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Abstract

This study has shown that the incomes of Danish fisheries fishing in the North Sea are at risk facing the impact of climate-driven long-term trends when some of the exploited stocks are “on the move” i.e. changing their spatial distribution permanently, as the North Sea cod. The study developed a new methodological approach based on the previous modelling to strengthen our predictive power in anticipating interlinked stocks and fisheries developments under changing environmental conditions or extreme events that would also affect their productivity and spatial distributions.

The method developed a high-resolution integration of fisheries and research survey data to establish and boost the description of fish spatial distribution and abundance fields by combining fisheries and survey catch data. On this basis, we evaluated the changes in fish distribution patterns in time and space and the persistence of density hotspots over the period 2001-2019 for main commercial species, including North Sea cod, dab, saithe, haddock, Atlantic mackerel present in the North Sea, plaice, sole, whiting, sprat, and North Sea herring. We then integrated this information into a high-resolution fisheries dynamics model in a broader fisheries management evaluation framework. This framework integrates an advanced individual vessel-based fisheries model for benchmarking fishing opportunities and scenarios constrained by ecological sustainability and assessing the economic viability and profitability of the use of marine living resources in the North Sea.

We found that the hotspot areas where the main density of stocks distributed, for juveniles and adults fish, and driven by the environmental factors, were quite stable at the scale of the North Sea over the period 2001-2019, for all the examined commercial stocks, except for the North Sea cod that showed a marked movement westwards, making the stock more distant from the Danish coastline, but without affecting the proportion of the stock falling into the UK EEZ (a fraction of the stock that would fall within the UK fisheries legislation). It is apparent that varying fish distributions and lack of knowledge of important factors driving fish occurrence may reduce the accessibility of the stocks to the fishers. This can jeopardize the profitability of the exploitation, redistribute the fisheries incomes among fleets and nations, and further enlarge a mismatch between fishing opportunities and allocation keys for EU quotas according to the EU Common Fisheries Policy (CFP) relative stability of quota distribution. However, because the persistence areas are found quite stable, the proportion of the North Sea stock abundances falling within the UK EEZ is also found stable. Science based approaches can help anticipate such (re)distributional effects by helping predict where the fish are and the hotspots, that is, where the high concentration of fish are, and identifying key factors determining fish occurrence and abundance, as well as where the fishes are likely to change their distribution areas, mainly from effects on stocks induced by the climate change.

One lesson learnt along the project was the current lack of knowledge to inform the fisheries modelling exercise properly with previous pieces of evidence. Although some aspects of the biology of most stocks were found to be linked to environmental factors, there was a lack of robust statistical models available to describe the likely species-specific linkages between individual biological features (growth, recruits, spatial distribution) and changing environmental conditions in the North Sea. Because of the lack of well-established relationships with environmental variables and climate in some case studies, ad hoc assumptions were made on the magnitude of the changes expected for the different environmental scenarios tested.

Another lesson learnt showed that it is challenging to organize a fine scale coupling between advanced statistical modelling of the spatial distribution of stocks and the dynamic fisheries modelling in the same platform provided the very high computer demand that such an inline, bidirectional coupling would require. Instead, the project implemented a one-way coupling where the fishing in the modelling has been influenced by the fish stock distribution but has not itself influenced the stock distribution. However, spatial distribution patterns may also be affected directly by fishery on different life stages, as well as indirectly by changing fish habitats, for example by altering the physical environment on the seafloor and their benthic community. Explicitly including factors that may influence the spatial and time distribution of the different stocks dynamically. Including these dynamics would then need additional investigations.

Notwithstanding the methodological and available knowledge limitation, the integrative platform and the North Sea application we developed in the project will likely enhance the knowledge on fish stocks dynamics and interlinkage with human (i.e. fisheries, climate change) and environmental factors. The tool is ready to anticipate the effects and stock levels, increasing economic efficiency in exploiting the marine resource on an explicit spatial and temporal scale within the EU CFP and EU Marine Strategy Framework Directive (MSFD) context and objectives. The platform is developed for evaluating the high-resolution social and economic distributional effects induced by the change in stock distribution and availability. The framework can further test how differently the current and new (CFP- or MSFD-related) measures could affect the catches, incomes, fuel consumption and environmental footprint of various fisheries and fishing communities at play.

Catches made by the Danish fleets in North Sea cod distribute over different habitat types. There are likely habitats that will be affected from a displacement of the fishing effort in response to new environmental conditions. Even though extensive spatial scenarios are not tested per fishery the spatial component is accounted for implicitly by locating the abundance hot spots and movements of those stocks in a 20 year period when that is the case (cod). As the hotspots (against expectations) for most species have been rather constant, then it has also limited the possibilities for evaluating effort-re-allocation scenarios. The cod case study has been picked out for further analysis of scenarios for re-allocation of effort - and potential changed pressure on the seafloor induced by the re-allocation in the fishery.
Original languageEnglish
Place of PublicationKgs. Lyngby, Denmark
PublisherDTU Aqua
Number of pages101
ISBN (Electronic)978-87-7481-330-9
Publication statusPublished - 2022
SeriesDTU Aqua-rapport
Number402-2022
ISSN1395-8216

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