The Greenland halibut of Cumberland Sound: Trends in catch rates and preferences in diet

Inaccessibility and harsh conditions of the Arctic frequently limit research on local fish and ecosystems. Cumberland Sound on southern Baffin Island houses a remote, winter fishery for Greenland halibut (Reinhardtius hippoglossoides) and presented a unique site for evaluating Arctic fish stock trends and feeding behavior from limited data. Relative abundance through time, 1987-2003, of the Greenland halibut stock was modeled hierarchically from catch per unit effort (CPUE) data with multiple fixed effects and location and fisherman as random effects. Month and the North Atlantic Oscillation were important predictors of CPUE. Additionally, fisherman behavior influenced CPUE, breaking the assumption that CPUE is proportionate to fish abundance. A second study using stable isotopes found pelagic feeding of the Greenland halibut and a dietary preference for capelin, consistent with studies in other systems. The combination of these studies is the first incorporation of fishery and ecological information to assess Cumberland Sound Greenland halibut

Preliminary assessment of Greenland halibut diet in Cumberland Sound using stable isotopes

We provide preliminary carbon (δ13C) and nitrogen (δ15N) stable isotope assessment of the Greenland halibut (Reinhardtius hippoglossoides) diet in Cumberland Sound, with focus on two possible prey sources: pelagic represented by capelin (Mallotus villosus) and epibenthic represented by shrimp (Lebbeus polaris). The δ13C for the Greenland halibut stock indicated a pelagic carbon source in Cumberland Sound while stable isotope mixing models, IsoSource and MixSIR, indicated a 99% dietary composition of capelin relative to the shrimp. The δ15N did not vary across Greenland halibut size ranges and placed them at a fourth trophic position relative to a primary herbivore. This study provides the starting point for more elaborate Cumberland Sound research on the local Greenland halibut feeding ecology by confirming pelagic feeding and establishing relative trophic position as well as identifying stable isotopes as a useful tool for the study of diet in cold water fish species. © 2009 Springer-Verlag

Diet and resource use among Greenland sharks (somniosus microcephalus) and teleosts sampled in icelandic waters, using δ\u3csup\u3e13\u3c/sup\u3eC, δ\u3csup\u3e15\u3c/sup\u3eN, and mercury

Stable carbon (δ13C) and nitrogen (δ15N) 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 δ13C, and relative trophic positions (TP, based on δ15N) ranged from 3.0 (Mallotus villosus) to 3.8 (e.g., Brosme brosme). Greenland shark δ13C indicated feeding on benthic and pelagic resources, with a high input of pelagic carbon, and δ15N indicated a relative TP of 4.3. Log[Hg] increased with δ15N (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 δ15N and δ13C-assigned resource use than by δ15N alone. Hg was useful for supporting the TPs suggested by δ15N, 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

Hierarchical analysis of a remote, Arctic, artisanal longline fishery

This is the first paper to explore trends in catch per unit effort (cpue) through time of a Greenland halibut Reinhardtius hippoglossoides stock targeted by an artisanal, winter fishery in Cumberland Sound on southern Baffin Island, Canada. We modelled cpue data from 1987 to 2003, looking at two questions: what factors have driven cpue trends, and is cpue an accurate index of a stock\u27s abundance? In the context of limited data availability, we used generalized linear models (GLMs) and hierarchical models to assess important predictors of cpue. Hierarchical models with multiple fixed environmental effects contained fishing location or individual fisher as random effects. A month effect showed greatest catch rates during February and March; the monthly North Atlantic Oscillation index was positively associated with catch rates; and a change from decreasing to increasing cpue after 1996 was linked to reduced fishery participation following a large storm. The best Akaike\u27s information criterion-ranked GLM identified a negative relationship of cpue with shark bycatch. Although data limitations precluded conventional stock assessment, our models implicated the environment and fisher behaviour as drivers of cpue trends. Additionally, using multiple hierarchical models to predict cpue provided a more informative analysis for understanding trends in cpue than a GLM alone. © Canadian Government, Department of Fisheries and Oceans and the Australian Government, Australian Institute of Marine Science 2009