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Atlantic salmon Salmo salar is a socio-economically important anadromous fish species that has suffered synchronous population declines around the North Atlantic over the last five decades. Reduced marine survival has been implicated as a key driver of the declines, yet the relative importance of different stressors causing mortality at sea is not well understood. This review presents a synopsis of the principal stressors impacting Atlantic salmon in estuarine and marine environments. It also applies a semi-quantitative 2-D classification system to assess the relative effects of these stressors on English salmon stocks and their likely development over the next decade. Climate change and predation were identified as the biggest threats at present and over the next decade. Poor water quality and bycatch were classified as relatively high impact stressors, but with a lower likelihood of becoming more prevalent in the future due to available mitigation measures. Other, less influential, stressors included tidal barrages, artificial light at night, impingement in power-station cooling waters and thermal discharges, pile-driving noise pollution, invasive non-native species, electromagnetic fields, salmon mariculture, and tidal lagoons. Salmon fisheries exploitation was not regarded as an important stressor currently because effective exploitation rate controls have been implemented to substantially reduce fishing pressure. Future research priorities include addressing knowledge gaps on expanding stressor impacts from climate change, predation, renewable energy developments, and artificial light at night. Local management actions directed towards improving freshwater and estuarine habitats to maximise ecosystem resilience to stressors and minimise their cumulative impacts are recommended.

Invasive non‐native species (NNS) are internationally recognized as posing a serious threat to global biodiversity, economies and human health. The identification of invasive NNS is already established, those that may arrive in the future, their vectors and pathways of introduction and spread, and hotspots of invasion are important for a targeted approach to managing introductions and impacts at local, regional and global scales. The aim of this study was to identify which marine and brackish NNS are already present in marine systems of the northeastern Arabia area (Arabian Gulf and Sea of Oman) and of these which ones are potentially invasive, and which species have a high likelihood of being introduced in the future and negatively affect biodiversity. Overall, 136 NNS were identified, of which 56 are already present in the region and a further 80 were identified as likely to arrive in the future, including fish, tunicates, invertebrates, plants and protists. The Aquatic Species Invasiveness Screening Kit (AS‐ISK) was used to identify the risk of NNS being (or becoming) invasive within the region. Based on the AS‐ISK basic risk assessment (BRA) thresholds, 36 extant and 37 horizon species (53.7% of all species) were identified as high risk. When the impact of climate change on the overall assessment was considered, the combined risk score (BRA+CCA) increased for 38.2% of all species, suggesting higher risk under warmer conditions, including the highest‐risk horizon NNS the green crab Carcinus maenas, and the extant macro‐alga Hypnea musciformis. This is the first horizon‐scanning exercise for NNS in the region, thus providing a vital baseline for future management. The outcome of this study is the prioritization of NNS to inform decision‐making for the targeted monitoring and management in the region to prevent new bio‐invasions and to control existing species, including their potential for spread., This review identifies and risk screens potentially invasive non‐native species (NNS) within the Regional Organization for the Protection of the Marine Environment Sea Area. In total, 136 NNS were identified, of which 56 are already present and a further 80 were identified as likely to arrive in the future.

The tropical waters of the Northern Arabian Gulf have a long history of maritime resource richness. High levels of biodiversity result from the complex matrix of coastal habitats, coral reefs and sea grass beds that characterise the region. Insight into the ongoing health of such habitats and the broader Kuwait maritime environment can be gauged by the status of indicator species found within these habitats. Here we review information on the occurrence, distribution and threats to key marine habitats and associated indicator species to provide an updated assessment of the state of the Kuwait's marine biodiversity. Critical evaluation of historic data highlights knowledge gaps needed inform the focus of future monitoring and conservation efforts. This assessment is designed to evaluate performance against environmental policy commitments, while providing a solid foundation for the design of comprehensive marine ecosystem management strategies.

