A shift in habitat use patterns of brown trout (Salmo trutta): A behavioural response to macrophyte removal.

Mass development of macrophytes is an increasing problem worldwide and they are frequently removed where they are in conflict with local waterway users. Yet, macrophytes can provide important refuge and nursery habitats for fish. Little is known about the consequences of macrophyte removal for fish behavioural space use and habitat selection. We hypothesised that macrophyte removal would affect brown trout (Salmo trutta) movement during the partial removal of the aquatic plant Juncus bulbosus (L.) in an oligotrophic impounded Norwegian river.We tagged 94 brown trout and tracked them using passive acoustic telemetry for 10 months and mapped the cover of J. bulbosus. Trout behavioural patterns were quantified as space use (utilisation areas 50% and 95%) which was linked to habitat use and selection for J. bulbosus. Removal of J. bulbosus influenced space use of brown trout by reducing the core utilisation area by 22%. Habitat use and selection were likewise influenced by removal with increased use and selection of areas with low J. bulbosus cover (<25%) with corresponding reduction in high J. bulbosus cover (>25-75%). Finally, diurnal differences in space use and habitat use were found, with 19% larger utilisation areas at night and higher use of areas with low J. bulbosus during daytime. Yet, all effect sizes were relatively small compared to the size of the study area. This research provides a detailed case study on the effects of macrophyte removal on fish behavioural patterns in a section of a large Norwegian river with macrophyte mass development. We found no large effects of removal on trout behaviour but noted an increased use of areas with low macrophyte cover. This research is relevant for water managers and policy makers of freshwater conservation and provides a template for using acoustic telemetry to study the effects of macrophyte removal on fish.

Direct evidence of increased natural mortality of a wild fish caused by parasite spillback from domestic conspecifics.

Parasite spillback from domestic animals can distort the balance between host and parasites in surrounding wildlife, with potential detrimental effects on wild populations. In aquatic environments, parasite spillback from aquaculture to wild salmon is one of the most contentious sustainability debates. In a 19 year time series of release group studies of Atlantic salmon, we demonstrated that (i) the effect of subjecting out-migrating salmon smolts to parasite treatment on marine survival has been reduced over a time, (ii) the relation between salmon lice levels in the out-migration route of the salmon and effect of treatment against the parasite is weak, but also (iii) the return rates in both treated and untreated groups of salmon are negatively correlated with salmon lice levels, and (iv) returns of wild salmon to the region are similarly negatively correlated with salmon lice levels during the out-migration year. Our study suggests that salmon lice can have a large effect on wild salmon populations that is not revealed with randomized control trials using antiparasitic drugs. This should be better accounted for when considering the impacts of farms on wild salmon populations.

Expanding conservation culturomics and iEcology from terrestrial to aquatic realms.

The ongoing digital revolution in the age of big data is opening new research opportunities. Culturomics and iEcology, two emerging research areas based on the analysis of online data resources, can provide novel scientific insights and inform conservation and management efforts. To date, culturomics and iEcology have been applied primarily in the terrestrial realm. Here, we advocate for expanding such applications to the aquatic realm by providing a brief overview of these new approaches and outlining key areas in which culturomics and iEcology are likely to have the highest impact, including the management of protected areas; fisheries; flagship species identification; detection and distribution of threatened, rare, and alien species; assessment of ecosystem status and anthropogenic impacts; and social impact assessment. When deployed in the right context with awareness of potential biases, culturomics and iEcology are ripe for rapid development as low-cost research approaches based on data available from digital sources, with increasingly diverse applications for aquatic ecosystems.

The paradox of predation studies.

Understanding the causal relationships that contribute to mortality in populations is a priority for epidemiology, animal husbandry and ecology. Of all the sources of mortality in nature, predation is perhaps the most important, while simultaneously being one of the most difficult to study and understand. In this opinion piece, we use the epidemiological concept of the sufficient-component cause model to outline why we believe that predation studies often misrepresent predators as sufficient cause of death (or natural mortality) in ecological studies. This is pivotal in conservation biology because such studies have often led to demands for predator removal throughout the world. We use the sufficient-component cause model to illustrate the paradox that multiple studies, each studying singular putative causes of mortality (including predation), will sum to more than 100% mortality when added together. We suggest that the sufficient-component framework should be integrated into both fundamental and applied ecology to better understand the role of predators in natural ecosystems.

