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  • 1.
    Eero, Margit
    et al.
    National Institute of Aquatic Resources, Technical University of Denmark, Charlottenlund, Denmark.
    Hjelm, Joakim
    Department of Aquatic Resources, Institute of Marine Research, Swedish University of Agricultural Sciences, Lysekil, Sweden.
    Behrens, Jane
    National Institute of Aquatic Resources, Technical University of Denmark, Charlottenlund, Denmark.
    Buchmann, Kurt
    Department of Veterinary Disease Biology, University of Copenhagen, Copenhagen, Denmark.
    Cardinale, Massimiliano
    Department of Aquatic Resources, Institute of Marine Research, Swedish University of Agricultural Sciences, Lysekil, Sweden.
    Casini, Michele
    Department of Aquatic Resources, Institute of Marine Research, Swedish University of Agricultural Sciences, Lysekil, Sweden.
    Gasyukov, Pavel
    AtlantNIRO, Kaliningrad, Russian Federation.
    Holmgren, Noél
    University of Skövde, School of Bioscience. University of Skövde, The Systems Biology Research Centre.
    Horbowy, Jan
    National Marine Fisheries Research Institute, Gdynia, Poland.
    Hüssy, Karin
    National Institute of Aquatic Resources, Technical University of Denmark, Charlottenlund, Denmark.
    Kirkegaard, Eskil
    International Council for the Exploration of the Sea (ICES), Copenhagen, Denmark.
    Kornilovs, Georgs
    Institute of Food Safety, Animal Health and Environment “BIOR”, Riga, Latvia.
    Krumme, Uwe
    Thünen Institute of Baltic Sea Fisheries, Rostock, Germany.
    Köster, Friedrich W.
    National Institute of Aquatic Resources, Technical University of Denmark, Charlottenlund, Denmark.
    Oeberst, Rainer
    Thünen Institute of Baltic Sea Fisheries, Rostock, Germany.
    Plikshs, Maris
    Institute of Food Safety, Animal Health and Environment “BIOR”, Riga, Latvia.
    Radtke, Krzysztof
    National Marine Fisheries Research Institute, Gdynia, Poland.
    Raid, Tiit
    Estonian Marine Institute, University of Tartu, Tallinn, Estonia.
    Schmidt, Jörn
    Department of Economics, Christian-Albrechts University of Kiel, Kiel, Germany.
    Tomczak, Maciej T.
    Stockholm University, Baltic Sea Centre, Stockholm, Sweden.
    Vinther, Morten
    National Institute of Aquatic Resources, Technical University of Denmark, Charlottenlund, Denmark.
    Zimmermann, Christopher
    Thünen Institute of Baltic Sea Fisheries, Rostock, Germany.
    Storr-Paulsen, Marie
    National Institute of Aquatic Resources, Technical University of Denmark, Charlottenlund, Denmark.
    Eastern Baltic cod in distress: biological changes and challenges for stock assessment2015In: ICES Journal of Marine Science, ISSN 1054-3139, E-ISSN 1095-9289, Vol. 72, no 8, p. 2180-2186Article in journal (Refereed)
    Abstract [en]

    The eastern Baltic (EB) cod (Gadus morhua) stock was depleted and overexploited for decades until the mid-2000s, when fishing mortality rapidlydeclined and biomass started to increase, as shown by stock assessments. These positive developments were partly assigned to effective managementmeasures, and the EB cod was considered one of the most successful stock recoveries in recent times. In contrast to this optimistic view, theanalytical stock assessment failed in 2014, leaving the present stock status unclear. Deteriorated quality of some basic input data for stock assessmentin combination with changes in environmental and ecological conditions has led to an unusual situation for cod in the Baltic Sea, which posesnew challenges for stock assessment and management advice.Anumber of adverse developments such as low nutritional condition and disappearanceof larger individuals indicate that the stock is in distress. In this study, we (i) summarize the knowledge of recent changes in cod biology andecosystem conditions, (ii) describe the subsequent challenges for stock assessment, and (iii) highlight the key questions where answers are urgentlyneeded to understand the present stock status and provide scientifically solid support for cod management in the Baltic Sea.