The threat posed by invasive non-native species worldwide requires a global approach to identify which introduced species are likely to pose an elevated risk of impact to native species and ecosystems. To inform policy, stakeholders and management decisions on global threats to aquatic ecosystems, 195 assessors representing 120 risk assessment areas across all six inhabited continents screened 819 non-native species from 15 groups of aquatic organisms (freshwater, brackish, marine plants and animals) using the Aquatic Species Invasiveness Screening Kit. This multi-lingual decision-support tool for the risk screening of aquatic organisms provides assessors with risk scores for a species under current and future climate change conditions that, following a statistically based calibration, permits the accurate classification of species into high-, medium-and low-risk categories under current and predicted climate conditions. The 1730 screenings undertaken encompassed wide geographical areas (regions, political entities, parts thereof, water bodies, river basins, lake drainage basins, and marine regions), which permitted thresholds to be identified for almost all aquatic organismal groups screened as well as for tropical, temperate and continental climate classes, and for tropical and temperate marine ecoregions. In total, 33 species were identified as posing a 'very high risk' of being or becoming invasive, and the scores of several of these species under current climate increased under future climate conditions, primarily due to their wide thermal tolerances. The risk thresholds determined for taxonomic groups and climate zones provide a basis against which area-specific or climate-based calibrated thresholds may be interpreted. In turn, the risk rankings help decision-makers identify which species require an immediate 'rapid' management action (e.g. eradication, control) to avoid or mitigate adverse impacts, which require a full risk assessment, and which are to be restricted or banned with regard to importation and/or sale as ornamental or aquarium/fishery enhancement. (c) 2021 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/)., Cefas Science Excellence fund; [TKP2020-NKA-16], This study is dedicated to our co-author, the late Prof. Olaf Weyl, whose sudden passing during field work in November 2020 was received by us with great sadness. This study represents a contribution to the term of reference 'd' (Advance knowledge base to further develop indicators to evaluate the status and impact of non-indigenous species in marine environments) of the ICES working group on Introductions and Transfers of Marine Organisms. The participation of GHC was supported by the Cefas Science Excellence fund. AW and AF were supported by TKP2020-NKA-16 project.

© 2017 The Author(s) and 2017 REABIC. The introduction of non-native species as contaminants of aquatic plant consignments is poorly documented. This paper reports on the introduction of pumpkinseed Lepomis gibbosus, a North American sunfish, into an angling lake as a contaminant of native aquatic plants during their stocking to enhance the fishery. Growth and life-history data for the L. gibbosus specimens captured in the water body provided biological evidence (relatively rapid juvenile growth and early maturation) that supports the assumption that L. gibbosus was accidentally introduced as a contaminant of the aquatic plant consignment. This study highlights the importance of adhering to current guidelines on the movement of aquatic plants (e.g. Great Britain’s “Be Plant Wise” educational initiative), which aims to prevent unwanted transfer of aquatic organisms.

This paper presents the first phase in the development and validation of a simple and reliable environmental (e)DNA method using conventional PCR to detect four species of non-native freshwater fish: pumpkinseed Lepomis gibbosus, sunbleak Leucaspius delineatus, fathead minnow Pimephales promelas and topmouth gudgeon Pseudorasbora parva. The efficacy of the approach was demonstrated in indoor tank (44 l) trials in which all four species were detected within 24 h. Validation was through two field trials, in which L. gibbosus was detected 6-12 h after its introduction into outdoor experimental ponds and P. parva was successfully detected in disused fish rearing ponds where the species was known to exist. Thus, the filtration of small (30 ml) volumes of pond water was sufficient to capture fish eDNA and the approach emphasised the importance of taking multiple water samples of sufficient spatial coverage for detecting species of random or patchy distribution.

To inform aquatic conservation policy and management decisions, translocated freshwater fish species, i.e. those native to part but not all of Great Britain (GB), were assessed with the Aquatic Species Invasiveness Screening Kit (AS-ISK) at two spatial levels (River Basin District [RBD] and GB overall), the outcome scores calibrated and analysed to determine the relevance of geographical scale (GB, RBD and freshwater ecoregion) on AS-ISK outcome score rankings. The 16 species assessed received scores that showed limited among-RBD variation, with all but only one species (silver bream Blicca bjoerkna) receiving the same risk ranking across all RBDs for which they were assessed. A trend of increasing AS-ISK score with decreasing RBD latitudinal location was observed, with two species (bleak Alburnus alburnus and tench Tinca tinca) found to have significantly higher AS-ISK scores in west-coast RBDs than in RBDs to the north and east, and one species (bleak Alburnus alburnus) to have significantly higher AS-ISK scores in southern RBDs than in northern RBDs. The Water Framework Directive classification of Scotland was found to be inconsistent with the latitudinal gradients in that country's environmental conditions, which are better reflected in the distinction of northern and southern freshwater ecoregions. The ramifications of these legislative classifications for aquatic conservation are discussed.

