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The male drumming signal of the stonefly Taeniopteryx nebulosa from Great Britain is described for the first time. It differs significantly from calls of European males in terms of number of beats and total call duration. As such, it justifies continued consideration of British specimens as a subspecies. Despite there being only one specimen examined we thought it was important to note the differences observed and to consider the significance for the status of the British subspecies.

A total of 230 anadromous Salmo trutta (brown trout) were sampled in five sheltered coastal fjords (or sea lochs) on the Isle of Skye, Scotland, U.K., in 2016 at varying distances from active Atlantic salmon Salmo salar farms. Statistical models were developed to investigate potential correlations between salmon lice Lepeophtheirus salmonis burdens on S. trutta hosts and their proximity to S. salar farm cages. Significant correlations were found between lice burdens and fish fork length and proximity to the nearest S. salar farm. The probability of the presence of L. salmonis on fish hosts increased with fish host size and with distance from the nearest S. salar farm, but total lice burdens were highest in fish sampled near S. salar farms and decreased with distance. The proportion of different life‐cycle stages of L. salmonis were also dependent on S. salar farm proximity, with higher juvenile lice numbers recorded at sites near S. salar farm cages. These results highlight the complexity of the relationship between S. trutta and L. salmonis infections on wild fish and emphasise the requirement of further research to quantify these effects to better inform conservation and management strategies, particularly in areas of active S. salar farm facilities.

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.

This study investigated the cumulative impact of weirs on the downstream migration of wild Atlantic salmon (Salmo salar) smolts in the River Foyle, Northern Ireland. In spring of 2013 fish were released in two tributaries of similar length; one tributary (impacted) had seven low‐head weirs along the migration pathway and the other was devoid of such structures (un‐impacted). Salmon smolts fitted with acoustic transmitters were monitored via a passive acoustic telemetry array during downstream migration. In 2014 the study was repeated only in the impacted tributary. Overall freshwater survival rates were high (>94%). There was no significant difference in mortality, movement pattern, delay or travel speeds between rivers or between years at any phase of migration. Escapement of salmon smolts through Lough Foyle (a marine sea lough) to the open ocean was low, approximately 18% in each year. Escapement did not differ between impacted and un‐impacted rivers. This study showed no postpassage effects of weirs on mortality, migration speed or escapement of downstream migrating smolts. This suggests that the elevated mortality at low‐head obstacles described in other studies is not inevitable in all river systems. Migration through rivers with natural riffle‐pool migration may result in similar effects as those from low‐head weirs. Causes of apparent high mortality in the early part of marine migration in this study, are unknown; however similar studies have highlighted the impact of fish predators on smolts.

The European bullhead (Cottus gobio) is widely distributed across Europe, and within the UK is native to England and Wales, where it is protected under the Habitats Directive. In Scotland, however, the species is considered invasive and thriving populations are recorded in the Forth and Clyde river catchments, and the Ale Water in the Scottish Borders. The genetic identity of the Scottish populations has not been established. There is also debate about the status of the European bullhead and its validity as single species, a species complex with several unresolved species, or distinct different species in its European distribution range. There is therefore a need to determine the taxonomy and likely source of the novel Scottish populations. Genetic analyses using cytochrome oxidase 1 (COI) mitochondrial DNA sequences were undertaken on specimens from the Forth and Clyde catchments, and combined with the results of morphological characteristics to provide a comprehensive assessment of the taxonomic classification for Scottish bullheads. There was considerable variation in morphological characteristics between populations within Scotland and a wider range of variability than previously recorded for English populations. Genetically the Scottish populations were very closely related to English specimens, supporting the hypothesis of introduction directly from England to Scotland. In terms of broader relationships, Scottish specimens are genetically more closely related to the ostensible species Chabot fluviatile Cottus perifretum, which has been suggested as one of a complex of species across Europe. Morphologically they exhibit characteristics on the spectrum between C. perifretum and C. gobio. There is an urgent need for the clarification of the taxonomy of Cottus sp(p). to avoid confusion in future publications, legislation and management practices relating to bullheads throughout the UK and Europe.

Mortality rates of wild Atlantic salmon Salmo salar smolts implanted with acoustic transmitters were assessed to determine if mortality was size dependent. The routinely accepted, but widely debated, ‘2% transmitter mass: body mass’ rule in biotelemetry was tested by extending the transmitter burden up to 12·7% of body mass in small [mean fork length (LF) 138·3 mm, range 115–168 mm] downstream migrating S. salar smolts. Over the short timescale of emigration (range 11·9–44·5 days) through the lower river and estuary, mortality was not related to S. salar size, nor was a relationship found between mortality probability and transmitter mass: body mass or transmitter length: LF ratios. This study provides further evidence that smolt migration studies can deviate from the ‘2% rule’ of thumb, to more appropriate study-specific measures, which enables the use of fishes representative of the body size in natural populations without undue effects.

