1. 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.2. 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).3. 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.

Ireland, being an island situated on Europe's western seaboard, has a fewer number of native species than mainland European Union Member States (MS). Increased numbers of vectors and pathways have reduced the island's biotic isolation, increasing the risk of new introductions and their associated impacts on native biodiversity. It is likely that these risks are greater here than they are in continental MSs, where the native biodiversity is richer. A horizon scanning approach was used to identify the most likely invasive alien species (IAS) (with the potential to impact biodiversity) to arrive on the island of Ireland within the next ten years. To achieve this, we used a consensus-based approach, whereby expert opinion and discussion groups were utilised to establish and rank a list of 40 species of the most likely terrestrial, freshwater and marine IAS to arrive on the island of Ireland within the decade 2017-2027. The list of 40 included 18 freshwater, 15 terrestrial and seven marine IAS. Crustacean species (freshwater and marine) were taxonomically dominant (11 out of 40); this reflects their multiple pathways of introduction, their ability to act as ecosystem engineers and their resulting high impacts on biodiversity. Freshwater species dominated the top ten IAS (seven species out of ten), with the signal crayfish (Pacifastacus leniusculus) highlighted as the most likely species to arrive and establish in freshwaters, while roe deer (Capreolus capreolus) (second) and the warm-water barnacle (Hesperibalanus fallax) (fifth), were the most likely terrestrial and marine invaders. This evidence-based list provides important information to the relevant statutory agencies in both the Republic of Ireland and Northern Ireland to prioritise the prevention of the most likely invaders and aid in compliance with legislation, in particular the EU Regulation on Invasive Alien Species (EU 1143/2014). Targeted biosecurity in both jurisdictions is urgently required in order to manage the pathways and vectors of arrival, and is vital to maintaining native biodiversity on the island of Ireland.

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Determining the timing and location of fish reproductive events is crucial for the implementation of correct management and conservation schemes. Conventional methods used to monitor these events are often unable to assess the spawning activity directly or can be invasive and therefore problematic. This is especially the case when threatened fish populations are the study subject, such as the Arctic charr (Salvelinus alpinus L.) populations in Windermere (Cumbria, UK). Arctic charr populations have been studied in this lake since the 1940s, and the locations and characteristics of spawning grounds have been described in detail using techniques such as hydroacoustics, as well as physical and visual surveys of the lake bottom. Here, in conjunction with established netting surveys, we added an environmental DNA (eDNA) metabarcoding approach to assess the spatial distribution of Arctic charr in the lake throughout the year to test whether this tool could allow us to identify spawning locations and activity. Sampling was carried out between October 2017 and July 2018 at three locations in the lake, covering putative and known spawning .