The freshwater Fish Invasiveness Screening Kit (FISK) has been applied in 35 risk assessment areas in 45 countries across the six inhabited continents (11 applications using FISK v1; 25 using FISK v2). The present study aimed: to assess the breadth of FISK applications and the confidence (certainty) levels associated with the decision-support tool’s 49 questions and its ability to distinguish between taxa of low-to-medium and high risk of becoming invasive, and thus provide climate-specific, generalised, calibrated thresholds for risk level categorisation; and to identify the most potentially invasive freshwater fish species on a global level. The 1973 risk assessments were carried out by 70 + experts on 372 taxa (47 of the 51 species listed as invasive in the Global Invasive Species Database www.iucngisd.org/gisd/ ), which in decreasing order of importance belonged to the taxonomic Orders Cypriniformes, Perciformes, Siluriformes, Characiformes, Salmoniformes, Cyprinodontiformes, with the remaining ≈ 8% of taxa distributed across an additional 13 orders. The most widely-screened species (in decreasing importance) were: grass carp Ctenopharyngodon idella, common carp Cyprinus carpio, rainbow trout Oncorhynchus mykiss, silver carp Hypophthalmichthys molitrix and topmouth gudgeon Pseudorasbora parva. Nine ‘globally’ high risk species were identified: common carp, black bullhead Ameiurus melas, round goby Neogobius melanostomus, Chinese (Amur) sleeper Perccottus glenii, brown bullhead Ameiurus nebulosus, eastern mosquitofish Gambusia holbrooki, largemouth (black) bass Micropterus salmoides, pumpkinseed Lepomis gibbosus and pikeperch Sander lucioperca. The relevance of this global review to policy, legislation, and risk assessment and management procedures is discussed.

© 2019, The Author(s). Environmental managers require a sensitive and reliable means to prove, with the highest level of confidence possible, where non-native fish species exist and where they do not. Therefore, a nested PCR (nPCR) protocol was developed to detect the environmental DNA (eDNA) of a case-study species, topmouth gudgeon Pseudorasbora parva, which was recently the subject of a national eradication campaign in the UK. The nPCR protocol was tested in the laboratory and in the field in a series of coordinated surveys (eDNA and conventional sampling with traps) at a commercial angling venue in southern England where an initial eDNA survey, based on conventional PCR (cPCR), found P. parva to be present in one of the seven ponds. In the laboratory, the nPCR protocol was on average 100× more sensitive than cPCR, providing a 100% detection rate at DNA concentrations of 3 × 10 −8 ng/µL (8 DNA copies per µL). In the field, nPCR and conventional trapping both detected P. parva in only one of the seven angling ponds, the same infested pond as in the previous cPCR-based study. Following eradication work on the infested pond, no eDNA of P. parva was detected using nPCR in either the formerly-infested pond or the adjacent pond, which had been used to quarantine large commercially-valuable fishes. In management applications where the veracity of negative results may be of equal importance as confirmation of positive detections, nPCR protocols provide a useful addition to the analytical toolkit available to inform decision makers responsible for non-native species management.

SUMMARY 1. The effect of a range of ecologically relevant broader spectrum street light intensities on the dispersal timing of Atlantic salmon (Salmo salar) fry was investigated to assess the efficacy of a proposed management tool, the dimming of lamp brightness, for reducing the ecological consequences of artificial night light on aquatic ecosystems. Dispersal timing under treatment street light intensities of 8, 4, 2 and 1 lux was compared to that under a control night light intensity of 0.1 lux, representative of approximately half that experienced from a full moon. 2. Dispersal timing was significantly delayed (by 1.4 to 2.2 days), and its diel pattern significantly disrupted under the treatment street light intensities. However, the dose–response for both delay and disruption effects was not linear, with a strong effect apparent at 1 lux, and little or no additional impact seen when the light intensity was increased further. Under control conditions, the mean time of dispersal was 3:58 h after dusk, with very few fry (

