MEPS 455:287-301 (2012)  -  DOI: https://doi.org/10.3354/meps09601

ABSTRACT: Although crabeater seals Lobodon carcinophaga are among the most abundant consumers of Antarctic krill Euphausia superba, their diet has rarely been studied throughout most of the species’ range. Using δ¹³C and δ¹⁵N values in vibrissae from 53 seals, we examined the trophic ecology of crabeater seals from the western Antarctic Peninsula (wAP) in 2001, 2002 and 2007. We observed a wide variability in individual seal mean δ¹³C values, which ranged from −19.8‰ to −24.9‰ , whereas mean δ¹⁵N value varied from 5.4‰ to 7.9‰. We identified a positive significant effect of seal mass on δ¹³C values, as well as a significant seasonal effect (higher δ¹³C values in austral winter), which likely resulted from changes in the composition of the community of primary producers. δ¹⁵N values for crabeater seals, on the other hand, were affected by year, with individuals in 2002 having higher δ¹⁵N values. The median (with range) contribution of Antarctic krill to the diet of crabeater seals, as estimated using the Bayesian mixing model MixSIR, was 87.9% (81.2 to 94.8%). During 2002, krill biomass in the wAP was at one of its lowest levels during the last 2 decades, coinciding with a slight reduction in the importance of krill for the diet of the seals that year, which reached 84.5% (75.1 to 92.4%). Despite the relative plasticity observed in the diet of crabeater seals, it is unknown to what extent, and at what rate, crabeater seals might be able to switch to a more generalized diet, which might impact their fitness, given the ongoing environmental change along the wAP.

KEY WORDS: Lobodon carcinophaga · Euphausia superba · Antarctic fish ·  Stable isotopes · Diet · Specialization