This study examined the abiotic and biotic characteristics of ecosystems that allow expression of a life history called ferox trout, the colloquial name given to brown trout Salmo trutta adopting a piscivorous life history strategy, an apex predator in post-glacial lakes in northern Europe. One hundred and ninety-two lakes in Scotland show evidence of currently, or historically, supporting ferox S. trutta; their presence was predicted in logistic models by larger and deeper lakes with a large catchment that also support populations of Arctic charr Salvelinus alpinus.

This study revealed between-lake genetic structuring between Coregonus lavaretus collected from the only two native populations of this species in Scotland, U.K. (Lochs Eck and Lomond) evidenced by the existence of private alleles (12 in Lomond and four in Eck) and significant genetic differentiation (FST = 0·056) across 10 microsatellite markers. Juvenile C. lavaretus originating from eggs collected from the two lakes and reared in a common-garden experiment showed clear phenotypic differences in trophic morphology (i.e. head and body shape) between these populations indicating that these characteristics were, at least partly, inherited. Microsatellite analysis of adults collected from different geographic regions within Loch Lomond revealed detectable and statistically significant but relatively weak genetic structuring (FST = 0·001–0·024) and evidence of private alleles related to the basin structure of the lake. Within-lake genetic divergence patterns suggest three possibilities for this observed pattern: (1) differential selection pressures causing divergence into separate gene pools, (2) a collapse of two formerly divergent gene pools and (3) a stable state maintained by balancing selection forces resulting from spatial variation in selection and lake heterogeneity. Small estimates of effective population sizes for the populations in both lakes suggest that the capacity of both populations to adapt to future environmental change may be limited.

The unimpeded downstream movement patterns and migration success of small female and male Anguilla anguilla through a catchment in north-west Europe were studied using an acoustic hydrophone array along the River Finn and into the Foyle Estuary in Ireland. Twenty silver-stage A. anguilla (total length, LT, range: 332–520 mm) were trapped 152 km upstream from a coastal marine sea-lough outlet and internally tagged with acoustic transmitters of which 19 initiated downstream migration. Migration speed was highly influenced by river flow within the freshwater (FW) compartment. Anguilla anguilla activity patterns were correlated with environmental influences; light, tidal direction and lunar phase all influenced the initiation of migration of tagged individuals. Migration speed varied significantly between upstream and lower river compartments. Individuals migrated at a slower speed in transitional water and sea-lough compartments compared with the FW compartment. While 88·5% survival was recorded during migration through the upper 121 km of the river and estuary, only 26% of A. anguilla which initiated downstream migration were detected at the outermost end of the acoustic array. Telemetry equipment functioned efficiently, including in the sea-lough, so this suggests high levels of mortality during sea-lough migration, or less likely, long-term sea-lough residence by silver A. anguilla emigrants. This has important implications for eel management plans.

The behaviour of returning Salmo salar (Linnaeus, 1758) approaching, and attempting to pass low-head weirs remains relatively unknown. A radio telemetry array was created at a low-head weir to enable the behaviour of S. salar (n = 120) to be observed as they approached and attempted to pass the barrier. The majority of fish successfully passed the barrier on their first or second attempt, some individuals required 11 attempts prior to successful passage occurring. Mean delay at the barrier per fish was 47.8 h (±SD 132.0 h), range 15 min to 31 days. Passage success on a fish’s initial attempt was significantly predicted by the amount of searching a fish undertook, fork length, and fat content. Fish were more likely to have a successful first passage attempt if it was smaller with a low fat content and exerted a greater effort in searching for a passage channel. Small-scale barriers cause delays and increased energy expenditure in migrating fish. Barriers may be creating an anthropogenic selection pressure for traits which enable passage success. The impact of a delay at a barrier and increased energy expenditure on reproduction and gonad development remains unknown but is likely to be negatively impacted by instream anthropogenic structures.

