Migrations between different habitats are key events in the lives of many organisms. Such movements involve annually recurring travel over long distances usually triggered by seasonal changes in the environment. Often, the migration is associated with travel to or from reproduction areas to regions of growth. Young anadromous Atlantic salmon (Salmo salar) emigrate from freshwater nursery areas during spring and early summer to feed and grow in the North Atlantic Ocean. The transition from the freshwater ('parr') stage to the migratory stage where they descend streams and enter salt water ('smolt') is characterized by morphological, physiological and behavioural changes where the timing of this parr-smolt transition is cued by photoperiod and water temperature. Environmental conditions in the freshwater habitat control the downstream migration and contribute to within- and among-river variation in migratory timing. Moreover, the timing of the freshwater emigration has likely evolved to meet environmental conditions in the ocean as these affect growth and survival of the post-smolts. Using generalized additive mixed-effects modelling, we analysed spatio-temporal variations in the dates of downstream smolt migration in 67 rivers throughout the North Atlantic during the last five decades and found that migrations were earlier in populations in the east than the west. After accounting for this spatial effect, the initiation of the downstream migration among rivers was positively associated with freshwater temperatures, up to about 10 °C and levelling off at higher values, and with sea-surface temperatures. Earlier migration occurred when river discharge levels were low but increasing. On average, the initiation of the smolt seaward migration has occurred 2.5 days earlier per decade throughout the basin of the North Atlantic. This shift in phenology matches changes in air, river, and ocean temperatures, suggesting that Atlantic salmon emigration is responding to the current global climate changes.

This paper reviews the life history of brown trout and factors influencing decisions to migrate. Decisions that maximize fitness appear dependent on size at age. In partly anadromous populations, individuals that attain maturity at the parr stage typically become freshwater resident. For individual fish, the life history is not genetically fixed and can be modified by the previous growth history and energetic state in early life. This phenotypic plasticity may be influenced by epigenetic modifications of the genome. Thus, factors influencing survival and growth determine life‐history decisions. These are intra‐ and interspecific competition, feeding and shelter opportunities in freshwater and salt water, temperature in alternative habitats and flow conditions in running water. Male trout exhibit alternative mating strategies and can spawn as a subordinate sneaker or a dominant competitor. Females do not exhibit alternative mating behaviour. The relationship between growth, size and reproductive success differs between sexes in that females exhibit a higher tendency to migrate than males. Southern populations are sensitive to global warming. In addition, fisheries, aquaculture with increased spreading of salmon lice, introduction of new species, weirs and river regulation, poor water quality and coastal developments all threaten trout populations. The paper summarizes life‐history data from six populations across Europe and ends by presenting new research questions and directions for future research.

–  A cooperative effort gathered a large European length‐at‐age data set (N = 45,759, Lat. 36S–61N Long. 10W–27E) for Anguilla anguilla, covering one century. To assess the effect of global warming during the last century and habitat effects on growth, a model was fitted on the data representing the conditions met at the distribution area scale. Two GLMs were designed to predict eel log(GR): one model was fitted to the whole data and the other was fitted to the female data subset. A model selection procedure was applied to select the best predictors among sex, age class, five temperature parameters and six habitat parameters (depth, salinity and four variables related to the position in the catchment). The yearly sum of temperatures above 13 °C (TempSUP13), the relative distance within the catchment, sex, age class, salinity class and depth class were finally selected. The best model predicted eel log(GR) with a 64.46% accuracy for the whole data and 66.91% for the female eel data. Growth rate (GR) was greater in habitats close to the sea and in deep habitats. TempSUP13 variable had one of the greatest predictive powers in the model, showing that global warming had affected eel growth during the last century.

Highlights:1. Loads of 9.5 t DOC km 2 year -1 and 6.2 t POC km 2 year -1 were exported from peatland. 2.Climatic factors explained 59.7% and 58.3% of deviance in stream DOC and POC.3. Soil temperature, discharge and drought were significant drivers of DOC concentrations. 4.Soil temperature, stream discharge rainfall were significant drivers of POC concentrations.Key words: Peat catchment, dissolved organic carbon, particulate organic carbon, high resolution monitoring, climate effects. AbstractCarbon export in streams draining peat catchments represents a potential loss of carbon from longterm stores to downstream aquatic systems and ultimately, through mineralisation, to the atmosphere. There is now a large body of evidence that dissolved organic carbon (DOC) export has 2 increased significantly in recent decades at many sites, although there is still debate about the drivers of this increase. In this study, DOC export and particulate organic carbon (POC) export were quantified from a forested peatland catchment in the west of Ireland over two years at a fine temporal resolution. The principle drivers of change in stream DOC and POC concentrations were investigated using a general additive modelling (GAM) approach. The study period included drought conditions in early summer 2010 and clearfelling of some commercial forestry in early 2011. The results indicated that annual loads of 9.5 t DOC km 2 year -1 and 6.2 t POC km 2 year -1 were exported from the catchment in 2010. This combined annual load of 15.7 t C km 2 year -1 would represent between 0.01 % and 0.02 % of typical estimates for peat soil carbon storage in the region. Soil temperature, river discharge and drought explained 59.7 % the deviance in DOC concentrations, while soil temperature, river discharge, and rainfall were the significant drivers of variation in POC concentrations, explaining 58.3 % of deviance. Although clearfelling was not a significant factor in either model, large spikes in POC export occurred in 2011 after the first forestry clearance. The results illustrate the complexity of the interactions between climate and land management in driving stream water carbon export. They also highlight the sensitivity of peatland carbon stores to changes in temperature and precipitation, which are projected to be more extreme and variable under future climate scenarios.3

