Overexploitation, Recovery, and Warming of the Barents Sea Ecosystem During 1950–2013

Abstract

The Barents Sea (BS) is a high-latitude shelf ecosystem with important fisheries, high and historically variable harvesting pressure, and ongoing high variability in climatic conditions. To quantify carbon flow pathways and assess if changes in harvesting intensity and climate variability have affected the BS ecosystem, we modeled the ecosystem for the period 1950–2013 using a highly trophically resolved mass-balanced food web model (Ecopath with Ecosim). Ecosim models were fitted to time series of biomasses and catches, and were forced by environmental variables and fisheries mortality. The effects on ecosystem dynamics by the drivers fishing mortality, primary production proxies related to open-water area and capelin-larvae mortality proxy, were evaluated. During the period 1970–1990, the ecosystem was in a phase of overexploitation with low top-predators’ biomasses and some trophic cascade effects and increases in prey stocks. Despite heavy exploitation of some groups, the basic ecosystem structure seems to have been preserved. After 1990, when the harvesting pressure was relaxed, most exploited boreal groups recovered with increased biomass, well-captured by the fitted Ecosim model. These biomass increases were likely driven by an increase in primary production resulting from warming and a decrease in ice-coverage. During the warm period that started about 1995, some unexploited Arctic groups decreased whereas krill and jellyfish groups increased. Only the latter trend was successfully predicted by the Ecosim model. The krill flow pathway was identified as especially important as it supplied both medium and high trophic level compartments, and this pathway became even more important after ca. 2000. The modeling results revealed complex interplay between fishery and variability of lower trophic level groups that differs between the boreal and arctic functional groups and has importance for ecosystem management.

Comparison Between Trophic Positions in the Barents Sea Estimated From Stable Isotope Data and a Mass Balance Model

“…Several mass-balance models with varying functional group resolution has been parametrized for the Barents Sea and Norwegian Sea (Blanchard et al, 2002;Dommasnes et al, 2002;Skaret and Pitcher, 2016;Bentley et al, 2017;Berdnikov et al, 2019;Pedersen et al, 2021), but so far no TP-comparisons between model and stable-isotope data have been performed for the area. For other ecosystems, comparisons between TP estimated from SI and mass-balance models generally show positive correlations between TPs estimated by the two methods (Kline et al, 1998;Milessi et al, 2010;Navarro et al, 2011;McCormack et al, 2019;Hoover et al, 2021).…”

“…Previous estimates of trophic positions of organisms in the Barents Sea from stable isotopes have been based on various baseline organisms and values for δ 15 N baseline and trophic enrichment factors. In this study, TPs from a recently developed mass-balance model (Ecopath) for the Barents Sea with high trophic resolution (Pedersen et al, 2021), will be compared with published data on stable isotopes and TP.…”

“…Both pelagic and demersal fishes, sea birds, seals, and whales are abundant, and polar bears is present in the northern part of the BS (Sakshaug et al, 1994). There are several distinct carbon flow pathways from lower to higher trophic FGs; the copepod pathway, the krill pathway, the microbial food web pathway, and the benthic invertebrate pathway (Pedersen et al, 2021). The large stocks of planktivorous fishes, e.g., capelin, polar cod, and small herring are major prey sources for whales, seals, birds, and large demersal and benthic fish FGs (Bogstad et al, 2015;Pedersen et al, 2021).…”

“…A trophically highly resolved mass-balance model for the Barents Sea for year 2000 has been developed (Pedersen et al, 2021) and was used to provide model based estimates of TPs. The model comprises 108 functional groups (FGs) (Table 2).…”

Environmental Drivers of an Intertidal Bryozoan Community in the Barents Sea: A Case Study

“…Interactions of the cold Arctic and warm Atlantic waters is the main feature of the Barents Sea [ 1 ] making this large marine ecosystem the most productive shelf region of the Arctic [ 2 , 3 ] and supporting abundant stocks of fish and shellfish [ 4 , 5 , 6 ]. The Barents Sea, like other Arctic regions, is being influenced by the effects of global warming and we are now witnessing significant shifts in the ecosystem components and processes including strong salinification of the upper Eurasian Basin, attendant reductions in stratification, and altered nutrient fluxes and primary production [ 7 , 8 , 9 ].…”