Application of machine learning and acoustic predation tags to classify migration fate of Atlantic salmon smolts.

Mortality and predation of tagged fishes present a serious challenge to interpreting results of acoustic telemetry studies. There is a need for standardized methods to identify predated individuals and reduce the impacts of "predation bias" on results and conclusions. Here, we use emerging approaches in machine learning and acoustic tag technology to classify out-migrating Atlantic salmon (Salmo salar) smolts into different fate categories. We compared three methods of fate classification: predation tag pH sensors and detection data, unsupervised k-means clustering, and supervised random forest combined with tag pH sensor data. Random forest models increased predation estimates by 9-32% compared to relying solely on pH sensor data, while clustering reduced estimates by 3.5-30%. The greatest changes in fate class estimates were seen in years with large class imbalance (one or more fate classes underrepresented compared to the others) or low model accuracy. Both supervised and unsupervised approaches were able to classify smolt fate; however, in-sample model accuracy improved when using tag sensor data to train models, emphasizing the value of incorporating such sensors when studying small fish. Sensor data may not be sufficient to identify predation in isolation due to Type I and Type II error in predation sensor triggering. Combining sensor data with machine learning approaches should be standard practice to more accurately classify fate of tagged fish.

Effects of tag type and surgery on migration of Atlantic salmon (Salmo salar) smolts.

Tagging salmon smolts to provide information about the timing of outmigration has been a common approach to monitor phenology and model the risk of encountering stressors. However, the validity of tagging has come under scrutiny because of the sensitivity of this parameter in various management systems. We studied the probability of migration, timing of migration and growth during migration for Atlantic salmon smolts tagged with three different tags in the River Dale, western Norway. Two groups were tagged with passive integrated transponder (PIT) tags via a small ventral nonsurgical incision, either a 12 mm or a new 16 mm PIT tag. Two groups were subjected to surgical implantation of either a dummy acoustic transmitter or a 12 mm PIT tag (a sham surgery). Overall, 71% of the tagged smolts were recaptured at the downstream Wolf trap. Smolts from the sham tagged group were recaptured most frequently (78%) compared to dummy acoustic transmitters and 16 mm PIT tags (both 68%), but the differences were not significant. Results agree with prior assessments that longer smolts migrated earlier, with about half a day earlier migration for each millimetre total length of the smolt, but did not suggest any difference in time of migration among the tag types. Growth in length was evident from release to recapture, with smaller smolts exhibiting greater growth and no effect of tagging treatment. Our findings suggest that inferences about the timing of outmigration for salmon smolts based on acoustic tagging should be made cautiously because of the relationship among tag size, suitable fish size and the timing of a tagged individual's migration.

The movement ecology of fishes.

Movement of fishes in the aquatic realm is fundamental to their ecology and survival. Movement can be driven by a variety of biological, physiological and environmental factors occurring across all spatial and temporal scales. The intrinsic capacity of movement to impact fish individually (e.g., foraging) with potential knock-on effects throughout the ecosystem (e.g., food web dynamics) has garnered considerable interest in the field of movement ecology. The advancement of technology in recent decades, in combination with ever-growing threats to freshwater and marine systems, has further spurred empirical research and theoretical considerations. Given the rapid expansion within the field of movement ecology and its significant role in informing management and conservation efforts, a contemporary and multidisciplinary review about the various components influencing movement is outstanding. Using an established conceptual framework for movement ecology as a guide (i.e., Nathan et al., 2008: 19052), we synthesized the environmental and individual factors that affect the movement of fishes. Specifically, internal (e.g., energy acquisition, endocrinology, and homeostasis) and external (biotic and abiotic) environmental elements are discussed, as well as the different processes that influence individual-level (or population) decisions, such as navigation cues, motion capacity, propagation characteristics and group behaviours. In addition to environmental drivers and individual movement factors, we also explored how associated strategies help survival by optimizing physiological and other biological states. Next, we identified how movement ecology is increasingly being incorporated into management and conservation by highlighting the inherent benefits that spatio-temporal fish behaviour imbues into policy, regulatory, and remediation planning. Finally, we considered the future of movement ecology by evaluating ongoing technological innovations and both the challenges and opportunities that these advancements create for scientists and managers. As aquatic ecosystems continue to face alarming climate (and other human-driven) issues that impact animal movements, the comprehensive and multidisciplinary assessment of movement ecology will be instrumental in developing plans to guide research and promote sustainability measures for aquatic resources.

