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The northern elephant seal (NES) females (Mirounga angustirostris) show a post-breeding and a post-molting migration in the same year. Californian NES females tracing by satellite indicate three migratory variants: coastal, costal-oceanic and oceanic that would lead to differences in the diet and stable isotopes signatures (?15N and ?13C). However stable isotope values in NES female vibrissae show Orly two clearly distinct signals corresponding to the ocean and coastal migrations. The aim of this work is to explore the proportions in the NES population from San Benito Islands (Mexico) in each migratory variant during the post-molting migration based on the isotopic signature measured in their pup´s fur. Assuming that pups should show enriched isotope values but proportional to those of their mothers, we sampled fur from 169 pups in February 2010 from the three San Benito Islands (East = 44; West = 53 and Centre = 71) and estimated their ?13C and ?15N values. After adjustment for mother-pup fractionation (0.5‰ carbon and 2‰ nitrogen), the NES isotope values clustered into two distinct groups: A likely oceanic group with mean values of ?13C and ?15N of -17.4‰ ± 0.3‰ and 17.4‰ ± 1.0‰ respectively, and a coastal group with values of -15.8‰ ± 0.4‰ and 19.2‰ ± 0.8‰. Similar to California (71% oceanic versus 29% coastal), the proportion of NES of San Benito showed higher numbers of females in the oceanic variant for each island (60%, 65% and 69% respectively).

Palabras clave: Guadalupe fur seal; Migratory destiny; elephant seals

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