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In this study, we assess prey consumption by the marine mammal community in the northeast Atlantic [including 21 taxa, across three regions: (I) the Icelandic shelf, Denmark Strait, and Iceland Sea (ICE); (II) the Greenland and Norwegian Seas (GN); and (III) the Barents Sea (BS)], and compare mammal requirements with removals by fisheries. To determine prey needs, estimates of energetic requirements were combined with diet and abundance information for parameterizing simple allometric scaling models, taking uncertainties into account through bootstrapping procedures. In total, marine mammals in the ICE, GN, and BS consumed 13.4 [Confidence Interval (CI): 5.6–25.0], 4.6 (CI : 1.9–8.6), and 7.1 (CI : 2.8–13.8) million tonnes of prey year–1. Fisheries removed 1.55, 1.45, and 1.16 million tonnes year–1 from these three areas, respectively. While fisheries generally operate at significantly higher trophic levels than marine mammals, we find that the potential for direct competition between marine mammals and fisheries is strongest in the GN and weakest in the BS. Furthermore, our results also demonstrate significant changes in mammal consumption compared to previous and more focused studies over the last decades. These changes likely reflect both ongoing population recoveries from historic whaling and the current rapid physical and biological changes of these high-latitude systems. We argue that changing distributions and abundances of mammals should be considered when establishing fisheries harvesting strategies, to ensure effective fisheries management and good conservation practices of top predators in such rapidly changing systems. [ABSTRACT FROM AUTHOR]

The Barents Sea system is often depicted as a simple food web in terms of number of dominant feeding links. The most conspicuous feeding link is between the Northeast Arctic cod Gadus morhua, the world's largest cod stock which is presently at a historical high level, and capelin Mallotus villosus. The system also holds diverse seabird and marine mammal communities. Previous diet studies may suggest that these top predators (cod, bird and sea mammals) compete for food particularly with respect to pelagic fish such as capelin and juvenile herring (Clupea harengus), and krill. In this paper we explored the diet of some Barents Sea top predators (cod, Black-legged kittiwake Rissa tridactyla, Common guillemot Uria aalge, and Minke whale Balaenoptera acutorostrata). We developed a GAM modelling approach to analyse the temporal variation diet composition within and between predators, to explore intra- and inter-specific interactions. The GAM models demonstrated that the seabird diet is temperature dependent while the diet of Minke whale and cod is prey dependent; Minke whale and cod diets depend on the abundance of herring and capelin, respectively. There was significant diet overlap between cod and Minke whale, and between kittiwake and guillemot. In general, the diet overlap between predators increased with changes in herring and krill abundances. The diet overlap models developed in this study may help to identify inter-specific interactions and their dynamics that potentially affect the stocks targeted by fisheries. [ABSTRACT FROM AUTHOR]

Aim: Assess the spatial and temporal turnover of bentho‐demersal marine fauna by integrating ecological metrics at the community and food web levels and evaluate their main environmental and anthropogenic drivers. Location: Barents Sea. Method: We analysed data of benthic and bentho‐pelagic fish and megabenthic invertebrates caught in the Barents Sea ecosystem survey in August–September 2009–2017 to characterize the spatial and temporal variability of bentho‐demersal communities and food webs. We used a trait dataset and highly resolved bentho‐demersal food web to calculate community and food web metrics in space and time. We spatially clustered the community and food web based on their properties using archetypal analysis and investigated their co‐variation with environmental and fishing pressure using (hierarchical) redundancy analysis. Result: The community and food web metrics partitioned the Barents Sea into four sub‐regions where different pressures act on the bentho‐demersal fauna, such as sea ice loss and fisheries. Multiple community metrics (e.g. mean body length and trophic level) varied along an environmental gradient of annual mean sea bottom temperature, trawling intensity and ice‐cover, whereas multiple food web metrics (e.g. nestedness and connectance) varied along an environmental gradient of depth and sediment composition. Communities had higher biomass‐weighted variability in body size and omnivory values in areas where the Atlantic and Arctic water masses mix. Several food web and community metrics co‐varied (e.g. food chain length and mean trophic level). We found no clear temporal trends in the ecological metrics in any of the four sub‐regions, but the metrics had large inter‐annual variability with some local minima or maxima coinciding with high sea temperature and ice‐cover anomalies. Conclusion: Analyses at the community and food web level are seldom integrated in ecological studies, while this integration gives complementary information to assess patterns and drivers of ecosystem state and to better prioritize conservation efforts. [ABSTRACT FROM AUTHOR]

The warming trend of the Arctic is punctuated by several record‐breaking warm years with very low sea ice concentrations. The nature and reversibility of marine ecosystem responses to these multiple extreme climatic events (ECEs) are poorly understood. Here, we investigate the ecological signatures of three successive bottom temperature maxima concomitant with surface ECEs between 2004 and 2017 in the Barents Sea across spatial and organizational scales. We observed community‐level redistributions of fish concurrent with ECEs at the scale of the whole Barents Sea. Three groups, characterized by different sets of traits describing their capacity to cope with short‐term perturbations, reacted with different timing and intensity to each ECE. Arctic species co‐occurred more frequently with large predators and incoming boreal taxa during ECEs, potentially affecting food web structures and functional diversity, accelerating the impacts of long‐term climate change. On the species level, responses were highly diversified, with different ECEs impacting different species, and species responses (expansion, geographical shift) varying from one ECE to another, despite the environmental perturbations being similar. Past ECEs impacts, with potential legacy effects, lagged responses, thresholds, and interactions with the underlying warming pressure, could constantly set up new initial conditions that drive the unique ecological signature of each ECE. These results highlight the complexity of ecological reactions to multiple ECEs and give prominence to several sources of process uncertainty in the predictions of climate change impact and risk for ecosystem management. Long‐term monitoring and studies to characterize the vertical extent of each ECE are necessary to statistically link demersal species and environmental spatial–temporal patterns. In the future, regular monitoring will be crucial to detect early signals of change and understand the determinism of ECEs, but we need to adapt our models and management to better integrate risk and stochasticity from the complex impacts of global change. [ABSTRACT FROM AUTHOR]

A food web is an ecological network and its topological description consists of the list of nodes, i.e., trophospecies, the list of links, i.e., trophic interactions, and the direction of interactions (who is the prey and who is the predator). Food web topologies are widely used in ecology to describe structural properties of communities or ecosystems. The selection of trophospecies and trophic interactions can be realized in different manners so that many different food webs may be constructed for the same community. In the Barents Sea, many simple food webs have been constructed. We present a comprehensive food web topology for the Barents Sea ecosystem, from plankton to marine mammals. The protocol used to compile the data set includes rules for the selection of taxa and for the selection and documentation of the trophic links. The resulting topology, which includes 244 taxa and 1589 trophic links, can serve as a basis for topological analyses, comparison with other marine ecosystems, or as a basis to build simulation models of the Barents Sea ecosystem. The data set consists of three related tables: (1) the hst of taxa, (2) the list of pairwise interactions, and (3) the list of bibliographical references. [ABSTRACT FROM AUTHOR]