Potential changes to the biology and challenges to the management of invasive sea lamprey Petromyzon marinus in the Laurentian Great Lakes due to climate change.

Control programs are implemented to mitigate the damage caused by invasive species worldwide. In the highly invaded Great Lakes, the climate is expected to become warmer with more extreme weather and variable precipitation, resulting in shorter iced-over periods and variable tributary flows as well as changes to pH and river hydrology and hydrogeomorphology. We review how climate change influences physiology, behavior, and demography of a damaging invasive species, sea lamprey (Petromyzon marinus), in the Great Lakes, and the consequences for sea lamprey control efforts. Sea lamprey control relies on surveys to monitor abundance of larval sea lamprey in Great Lakes tributaries. The abundance of parasitic, juvenile sea lampreys in the lakes is calculated by surveying wounding rates on lake trout (Salvelinus namaycush), and trap surveys are used to enumerate adult spawning runs. Chemical control using lampricides (i.e., lamprey pesticides) to target larval sea lamprey and barriers to prevent adult lamprey from reaching spawning grounds are the most important tools used for sea lamprey population control. We describe how climate change could affect larval survival in rivers, growth and maturation in lakes, phenology and the spawning migration as adults return to rivers, and the overall abundance and distribution of sea lamprey in the Great Lakes. Our review suggests that Great Lakes sea lamprey may benefit from climate change with longer growing seasons, more rapid growth, and greater access to spawning habitat, but uncertainties remain about the future availability and suitability of larval habitats. Consideration of the biology of invasive species and adaptation of the timing, intensity, and frequency of control efforts is critical to the management of biological invasions in a changing world, such as sea lamprey in the Great Lakes.

Sentiment analysis as a measure of conservation culture in scientific literature.

Culturomics is emerging as an important field within science, as a way to measure attitudes and beliefs and their dynamics across time and space via quantitative analysis of digitized data from literature, news, film, social media, and more. Sentiment analysis is a culturomics tool that, within the last decade, has provided a means to quantify the polarity of attitudes expressed within various media. Conservation science is a crisis discipline; therefore, accurate and effective communication are paramount. We investigated how conservation scientists communicate their findings through scientific journal articles. We analyzed 15,001 abstracts from articles published from 1998 to 2017 in 6 conservation-focused journals selected based on indexing in scientific databases. Articles were categorized by year, focal taxa, and the conservation status of the focal species. We calculated mean sentiment score for each abstract (mean adjusted z score) based on 4 lexicons (Jockers-Rinker, National Research Council, Bing, and AFINN). We found a significant positive annual trend in the sentiment scores of articles. We also observed a significant trend toward increasing negativity along the spectrum of conservation status categories (i.e., from least concern to extinct). There were some clear differences in the sentiments with which research on different taxa was reported, however. For example, abstracts mentioning lobe finned fishes tended to have high sentiment scores, which could be related to the rediscovery of the coelacanth driving a positive narrative. Contrastingly, abstracts mentioning elasmobranchs had low scores, possibly reflecting the negative sentiment score associated with the word shark. Sentiment analysis has applications in science, especially as it pertains to conservation psychology, and we suggest a new science-based lexicon be developed specifically for the field of conservation.

