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The European whitefish Coregonus lavaretus complex represents one of the most diverse radiations within salmonids, with extreme morphological and genetic differentiation across its range. Such variation has led to the assignment of many populations to separate species. In Great Britain, the seven native populations of C. lavaretus (two in Scotland, four in England, one in Wales) were previously classified into three species, and recent taxonomic revision resurrected the previous nomenclature. Here we used a dataset of 15 microsatellites to: (1) investigate the genetic diversity of British populations, (2) assess the level of population structure and the relationships between British populations. Genetic diversity was highest in Welsh (HO = 0.50, AR = 5.29), intermediate in English (HO = 0.41–0.50, AR = 2.83–3.88), and lowest in Scottish populations (HO = 0.28–0.35, AR = 2.56–3.04). Population structure analyses indicated high genetic differentiation (global FST = 0.388) between all populations but for the two Scottish populations (FST = 0.063) and two English populations (FST = 0.038). Principal component analysis and molecular ANOVA revealed separation between Scottish, English, and Welsh populations, with the Scottish populations being the most diverged. We argue that the data presented here are not sufficient to support a separation of the British European whitefish populations into three separate species, but support the delineation of different ESUs for these populations.

This project investigated the effectiveness of a technique for stopping the release of phosphorus from lake sediments.

Editorial to special issue.

A special issue of: Journal of Fish Biology 92(3), March 2018. Papers presented at the Fisheries Society of the British Isles 50th anniversary symposium.

Lakes are highly connected systems that are affected by a hierarchy of stressors operating at different scales, making them particularly sensitive to anthropogenic perturbation. Traditionally, lakes are studied as a whole system ‘from physics to fish’ and long-term monitoring programmes were initiated on this basis, some starting over a century ago. This chapter describes the long-term monitoring programme on the Cumbrian lakes, UK, how it is operated and how its scientific value is increased by combining it with additional activities. Case-studies are presented on the advances long-term research has made to testing ecological theory and understanding teleconnexions and phenology. Automatic high-frequency measurements are an important complementary approach that has been made possible by technological revolutions in computing, and telecommunications. They provide a window into the true dynamic nature of lakes that cannot be achieved by manual sampling. The large volume of data produced can now be quality controlled and analysed by bespoke software that has been developed in recent years by a global network of lake and data scientists. Finally, lake models constructed using the insights from monitoring, as well as experiments, are powerful ways to identify knowledge gaps and allow forecasts to be made of future responses to environmental change or management intervention. As other approaches become incorporated into lake research, such as Earth Observation and citizen science, the scale of knowledge about the system will increase, improving our ability to provide robust scientific advice for the sustainable management of these fragile, but important ecosystems.

1. This report presents information resulting from a survey of the limnology of the 20 major lakes and tarns in the English Lake District based on samples taken in January, April, July and October 2015. This ‘Lakes Tour’ supplements similar tours in 1984, 1991, 1995, 2000, 2005 and 2010. 2. On each sampling occasion, depth-profiles were collected of water temperature and oxygen concentration and Secchi depth was measured. An integrated water sample was analysed for pH, alkalinity, major anions and cations, heavy metals, micro-organic pollutants, plant nutrients, phytoplankton chlorophyll a and species composition and zooplankton abundance and species composition. Some of the field work and chemical analyses were carried out collaboratively between staff from CEH and the Environment Agency. 3. The lakes had a range in tendency to stratify in summer with the weakest stratification in large, relatively shallow and exposed lakes such as Bassenthwaite Lake. During summer stratification, oxygen-depletion at depth was only found in the more productive lakes. 4. Water clarity, assessed by Secchi disc, varied between about 12 m in clear unproductive lakes such as Wastwater in January, to 2 m in the more productive lakes during summer such as Esthwaite Water in October. 5. Major ion composition varied with geology and altitude. Lakes on the Silurian slates (those in the Windermere and Coniston Water catchments) tended to have anions dominated by alkalinity (bicarbonate) and cations dominated by calcium whereas the other lakes tended to have anions dominated by chloride and cations dominated by sodium. 6. Availability of phosphorus is the main factor that affects lake productivity. Concentrations of total phosphorus were lowest in Wastwater and Crummock Water and highest in Blelham Tarn and Elterwater. Nitrate was the dominant form of nitrogen. Nitrate concentrations tended to be lowest in July because of biological uptake and seasonal fluctuations were most marked in the prod

