Feeding ecology and the concentration of organochlorines in glaucous gulls

We investigated the blood concentrations of organochlorines (OCs) and the d iet of glaucous gulls Larus hyperboreus breeding in two neighbouring areas at Bear Island in the Barents Sea, north-eastern Atlantic. One area was sit uated on the edge of the large seabird cliff, about 100-150 m above sea lev el. The second area was about 1-2 km from the seabird cliff, and 10-50 m ab ove sea level. In both 1997 and 1998 there were significant differences bet ween the breeding areas for five OCs (HCB, HCH, Oxychlordan, DDE and PCB) m easured, with the birds breeding on the cliff having higher levels. These d ifferences were accompanied by a difference in diet between the areas. Bird s in the former area had at least four times higher intake of guillemot Uri a spp. eggs, while the birds near sea level seemed to have a much higher in take of fish. This study demonstrates the importance of feeding ecology for the distribution of OCs within populations. The results have important imp lications for the establishment of monitoring programs for OC contamination of the glaucous gull in the Arctic.