The role of Greenland sharks (Somniosus microcephalus) in an Arctic ecosystem: assessed via stable isotopes and fatty acids

The Greenland shark (Somniosus microcephalus) is the only shark species known to inhabit ice-covered seas in the North Atlantic, but remains a missing component in most studies of Arctic food webs. In the present study, stable isotopes (SIs) of nitrogen (δ¹⁵N) and carbon (δ¹³C) and fatty acids (FAs) were analyzed to identify the role of Greenland sharks (sampled during June 2008–2009) in Kongsfjorden, a productive fjord on the west coast of Svalbard, Norway (~79ºN, 12–13ºE). The Greenland shark fed at a high trophic position (4.8) based on δ¹⁵N values, and δ¹³C confirmed that most (70 %) of their carbon was derived from phytoplankton-based food chains, which is consistent with a heavy reliance on pelagic teleosts and seals. Greenland sharks from Kongsfjorden had fatty acid profiles in both muscle and plasma (e.g., low 20:1n-9, high 22:5n-3) that suggested a low portion of Greenland halibut (Reinhardtius hippoglossoides) and high proportion of gadoids and seals in their diet compared to Greenland sharks sampled in Cumberland Sound, Canada, during April 2008, which were previously shown to derive much of their energy from Greenland halibut. The high proportions of seal fatty acids in both slow- (muscle) and fast- (plasma) turnover tissues indicate that trophic interactions between Greenland sharks and seals in Kongsfjorden are a common occurrence. Results from the present study suggest that Greenland sharks likely play a unique and significant role in Arctic marine food webs as a top predator of fishes and marine mammals.     

Essential and non-essential element concentrations in two sleeper shark species collected in arctic waters

A number of elements/metals have increased in arctic biota and are of concern due to their potential toxicity. Most studies on elements in the Arctic have focused on marine mammals and seabirds, but concentrations in the Greenland shark (Somniosus microcephalus) and Pacific sleeper shark (Somniosus pacificus), the only two shark species known to regularly inhabit arctic waters, have never been reported. To address this data gap, concentrations and patterns of 25 elements were analyzed in liver of Greenland sharks collected about Cumberland Sound (n=24) and Pacific sleeper sharks collected about Prince William Sound (n=14). Several non-essential elements differed between species/locations, which could suggest geographical exposure differences or ecological (e.g., diet) differences between the species. Certain essential elements also differed between the two sleeper sharks, which may indicate different physiological requirements between these closely related shark species, although information on such relationships are lacking for sharks and fish.