  • 2.
    Holmgren, Noél M. A.
    et al.
    University of Skövde, School of Life Sciences. University of Skövde, The Systems Biology Research Centre.
    Norrström, Niclas
    University of Skövde, School of Life Sciences. University of Skövde, The Systems Biology Research Centre.
    Aps, Robert
    University of Tartu, Estonian Marine Institute, Tallin, Estonia.
    Kuikka, Sakari
    Fisheries and Environmental Management Group, Department of Environmental Sciences, University of Helsinki, Finland.
    MSY-orientated management of Baltic Sea herring (Clupea harengus) during different ecosystem regimes2012In: ICES Journal of Marine Science, ISSN 1054-3139, E-ISSN 1095-9289, Vol. 69, no 2, p. 257-266Article in journal (Refereed)
    Abstract [en]

    The Baltic Sea ecosystem has undergone dramatic changes, so-called ecosystem regime shifts, during the past four decades. Baltic Sea herring (Clupea harengus) spawning-stock biomass has declined to a third, and weight-at-age has halved as a result of food shortages and competition with sprat (Sprattus sprattus). The management objective for the herring stock is currently in transition from precautionary to maximum sustainable yield (MSY). The main basin Baltic Sea herring was modelled under the current ecosystem regime and the effect of a recovery of the cod (Gadus morhua) stock and the availability of planktonic food to levels found in the early 1980s analysed. A target of F-MSY = 0.16 for herring, which should decline to F-MSY = 0.10 with recovery of the cod stock, is proposed. An increase in the availability of planktonic food is estimated to more than double the yield at F-MSY = 0.27, overriding the negative effects of cod predation should there be a simultaneous increase in both cod and availability of planktonic food. The estimated net increase in yield is 40% at F-MSY = 0.20. Functions are presented to calculate FMSY and to estimate the expected yield depending on the abundance of cod and food availability. Retrospective application of the functions is indicative of overfishing of herring in the 1990s and early 2000s, and a net loss in yield, with a landing value of some E440 million.

  • 3.
    Norrström, Niclas
    et al.
    University of Skövde, School of Bioscience. University of Skövde, The Systems Biology Research Centre.
    Casini, Michele
    Swedish University of Agricultural Sciences, Department of Aquatic Resources, Institute of Marine Research, Lysekil, Sweden.
    Holmgren, Noél M. A.
    University of Skövde, School of Bioscience. University of Skövde, The Systems Biology Research Centre.
    Nash equilibrium can resolve conflicting maximum sustainable yields in multi-species fisheries management2017In: ICES Journal of Marine Science, ISSN 1054-3139, E-ISSN 1095-9289, Vol. 74, no 1, p. 78-90Article in journal (Refereed)
    Abstract [en]

    The current fisheries management goals set by the European Commission states that fish stocks should be harvested to deliver maximum sustainable yields (MSY) and simultaneously, management should take ecosystem considerations into account. This creates unsolved trade-offs for the management of the stocks. We suggest a definition of a multi-species-MSY (MS-MSY) where no alternative fishing mortality (F) can increase yield (long term) for any ecologically interacting stock, given that the other stocks are fished at constant efforts (Fs). Such a MS-MSY can be solved through the game theoretic concept of a Nash equilibrium and here we explore two solutions to this conflict in the Baltic Sea. We maximize the sustainable yield of each stock under two constraints: first, we harvest the other stocks at a fixed F (FNE); second, we keep the spawning stock biomasses of the other stocks fixed [biomass Nash equilibrium (BNE)]. As a case study, we have developed a multi-species interaction stochastic operative model (MSI-SOM), which contains a SOM for each of the three dominant species of the Baltic Sea, the predator cod (Gadus morhua), and its prey herring (Clupea harengus), and sprat (Sprattus sprattus). For our Baltic Sea case, MS-MSYs exist under both the FNE and the BNE, but there is no guarantee that point solutions exists. We found that the prey species’ spawning stock biomasses are additive in the cod growth function, which allowed for a point solution in BNE. In the FNE, the herring MSY was found to be relatively insensitive to the other species’ fishing mortalities (F), which facilitated a point solution. The MSY targets of the BNE and the FNE differ slightly where the BNE gives higher predator yields and lower prey yields.

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