El Análisis de Opinión como Medida de la Cultura de Conservación en la Literatura Científica Lennox et al. Resumen La culturomía está emergiendo como un campo importante dentro de la ciencia pues es una manera de medir las actitudes, creencias y sus dinámicas a través del tiempo y el espacio por medio de un análisis cuantitativo de datos digitalizados a partir de la literatura, las noticias, las películas, las redes sociales y otros medios. El análisis de opinión es una herramienta de la culturomía que, en la última década, ha proporcionado los medios para cuantificar la polaridad de las actitudes expresadas en varios medios. La ciencia de la conservación es una disciplina de crisis; por lo tanto, la comunicación certera y efectiva es de suma importancia. Investigamos cómo los científicos de la conservación comunican sus hallazgos por medio de los artículos en las revistas científicas. Analizamos 15,001 resúmenes de artículos publicados entre 1998 y 2017 en seis revistas enfocadas en la conservación que fueron seleccionados con base en los índices de las bases de datos científicos. Categorizamos los artículos por año, taxón de enfoque y el estado de conservación de la especie focal. Calculamos la opinión promedio para cada resumen (puntaje z ajustado a la media) con base en cuatro lexicones (Jockers-Rinker, National Research Council, Bing y AFINN). Encontramos una significativa tendencia positiva anual en los puntajes de opinión de los artículos. También observamos una tendencia significativa hacia el incremento en la negatividad a lo largo del espectro de categorías de estado de conservación (es decir, de aquellas de menos preocupación a aquellas en peligro crítico o extintas). Sin embargo, hubo algunas diferencias claras en las opiniones con las cuales se reportaron las investigaciones sobre los diferentes taxones. Por ejemplo, los resúmenes que mencionaron a los peces de aletas lobuladas tendieron hacia los puntajes altos de opinión, lo que podría relacionarse con el redescubrimiento del celacanto como causa de una narrativa positiva. En contraste, los resúmenes que mencionaron a los elasmobranquios tuvieron puntajes bajos, lo que refleja el puntaje de opinión negativa asociado con la palabra tiburón. El análisis de opinión tiene aplicaciones en la ciencia, especialmente como parte de la psicología de la conservación, y sugerimos que se desarrolle un nuevo lexicón basado en la ciencia específicamente para el campo de la conservación.

How pathogens affect the marine habitat use and migration of sea trout (Salmo trutta) in two Norwegian fjord systems.

Wild fish are confronting changing pathogen dynamics arising from anthropogenic disturbance and climate change. Pathogens can influence animal behaviour and life histories, yet there are little such data from fish in the high north where pathogen dynamics may differ from comparatively southern regions. We aimed to compare the pathogen communities of 160 wild anadromous brown trout in two fjords in northern Norway and to determine whether pathogens influenced area use or return to spawn. Application of high-throughput qPCR detected 11 of the 46 pathogens screened for; most frequently encountered were Ichthyobodo spp., Flavobacterium psychrophilum and Candidatus Branchiomonas cysticola. The rate of returning to freshwater during the spawning season was significantly lower for the Skjerstadfjord fish. Piscichlamydia salmonis and F. psychrophilum were indicator species for the Skjerstadfjord and pathogen communities in the two fjords differed according to perMANOVA. Individual length, Fulton's condition factor and the time between first and last detection of the fish were not related to the presence of pathogens ordinated using non-metric multidimensional scaling (NMDS). However, there was evidence that pathogen load was correlated with the expression of smoltification genes, which are upregulated by salmonids in freshwater. Correspondingly, percentage of time in freshwater after release was longer for fish with greater pathogen burdens.

Susceptibility of European freshwater fish to climate change: Species profiling based on life-history and environmental characteristics.

Climate change is expected to strongly affect freshwater fish communities. Combined with other anthropogenic drivers, the impacts may alter species spatio-temporal distributions and contribute to population declines and local extinctions. To provide timely management and conservation of fishes, it is relevant to identify species that will be most impacted by climate change and those that will be resilient. Species traits are considered a promising source of information on characteristics that influence resilience to various environmental conditions and impacts. To this end, we collated life-history traits and climatic niches of 443 European freshwater fish species and compared those identified as susceptible to climate change to those that are considered to be resilient. Significant differences were observed between the two groups in their distribution, life history, and climatic niche, with climate-change-susceptible species being distributed within the Mediterranean region, and being characterized by greater threat levels, lesser commercial relevance, lower vulnerability to fishing, smaller body and range size, and warmer thermal envelopes. Based on our results, we establish a list of species of highest priority for further research and monitoring regarding climate-change susceptibility within Europe. The presented approach represents a promising tool to efficiently assess large groups of species regarding their susceptibility to climate change and other threats, and to identify research and management priorities.

