Christian Skov

Biomanipulation via removal of benthivorous and zooplanktivorous fish is a common method for restoring eutrophic lakes. By affecting zooplankton and nutrient resuspension, these fish increase algal biomass and reduce water clarity. Seine netting is widely used for fish removal, but its efficiency requires further assessment, particularly in relation to the target species’ behaviour. This study examines roach ( Rutilus rutilus ), a prevalent zooplanktivorous fish in European lakes, aiming to (1) estimate seine net efficiency by assessing overall removal efficiency and specific haul efficiency based on the spatial–temporal overlap between individual fish and net trajectories in small shallow lakes and (2) assess the behaviour of acoustically tagged adult roach at varying population densities to optimize removal timing and locations. Results showed a high overall removal efficiency (93.3%) across 23 hauls, a high specific haul efficiency of 88.8% ± 28.8%, and an overall low escape rate of 6.4%. Roach exhibited seasonal and diurnal aggregation patterns, dispersing in littoral zones during spawning, but forming dense pelagic aggregations in autumn mornings, especially at low densities. This period therefore appears optimal for cost-effective and repeated removal efforts. Further studies across different lake systems are necessary to generalize findings on roach aggregation and seine net efficiency.

Recreational fishers who interact with internet-connected and smart devices generate large volumes of digital data that can be mined to gain valuable and often unique insight into recreational fisher behaviours. Common sources of digital data include general online activity (e.g., searches, page views), social media (e.g., fishing forums, Facebook), smartphone applications, and connected devices (e.g., smartphones, fish finders). Research is stimulating a great deal of interest in these data, but fisheries monitoring and management applications are rare. Our aim is to facilitate research and the appropriate adoption and integration of digital behaviour data within fisheries research, management, and governance. We begin with an inventory of available data sources, the types of fisher behaviours described, and methods for obtaining suitable and relevant datasets. We then identify barriers to the use of these data within a solutions-oriented framework that emphasises privacy and transparency, standardisation, non-probabilistic techniques, validation, and integration. Although digital data for describing fisher behaviours tend to accumulate passively, we describe digital platforms as a rare opportunity to engage large numbers of fishers in active data collection, and influence behaviours through education and outreach.

Marine recreational fishing (MRF) is a socially and economically relevant fishing activity in Europe, but its impacts on ecosystems and the economy remain poorly understood, and management is limited. This paper evaluates the current European fisheries governance, particularly the Common Fisheries Policy, in addressing MRF issues. Our evaluation highlights the lack of explicit recognition of MRF in European Union legislation, where recreational fisheries are not or insufficiently managed within a commercial fisheries-oriented policy framework. We recommend policy reform that explicitly recognizes recreational fisheries as a distinct fisheries sector with its own interests, values and objectives, and dynamics that differ from those typical in commercial fisheries. On the operational level, we recommend involving key organizations representing MRF interests in advisory groups dealing with marine fisheries, nature conservation, and marine spatial use, and encourage sustainable fishing practices among all types of fisheries. To achieve this, there is a need for better and more comprehensive data collection, stakeholder engagement, and outreach to support effective MRF governance and management. By addressing these issues, Europe can maximize the benefits of MRF, while ensuring the sustainability of fisheries.

Genetic data have greatly increased means to understand fish marine migration behaviours at large spatial scale within a quantitative framework. The anadromous sea trout is a prized target of recreational fishery and an important ecosystem component in freshwater and marine coastal habitats in large parts of temperate northern Europe. Nonetheless, little is known about population distributions while feeding at sea. To reconcile notions about feeding migrations being predominantly locally restricted or not, we used SNP data for 3465 trout representing >100 rivers to identify population origins of 903 coastally feeding fish captured throughout the North Sea-Baltic Sea transition area. Across areas, coastal collections generally showed marked stock-mixing and overall 70:30% native:non-native fish with seasonal variation corresponding with spawning run timing. Data revealed strong spatial feeding segregation between trout from the Scandinavian Peninsula and the European continent. This is surprising given the short distances between areas, but is in alignment with strong genetic differentiation between populations in these areas. Estimation of stock complexity of coastal feeding aggregations showed no spatial trend through the North Sea-Baltic Sea transition area otherwise characterized by strong environmental clines. Analyses of scale samples collected in the 1950s indicate that stock-mixing was consistent over almost 70 years.

The Delphi method was used to gather assessments from 93 experts about drivers of future angling participation by locals and tourist anglers in Denmark, Finland, Iceland, Norway, and Sweden. The main drivers of future angling participation related to habitat and fish populations, and access to and information about fishing. For Norway and Finland, the predicted future decline in local angler numbers was consistent with a life‐cycle model of recreational fisheries, while the anticipated increase for the three other countries contradicted the model. For tourist anglers, growth was expected for both domestic and foreign tourists. Long‐term and societal drivers, such as urbanization, sociocultural changes, and climate change were not seen as strong drivers, and may be considered out of reach by managers, but should be included with information and conservation drivers in angler recruitment and retention strategies.

Sustainable management of lakes requires us to overcome ecological, economic, and social challenges. These challenges can be addressed by focusing on achieving ecological improvement within a multifaceted, co‐beneficial context. In‐lake restoration measures may promote more rapid ecosystem responses than is feasible with catchment measures alone, even if multiple interventions are needed. In particular, we identify restoration methods that support the overarching societal target of a circular economy through the use of nutrients, sediments, or biomass that are removed from a lake, in agriculture, as food, or for biogas production. In this emerging field of sustainable restoration techniques, we show examples, discuss benefits and pitfalls, and flag areas for further research and development. Each lake should be assessed individually to ensure that restoration approaches will effectively address lake‐specific problems, do not harm the target lake or downstream ecosystems, are cost‐effective, promote delivery of valuable ecosystem services, minimize conflicts in public interests, and eliminate the necessity for repeated interventions. Achieving optimal, sustainable results from lake restoration relies on multidisciplinary research and close interactions between environmental, social, political, and economic sectors.This article is categorized under: Science of Water > Water Quality Water and Life > Stresses and Pressures on Ecosystems Water and Life > Conservation, Management, and Awareness

The global COVID-19 pandemic resulted in many jurisdictions implementing orders restricting the movements of people to inhibit virus transmission, with recreational angling often either not permitted or access to fisheries and/or related infrastructure being prevented. Following the lifting of restrictions, initial angler surveys and licence sales suggested increased participation and effort, and altered angler demographics, but with evidence remaining limited. Here, we overcome this evidence gap by identifying temporal changes in angling interest, licence sales, and angling effort in world regions by comparing data in the ‘pre-pandemic’ (up to and including 2019); ‘acute pandemic’ (2020) and ‘COVID-acclimated’ (2021) periods. We then identified how changes can inform the development of more resilient and sustainable recreational fisheries. Interest in angling (measured here as angling-related internet search term volumes) increased substantially in all regions during 2020. Patterns in licence sales revealed marked increases in some countries during 2020 but not in others. Where licence sales increased, this was rarely sustained in 2021; where there were declines, these related to fewer tourist anglers due to movement restrictions. Data from most countries indicated a younger demographic of people who participated in angling in 2020, including in urban areas, but this was not sustained in 2021. These short-lived changes in recreational angling indicate efforts to retain younger anglers could increase overall participation levels, where efforts can target education in appropriate angling practices and create more urban angling opportunities. These efforts would then provide recreational fisheries with greater resilience to cope with future global crises, including facilitating the ability of people to access angling opportunities during periods of high societal stress.