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

Abstract

Stable carbon (d 13 C) and nitrogen (d 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 d 13 C, and relative trophic positions (TP, based on d 15 N) ranged from 3.0 (Mallotus villosus) to 3.8 (e.g., Brosme brosme). Greenland shark d 13 C indicated feeding on benthic and pelagic resources, with a high input of pelagic carbon, and d 15 N indicated a relative TP of 4.3. Log[Hg] increased with d 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 d 15 N and d 13 C-assigned resource use than by d 15 N alone. Hg was useful for supporting the TPs suggested by d 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. Résumé: Les isotopes stables de carbone (d 13 C) et d'azote (d 15 N) et le mercure total (Hg) nous ont servi à étudier le ré-gime alimentaire et l'utilisation des ressources chez la laimargue atlantique (Somniosus microcephalus) et 14 téléostéens habitant les eaux islandaises. Les estomacs de laimargues atlantiques contenaient 11 des téléostéens échantillonnés, ainsi que des tissus d'autres poissons et de mammifères marins. L'utilisation de la ressource de téléostéens comprenait des poissons de pélagiques (par ex., Argentina silus) à benthiques (par ex., Anarhichas lupus) d'après d 13 C et leurs positions trophiques relatives (TP, basée sur d 15 N) variaient de 3,0 (Mallotus villosus) à 3,8 (par ex., Brosme brosme). Le d 13 C des laimargues atlantiques indique qu'elles se nourrissent de ressources benthiques et pélagiques, avec un apport élevé de carbone pélagique et leur d 15 N indique une TP relative de 4,3. Log[Hg] augmente en fonction de d 15 N (c'est-à-dire la TP) des téléostéens aux laimargues atlantiques et est plus élevé chez les téléostéens du large que chez ceux de la côte. Des régres-sions linéaires montrent que log[Hg] est mieux décrit par l'utilisation des ressources assignées à la fois par d 15 N et d 13 C que par d 15 N seul. Le Hg est utile pour appuyer les TP indiquées par d 15 N et les concentrations plus élevées de Hg dans les poissons du large pourraient aider à expliquer les fortes concentrations de Hg dans les laimargues atlantiques. Les ré-sultats de notre étude démontrent l'utilité potentielle de Hg comme traceur alimentaire chez les poissons marins. [Traduit par la Rédaction]

Archival pop-off tag tracking of Greenland sharks Somniosus microcephalus in the High Arctic waters of Svalbard, Norway

“…Stomach content analysis of Greenland sharks collected in the same area and at the same time as the present study revealed that benthic fish species and marine mammals were the most commonly consumed prey (LeClerc et al 2012). This is consistent with studies carried out in the Canadian Arctic (Fisk et al 2002) and in Iceland (McMeans et al 2010). As 9 of 14 sharks reached depths of <16 m, it is probable that they actively search for prey near the surface quite routinely.…”

“…Given the potentially large population size, wide geographic range and broad feeding niche, which includes a top predator component (Fisk et al 2002, McMeans et al 2010, LeClerc et al 2012, there is a need to understand the movements and habitat preferences of Greenland sharks. To address this knowledge gap, 20 ind.…”

“…The fishery for this species terminated decades ago, when synthetic oils replaced shark oil in the market, and it is likely that the population has in creased during the intervening period. Changes in biomass and population size of large marine vertebrates can have profound effects on ecosystem functioning (Pershing et al 2010), perhaps particularly in Arctic waters that have fairly simple food webs and limited annual primary production.Given the potentially large population size, wide geographic range and broad feeding niche, which includes a top predator component (Fisk et al 2002, McMeans et al 2010, LeClerc et al 2012, there is a need to understand the movements and habitat preferences of Greenland sharks. To address this knowledge gap, 20 ind.…”

A missing piece in the Arctic food web puzzle? Stomach contents of Greenland sharks sampled in Svalbard, Norway

“…This species is generally described as an opportunistic scavenger (Beck and Mansfield 1969;Fisk et al 2002). Many different prey species have been found in the stomach of these sharks, including crustaceans, cephalopods, various fish species and marine mammals (Ridoux et al 1998;Fisk et al 2002;Yano et al 2007;McMeans et al 2010). Stomach content analyses, conducted in West Greenland and Icelandic waters, have shown that Greenland sharks in these areas mainly consume various fish, such as Greenland halibut (Reinhardtius hyppoglossoides), Arctic cod (Boreogadus saida), Atlantic cod, redfish (Sebastes spp.…”

“…Stomach content analyses, conducted in West Greenland and Icelandic waters, have shown that Greenland sharks in these areas mainly consume various fish, such as Greenland halibut (Reinhardtius hyppoglossoides), Arctic cod (Boreogadus saida), Atlantic cod, redfish (Sebastes spp. ), Atlantic wolffish and the starry ray (Raja radiata) (Yano et al 2007;McMeans et al 2010). But in addition, the Greenland shark's diet is also known to include a variety of seal species, such as hooded seals, harbour seals (Phoca vitulina), bearded seals and ringed seals (Fisk et al 2002;Yano et al 2007).…”