Stable isotope analysis and fin whale subpopulation structure in the eastern North Atlantic

The North Atlantic fin whale was subject to heavy exploitation in the past and, despite partial recovery, it is still considered endangered. Recent research has questioned its currently accepted subpopulation structure and migratory movements, challenging management and conservation efforts. Here we contribute to this discussion by presenting results of stable isotope analysis of fin whale bones and krill samples collected from fin whale stomachs from two exploited areas, west Iceland and northwest Spain, and comparing these results with North Atlantic isoscapes. In krill, N-15 values were highly variable and no significant differences in N-15 and C-13 between areas emerged. N-15 and C-13 values in bone were higher than in krill, due to trophic enrichment, and were not significantly different between areas. Both krill and bone results were slightly inconsistent with the local isoscapes, maybe due to seasonal variations in local productivity and in krill diet and, in the case of bone, to its capability to integrate long-term isotopic values, derived from food consumed in distant areas. Conversely, O-18 values, which reflect the basal signal of sea water, were consistent with isoscapes and significantly higher in whales from northwestern Spain, possibly indicating migration to breeding grounds located at lower latitudes.