Macquarie Island southern elephant seal demography
Volzke, Sophia (2021), Macquarie Island southern elephant seal demography, Dryad, Dataset, https://doi.org/10.5061/dryad.zpc866t7f
The Southern Ocean has been disproportionately affected by climate change and is therefore an ideal place to study the influence of changing environmental conditions on ecosystems. Changes in the demography of predator populations are indicators of broader shifts in food-web structure, but long-term data are required to study these effects. Southern elephant seals (Mirounga leonina) from Macquarie Island have consistently decreased in population size while all other major populations across the Southern Ocean have recently stabilised or are increasing. Two long-term mark-recapture studies (1956-1967 and 1993-2009) have monitored this population, which provides an opportunity to investigate demographic performance over a range of climatic conditions. Using a 9-state matrix population model, we estimated climate influences on female survival by incorporating two major climatic indices into our model: The Southern Annular Mode (SAM) and the Southern Oscillation Index (SOI). Our best model included a one year lagged effect of SAM and an unlagged SOI as covariates. A positive relationship with SAM1 (lagged), related the previous year’s SAM with juvenile survival, potentially due to changes in local prey availability surrounding Macquarie Island. The unlagged SOI had a negative effect on both juvenile and adult seals, indicating that sea-ice dynamics and access to foraging grounds on the East Antarctic continental shelf could explain the different contributions of ENSO events on the survival of females in this population.
Between 1951-1965 and 1993-1999 weaned Southern Elephant Seals were captured and marked permanently by hot iron branding. Seals were recorded in regular re-sights varying from daily isthmus searches during the breeding season to ad-hoc sightings outside of active monitoring.
Biological data from individual short-term scientific projects includes information on physical condition for a portion of pups and adult seals.