Using anthropogenic contaminants and stable isotopes to assess the feeding ecology of Greenland sharks
Arctic, Elasmobranchs, Feeding ecology, Greenland shark, Marine mammals, Organochlorine contaminants, Pollutants, Seals, Stable isotopes, Trophic position
Organochlorine contaminants (OCs) are a large group of ubiquitous pollutants that have potential as tracers of ecological processes. To examine this utility, we measured OCs, stable isotopes of nitrogen (δ15N) and carbon (δ15C), and stomach contents in a large Arctic marine fish, the Greenland shark (Somniosus microcephalus), collected in the Davis Strait region to examine the feeding ecology of this little studied elasmobranch. Stable isotopes and OCs were also measured in the turbot (Reinhardtius hippoglossoides) and stable isotopes in the ringed seal (Phoca hispida) and harp seal (Pagophilus groenlandicus) to put the shark results in context. Values of δ15N suggest that the Greenland shark feeds at a similar trophic level as the turbot and ringed seal (about the fourth trophic level) and at a higher trophic level than harp seals, despite the presence of many turbot and a single ringed seal in the stomach contents of 14 sharks. Values of δ13C indicate that source of carbon in turbot and Greenland shark is of a more pelagic origin than in ringed and harp seals. High concentrations of biomagnifying OCs in the sharks compared with the turbot (concentration 10-100X lower) and ringed seals (3-10X lower) suggest that the sharks feed at a higher trophic level than implied by stable isotopes. High urea levels found in the tissues of sharks may influence δ15N values, resulting in an underestimate of shark trophic position, and requires additional study. The presence of a ringed seal in the stomach of one shark, relatively high levels of a contaminant metabolite (oxychlordane; slowly formed in fish) in some sharks, and high OC levels suggest that seals may be a common food item of some Greenland sharks. This study shows the utility of using OCs in ecological study and suggests caution when interpreting stable-isotope data as a single indicator of trophic position.
Fisk, Aaron T.; Tittlemier, Sheryl A.; Pranschke, Jennifer C.; and Norstrom, Ross J.. (2002). Using anthropogenic contaminants and stable isotopes to assess the feeding ecology of Greenland sharks. Ecology, 83 (8), 2162-2172.