MEPS 753:175-189 (2025)  -  DOI: https://doi.org/10.3354/meps14768

ABSTRACT: Southern elephant seals Mirounga leonina are top predators in the Southern Ocean and significant consumers of mesopelagic mid-trophic level prey while spending most of the year foraging out at sea. Yet, there is still considerable uncertainty regarding variability in the dietary composition between individuals and over time. We ran a suite of mixing models using carbon and nitrogen stable isotope ratios from the vibrissae of 54 adult female southern elephant seals from the South Georgia population (2005-2009) and potential fish, squid, and krill prey. Our goals were to (1) estimate the dietary composition of this population as a whole, (2) compare the dietary composition of individuals between previously identified foraging strategies, and (3) quantify the degree of dietary consistency at the individual level throughout a long foraging migration. Models indicate that myctophid fish were the dominant prey item consumed (mean 45% of diet), followed by Antarctic krill and Antarctic jonasfish. However, there was considerable variability within and among groups of seals regarding specific prey items consumed and the degree of individual dietary specialization, possibly as a means of reducing intraspecific competition. Finally, our models provide evidence of most seals displaying dietary consistency throughout a foraging migration. These findings have important management implications for the South Georgia population in an uncertain future and highlight the need for more effective krill management along the western Antarctic Peninsula.

KEY WORDS: Stable isotopes · Mixing models · Krill · Lanternfish · Diet · Vibrissa · Elephant seals