The use of the CEN (European Committee for Standardization) standard method for sampling fish in lakes using multi-mesh gillnets allowed the collection of fish assemblages of 445 European lakes in 12 countries. The lakes were additionally characterised by environmental drivers and eutrophication proxies. Following a site-specific approach including a validation procedure, a fish index including two abundance metrics (catch per unit effort expressed as fish number and biomass) and one functional metric of composition (abundance of omnivorous fish) was developed. Correlated with the proxy of eutrophication, this index discriminates between heavily and moderately impacted lakes. Additional analyses on a subset of data from Nordic lakes revealed a stronger correlation between the new fish index and the pressure data. Despite an uneven geographical distribution of the lakes and certain shortcomings in the environmental and pressure data, the fish index proved to be useful for ecological status assessment of lakes applying standardised protocols and thus supports the development of national lake fish assessment tools in line with the European Water Framework Directive.

A key for three putative species apparently found in three geographic areas, i.e. Coregonus clupeoides (in Scotland), Coregonus stigmaticus (in England), and Coregonus pennantii (in Wales) given in a recent review was tested quantitatively using 544 individuals from nine populations. The classification success of the key was very low (27%). It was concluded that there is currently no robust evidence for the recognition of the three putative species. Furthermore, the use of phenotypic characters alone to distinguish putative species in postglacial fish species such as those of the genus Coregonus that show homoplasy in many of these traits is questioned. In the absence of further evidence, it was concluded that a single highly variable species best describes the pattern of phenotypic variation in these U.K. populations. On this basis it is argued that taxonomic subdivision of U.K. European coregonids is inappropriate and that Coregonus lavaretus should prevail as the species name applicable to all populations.

An invasive species is defined as an alien (or introduced or non-native) species whose establishment and spread threaten ecosystems, habitats or species with harm. Such threats to UK lake fish communities have long been appreciated and this review assembles case histories, including new data, from the largest lakes of Scotland, Northern Ireland, Wales and England to examine the hypothesis that at least some of these introductions have become invasive. Loch Lomond in Scotland has experienced six introductions [chub (Leuciscus cephalus), common bream (Abramis brama), crucian carp (Carassius carassius), dace (Leuciscus leuciscus), gudgeon (Gobio gobio) and ruffe (Gymnocephalus cernuus)], of which the most significant has been that of the percid ruffe, which has been implicated in a recent decline of the native coregonid whitefish (Coregonus lavaretus). In Northern Ireland, the introduction of the cyprinid roach (Rutilus rutilus) to Lough Neagh has apparently had a negative impact on some overwintering waterfowl, although the native coregonid pollan (Coregonus autumnalis) remains abundant. Llyn Tegid in Wales has received three introductions [rudd (Scardinius erythrophthalmus), ruffe and silver bream (Blicca bjoerkna)], although no impacts on the native whitefish or other fish populations have been observed. In England, individuals of at least 12 native and non-native fish species have been brought to Windermere for the purpose of live-baiting, although only those of the cyprinids roach and common bream have established abundant populations. At the same time, the native salmonid Arctic charr (Salvelinus alpinus) has declined markedly while the native esocid pike (Esox lucius) has shown changes in abundance, distribution and individual condition, although these developments have not been shown to be causally linked. None of these introductions were sanctioned by appropriate fisheries or other regulatory bodies and almost all of them probably arose from the release or esc

In the face of widespread environmental change impacts, there is a need to better understand mechanisms promoting flexibility and resilience of ecosystem components to such change to inform strategies for conservation. Glacial relict species are especially vulnerable to such changes. We investigated the behavioural responses of a native, glacial relict species, Arctic charr (Salvelinus alpinus) to long-term environmental changes. It was hypothesised that changes in feeding behaviour would occur as a key intermediary to reduction in habitat availability (through climate change and eutrophication) or competitive interactions [with introduced roach (Rutilus rutilus)]. Stomach content analysis was used to assess the diet of 199 charr caught from Windermere, United Kingdom, in the months of March, June, September and November 2003–2007. The results were compared to data from 1940 to 1951 prior to the environmental changes and revealed a marked increase in the contribution of benthic invertebrates in the present diet. Stable isotope analysis confirms the results of the stomach analysis, suggesting that the charr have switched their diet from zooplanktivory towards benthivory. We discuss the possibility that habitat modification and roach population expansion in Windermere have contributed to changes in charr diet. Complementary studies suggest that this diet shift is more likely to be a response to the increasing roach population than to habitat modification; however, further study in Windermere would be required to elucidate the exact mechanism. Long-term data sets such as these provide information that is useful for determining the directivity of ecological change and the capability of species to respond to change.

