Disentangling environmental from individual factors in isotopic ecology: A 17-year longitudinal study in a long-lived seabird exploiting the Canary Current

•δ13C declined over the last two decades even when corrected by Suess effect.•Avian trophic level appears unaffected by the overexploitation of the Canary Current.•Shearwaters responded isotopically to changes in upwelling intensity.•Individual strategies can range from very specialist to very generalist individuals.•Repeated individual sampling of feathers is a sensitive indicator of the environment.