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In the Barents Sea, strong top predator responses to repeated stock collapses of the forage fish capelinMallotus villosushave been observed. The white-beaked dolphinLagenorhynchus albirostris, a flexible predator with a diverse diet in other marine systems, has been associated with capelin in the Barents Sea. Yet, their distribution and foraging ecology in this ecosystem remain largely unknown. Here we use synoptically collected dolphin and prey spatial data to investigate the dolphins' distribution and spatial associations with potential prey species, including the spatial responses to a capelin stock collapse of 2003–2006 and recovery in 2007–2009. Since dolphin–prey associations may be scale-dependent, analyses were conducted at two spatial scales: (1) the habitat scale, by investigating spatial associations between species distributions averaged across years, and (2) the mesoscale, by investigating spatial associations within 50 × 50 km grid cells. At the habitat scale, dolphins overlapped with different prey species in different parts of their habitat. At the mesoscale, the dolphins were associated with blue whiting in southern Atlantic waters, while no prey associations were identified in the Polar Front area, where both capelin and gadoids are abundant. The poor dolphin–prey associations in this area could indicate dolphin distributions spatially constrained by physiological limitations, habitat productivity, or niche partitioning. No strong dolphin responses to capelin collapse and recovery were observed, indicating sufficient availability of alternative prey during the collapse. [ABSTRACT FROM PUBLISHER]

Knowledge of trophic interaction is necessary to understand the dynamics of ecosystems and develop ecosystem‐based management. The key data to measure these interactions should come from large‐scale diet analyses with good taxonomic resolution. To that end, molecular methods that analyze prey DNA from guts and feces provide high‐resolution dietary taxonomic data. However, molecular diet analysis may also produce unreliable results if the samples are contaminated by external sources of DNA. Employing the freshwater European whitefish (Coregonus lavaretus) as a tracer for sample contamination, we studied the possible route of whitefish in beaked redfish (Sebastes mentella) guts sampled in the Barents Sea. We used whitefish‐specific COI primers for diagnostic analysis, and fish‐specific 12S and metazoa‐specific COI primers for metabarcoding analyses of intestine and stomach contents of fish samples that were either not cleaned, water cleaned, or bleach cleaned after being in contact with whitefish. Both the diagnostic and COI metabarcoding revealed clear positive effects of cleaning samples as whitefish were detected in significantly higher numbers of uncleaned samples compared to water or bleach‐cleaned samples. Stomachs were more susceptible to contamination than intestines and bleach cleaning reduced the frequency of whitefish contamination. Also, the metabarcoding approach detected significantly more reads of whitefish in the stomach than in intestine samples. The diagnostic analysis and COI metabarcoding detected contaminants in a higher and comparable number of gut samples than the 12S‐based approach. Our study underlines thus the importance of surface decontamination of aquatic samples to obtain reliable diet information from molecular data. [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]

Marine mammals are important players in the Barents Sea ecosystem but their structural role in the foodweb has been little explored. We compare foodweb-related characteristics within and between phylogenetic groups for 19 marine mammals. As a group, they directly connect to the most central species (i.e cod and haddock) in the Barents Sea (i.e. cod and haddock) and consume over half of the available species. Pinnipeds are the most homogenous phylogenetic group with high omnivory and high prey richness. Mysticetes are split between well-connected species with high omnivory like the humpback whale, and peripheral specialists like the blue whale. Based on foodweb-derived indices some species consistently cluster together forming two groups, suggesting topological redundancy within them. One is dominated by Arctic seals and the other includes most of the baleen whales. Marine mammals generally contribute to network modularity as their trophic links are mainly within their own module. However, Atlantic species such as the grey seal act as a module connector decreasing modularity. This might negatively affect ecosystem robustness with perturbation effects spreading further and quicker in the foodweb. In the Arctic reaches of the Barents Sea, climate warming is likely to bring about extensive changes in the foodweb structure through a redistribution of species. [ABSTRACT FROM AUTHOR]

Balanced fishing proposes a considerable change to current fisheries management to increase overall biomass harvested while reducing the ecosystem impacts of large-scale fisheries. However, to date, the work to a large degree has focused on simplified models, which exclude much of the variability in real ecosystems, as well as basing harvesting rates on a perfect, but unrealistic, knowledge on stock productivity. Furthermore, the published studies have avoided examining the practicalities of implementing balanced fishing in a real world. This has resulted in a gap that remains to be overcome before balanced fishing can be considered a viable management strategy for large marine ecosystems.Wediscuss variability in recruitment, in biology and life history characteristics, in data quality, and in fishing practice and management, and their implications for implementation of balanced fishing, using examples from the Barents Sea. We try to outline the complexities that need to be investigated as a precursor tomoving balanced fishing from an academic exercise to a practical management scheme. Given the difficulties in moving to "full" balanced fishing, we highlight the importance of investigating to what extent benefits can be gained by implementing only the most achievable parts of a balanced fishing regime. [ABSTRACT FROM AUTHOR]