The mechanisms by which phenotypic and genetic divergence may occur among sympatric, conspecific populations have been widely discussed but are still not well understood. Possible mechanisms include assortative mating based on morphology or variation in the reproductive behaviour of phenotypes, and both have been suggested to be relevant to the differentiation of salmonid populations in post-glacial lakes. Here, we studied Arctic charr (Salvelinus alpinus) in Windermere, where putative populations are defined by spatial and temporal variation in spawning. Genetic differentiation was assessed based on nine microsatellite loci, and phenotypic variation was assessed from morphometric characters. We test hypotheses about the relative role of morphology, spawning season and spawning habitat in the evolution of genetic divergence among these populations. Distinct from other lake systems, we find that both morphological and genetic differentiation are restricted primarily to one of two interconnecting basins, that genetic and morphological differentiation are decoupled in this lake and that both phenotype and environment have changed over the last 20 years. The implication is that breeding habitat plays a primary role in isolating populations that differentiate by drift and that phenotypically plastic changes, potentially related to foraging specializations, have either become secondarily decoupled from the genetically defined populations or were never fundamental in driving the evolution of genetic diversity in the Windermere system.

1. This report presents information resulting from a survey of the limnology of the 20 major lakes and tarns in the English Lake District based on samples taken in January, April, July and October 2010. This ‘Lakes Tour’ supplements similar tours in 1984, 1991, 1995, 2000 and 2005. 2. On each sampling occasion depth-profiles were collected of water temperature and oxygen concentration and Secchi depth was measured. An integrated water sample was analysed for pH and alkalinity, major cations and anions, plant nutrients, phytoplankton chlorophyll a and species composition and zooplankton abundance and species composition. Some of the field work and chemical analyses were carried out collaboratively between staff from CEH and the Environment Agency. 3. The lakes had a range in tendency to stratify in summer with the weakest stratification in large, relatively shallow and exposed lakes such as Bassenthwaite Lake. During summer stratification oxygen-depletion at depth was only found in the more productive lakes. 4. Water clarity, assessed by Secchi disc, varied between about 13 m in clear unproductive lakes such as Wastwater to less than 2 m in the more productive lakes during summer such as Esthwaite Water. 5. Major ion composition varied with geology and altitude. Lakes on the Silurian slates (those in the Windermere and Coniston Water catchments) tended to have anions dominated by alkalinity (bicarbonate) and cations dominated by calcium whereas the other lakes tended to have anions dominated by chloride and cations dominated by sodium. 6. Availability of phosphorus is the main factor that affects lake productivity. Concentrations were lowest in Wastwater and Ennerdale Water and highest in Elterwater and Esthwaite Water. Nitrate was the dominant form of nitrogen. Nitrate concentrations tended to be lowest in July because of biological uptake and seasonal fluctuations were most marked in the productive lakes. Silica, an essential nutrient for diatoms, showed a similar

Fisheries management has a considerable capacity to precipitate legal and illegal introductions of fish species to new geographical areas. Consequently, there are many examples of such introductions and their subsequent short-term effects on native fish. However, longer-term impacts which may be expected to be more substantial have been less frequently studied in detail. For this overview, long-term datasets up to a number of decades in duration have been assembled from published and unpublished sources on the native lake fish communities of the English Lake District in north-west England, UK. These communities are dominated by simple salmonid-percid assemblages and contain England's only vendace (Coregonus albula), whitefish (Coregonus lavaretus) and Arctic charr (Salvelinus alpinus) populations, all of which are protected under nature conservation legislation. In addition, they have historically supported commercial or semi-commercial fisheries for perch (Perca fluviatilis), whitefish and Arctic charr, the latter of which still persist on two major lakes. In recent years, fisheries activities have resulted in the region experiencing a number of illegal fish introductions including the cyprinids roach (Rutilus rutilus) and dace (Leuciscus leuciscus) and the percid ruffe (Gymnocephalus cernuus). Although these introductions have benefited some local recreational fisheries, several instances of cultural eutrophication and a more widespread increase in lake temperature are likely to benefit these introduced species and disadvantage native salmonids and percids. The resulting changes in fish community compositions and the performances of local fisheries are described and discussed.