Climate projections indicate that the frequency and severity of extreme precipitation events will increase over the next century. Although a large number of lakes across the globe are systematically monitored, it is rare to have a wide range of ecological indices measured at high enough frequency and over a sufficient time scale to allow characterisation of the response of a lake ecosystem to such events. We present data from Lough Feeagh, a relatively large oligotrophic lake in Ireland, which was at the epicentre of a once in 250-year precipitation event in July 2009 when 50 mm of rain fell in less than 2 hours. The effects of the resulting flood on the water column stability, chemistry, biology, and metabolism were examined, and data from multiple years before and after the event were used to ascertain the significance and longevity of any observed changes. The flood caused the water column to destabilise prematurely and depressed primary production. Bacterial biomass was high in the month after the flood, and zooplankton assemblages in late 2009 were significantly different from those of other years. Changes in all these variables combined to produce lower rates of gross primary production and higher rates of respiration than those measured between 2010 and 2014, resulting in more pronounced negative net ecosystem production than in the other years. Despite all these changes, the normal seasonal cycles resumed in 2010, and it appears that this rare but significant event did not have a long-term impact on the ecosystem functioning of the lake.

Many animals perform long‐distance migrations in order to maximize lifetime reproductive success. The European eel migrates several thousand kilometers between their feeding habitats in continental waters (fresh‐, brackish, and sea water) and their spawning area in the Sargasso Sea. Eels residing in freshwaters usually initiate their spawning migration as silver eels during autumn, triggered by diverse environmental cues. We analyzed the time series of silver eel downstream migration in Burrishoole, Ireland (1971–2015), and Imsa, Norway (1975–2015), to examine factors regulating the silver eel migration from freshwater to the sea. The migration season (90% of the run) generally lasted from 1 August to 30 November. Environmental factors acting in the months before migration impacted timing and duration of migration, likely through influencing the internal processes preparing the fish for migration. Once the migration had started, environmental factors impacted the day‐to‐day variation in number of migrants, apparently stimulating migration among those eels ready for migration. Both the day‐to‐day variation in the number of migrants and the onset of migration were described by nearly identical models in the two rivers. Variables explaining day‐to‐day variation were all associated with conditions that may minimize predation risk; number of migrants was reduced under a strong moon and short nights and increased during high and increasing water levels. Presence of other migrants stimulated migration, which further indicates that silver eel migration has evolved to minimize predation risk. The onset of migration was explained mainly by water levels in August. The models for duration of the migration season were less similar between the sites. Thus, the overall migration season seems governed by the need to reach the spawning areas in a synchronized manner, while during the actual seaward migration, antipredator behavior seems of overriding importance.

1The aim of this study was to investigate the release of phosphorus (P) to receiving waters resulting 2 from harvesting 34-year-old lodgepole pine trees in an upland peat catchment. The study site was 3 within a 25.3-hectare (ha) area, and was drained by a stream that received flows from ploughed 4 furrows, mainly, via collector drains, and discharged directly to the salmonid Shrahrevagh River,

European eel (Anguilla anguilla) recruitment has been declining at least since the early 1980s at the scale of its distribution area. Since the population is panmictic, its stock assessment should be carried out on a range-wide basis. However, assessing the overall stock during the continental phase remains difficult given its widespread distribution among heterogeneous and separate river catchments. Hence, it is currently considered by the International Council for the Exploration of the Sea (ICES) more feasible to use glass eel recruitment data to assess the status of the overall population. In this study, we used Glass Eel Recruitment Estimation Model (GEREM) to estimate annual recruitment (i) at the river catchment level, a scale for which data are available, (ii) at an intermediate scale (6 European regions), and (iii) at a larger scale (Europe). This study provides an estimate of the glass eel recruitment trend through a single index, which gathers all recruitment time-series available at the European scale. Results confirmed an overall recruitment decline to dramatically low levels in 2009 (3.5% of the 1960–1979 recruitment average) and highlighted a more pronounced decline in the North Sea area compared to elsewhere in Europe.