeding state at time i+1, conditional on surviving from time i to i+1. The method accounts for many of the biases inherent in traditional estimates of reproductive rate since re-sight rates can vary between breeding states and survivorship is also incorporated. Publication of these results is currently in progress with the Journal of Animal Ecology. Summary 1.An efficient method of describing change in Antarctic marine ecosystems is long-term monitoring of land-breeding marine predators. High-level predators are used to index the state of environment on the notion that perturbations in the ecosystem will affect their diet, reproductive performance and other demographics. For this purpose, Weddell seals breeding at the Vestfold Hills have been marked and re-sighted for the past 28 years (1973 - 2000). 2.Successful reproduction requires considerable energetic resources. The difference between rates of conception and rates of parturition suggests pregnant females abort reproductive attempts when their energy stores are low. In this way, annual rates of reproduction (i.e. parturition) are a measure of foraging efficiency. 3.Previous attempts to estimate Weddell seal reproduction have been biased by different rates of re-sighting breeding and non-breeding females. We used multistate mark and re-sight models to account for this and other variables when estimating reproductive rate. 4.The amplitude of temporal variation was much greater for reproduction than for survivorship, indicating that parous ...
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