Species translocation leads to disease emergence in native species of considerable economic importance. Generalist parasites are more likely to be transported, become established and infect new hosts, thus their risk needs to be evaluated. Freshwater systems are particularly at risk from parasite introductions due to the frequency of fish movements, lack of international legislative controls for non-listed pathogens and inherent difficulties with monitoring disease introductions in wild fish populations. Here we used one of the world's most invasive freshwater fish, the topmouth gudgeon, Pseudorasbora parva, to demonstrate the risk posed by an emergent generalist parasite, Sphaerothecum destruens. Pseudorasbora parva has spread to 32 countries from its native range in China through the aquaculture trade and has introduced S. destruens to at least five of these. We systematically investigated the spread of S. destruens through Great Britain and its establishment in native fish communities through a combination of phylogenetic studies of the host and parasite and a novel environmental DNA detection assay. Molecular approaches confirmed that S. destruens is present in 50% of the P. parva communities tested and was also detected in resident native fish communities but in the absence of notable histopathological changes. We identified specific P. parva haplotypes associated with S. destruens and evaluated the risk of disease emergence from this cryptic fish parasite. We provide a framework that can be applied to any aquatic pathogen to enhance detection and help mitigate future disease risks in wild fish populations.

The aim of the present study was to risk screen 45 jellyfish species (30 hydromedusae, 14 scyphomedusae, one cubomedusa) for their potential invasiveness in the Mediterranean Sea to aid managers in making informed decisions on targeting appropriate species for management. Using the Aquatic Species Invasiveness Screening Kit (AS-ISK), calibrated basic and climate-change threshold assessment scores of 6.5 and 12.5, respectively, were identified for distinguishing reliably between species that pose 'low-to-medium' and 'high' risk of becoming invasive in the risk assessment area. Using these thresholds, 16 species were classified as high risk, 23 as medium risk and six as low risk under current climate conditions. Whereas, under future climate conditions, 13, 30 and two species, respectively, were classified as high, medium and low risk, respectively. Upside-down jellyfish Cassiopea andromeda, Australian spotted jellyfish Phyllorhiza punctata, sea nettle Chrysaora quinquecirrha and Rhopilema nomadica were the highest-scoring species, with the maximum increase in risk score under predicted climate change conditions being achieved by C. andromeda.

The downstream migratory behaviour of wild Atlantic salmon Salmo salar smolts was monitored using passive integrated transponder (PIT) antennae systems over 10 years in the lower reaches of a small chalk stream in southern England, U.K. The timing of smolt movements and the likely occurrence of schooling were investigated and compared to previous studies. In nine of the 10 consecutive years of study, the observed diel downstream patterns of S. salar smolt migration appeared to be synchronized with the onset of darkness. The distribution of time intervals between successive nocturnal detections of PIT-tagged smolts was as expected if generated randomly from observed hourly rates. There were, however, significantly more short intervals than expected for smolts detected migrating during the day. For each year from 2006 to 2011, the observed 10th percentile of the daytime intervals was

The predation impact of recently stocked triploid brown trout, Salmo trutta L., on migrating wild Atlantic salmon, Salmo salar L., smolts was investigated in two field-based experiments. The first experiment employed a unique experimental facility to monitor 57 wild S. salar smolts through an enclosure containing a known density of stocked S. trutta to determine a predation rate. None of these smolts were preyed upon by the stocked S. trutta. The second experiment investigated the diet of free-ranging stocked triploid S. trutta in a chalk stream during the spring. Although at least 6% of the free-ranging stocked triploid S. trutta became piscivorous on Phoxinus phoxinus (L.), the results suggest that large, recently stocked, triploid S. trutta with a high condition factor do not represent a predation threat to wild S. salar smolts. However, it is recommended that a precautionary approach is maintained and the findings are not generalised until further investigation permits explicit management advice to be developed, and that the stocking of large triploid S. trutta is avoided before May/ June (regional variations to apply) each calendar year, where this can reasonably be achieved.

