Stable isotope analyses reveal individual variability in the trophic ecology of a top marine predator, the southern elephant seal
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Identifying individuals’ foraging strategies is critical to understanding the ecology of a species, and can provide the means to predict possible ecological responses to environmental change. Our study combines stable isotope analysis and satellite telemetry to study the variability in individual foraging strategies of adult female southern elephant seals (Mirounga leonina). Our hypothesis is that female elephant seals from the Western Antarctica Peninsula (WAP) display individual specialization in their diets. We captured adult female elephant seals (n = 56, 2005–2009) at Livingston Island (Antarctica), and instrumented them with SMRU-CTD satellite tags. We collected blood, fur, and vibrissae samples for δ13C and δ15N analyses. The mean values for all vibrissae were −21.0 ± 0.7‰ for δ13C, and 10.4 ± 0.8‰, for δ15N. The individual variability of δ13C (60%) was more important than the within-individual variability (40%) in explaining the total variance observed in our data. For δ15N, the results showed the opposite trend, with the within-individual variability (64%) contributing more to the total variance than the individual variability (36%), likely associated with the effect that the fasting periods have on δ15N values. Most individuals were specialists, as inferred from the low intra-individual variability of δ13C values with respect to the population variability, with half the individuals utilizing 31% or less of their available niche. We found eight different foraging strategies for these animals. Female elephant seals from the WAP are a diverse group of predators with individuals utilizing only a small portion of the total available niche, with the consequent potential to expand their foraging habits to exploit other resources or environments in the Southern Ocean.
KeywordsMirounga leonina Foraging strategies δ13C δ15N Telemetry
We thank S. Simmons, K. Goetz, B. Nickel, B. Walker, J. Lehman, L. Roland, S. Kim, D. Andreasen, A-L. Harrison, N. Teutschel, S. Peterson and Cape Shirreff field crews (2005–2009) for assisting with collection and analysis of the data. US-AMLR program, NSF, USAP, and Raytheon Polar Services provided logistic support. Funding was provided by NSF (ANT-0840375, ANT-0440687, ANT-0523332 and ANT-0838937), NOPP (N00014-05-1-0645), Marine Mammal Commission, Friends of Long Marine Lab, and CDELSI-UCSC. L.A.H.’s doctoral studies were supported by Fulbright-CONICYT (Chile).
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