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Extinctions occur naturally in all environments, but rates have accelerated rapidly during the Anthropocene, especially in fresh water. Despite supporting many fish species of conservation importance, there has never been a formal assessment of their extinction risks in Britain, which has impeded their inclusion in relevant legislation and policy. This study therefore used the International Union for the Conservation of Nature (IUCN) Red List of Threatened Species™ Categories and Criteria to conduct the first systematic assessment of the extinction risks and threats facing the native freshwater and diadromous fishes of Britain. In addition, national assessments were produced for England, Scotland and Wales, reflecting the level at which environmental policy decisions are taken in Britain.Seven species were categorized as being threatened with extinction at the regional level, with European eel Anguilla anguilla and allis shad Alosa alosa classified as Critically Endangered, Atlantic salmon Salmo salar, vendace Coregonus albula and European whitefish Coregonus lavaretus classified as Endangered, and Arctic charr Salvelinus alpinus and twaite shad Alosa fallax classified as Vulnerable. In addition, burbot Lota lota was classified as Regionally Extinct, ferox trout Salmo ferox was categorized as Data Deficient, and 25 species were categorized as Least Concern. European sturgeon Acipenser sturio and houting Coregonus oxyrinchus, although probably native, qualified as only vagrants in fresh water, so were categorized as Not Applicable.The assessments provide objective baselines against which future changes can be determined, and a key evidence base to support policy and management decisions for the conservation of freshwater and diadromous fish species and their habitats in Britain. It is recommended that the assessments are repeated every 10 years, which would enable changes in conservation status, the effectiveness of policies and where targeted interventions may be required to be examined using the Red List Index. [ABSTRACT FROM AUTHOR]

Accurate, cost‐effective monitoring of fish is required to assess the quality of lakes under the European Water Framework Directive. Recent studies have shown that environmental DNA (eDNA) metabarcoding is an effective and non‐invasive method, which can provide semi‐quantitative information about fish communities in large lakes.This study further investigated the potential of fish‐based eDNA metabarcoding as a tool for lake assessment by collecting and analysing water samples from eight Welsh lakes and six meres in Cheshire, England, with well‐described fish faunas. Water samples (N = 252) were assayed using two mitochondrial DNA regions (Cytb and 12S rRNA).eDNA sampling indicated the presence of very similar species in the lakes compared to those expected on the basis of existing and historical information. Firstly, 24 species were detected, with a total of 111 species occurrences in the lakes studied using eDNA. Secondly, there was a significant positive correlation between expected faunas and eDNA data in terms of confidence of species occurrence (Spearman's r = 0.74, df = 109, p < 0.001). Thirdly, eDNA data can estimate relative abundance with the standard five‐level classification scale ('DAFOR'). Lastly, four ecological fish communities were characterized using eDNA data which agree with the predefined lake types according to environmental characteristics.Synthesis and applications. There are some limitations when using conventional captured‐based methods for surveying species richness and relative abundance, such as morphological identification bias, difficulties in recording small‐bodied, rare and/or elusive species and destructive impacts on the environment. This study provides further evidence that environmental DNA metabarcoding outperforms other captured‐based survey techniques in a wide range of lake types for community‐level analysis whether in species detection, relative abundance estimate using the standard five‐level classification scale or characterization ecological fish communities. Therefore, the fish‐based environmental DNA metabarcoding, a non‐invasive genetic method, has great potential as an assessment tool for lake quality under the European Water Framework Directive. There are some limitations when using conventional captured‐based methods for surveying species richness and relative abundance, such as morphological identification bias, difficulties in recording small‐bodied, rare and/or elusive species and destructive impacts on the environment. This study provides further evidence that environmental DNA metabarcoding outperforms other captured‐based survey techniques in a wide range of lake types for community‐level analysis whether in species detection, relative abundance estimate using the standard five‐level classification scale or characterization ecological fish communities. Therefore, the fish‐based environmental DNA metabarcoding, a non‐invasive genetic method, has great potential as an assessment tool for lake quality under the European Water Framework Directive. [ABSTRACT FROM AUTHOR]

Llangorse Lake is the largest natural lake in South Wales, UK, and is of European conservation importance. The site has a long history of eutrophication problems and, in recent years, significant efforts have been made to meet water quality restoration targets at this site by reducing the input of phosphorus (P) from external sources. Although the lake has improved substantially in quality since the late 1970s, it is still not meeting its ecological targets. Phosphorus concentrations have remained high and there has been little reduction in algal biomass. Management decisions to reduce P input were originally based on the widely held assumption that shallow lakes are P-limited in summer. However, this study clearly shows that this is not always the case; Llangorse Lake, at least, is strongly nitrogen (N) limited over the summer months. As a result, bio-available P released from the sediments cannot be used by the phytoplankton population. So, it accumulates in the water column, causing very high concentrations to occur in late summer. This puts the lake at very high risk of developing algal blooms when N availability increases, usually in early autumn. The study also found that the hydrology of the lake was strongly affected by sub-surface flow. This suggested that nutrients and water could be delivered to the lake from areas beyond the topographically defined surface water catchment. These findings have widespread implications for the successful management of external inputs to lakes, which currently tends to focus on management of the surface water catchment only. The results are discussed in relation to the restoration and management of nitrogen-limited lakes, and of those that are significantly affected by sub-surface flow.