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

Marine ecosystems evolve under many interconnected and area-specific pressures. To fulfil society's intensifying and diversifying needs while ensuring ecologically sustainable development, more effective marine spatial planning and broader-scope management of marine resources is necessary. Integrated ecological-economic fisheries models (IEEFMs) of marine systems are needed to evaluate impacts and sustainability of potential management actions and understand, and anticipate ecological, economic and social dynamics at a range of scales from local to national and regional. To make these models most effective, it is important to determine how model characteristics and methods of communicating results influence the model implementation, the nature of the advice that can be provided and the impact on decisions taken by managers. This article presents a global review and comparative evaluation of 35 IEEFMs applied to marine fisheries and marine ecosystem resources to identify the characteristics that determine their usefulness, effectiveness and implementation. The focus is on fully integrated models that allow for feedbacks between ecological and human processes although not all the models reviewed achieve that. Modellers must invest more time to make models user friendly and to participate in management fora where models and model results can be explained and discussed. Such involvement is beneficial to all parties, leading to improvement of models and more effective implementation of advice, but demands substantial resources which must be built into the governance process. It takes time to develop effective processes for using IEEFMs requiring a long-term commitment to integrating multidisciplinary modelling advice into management decision-making. K E Y W O R D Sbio-economic models, comparative model evaluation, fisheries management advice, integrated ecological-economic fisheries models, marine spatial planning and cross-sector management, performance criteria and scales and risks, use and acceptance and implementation and communication and flexibility and complexity | INTRODUCTIONThere is a growing need for tools to evaluate policies and assess tradeoffs in management of marine resources and provision of ecosystem services such as fishing, aquaculture, renewable energy, shipping, conservation and recreation (Cormier, Kannen, Elliott, & Hall, 2015;Degnbol & Wilson, 2008;EU 2014;Langlois, Fréon, Steyer, Delgenés, & Hélias, 2014;White et al., 2012). It is necessary to elaborate and apply common principles and broader, interdisciplinary management evaluation in the use of marine space involving several types of activities and sectors Soma et al., 2013;Stelzenmüller et al., 2013;Sundblad et al., 2014). Policymakers need to know the costs and benefits of conserving ecosystem goods and services to manage them sustainably. Moreover, according to an ecosystembased approach to management, specific pressures, associated uncertainties and risks need to be taken into account (Douvere, 2008;Ehler & Douvere, 2009;Gi...

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Background. At the end of 1980s, ecological regime shifts occurred in the Baltic. Since, the Baltic fish assemblage has been dominated by sprats, whereas before cod was the dominant fish species. The majority of previous food studies refer to the period before the shift. This raises the question, how changes in the Baltic ecosystem have affected the diet of cod. The aim of the presently reported study was to identify the differences in the food composition of cod depending on the area, depth, season, and the cod size and compare it with the findings from the 1970s and 1980s. Materials and methods. Food composition and selection of prey size for Baltic cod was evaluated by examining the stomach contents of 556 adult cod, collected in 2006 and 2007. Fish stomachs were sampled from research catches within the Polish Exclusive Economic Zone. Results. The main component of the cod diet were the clupeids, constituting more than 67% of the total weight of the food recovered from the specimens studied. Other fishes in the diet represented Gobiidae, Ammodytidae, as well as young cod. The dominant invertebrate in the diet was the isopod Saduria entomon which accounted for 13% of the diet by weight. The weight proportion of larger fish, such as herring, Clupea harengus (L.), and cod, increased with the cod size, while the proportion of small-and medium-sized fish (sprats, gobies) decreased. The food composition of cod varied seasonally. The weight proportion of European sprat, Sprattus sprattus (L.), was much higher in winter (55%) than in fall (27%), while the proportion of cod in the diet was higher in the fall (10%) than in winter (4%). The proportion of sprat in the diet increased with depth, while that of Ammodytidae and Gobiidae showed a decreasing trend. At depths greater than 40 m, the proportion of invertebrates in cod stomachs decreased. This study demonstrated a significant area effect for sprat; year effect for sprat and Saduria entomon; a seasonal effect for young cod and S. entomon; and a depth effect for sprat, young cod, and S. entomon. The occurrences of herring and small cod increased in the stomach as the predator increased, while no significant relation was found for sprat and S. entomon. The data collected do not indicate that cod select a specific size of sprat or herring, though cod were found to use size selection for S. entomon and juvenile cod. Conclusion. The food composition of cod has undergone certain changes compared to results of Załachowski (1977, 1985), which covered the 1970s and 1980s. Currently, the proportion of clupeids in the food is approximately 67% (in weight), while during the 1977-1982 it was in the range of 25%-50% depending on cod length. In 2006 and 2007 sprat was the main cod diet component rather than herring.