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

The measurement of stable isotopes of nitrogen and carbon in tissues of marine consumers can provide trophic-level information that is a time-integrated approximation of assimilated diet. By measuring 6I5N and 613C concentrations in liver, muscle and bone collagen of 7 species of seabirds inhabiting the Barrow Strait-Lancaster Sound region, Northwest Territories. Canada, estimates of short-, intermediate-, and long-term trophic level (TL), respectively, were established. Trophic estimates were based on a simple model incorporating diet-tissue fractionation established through the captive rearing of piscivorous birds on known isotopic diets. 613C 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. 615N was a useful indicator and ranged from 12.7 f 0.3%0 (TL 3.3) in liver of dovekies Alle aUe to 19.1 + 0.8% in the bone collagen of glaucous gulls Larus hyperboreus.