Stable nitrogen and carbon isotope ratios in multiple tissues of the northern fur seal Callorhinus ursinus: implications for dietary and migratory reconstructions

We investigated changes in trophic level and feeding location over time in juvenile male northern fur seals Callorhinus ursinus from the Pribilof Islands, Alaska, using stable nitrogen (δ 15 N) and carbon (δ 13 C) isotope analyses of their fur, muscle, blubber, brain, liver, and kidney tissues. Mean δ 15 N values were non-uniform between tissues and ranged from 14.9‰ (fur) to 17.1‰ (lipid extracted blubber). Mean δ 13 C values also varied with tissue type and ranged from -24.7‰ (non-lipid extracted blubber) to -17.5‰ (fur). Mean isotope values of tissues clustered into groups coincident with their estimated protein and isotope turnover times, with fur representing the most remote incor