Intraspecific variation in trophic feeding levels and organochlorine concentrations in glaucous gulls (Larus hyperboreus) from Bjørnøya, the Barents Sea.

Biomagnification contributes to high concentrations of persistent organochlorines (OC) in some Arctic vertebrates. Glaucous gulls (Larus hyperboreus) on Bjørnøya in the western Barents Sea were studied to compare the intraspecific variation in OC concentration with variation in trophic feeding levels, estimated from ratios of nitrogen isotopes. Liver tissue samples from 40 adult glaucous gulls were analysed for hexachlorobenzene (HCB), oxychlordane, p,p'-dichlorodiphenyltrichloroethane (DDT) and its metabolite p,p'-DDE, Mirex, and nine congeners of polychlorinated biphenyl (PCB). The ratios of the heavier to lighter isotope of carbon (13C/12C) and nitrogen (15N/14N), expressed as delta13C and delta15N, were measured in liver and muscle. Hepatic concentrations of the nine PCB congeners (Sigma 9 PCB) ranged from 16 microg/g lipid weight to 292 microg/g lipid weight. The delta15N ranged from 14.0/1000 to 15.3/1000 in muscle. Seven of the 14 OC measured, sigma DDT, and sigma 9 PCB were positively correlated to delta15N from muscle tissue. No correlations were found between OC and delta13C. The present results indicate that OC concentrations are partly dependent on the foraging strategy of the gull. The r2 of the linear regressions suggests that up to 18% of the variation in the OC concentrations could be explained by variation in food preference.