Early-life density-dependence effects on growth and survival in subantarctic fur seals.

International audienceUnderstanding the regulation of natural populationshas been a long-standing research program in ecology.Current knowledge on marine mammals and seabirdsis biased toward the adult component of populations andlacking are studies investigating the juvenile component.Our goal was to estimate demographic parameters on thepre-weaning stage of a subantarctic fur seal (Arctocephalustropicalis) population on Amsterdam Island, suspectedto be regulated by density-dependence. The influence ofabundance on growth parameters (length and weight) andsurvival was assessed over a study period spanning 16years. We evidenced a negative trend in population growthrate when density increased. Density-dependence modelswere favored for pup body size and mass growth. Abundancehad a clear influence on body length at high population-density, pups grew slower and were smaller at weaningthan pups born in years with low population density.Abundance partly explained pup body mass variation anda weak effect was detected on pre-weaning survival. Thecausal mechanisms may be increased competition for foodresources between breeding females, leading to a reductionof maternal input to their pups. Our results suggested thatpup favored survival over growth and the development of their diving abilities in order to withstand the extreme fastingperiods that are characteristic of this fur seal population.This analysis provides significant insight of densitydependentprocesses on early-life demographic parametersof a long lived and top-predator species, and more specificallyon the pre-weaning stage with important consequencesfor our understanding of individual long-term fitnessand population dynamics