Trophic relationships among high Arctic seabirds: insights from tissue-dependent stable-isotope models

Abstract

Measurement of stable isotopes of N and C in tissues of marine consumers can provide trophic-level information that is a time-integrated approximation of assimilated diet. By measuring δ15N and δ13C concentrations in liver, muscle and bone collagen of seven species of seabirds inhabiting the Barrow Strait-Lancaster Sound region, Northwest Territories, estimates of short-, intermediate-, and long-term trophic level (TL), respectively, were established. δ13C was not a useful indicator of trophic position in this marine food web but may indicate inshore or benthic vs offshore or pelagic feeding preferences in seabirds. δ15N was a useful indicator and ranged from 12.7 ± 0.3‰ (TL 3.3) in liver of dovekies Alle alle to 19.1 ± 0.8‰ in the bone collagen of glaucous gulls Larus hyperboreus. Consistent with their known diets, dovekies and common eiders Somateria mollissima showed lowest trophic positions for all tissues; black-legged kittiwakes Rissa tridactyla, thick-billed murres Uria lomvia, northern fulmars Fulmarus glacialis and black guillemots Cepphus grylle showed intermediate trophic positions (TL 3.9-4.3) and glaucous gulls showed highest trophic position (TL 4.5-4.8). In general, seabirds increased their consumption of lower-trophic-level invertebrates during the breeding season over their lifetime averages but fed their chicks diets consisting of high proportions of fish. -from Author