Life-history characteristics of an exploited bonefish Albula glossodonta population in a remote South Pacific atoll.

Bonefishes Albula spp. are important components of subsistence fisheries and lucrative sport fishing industries throughout their circumtropical distribution. In Oceania, however, Albula spp. have historically been overexploited and there is a growing need to balance the demands of competing fishing sectors, making the description of their life history a regional priority. To this aim, we collected biological samples from Albula spp. of Anaa atoll, French Polynesia, to identify the species that compose the stock and estimate their life-history parameters including age, growth, reproduction and natural mortality. Our results indicate that Albula glossodonta is the species of bonefish present, with a maximum age that is below the, 20 year longevity of the genus (8 years in males and 10 years in females). Differential growth patterns existed between the two sexes (L∞ = 58, 78 cm fork length (LF ) and K = 0.38, 0.21 for males and females, respectively). Males attained sexual maturity at 43 cm LF (c. 3 years) whereas females matured at 48 cm LF (c. 4 years) and oocyte production was significantly related to body mass, with a maximum batch fecundity of 1,133,767 oocytes in a 4406 g (70 cm LF ) female. The gonado-somatic index of harvested fishes indicated that the spawning season extends from March through September. Based on the observation of a, 20 year bonefish at the proximate Tetiaroa Atoll and several empirical models, estimates of natural mortality ranged from 0.21 to 0.68; however, an estimate of 0.21 was deemed most appropriate. This information facilitated the resurgence of a Rahui (temporary fishing closure) and community-based management to protect A. glossodonta during a critical portion of their spawning season and in this context our results provide an important demographic baseline in evaluating the recovery of this fishery.

Searching for responsible and sustainable recreational fisheries in the Anthropocene.

Recreational fisheries that use rod and reel (i.e., angling) operate around the globe in diverse freshwater and marine habitats, targeting many different gamefish species and engaging at least 220 million participants. The motivations for fishing vary extensively; whether anglers engage in catch-and-release or are harvest-oriented, there is strong potential for recreational fisheries to be conducted in a manner that is both responsible and sustainable. There are many examples of recreational fisheries that are well-managed where anglers, the angling industry and managers engage in responsible behaviours that both contribute to long-term sustainability of fish populations and the sector. Yet, recreational fisheries do not operate in a vacuum; fish populations face threats and stressors including harvest from other sectors as well as environmental change, a defining characteristic of the Anthropocene. We argue that the future of recreational fisheries and indeed many wild fish populations and aquatic ecosystems depends on having responsible and sustainable (R&S) recreational fisheries whilst, where possible, addressing, or at least lobbying for increased awareness about the threats to recreational fisheries emanating from outside the sector (e.g., climate change). Here, we first consider how the concepts of R&S intersect in the recreational fishing sector in an increasingly complex socio-cultural context. Next, we explore the role of the angler, angling industry and decision-makers in achieving R&S fisheries. We extend this idea further by considering the consequences of a future without recreational fisheries (either because of failures related to R&S) and explore a pertinent case study situated in Uttarakahand, India. Unlike other fisheries sectors where the number of participants is relatively small, recreational angling participants are numerous and widespread, such that if their actions are responsible, they have the potential to be a key voice for conservation and serve as a major force for good in the Anthropocene. What remains to be seen is whether this will be achieved, or if failure will occur to the point that recreational fisheries face increasing pressure to cease, as a result of external environmental threats, the environmental effects of recreational fishing and emerging ethical concerns about the welfare of angled fish.

Estimating fish swimming metrics and metabolic rates with accelerometers: the influence of sampling frequency.

Accelerometry is growing in popularity for remotely measuring fish swimming metrics, but appropriate sampling frequencies for accurately measuring these metrics are not well studied. This research examined the influence of sampling frequency (1-25 Hz) with tri-axial accelerometer biologgers on estimates of overall dynamic body acceleration (ODBA), tail-beat frequency, swimming speed and metabolic rate of bonefish Albula vulpes in a swim-tunnel respirometer and free-swimming in a wetland mesocosm. In the swim tunnel, sampling frequencies of ≥ 5 Hz were sufficient to establish strong relationships between ODBA, swimming speed and metabolic rate. However, in free-swimming bonefish, estimates of metabolic rate were more variable below 10 Hz. Sampling frequencies should be at least twice the maximum tail-beat frequency to estimate this metric effectively, which is generally higher than those required to estimate ODBA, swimming speed and metabolic rate. While optimal sampling frequency probably varies among species due to tail-beat frequency and swimming style, this study provides a reference point with a medium body-sized sub-carangiform teleost fish, enabling researchers to measure these metrics effectively and maximize study duration.