There has been a decline in the abundance of Atlantic salmon (Salmo salar) despite significant conservation measures designed to reduce fishing mortality. Populations at the southern edge of their historical distribution, where anthropogenic impacts on the freshwater environment may be greater, have suffered the largest decline. In this investigation, we compared the timing of Atlantic salmon fry dispersal from incubators in an aquarium under control and ecologically relevant broad spectrum street-lit conditions (median night light intensity = 12 lx). Fry dispersal occurred 2.8 days later (F = 82.9, df = 1,8, p < 0.001), and on average the fry were smaller at dispersal (0.017 g, se = 0.0012, p < 0.001, n = 730), in the incubators exposed to street lighting. Significant disruption to the diel pattern of fry dispersal was also observed. Dispersal under control conditions was significantly directed around a mean time of 4:17 h after dusk (p < 0.001, r = 0.76, n = 1990) with very few fry (

Advances in the field of telemetry techniques during the last few decades have greatly expanded our knowledge on migratory behaviour and provided the opportunity to obtain practically useful data for the conservation and management of salmonid populations. However, applying this information to the development of much needed population-based migration models has been limited. Furthermore, this research has generally been restricted to assessing the role of river flow on fish movement. Models derived from a 6-year telemetry study on the movements of Atlantic salmon, Salmo salar L., and sea trout, Salmo trutta L., in the River Tyne are presented together with an assessment of counter data from the same river to highlight the importance of additional environmental and physiological parameters in regulating fish movement. The data are discussed in relation to the advantages of telemetry data, the need to develop predictive models, the statistical methods used and the potential direction of future work in this area.

In recognition of the potential threat posed by introduced species to ecosystem function, the incidence of non-native fishes in rivers and streams of the UK was examined for the years 1961 to 2000 inclusive using data from the Database and Atlas of Freshwater Fishes. The proportion of records pertaining to non-native fishes has remained more or less constant, but the mean number of non-native species was found to be significantly higher in 1991-2000 than in earlier decades, and the proportion of records pertaining to certain species have increased whilst others have decreased.

Artificial light at night (ALAN) is known to disrupt the nocturnal dispersal behaviour of Atlantic salmon fry, yet the underlying physiological mechanism is unknown. Here novel methodologies are utilised to examine whether behavioural disruption seen in dispersing fry is mediated via a cortisol stress response. Fry showed the capacity to mount a stress response, however, the two methods for sampling cortisol provide conflicting results as to whether ALAN acts as a stressor to dispersing fry., Artificial light at night (ALAN) is gaining recognition as having an important anthropogenic impact on the environment, yet the behavioural and physiological impacts of this stressor are largely unknown. This dearth of information is particularly true for freshwater ecosystems, which are already heavily impacted by anthropogenic pressures. Atlantic salmon (Salmo salar L.) is a species of conservation and economic importance whose ecology and behaviour is well studied, making it an ideal model species. Recent investigations have demonstrated that salmon show disrupted behaviour in response to artificial light; however, it is not yet clear which physiological processes are behind the observed behavioural modifications. Here, two novel non-invasive sampling methods were used to examine the cortisol stress response of dispersing salmon fry under different artificial lighting intensities. Fish egg and embryos were reared under differing ALAN intensities and individual measures of stress were subsequently taken from dispersing fry using static sampling, whereas population-level measures were achieved using deployed passive samplers. Dispersing fry exposed to experimental confinement showed elevated cortisol levels, indicating the capacity to mount a stress response at this early stage in ontogenesis. However, only one of the two methods for sampling cortisol used in this study indicated that ALAN may act as a stressor to dispersing salmon fry. As such, a cortisol-mediated response to light was not strongly supported. Furthermore, the efficacy of the two non-invasive methodologies used in this study is, subject to further validation, indicative of them proving useful in future ecological studies.

For species with extended spawning seasons, short periods of beneficial conditions often lead to disproportionate survival of sub-sets of the offspring. This has been demonstrated for freshwater fish and for marine pelagic species, but has been less frequently tested for other teleost groups. Using offshore plankton surveys, we constructed egg production curves for plaice Pleuro- nectes platessa L. in the eastern Irish Sea. Data from 5 yr showed that spawning began sometime before January and was completed by the end of April. Over these years the timing of peak spawn- ing varied between mid-February and mid-March. In 2001, 2002 and 2003, we also sampled post- settlement plaice from inshore nursery grounds. Otolith micro-increment analyses and temperature- dependent egg development rates were used to back-calculate the birth dates of the settled fish. By June, immigration to the nursery grounds was largely completed and the shape of the reconstructed birth-date distributions corresponded closely to the relevant egg production curves. In contrast to many other studies, there was little evidence for significantly disproportionate survival of specific portions of the egg production curve between spawning and the recently post-settled stages. Such a survival pattern could be generated by a gradual switch from starvation to predation as the principal cause of larval mortality as the spawning season progressed.