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1. The complex life cycle of the globally threatened Margaritifera margaritifera includes a parasitic stage, where glochidia attach to the gills of fishes of the genus Salmo; however, the species of Salmo used appears to vary across its range. In previous literature the reported primary host in Scotland, home to a high proportion of the world's remaining M. margaritifera populations, is the Atlantic salmon Salmo salar, and in its absence the brown trout Salmo trutta.2. In this study, the prevalence of infection in putative Salmo hosts in eight rivers in north-west Scotland was determined. At a selected site on each river, where both S. trutta and S. salar were collected in abundance, S. trutta was the preferred host.3. At sites where S. salar were abundant but S. trutta were at low density, however, S. salar showed a high prevalence of infection (with the exception of one river where neither S. salar nor S. trutta were infected). Thus, the primary host appears to be very site-specific in the rivers sampled.4. We speculate that this may be because M. margaritifera have population-specific responses to cues for attachment to a host. Alternatively, it may be that host population-specific immune responses mediate infections by glochidia. In addition, larger fish were less likely to be infected than smaller fish, and gills 1 and 5 were less heavily infected than gills 2-4. 5. One consequence of this finding, for both national and international conservation management of this globally endangered species, is that any current or future management activity must take into account local population host preferences, otherwise conservation efforts may be in vain.

This study assessed the usefulness of passing euthanized Atlantic salmon Salmo salar smolts through an Archimedean screw turbine to test for external damage, as compared with live, actively swimming smolts. Scale loss was the only observed effect. Severe scale loss was 5·9 times more prevalent in euthanized turbine-passed fish (45%) than the live fish (7·6%). Additionally, distinctive patterns of scale loss, consistent with grinding between the turbine helices and housing trough, were observed in 35% of euthanized turbine-passed smolts. This distinctive pattern of scale loss was not seen in live turbine-passed smolts, nor in control groups (live and euthanized smolts released downstream of the turbine), which suggests that the altered behaviour of dead fish in turbine flows generates biased injury outcomes.

1. The aim of this study was to assess the extent to which the behavioural traits of freshwater mussels provide suitable indicators of stress in individuals, towards the advancement of non-invasive, remote monitoring techniques to examine population condition.2. Variation in the expression of particular behavioural metrics was examined in accordance with measurements of oxygen consumption, across environmental stressors (aerial exposure and high concentrations of total suspended solids), and between two freshwater mussel species (Margaritifera margaritifera and Anodonta anatina)3. Aerobic metabolic rate was quantified using intermittent respirometry, and behaviour was observed using time-lapse footage. Comparisons of metabolic response and the occurrence of behavioural traits, across the two stressors, focused on differences between the 24 h pre-exposure period (pre-exposure), the first 3 h of post-exposure (immediate post-exposure), and the time following the initial 3 h of post-exposure until the end of the experimental run (extended postexposure).4. The results of this study demonstrated a relationship between the frequency of occurrence of behavioural responses to stress exposure, associated with valve activity, and significant changes in the metabolic functioning of A. anatina and M. margaritifera mussels. The findings from the study also highlighted substantial intraspecific variation across species and stressors.

We report characteristics of seven tree cavities used as day-roosts by female northern long-eared bats (Myotis septentrionalis) during the maternity season in a deciduous forest in north-central Kentucky. Understanding the characteristics of cavities selected by bats will help us better understand the ecology of cavity roosting bats and the tree species and condition necessary for providing day-roost habitat. Cavity openings were created by either fungal decay or primary excavators. Length and volume of cavities were positively related to number of entrances. Mean area of entrances was positively related to the proportion of entrances created by primary excavators. The use of trade, fi rm, or corporation names in this publication is for the information and convenience of the reader. Such use does not constitute an official endorsement or approval by the U.S. Department of Agriculture or the Forest Service of any product or service to the exclusion of others that may be suitable. Quality Assurance This publication conforms to the Northern Research Station's Quality Assurance Implementation Plan which requires technical and policy review for all scientifi c publications produced or funded by the Station. The process included a blind technical review by at least two reviewers, who were selected by the Assistant Director for Research and unknown to the author. This review policy promotes the Forest Service guiding principles of using the best scientifi c knowledge, striving for quality and excellence, maintaining high ethical and professional standards, and being responsible and accountable for what we do. Cover Photo A white oak (Quercus alba) snag provides roosting opportunities for female northern longeared bats on the Fort Knox Military Reservation, Kentucky, USA. Photo by Alexander Silvis, Virginia Tech, used with permission.

Alterations to water management practices, in response to a growing demand to maximize energy production from renewable sources, threaten to exacerbate anticipated future water shortages caused by severe drought episodes, brought on by climate change. Across Scotland, many highly managed systems are inhabited by some of the last remaining reproductively viable populations of the freshwater pearl mussel, Margaritifera margaritifera. A lack of empirical evidence concerning mussel responses to alterations in flow is inhibiting the development of effective conservation management practices to prolonged drought. This study addressed this knowledge gap by examining the response of M. margaritifera to controlled water level drawdowns in laboratory and field settings. Using a laboratory flume, the responses of M. margaritifera from two different populations (a regulated system versus an unregulated system) were compared across rates of drawdown and density treatments. An analogous field trial was undertaken to examine the responses of M. margaritifera in a regulated system, with a hydroelectric dam facilitating a controlled drawdown. The study showed that M. margaritifera can detect alterations in flow depth, which culminate in the emersion of mussel beds, and respond by undertaking vertical and horizontal movements to mitigate the risk of prolonged aerial exposure. Results from the field trial corroborated findings from the flume experiments, with 80% of mussels shown to avoid emersion successfully by tracking receding water levels. Findings from this study support the role of controlled drawdowns in regulated rivers to reduce mortalities associated with receding water levels during prolonged low‐flow episodes. Differences between populations in response highlight a need to adopt a context‐dependent approach to conservation efforts.

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