Dmitry Prozorkevich

Marine living resources of the Barents Sea Ecosystem understanding and monitoring in a climate change perspective

Abstract 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 climate-driven 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.

Biomass of Scyphozoan Jellyfish, and Its Spatial Association with 0-Group Fish in the Barents Sea

An 0-group fish survey is conducted annually in the Barents Sea in order to estimate fish population abundance. Data on jellyfish by-catch have been recorded since 1980, although this dataset has never been analysed. In recent years, however, the ecological importance of jellyfish medusae has become widely recognized. In this paper the biomass of jellyfish (medusae) in 0–60 m depths is calculated for the period 1980–2010. During this period the climate changed from cold to warm, and changes in zooplankton and fish distribution and abundance were observed. This paper discusses the less well known ecosystem component; jellyfish medusae within the Phylum Cnidaria, and their spatial and temporal variation. The long term average was ca. 9×108 kg, with some years showing biomasses in excess of 5×109 kg. The biomasses were low during 1980s, increased during 1990s, and were highest in early 2000s with a subsequent decline. The bulk of the jellyfish were observed in the central parts of the Barents Sea, which is a core area for most 0-group fishes. Jellyfish were associated with haddock in the western area, with haddock and herring in the central and coastal area, and with capelin in the northern area of the Barents Sea. The jellyfish were present in the temperature interval 1°C<T<10°C, with peak densities at ca. 5.5°C, and the greatest proportion of the jellyfish occurring between 4.0–7.0°C. It seems that the ongoing warming trend may be favourable for Barents Sea jellyfish medusae; however their biomass has showed a recent moderate decline during years with record high temperatures in the Barents Sea. Jellyfish are undoubtedly an important component of the Barents Sea ecosystem, and the data presented here represent the best summary of jellyfish biomass and distribution yet published for the region.

An evaluation of 0-group abundance indices of Barents Sea fish stocks

The International 0-group fish survey in the Barents Sea (1965-2002) aimed to give initial indication of the re- cruiting year class strengths. Since 2003 the 0-group survey has been a part of a Joint Norwegian-Russian ecosystem sur- vey 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 pe- riod 1980-2006. Two separate sets of 0- group indices were re-estimated, both with and without correction for capture ef- ficiency, 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 assessment- models and recruitment studies.

Assessment of marine litter in the Barents Sea, a part of the joint Norwegian-Russian ecosystem survey

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 60m, 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 2265 pelagic trawls and 1860 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.