Trophic interactions in the Barents Sea - steps towards an Integrated Ecosystem Assessment

This strategic initiative aims to improve our understanding of the trophic interactions, food web structure and function, and energy flow in the Barents Sea ecosystem. Important aspects of the initiative are to strengthen theoretical and practical competence in, and develop methodology with emphasis on integration of field work, quantitative ecological analyses and integrated assessment of the Barents Sea ecosystem that is part of ecosystem based management. The TIBIA carried out field work in 2015-2016 and collected 30,000 fish stomach from 70 fish species. Analyses of collected stomach samples were carried out in 2017-2018, while the results were prepared for scientific publication in 2018-2019. The first article of five planned described the collection effort, methodology, fish diet 68 species and publish the data. Results can be used directly in ecosystem models. The project carried out significant collection of isotope samples for studying trophic interactions. Analyses of stable isotopes are time consuming and over 900 isotope samples from 101 species were analysed. A Postdoc scholar has prepared manuals for collecting and processing of samples and analysed the extensive data material. We have created a complete set of literature-based trophic levels for 595 species and identified stable isotope-based relative trophic positions for key species. WP3 has investigated the dynamics of the phyto- and zooplankton in time and space in the Barents Sea over the last three decades using satellite data and in-situ measurements and observations. Ph.d. research fellow studied the connection between zooplankton distribution and grazing conditions for pelagic fish using the IMR database (over 30 years). We have also made a summary of zooplankton studies of HI in the Barents Sea since 1979 and have compared catchability with different plankton nets (use in IMR and PINRO). WP5 studied the influence of parasites on the structure of the Barents Sea ecosystem food web. To do this, a through a large network of collaborators, an extensive survey for parasites in fish and benthic and pelagic invertebrate host species has been carried out, and unpublished data on parasites of marine mammals has been made available to the project. Several parasitological papers are being written up, including descriptions of the more than 10 species new to science that have been found during the project. From this, papers are being written on methods for assessing food web structure and on applications and challenges of food web ecology and modelling for marine resource management. Together with the parasite data, stomach and isotopes data have been used to improve our estimate of the Barents Sea food web topology. This has provided the basis for exploring variation in food web topology in time and space. Cod is important both economically and ecologically and stocks are currently at a historically high level with a very wide spatial distribution. WP6 studied the dynamics and ecological role of cod in the ecosystem and explained how cod has been able to maintain the large stock size and individual growth over the past decade. This knowledge also has implications for the potential carrying capacity of cod stock in the Barents Sea during climate change. Integration of TIBIA results is done by creating a budget for biomass distribution for species and groups as a basis for estimating production, food needs and consumption for various components of the ecosystem. The aim is to use this to assess trophic structure and efficiency and the ecosystem's carrying capacity at various trophic levels through some ten years of climate change, heating and ice loss. The Barents Sea is divided into 15 polygons new time series have been established. These compound data with time series are used to create reviews of biomass distributions for species and groups and combined with results from studies of diet and stable isotopes (WP2 and 5) and general information from the literature on diet, growth and turnover, this will form the basis for schematic overviews (box models) of trophic structure in the Barents Sea. Another synthesis work in WP1 has been to analyse patterns in time (interannual) and space for the pelagic compartment of the ecosystem that provides the food resources for the rest of the ecosystem. Much of the dynamics of the ecosystem is driven by variable recruitment, and we analysed temporal and spatial variations in the 0-group fish for six species will relation this to climate variability in order to elucidate this in relation to physical environment, trophic interactions in the ecosystem. The TIBIA together with SI-Arctic has assigned the special issue in Progress in Oceanography to summarize results. WGIBAR is an important channel for dissemination of TIBIA results and new knowledge into management-directed work aimed to contributing to the implementation of ecosystem approach to management.

TIBIA har bidratt til ICES WGIBAR ved å etablere nye og oppdatere eksisterende tidsserier som beskriver tilstand og endringer av økosystem komponenter og disse oppdateringer av status og endringer i økosystemet har blitt brukt i arbeidet med Forvaltningsplanen for Barentshavet og Lofoten. Vi gjort en omfattende kartlegging av trofiske interaksjoner ved å beskrive dietten hos 70 fiskearter og trofiske posisjoner av 101 nøkkel arter. Dette brukes i utvikling av økosystemmodeller som er et verktøy i integrert økosystem assessment. omfatter en rekke spørsmål som vanligvis ikke har blitt adressert tidligere. TIBIA har vi bidratt til instituttets aktivitet rettet mot å bedre forståelse av trofiske interaksjoner, struktur og funksjon av næringsnett, samt styrke teoretisk og praktisk kompetanse som grunnlag for integrert vurdering av tilstanden i økosystemet i Barentshavet som en del av økosystembasert forvaltning.

By aiming at improving our understanding of trophic interactions, food web structure and functions and energy flow in the Barents Sea, this Strategic Initiative (SI) addresses core needs arising from implementation of the ecosystem approach to management in the Barents Sea as well as in other Norwegian waters. Important aspects of the initiative are to strengthen the theoretical and practical competence in, and develop methodology for trophic studies, with emphasis on integration of field sampling, experi ments, quantitative ecological analyses and ecosystem modeling. Four work packages will address key aspects and processes in the Barents Sea ecosystem: Carrying capacity and energy flow through the food web (WP 3), pelagic-benthic coupling in 3 selected r egions (WP 4), food web structure and dynamics in time and space (WP 5), and dynamics and role of a key species, Atlantic cod, in the Barents Sea ecosystem (WP 6). A separate work package will deal with development of a sampling program needed to carry ou t these studies (WP 2). This will also give input to plans for the data gathering required when the results of the SI are to be implemented in practical ecosystem based management. A separate work package contains the management and coordination of the SI and will be responsible for literature reviews, synthesis of the results from all work packages including modeling, and delivering input to integrated ecosystem assessments (WP 1).