Influences of fasting on stable isotope ratios in male southern elephant seals

Stable isotope signatures are used as biomarkers to investigate dietary behaviour in ecology, anthropology and archaeology. As naturally occurring stable isotopes fractionate between predator and their prey (i.e the relative... [ view full abstract ]

Stable isotope signatures are used as biomarkers to investigate dietary behaviour in ecology, anthropology and archaeology. As naturally occurring stable isotopes fractionate between predator and their prey (i.e the relative proportions of different isotopes of the same element change predictably), stable isotope signatures are used to predict the trophic level within a food web at which a predator is feeding. However, it has been proposed that the predictable change in stable isotopes between a consumer and their diet may not hold true when animals are undergoing extreme physiological and biochemical processes (the δ15N enrichment by fasting theory). Fasting animals are naturally adapted to use higher levels of lipid stores than protein stores, though little is known about how this affects their stable isotope ratios. We used male southern elephant seals (Mirounga leonina) as a model to determine whether stable isotopes are still indicative of diet while animals fast over their breeding season. These animals experience one of the most prolonged periods of food deprivation of any species. Nitrogen stable isotopes were measured in whole blood and serum from fasting male elephant seals at King George Island throughout the breeding season.