Persistent organic pollution in a high-Arctic top predator: sex-dependent thresholds in adult survival

In long-lived species, any negative effect of pollution on adult survival may pose serious hazards to breeding populations. In the present study we measured concentrations of various organochlorines (OCs: PCB and organochlorine pesticides) in the blood of a large number of adult glaucous gulls (Larus hyperboreus) breeding on Bjørnøya (Bear Island) in the Norwegian Arctic, and modelled their local survival using capture–recapture analysis. Survival was negatively associated with concentrations of OCs in the blood. The effect of OCs was nonlinear and evident only among birds with the highest concentrations (the uppermost deciles of contamination). The threshold for depressed survival differed between the sexes, with females being more sensitive to contamination. For birds with lower OC concentration, survival was very high, i.e. at the upper range of survival rates reported from glaucous and other large gull species in other, presumably less contaminated populations. We propose two non-e...