The UK lies towards the southernmost distribution limit of the circumpolar Arctic charr (Salvelinus alpinus), and native populations of high national conservation value occur in all four component countries. However, given the temperature requirements of this species and the already relatively mild UK climate, there is strong reason to expect a significant negative impact of climate change on local populations. Data were assembled from repeated Arctic charr population assessments using combinations of hydroacoustics, gill netting, entrapment records and fisheries catches at five Scottish populations, five English populations and one Welsh population. These data were then used to test the hypotheses that there has been a widespread decline of Arctic charr in the UK and that it can be attributed at least in part to climate change. Ten of the 11 studied populations exhibited significant 1990-onwards declines in abundance, while only the most northerly population showed a significant increase. Overall, there was a significant positive relationship between the observed population decline ranking and a vulnerability to climate change ranking based on water body latitude, altitude and mean depth. These observations support the hypothesis that this species has suffered a recent and widespread decline in the UK, and although additional factors are undoubtedly also involved in some specific cases, climate change is a significant factor.

Hydroacoustic surveys are an important tool for assessing the abundance of Arctic charr (Salvelinus alpinus (L.)) in lakes, the requirement for which is increasing because of new environmental legislation. Consequently, survey demand is now such that assessments must be undertaken with the minimum of effort compatible with scientific validity. One major complication is seasonal variability in abundance, with which surveyors have attempted to deal by defining somewhat arbitrary seasonal sampling windows. The definition of more objective windows was pursued by analysing variations in the seasonal abundance of Arctic charr in Windermere, UK, recorded using day and night hydroacoustic surveys at monthly intervals from 1991 to 2001. Two alternative sampling windows for night surveys free of significant internal seasonal effects were revealed, i.e., December to September and September to December. It was also found that day surveys gave a useful, although lower, estimate of abundance as compared with night surveys.

Data comprise concentrations of elements in ashed fish sampled from lakes in the English Lake District in 2012 and 2013. Fish were collected from three lakes (Windermere, Bassenthwaite Lake and Derwent Water) by the Centre for Ecology & Hydrology (CEH) Lake Ecosystems group. Fish species collected were Roach (Rutilus rutilus), Perch (Perca fluviatilis), Ruffe (Gymnocephalus cernua), Trout (Salmo trutta), Pike (Esox Lucius) and Vendace (Coregonus vandesius). All samples were ashed prior to analysis by ICPMS or ICPOES to determine elemental concentrations.

Data comprise concentrations of elements in ashed fish sampled from lakes in the English Lake District in 2012 and 2013. Fish were collected from three lakes (Windermere, Bassenthwaite Lake and Derwent Water) by the Centre for Ecology & Hydrology (CEH) Lake Ecosystems group. Fish species collected were Roach (Rutilus rutilus), Perch (Perca fluviatilis), Ruffe (Gymnocephalus cernua), Trout (Salmo trutta), Pike (Esox Lucius) and Vendace (Coregonus vandesius). All samples were ashed prior to analysis by ICPMS or ICPOES to determine elemental concentrations.

© 2019, The Author(s). Invasive alien species (IAS) are one of the major drivers of change that can negatively affect biodiversity, ecosystem functions and services and human health; islands are particularly vulnerable to biological invasions. Horizon scanning can lead to prioritisation of IAS to inform decision-making and action; its scale and scope can vary depending on the need. We focussed on IAS likely to arrive, establish and affect biodiversity and human health on the Mediterranean island of Cyprus. The scope of the horizon scanning was the entire island of Cyprus. We used a two-step consensus-building process in which experts reviewed and scored lists of alien species on their likelihood of arrival, establishment and potential to affect biodiversity, ecosystems and/or human health in the next 10 years. We reviewed 225 alien species, considered to be currently absent on Cyprus, across taxa and environments. We agreed upon 100 species that constituted very high, high or medium biodiversity risk, often arriving through multiple pathways of introduction. The remaining 125 species were ranked as low risk. The potential impacts on human health were documented for all 225 species; 82 species were considered to have a potentially negative impact on human health ranging from nuisance to disease transmission. The scope of the horizon scanning was the entire island of Cyprus, but the thematic groups also considered the relevance of the top 100 species to the Sovereign Base Areas of Cyprus, given their differing governance. This horizon scan provides the first systematic exercise to identify invasive alien species of potential concern to biodiversity and ecosystems but also human health within the Mediterranean region. The process and outcomes should provide other islands in the region and beyond with baseline data to improve IAS prioritisation and management.