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Mixed fisheries occur when multiple species are caught together and harvested by multiple fleets. The biological and technical interactions in mixed fisheries distinguish them from single-species fisheries, which makes them challenging for their assessment and management. The present knowledge synthesis reviewed pertinent policy documents and academic databases for twenty-three mixed fisheries worldwide; aiming to characterize attributes of mixed fisheries, provide overviews on their assessment and management, assess current research progress, and identify key factors that impact management effectiveness. Mixed fisheries were found to exhibit varying characteristics worldwide, rendering the implementation of universal management solutions unlikely. While mixed fisheries stock assessment and management are mostly based on single-species approaches, additional mixed fisheries considerations were incorporated at various scales, including multispecies, sector-specific, fishery, and ecosystem levels. Ecosystem-wide management considerations were the most significant contributor to improved management performance in terms of conserving stock biomass and preventing overfishing, underscoring the merits of the Ecosystem-based Fisheries Management (EBFM) principle. Mixed fisheries research demonstrated regional and thematic variations, with the most popular topics addressing immediate and practical management concerns, and the less frequently discussed topics offering valuable insights related to climate change and socio-ecological perspectives. The synthesis identified the available management approaches for mixed fisheries from different jurisdictions, yet their diversity highlighted a lack of global consensus on best management practices. Future mixed fisheries will benefit from balancing tradeoffs between ecological and socio-economic needs, implementing EBFM, adopting diverse and harmonized management tools, and prioritizing monitoring efforts. [ABSTRACT FROM AUTHOR]

Technical interactions (multiple fleets fishing multiple species with various gears, as either target or bycatch), bycatch regulations through a landing obligation, and biological and economic effects of climate change, affecting fisheries yield and profits, provide a challenge for demersal mixed fisheries of the North Sea. A multi‐stock, multi‐fleet, bioeconomic model was used to understand management options under these combined influences. Scenarios considered climate change effects on recruitment of three main gadoid stocks (cod – Gadus morhua, saithe – Pollachius virens, whiting – Merlangius merlangus), possible future developments of fuel and fish prices, and strict implementation of a landing obligation. The latter leads to decreased yield and profits in the short term due to increased choke effects, mainly of North Sea cod, being influenced by climate‐induced productivity changes. Allowing fishing above FMSY, but within sustainable limits, or limiting year‐to‐year quota changes, could help buffer initial losses at the expense of decreased profits in the mid‐ to long‐term. Economic performance of individual fleets was linked to their main target's stock status, cost structure, and fuel and fish prices. The results highlight a need to consider both biological and economic consequences of climate change in the management of mixed fisheries. [ABSTRACT FROM AUTHOR]

Previous studies have identified changes in habitat temperature as a major factor leading to the geographical displacement of North Sea cod in the last decades. However, the degree to which thermal suitability is presently changing in different regions of the North Sea is still unclear, or if temperature alone (or together with fishery) is responsible for this displacement. In this study, the spatial distribution of different life stages of cod was modelled from 1967 to 2015. The model is fit point-to-point, spatially resolved at scales of 20 km. The results show that suitability has decreased south of 56°N (>12% in the Southern Bight) and increased north of it (with maximum of roughly 10% in southern Skagerrak). Future changes to suitability were estimated throughout the century using temperature projections from a regional climate model under the Intergovernmental Panel on Climate Change scenario RCP8.5. The results show that southern Skagerrak, the central and northern North Sea and the edge of the Norwegian trench will remain thermally suitable for North Sea cod throughout the century. This detailed geographical representation of thermally suitable key zones for North Sea cod under climate change is revealed for the first time through the improved resolution of this analysis. [ABSTRACT FROM AUTHOR]

The understanding of spatio-temporal dynamics of marine ecosystems is crucial for ecosystem-based fisheries management and climate change impact assessments. We quantified temporal changes in the distribution of 0-group cod ( Gadus morhua) and grey gurnard ( Eutriglia gurnardus), a primary predator of 0-group cod, with the help of regression kriging and assessed the temporal dynamics of the related spatial predator-prey overlap of these two species at different spatial scales. We analysed the robustness of relationships among abiotic habitat properties (temperature, salinity and depth) and abundance. Small cod was mainly found in low salinity areas of the Skagerrak but larger year classes were able to expand their distribution area towards the central and northern North Sea. In contrast, grey gurnard was mainly found in waters with salinities above 33 and temperatures above 14°C. This species has expanded its high density areas in the central North Sea northward over the last two decades. Recruitment success of cod was negatively correlated to a Moran's I cross-correlation index, a proxy for the degree of spatial overlap between both species. Strong cod year classes overlapped less with grey gurnard at the large and medium spatial scale. In general, the relationships between abiotic habitat properties and abundance showed an increased inter-annual variability, which was likely caused by underlying factors not taken into account in the distribution models. Thus assemblage modeling approaches combining the strength of different model types should be considered in the future to predict potential distribution patterns under climate change scenarios. [ABSTRACT FROM AUTHOR]