Project SummaryDefineIt will construct operational models of fish stock dynamics explicitly taking account of exploitation and climatic conditions and combine these models with economic models. To ensure an outstanding scientific level in each of these a reas, the project brings together key competences in operational multispecies modelling, stock recruitment relationships, population dynamics of non-target fish species and economic modelling of fisheries from a wide geographic area ranging from the Baren ts Sea to the Mediterranean.In sustainable ecosystem management, it is crucial to account for the fact that increasing the amount of predatory fish leads to increased predation. The project will use multispecies models to investigate changes in predation induced by differences in distribution and the amount of alternative food. Effects of technical interactions in the fishing process will be considered to avoid delivering management advice for different stocks which is mutually inconsistent. Multispecies models have historically mainly been applied to Northatlantic areas but within this project, we will increase the coverage to include the Aegean Sea and for the first time develop such a model for the eastern Mediterranean. Integrating the knowledge gain ed, the project will identify relevant multispecies indicators and suggest methods for estimating reference points.To understand the causes of the year to year variation in recruitment, both large scale temporal patterns, variability in the production of eggs, sub-stock structure and survival of eggs and larvae must be considered. The project will identify the main causes of variation in recruitment patterns between stocks as well as the key processes from spawning to recruitment of selected stocks. The consequences of using proxies to describe stock reproductive potential will be determined and survival during early life stages investigated to identify the role of the physical and biological environment. The effects of stock sub-structure and compositio n on recruitment will be investigated by using genomic differences to define sub-stocks and estimating the relative contributions to survivors of population sub-components under differing climatic conditions. The improved understanding of recruitment vari ability will be used in both individual stock assessment and included in multispecies models to provide reliable predictions.The effect of technical interactions in the fishing process on bycatch of non-target species will be assessed by identifying susc eptible species and determining the information required to develop management plans. The maximum level of fishing effort consistent with sustainment of these species will be estimated along with the effect of discard of bycatch on economic yield. Options for protecting non-target species will be evaluated using Management Strategy Evaluation in order to develop Robust Management.The project will develop resource indicators that combine economic, social and biological indicators and relate directly to the benefit for the society. The annual user value of the selected fisheries will be identified and the maximum resource rent calculated based on combined economic and multispecies models. Further, a stochastic approach to economic indicators will be investi gated since variance and uncertainty are critical issues in relation to the economic performance of natural resource systems.Future stock dynamics, limits to sustainable ecosystem exploitation and the fishing levels delivering maximum sustainable economi c yield under selected climatic scenarios will be analysed in unison to ensure the delivery of mutually consistent management advice. General properties of the ecosystems will be used to suggest rules of thumb for management in areas where the amount of d ata available is insufficient to construct similar models. Finally, we will disseminate project results to both the scientific community, managers, stakeholders and the general public to ensure that results are used in practical management.