This study examines juvenile Anguilla anguilla (

There is increasing interest in understanding the implications of biological invasions within the context of ecosystem functioning. Non-native crustaceans are of particular interest within fresh waters because of their important contributions to leaf-litter processing. The alien amphipod Dikerogammarus villosus is spreading rapidly through Europe where it has displaced native gammarids including Gammarus pulex. The resultant change in shredder communities has considerable implications for the dynamics of resource availability within invaded systems. The invasive success of D. villosus has been attributed to many characteristics, including its ability to tolerate a wide range of environmental conditions and to exploit a wide feeding niche. These characteristics are thought to give D. villosus an advantage over native species, especially in habitats subject to changing environmental conditions. The leaf (Salix alba) shredding efficiency, defined as the leaf mass consumed over the 4-day experiment per amphipod-day, was measured for D. villosus and G. pulex under extreme temperature and conductivity conditions, in single species and mixed species aquaria. At high temperatures (25°C), D. villosus shredded significantly more leaves than size-matched G. pulex. Conductivity extremes had no species effect; overall leaf-shredding efficiency was significantly greater at low conductivity (250 μS cm-1) than high conductivity (1870 μS cm-1). An inspection of daily leaf disc consumption found that the two species showed significantly different leaf consumption patterns, with D. villosus consuming more leaves earlier in the experiment. These results suggest that D. villosus invasion could lead to ecosystem-level changes in leaf processing, such as greater leaf processing earlier in autumn and at higher temperatures, which could alter nutrient dynamics and community assemblages within invaded systems. Such effects may not be reflected in biotic indices used to assess ecological status, as these indices do not currently distinguish between native and invasive species in the same family. Copyright © 2013 John Wiley & Sons, Ltd.

Partial migration, in which some individuals of a population migrate and others remain sedentary, is a phenomenon that occurs across a wide range of taxa, but the factors that predispose particular individuals to one or the other strategy are usually unknown. Brown trout (Salmo trutta) initially compete for feeding territories in freshwater streams, but while some individuals remain resident in fresh water throughout their lives, others undertake an anadromous migration. Because one of the drivers for migration is the relative rates of resource acquisition in different habitats, we compared the ability of juvenile offspring from freshwater-resident and anadromous parents to compete for feeding territories; we also tested how this depended on the quality of the environment previously experienced. Brown trout derived from freshwater-resident or anadromous parents were reared for ~7 months under high-, mid-, or low-food regimes and were then induced to compete for feeding territories in a seminatural stream channel. We found that the parental type had a significant effect on dominance status in territorial interactions, with offspring of anadromous fish being dominant over size-matched offspring of freshwater residents, but only when both had been raised under intermediate levels of food availability. The results suggest that the migration strategy of the parents interacts with the environmental conditions experienced by the offspring to potentially influence its motivation to compete for feeding territories and hence its probability of migration.

A fixed receiver array was used to examine the movement patterns and space use of the European eel Anguilla anguilla in an oligotrophic Irish lake between July and September. We assessed home range size, temporal change in spatial behaviour and activity patterns of broad-headed (n = 11) and narrow-headed (n = 8) morphotypes. Broad-headed individuals displayed a larger home range (mean KUD95 (km2):0.296 ± 0.04 S.E.) in comparison to narrow-headed individuals (mean KUD95 (km2):0.143 ± 0.02 S.E.). Eel activity was strongly dependent on light conditions. Narrow-headed individuals’ movement peaks occurred at dawn and dusk in comparison to broad-headed individuals which exhibited a more stable movement pattern throughout night and into dawn, suggesting that narrow-headed eels are more crepuscular in nature whereas broad-headed individuals are more nocturnal. Lunar phase period also influenced eel movement within the lake. These results provide valuable insights into the spatio-temporal distribution of yellow eels in a lake system, demonstrating that individuality in foraging behaviour has direct influence on spatial patterns.

The success of invading species can be restricted by interspecific interactions such as competition and predation (i.e. biotic resistance) from resident species, which may be natives or previous invaders. Whilst there are myriad examples of resident species preying on invaders, simply showing that such an interaction exists does not demonstrate that predation limits invader establishment, abundance or spread. Support for this conclusion requires evidence of negative associations between invaders and resident predators in the field and, further, that the predator-prey interaction is likely to strongly regulate or potentially de-stabilise the introduced prey population. Moreover, it must be considered that different resident predator species may have different abilities to restrict invaders. In this study, we show from analysis of field data that two European predatory freshwater amphipods, Gammarus pulex and G. duebeni celticus, have strong negative field associations with their prey, the invasive North American amphipod Crangonyx pseudogracilis. This negative field association is significantly stronger with G. pulex, a previous and now resident invader in the study sites, than with the native G. d. celticus. These field patterns were consistent with our experimental findings that both resident predators display potentially population de-stabilising Type II functional responses towards the invasive prey, with a significantly greater magnitude of response exhibited by G. pulex than by G. d. celticus. Further, these Type II functional responses were consistent across homo- and heterogeneous environments, contrary to the expectation that heterogeneity facilitates more stabilising Type III functional responses through the provision of prey refugia. Our experimental approach confirms correlative field surveys and thus supports the hypothesis that resident predatory invertebrates are differentially limiting the distribution and abundance of an introduced invertebrate. We discuss how the comparative functional response approach not only enhances understanding of the success or failure of invasions in the face of various resident predators, but potentially also allows prediction of population- and community-level outcomes of species introductions.