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MEPS prepress abstract   -  DOI:

Extreme dietary specialisation in adult male southern elephant seals: determining variation between individual trophic diets

Andrea Cormack*, Eve Slavich, Javier Negrete, Horst Bornemann, Gustavo A. Daneri, Tracey L. Rogers

*Corresponding author:

ABSTRACT: Although dietary studies have provided important insights into the causes and ramifications of diet variation for the southern elephant seal (SES) (Mirounga leonina), adult males are comparatively underrepresented within that literature. Individual males can vary morphologically, as well as behaviourally, leading to differences in their life history trajectories and outcomes. Therefore, to improve our understanding of the male diet we sought to determine the degree of dietary variation between, as well as within, individuals from the west Antarctic Peninsula (WAP). Secondly, we investigated whether individual morphological traits, seasonality, and year influenced their dietary variation. Whiskers were sampled from 31 adult male seals and used to measure the bulk stable isotope nitrogen (δ15N). We sequentially segmented each whisker to create a time series of datapoints for each individual, allowing us to compare δ15N variation within each seal, as well as assess variation between the seals. We then investigated the effects of body length, girth, season, and year on male dietary variation. We found that adult male SES maintained an extremely specialised diet. Variation between individuals was strongly correlated with their body size with larger seals feeding higher up the trophic web. Interestingly, seasonality and year both influenced variation within the seals’ diets, but only year was seen to influence the variability between seals. We discuss the possible causes and ramifications of dietary specialisation for the SES and highlight the need for combined tracking/stable isotope investigations to improve our understanding of the ontogeny of the seals’ dietary specialisation.