Influence of harvest restrictions on angler release behaviour and size selection in a recreational fishery.

Fishing regulations such as harvest restrictions are implemented to limit the exploitation of many fish stocks and ensure the sustainability of fisheries. In Norway, inland recreational fisheries are co-managed by the government and by local riparian rights holders, meaning that Atlantic salmon Salmo salar harvest restrictions differ somewhat among rivers. Data from Norwegian rivers from 2009 to 2013 were used to test for variation in the proportion of salmon released by anglers and the relative size of salmon harvested and released by anglers in rivers that had varying harvest restrictions in terms of quotas, size restrictions, and/or female harvest restrictions. The proportion of the catch released by anglers was higher in rivers where there were harvest restrictions (proportion released = 0.09-0.24) than in rivers with no such restrictions (proportion released = 0.01). On average, salmon released in rivers with size restrictions larger (average mass difference between harvested and released salmon = -1.25 kg) than those released in rivers without harvest restrictions (difference = 0.60 kg). The proportion of the catch released was larger in rivers with seasonal quotas (0.29) than in rivers with daily (0.07) or collective (i.e. total catch for the river; 0.06) quotas. Rivers with low daily (one salmon per angler per day) or seasonal (<5 salmon per angler per year) quotas had a larger proportion of salmon released (0.23, 0.38, respectively) than rivers with moderate (0.10, 0.21) or high (0.07, 0.16) quotas. High seasonal quotas resulted in larger individuals harvested than released (difference = 1.16 kg), on average, compared to moderate (1.22 kg) and high seasonal quotas (-0.30 kg). We conclude that harvest restrictions influenced the extent to which fish were released and thus the stock composition (i.e. size distribution) escaping the recreational fishery with the potential to spawn.

Habitat and movement selection processes of American lobster/jakej within a restricted bay in the Bras d'Or Lake/Pitu'paq, Nova Scotia, Canada.

American lobster inhabit the unique, brackish Bras d'Or Lake system, although densities are low compared to areas with similar habitats in the Atlantic Ocean. Nevertheless, lobsters are an important part of local First Nation (Mi'kmaq) food and culture. We used acoustic telemetry and habitat mapping, combined with local Mi'kmaw knowledge, to document the movements and habitat use of adult lobsters within a section of the Lake. Movement patterns of acoustically tagged individual lobsters were analyzed with both resource selection functions and integrated step selection functions using data obtained from a high-resolution VEMCO Positioning System within a restricted bay in the Bras d'Or Lake. The resource selection function suggested stronger selections of substrates that contained a combination of soft and hard sediments. While the integrated step selection functions found substantial individual variability in habitat selections, there was a trend for lobsters to exhibit more resident behaviour on the combined soft/hard substrates despite the fact these sediments provided little in the way of obvious shelters for the animals. Adult lobsters at this site have very little risk of predation, which presumably allows them to freely exhibit exploratory behaviours and reduce their association with substrates that provide shelters.

Seasonal habitat use and diel vertical migration in female spurdog in Nordic waters.

