Diet and resource use among Greenland sharks (Somniosus microcephalus) and teleosts sampled in Icelandic waters, using δ¹³C, δ¹⁵N, and mercury

Stable carbon (δ 13 C) and nitrogen (δ 15 N) isotopes and total mercury (Hg) were used to investigate diet and resource use among Greenland sharks ( Somniosus microcephalus ) and 14 teleosts inhabiting Icelandic waters. Greenland shark stomachs contained 11 of the teleosts sampled, along with other fishes and marine mammal tissues. Teleost resource use ranged from pelagic (e.g., Argentina silus ) to benthic (e.g., Anarhichas lupus ) based on δ 13 C, and relative trophic positions (TP, based on δ 15 N) ranged from 3.0 ( Mallotus villosus ) to 3.8 (e.g., Brosme brosme ). Greenland shark δ 13 C indicated feeding on benthic and pelagic resources, with a high input of pelagic carbon, and δ 15 N indicated a relative TP of 4.3. Log[Hg] increased with δ 15 N (i.e., TP) from teleosts to Greenland sharks and was higher in offshore vs. inshore teleosts. Linear regressions revealed that log[Hg] was better described by both δ 15 N and δ 13 C-assigned resource use than by δ 15 N alone. Hg was useful for supporting the TPs suggested by δ 15 N, and the higher Hg in offshore fishes could help explain the high Hg of Greenland sharks. Results from this study demonstrated the potential use of Hg as a dietary tracer in marine fishes.