Abstract: Capture–recapture (CR) approaches are extensively used to estimate demographic parameters. Their robustness relies on the selection of suitable statistical models, but also on the sampling design and effort deployed in the field. In colonial or territorial species showing breeding site fidelity, recurrent local perturbations, such as predation-induced breeding failure, may lead individuals to disperse locally or regionally. This might induce heterogeneity in individual CR histories and biases in demographic parameter estimates. Here, we assessed the effect of buffer areas and multi-site designs on annual survival estimate accuracy and precision. First, using simulated data with and without a multi-site design, we compared survival estimates for different scenarios involving contrasted local and regional dispersal. Then, using data from a local multi-site long-term monitoring survey carried out in a colony of black-legged kittiwakes, we tested the homogeneity of individual CR histories and compared survival estimates from three datasets including one or several breeding cliffs with or without buffer areas. Results from simulations highlighted that a single-site design consistently led to underestimated or less precise survival values compared to a multi-site design. Similarly, a multi-site design allowed detecting significant temporal trends while a single-site one did not. In the field-based study, adding buffer areas reduced individual heterogeneity, but all three datasets suffered from strong trap-dependence possibly due to individual breeding success affecting nest-site fidelity. Implementing a multi-site design significantly improved the accuracy and precision of annual survival estimates, regardless of CR models applied. Adapting the spatial scale of sampling design to the local environment and species behaviour is essential to provide robust parameters of key relevance for population monitoring and management. We show that implementing buffer areas and/or multi-site designs may be especially beneficial for long-lived species facing regular local perturbation events leading to local dispersal.

Abstract: Southern Elephant Seals are upper marine predators of the Southern Ocean. As such, their population dynamics and fluctuations reflect environment conditions. Their worldwide populations crashed during the second half of the twentieth century for reasons not yet completely elucidated. Here, we studied the largest population of Southern Elephant Seals within the South Indian Ocean that are breeding on îles Kerguelen. In a previous analysis, Guinet et al. in Antarct Sci 11:193197, 1999) suggested that the decline on îles Kerguelen might be over, as observed elsewhere. Using 10 years of additional data, we updated this analysis using state-of-the-art statistical methods to account for most uncertainties associated with count data. We showed that the population of female Southern Elephant Seals breeding on îles Kerguelen has been stable over the past 20 years. Despite concomitant global changes within the Southern Ocean, we did not find any evidence of a phenological shift in peak haul-out date of breeding females between the 1970s and the 2000s.

Abstract: Maternal effects are widespread in ecology and can alter the dynamics of a population. We investigated the impact of maternal foraging strategies on offspring weaning massa proxy of maternal foraging success and of offspring survivalin southern elephant seals on îles Kerguelen. Using 4 years of data, we modelled pup weaning mass as a two-component mixture and used blood stable isotope values to discriminate between maternal foraging strategies previously identified from bio-logging studies. Carbon isotope ratio was a strong predictor of weaning mass, but the relationship was non-monotonic in contrast to a priori expectations. Females foraging in the interfrontal zone weaned pups with a smaller mass compared with females foraging in Antarctic waters. Pup mass was positively correlated with a proxy of global primary production in the interfrontal zone for small weanlings. Maternal effects, via a poor foraging efficiency in the 1970s, may help explain the large population decrease observed at that time on îles Kerguelen because of an overall decrease in pup weaning mass, survival and subsequent recruitment.