The Arctic is of special importance to the world, and it is changing rapidly. Uncovering the relationship between drivers of change and biological responses in the Barents Sea is therefore crucial for understanding the potential effects of climate change on the ecosystem in general and on commercially important species in particular. This thematic review provides an overview of the discussions related to long-and short-term variations in climate in the Barents Sea, what these physical changes really are, and how they may develop in the future. Furthermore, questions related to how these predicted climatedriven physical changes may alter ecosystems and the implications and future challenges that this represents for the management of resources in the area are raised. There is no doubt that to better understand the structure and function of an ecosystem, as well as to investigate the possible effects of climate changes, there is a need for thorough monitoring and data collection. The Barents Sea Ecosystem Survey (BESS) is used in several of the studies highlighted in this review. Therefore, we can provide a detailed description of the BESS and relate BESS research activities to other research initiatives in a thematic context.

A B S T R A C TThe Barents Sea, a large, high-latitude shelf sea, has been monitored and investigated for more than a century. More than 1800 occasional expeditions have been organized both by Norway and Russia, and since the1960s the collaboration between the Institute of Marine Research (IMR, Bergen) and the Knipovich Polar Research Institute of Marine Fisheries and Oceanography (PINRO, Murmansk) has been strengthened by developing and carrying out joint surveys. Monitoring changes in the Barents Sea fish stocks and collecting information needed for stock assessments and advice for fisheries management were the driving forces behind the increased effort spent on marine research. This triggered the development of sampling and observation methodology, the design of scientific research vessels for using various equipment and gear, and the development of new technologies for processing several types of samples. Increased data collection generated a need for the development of complex database systems and software that, could analyze larger data sets. Joint large-scale monitoring over the last 50 years, together with joint management of living marine resources during the last 20 years, resulted in high stock biomasses of commercially important fish stocks and thus the successful development of fisheries in the Barents Sea. Here, we describe the development of Barents Sea monitoring from single species (or fishery) surveys that were focused on target species/groups to integrated ecosystem surveys that aim to describe the status and main changes in the Barents Sea ecosystem.

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Abstract:The International 0-group fish survey in the Barents Sea (1965Sea ( -2002 aimed to give initial indication of the recruiting year class strengths. Since 2003 the 0-group survey has been a part of a Joint Norwegian-Russian ecosystem survey of the Barents Sea, conducted by IMR (Norway) and PINRO (Russian Federation). The electronic 0-group databases were missing some data and contained errors, therefore the databases have been quality checked and corrected for the period 1980-2006. Two separate sets of 0-group indices were re-estimated, both with and without correction for capture efficiency, using a stratified sample mean approach, and 0-group indices were correlated with other appropriate abundance indices. The exclusion of errors from the database has improved our confidence in the indices and analysis. In general, the 0-group indices seem to be reliable predictors of year class strengths and are adequate to use as input in stock assessmentmodels and recruitment studies.

This study presents a large-scale monitoring of marine litter performed in the joint Norwegian-Russian ecosystem monitoring surveys in the period from 2010 to 2016 and contribute to documentation of the extent of marine litter in the Barents Sea. The distribution and abundance of marine litter were calculated by recordings of bycatch from the pelagic trawling in upper 60 m, from bottom trawling close to the sea floor, and floating marine debris at surface by visual observations. The study is comprehensive regarding coverage and number with registrations from 2,265 pelagic trawls and 1,860 bottom trawls, in addition to surface registration between the stations. Marine litter has been recorded from 301 pelagic and 624 of the bottom trawl catches. In total, 784 visual observations of floating marine debris were recorded during the period. Marine litter has been categorized according to volume or weight of the material types plastic, wood, metal, rubber, glass, paper, and textile. Marine litter is observed in the entire Barents Sea and distribution vary with material densities, ocean currents and depth. Plastic dominated number of observations with marine litter, as 72% of surface observations, 94% of pelagic trawls, and 86% of bottom trawls contained plastic. Observations of wood constituted 19% of surface observations, 1% of pelagic trawls, and 17% of bottom trawls with marine litter. Materials from other categories such as metal, rubber, paper, textile, and glass were observed sporadically. Recordings of wood dominated surface observations (61.9 ± 21.6% by volume) and on seafloor (59.4 ± 35.0% by weight), while plastic dominated marine litter observations in upper 60 m depth (86.4 ± 16.5% by weight) over these 7 years. Based on recordings and volume or area covered, mean levels of plastic in the upper 60 m of the Barents Sea were found to 0.011 mg m −3 (pelagic) and 2.9 kg km −2 at sea floor over the study period. Average levels of marine litter (all material types) at the sea floor were found to be 26 kg km −2 .