BACKGROUND: Studying habitat use and vertical movement patterns of individual fish over continuous time and space is innately challenging and has therefore largely remained elusive for a wide range of species. Amongst sharks, this applies particularly to smaller-bodied and less wide-ranging species such as the spurdog (Squalus acanthias Linnaeus, 1758), which, despite its importance for fisheries, has received limited attention in biologging and biotelemetry studies, particularly in the North-East Atlantic. METHODS: To investigate seasonal variations in fine-scale niche use and vertical movement patterns in female spurdog, we used archival data from 19 pregnant individuals that were satellite-tagged for up to 365 days in Norwegian fjords. We estimated the realised niche space with kernel densities and performed continuous wavelet analyses to identify dominant periods in vertical movement. Triaxial acceleration data were used to identify burst events and infer activity patterns. RESULTS: Pregnant females frequently utilised shallow depths down to 300 m at temperatures between 8 and 14 °C. Oscillatory vertical moments revealed persistent diel vertical migration (DVM) patterns, with descents at dawn and ascents at dusk. This strict normal DVM behaviour dominated in winter and spring and was associated with higher levels of activity bursts, while in summer and autumn sharks predominantly selected warm waters above the thermocline with only sporadic dive and bursts events. CONCLUSIONS: The prevalence of normal DVM behaviour in winter months linked with elevated likely foraging-related activity bursts suggests this movement behaviour to be foraging-driven. With lower number of fast starts exhibited in warm waters during the summer and autumn months, habitat use in this season might be rather driven by behavioural thermoregulation, yet other factors may also play a role. Individual and cohort-related variations indicate a complex interplay of movement behaviour and habitat use with the abiotic and biotic environment. Together with ongoing work investigating fine-scale horizontal movement as well as sex- and age-specific differences, this study provides vital information to direct the spatio-temporal distribution of a newly reopened fishery and contributes to an elevated understanding of the movement ecology of spurdog in the North-East Atlantic and beyond.

Assessing the potential for gas supersaturation downstream of hydropower plants in Norway, Austria and Germany.

Hydroelectric power facilities can generate episodic total dissolved gas supersaturation (TDGS), which is harmful to aquatic life. We developed a decision tree-based risk assessment to identify the potential for TDGS at hydropower plants and conducted validation measurements at selected facilities. Applying the risk model to Norway's hydropower plants (n = 1696) identified 473 (28 %) high-risk plants characterized by secondary intakes and Francis or Kaplan turbines, which are prone to generating TDGS when air is entrained. More than half of them discharge directly to rivers (283, 17 % of total). Measurements at 11 high-risk plants showed that 8 of them exhibited biologically relevant TDGS (120 % to 229 %). In Austria and Germany, the analysis of hydropower plants was limited due to significant data constraints. Out of 153 hydropower plants in Austria, 80 % were categorized at moderate risk for TDGS. Two Austrian plants were monitored, revealing instances of TDGS in both (up to 125 %). In Germany, out of 403 hydropower plants, 265 (66 %) fell into the moderate risk, with none in the high-risk category. At a dam in the Rhine River, TDGS up to 118 % were observed. Given the uncertainty due to limited data access and the prevalence of run-of-river plants in Austria and Germany, there remains an unclarified risk of TDGS generation in these countries, especially at spillways of dams and below aerated turbines. The results indicate a previously overlooked potential for the generation of biologically harmful TDGS at hydropower installations. It is recommended to systematically screen for TDGS at hydropower installations through risk assessment, monitoring, and, where needed, the implementation of mitigation measures. This is increasingly critical considering the expanding global initiatives in hydropower and efforts to maintain the ecological status of freshwater ecosystems.

Animal migration in the Anthropocene: threats and mitigation options.

Animal migration has fascinated scientists and the public alike for centuries, yet migratory animals are facing diverse threats that could lead to their demise. The Anthropocene is characterised by the reality that humans are the dominant force on Earth, having manifold negative effects on biodiversity and ecosystem function. Considerable research focus has been given to assessing anthropogenic impacts on the numerical abundance of species/populations, whereas relatively less attention has been devoted to animal migration. However, there are clear linkages, for example, where human-driven impacts on migration behaviour can lead to population/species declines or even extinction. Here, we explore anthropogenic threats to migratory animals (in all domains - aquatic, terrestrial, and aerial) using International Union for the Conservation of Nature (IUCN) Threat Taxonomy classifications. We reveal the diverse threats (e.g. human development, disease, invasive species, climate change, exploitation, pollution) that impact migratory wildlife in varied ways spanning taxa, life stages and type of impact (e.g. from direct mortality to changes in behaviour, health, and physiology). Notably, these threats often interact in complex and unpredictable ways to the detriment of wildlife, further complicating management. Fortunately, we are beginning to identify strategies for conserving and managing migratory animals in the Anthropocene. We provide a set of strategies that, if embraced, have the potential to ensure that migratory animals, and the important ecological functions sustained by migration, persist.