Critically, our approach can be applied retrospectively, and the influence of long-term climate variation on the spatial distribution of populations can be studied. Stable isotope-based techniques can be applied to any marine pelagic species (e.g. tuna, herring, turtles, seabirds etc.) for which long-term tissue archives are available or could be initiated, and would be particularly valuable in identifying regions suitable for marine no-take zones or protected areas.