Data from: Multiple stressors in a top predator seabird: potential ecological consequences of environmental contaminants, population health and breeding conditions

Environmental contaminants may have impacts on reproduction and survival
in wildlife populations suffering from multiple stressors. This study
examined whether adverse effects of persistent organic pollutants (POPs)
increased with poor population health and breeding conditions in three
colonies (60–74°N) of great skua (Stercorarius skua) in the north-eastern
Atlantic (Shetland, Iceland and Bjørnøya [Bear Island]). POPs
(organochlorines [OCs] and polybrominated diphenyl ethers [BDEs]) were
measured in plasma of incubating birds (n = 222), concentrations differing
nearly tenfold among colonies: Bjørnøya (2009) > Bjørnøya (2010)
> Iceland (2009) > Shetland (2009). Reproductive success
(hatching success and chick survival) showed that breeding conditions were
favourable in Shetland and at Bjørnøya (2010), but were very poor in
Iceland and at Bjørnøya (2009). Biomarkers indicated that health was poor
in the Shetland population compared to the other populations. Females
whose chicks hatched late had high POP concentrations in all colonies
except at Bjørnøya (2010), and females losing their eggs at Bjørnøya
(2009) tended to have higher concentrations than those hatching. Moreover,
there was a negative relationship between female POP concentrations and
chick body condition at hatching in Iceland and at Bjørnøya (2010).
Supplementary feeding experiments were conducted, and in Iceland where
feeding conditions were poor, significant negative relationships were
found between female POP concentrations and daily growth-rate in
first-hatched chicks of control nests, but not in food supplemented nests.
This suggests that negative impacts of POPs were mitigated by improved
feeding conditions. For second-chicks, there was a strong negative
relationship between the female POP concentrations and growth-rate, but no
effects of supplementary feeding. Lowered adult return-rate between
breeding seasons with increasing POP loads were found both at Bjørnøya
(2009) and in Shetland, especially related to BDEs. This indicates
stronger fitness consequences of POPs following seasons with very poor
breeding conditions and/or high reproductive effort. This study suggests
that the impacts of POPs may differ depending on population health and
breeding conditions, and that even low concentrations of POPs could have
ecological consequences during adverse circumstances. This is important
with regard to risk assessment of biomagnifying contaminants in marine
ecosystems.