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Acoustic telemetry represents the state-of-the-art technology for monitoring behaviour of aquatic organisms in the wild. Yet, the performance of different systems is rarely evaluated across species and environments. In this study, we evaluate two different acoustic telemetry systems, a commonly used analogue pulse-position-modulation-based system (VEMCO PPM) and a newly developed high-residency digital binary phase shift key-based system (VEMCO HR2), in ability to track downstream migrating Atlantic salmon smolt (Salmo salar) and European eel (Anguilla anguilla) around hydropower facilities. High-precision GPS were used to evaluate precision and accuracy of hyperbolically positioned data derived from each system. The PPM-based system had higher detection range than HR2 and generated more positions per transmission for eels migrating close to bottom than for surface-oriented salmon smolts. HR2 generated tenfold more positions per time unit than PPM, were less sensitive to noise, achieved submetre positional precision, and were considerably more accurate than PPM-derived positions after filtering. HR2 was deemed more capable than PPM in fine-scale positioning at moderate distances at hydropower facilities. La telemetrie acoustique represente la fine pointe de la technologie pour la surveillance des comportements d'organismes aquatiques dans la nature. La performance des differents systemes de telemetrie est toutefois rarement evaluee pour differentes especes et differents milieux. Nous evaluons deux systemes de telemetrie acoustique, soit un systeme analogue base sur la modulation de la localisation des impulsions (VEMCO PPM) couramment utilise et un systeme numerique mis au point recemment a long temps de residence base sur la modulation binaire a deplacement de phase (VEMCO HR2), afin d'etablir leur capacite de suivre des saumoneaux de saumon atlantique (Salmo salar) et des anguilles europeennes (Anguilla anguilla) en devalaison pres d'installations hydroelectriques. Le GPS de haute precision est utilise pour evaluer la precision et l'exactitude de donnees de localisation hyperbolique obtenues de chacun des systemes. Le systeme PPM a une meilleure portee de detection que le systeme HR2 et produit plus de localisations par transmission pour les anguilles migrant pres du fond que pour les saumoneaux qui demeurent plus pres de la surface. Le systeme HR2 produit dix fois plus d'emplacements par unite de temps que le systeme PPM, est moins sensible au bruit, atteint une precision submetrique de la localisation et donne des emplacements considerablement plus exacts que le systeme PPM apres filtrage. Les capacites du systeme HR2 sont jugees plus grandes que celles du systeme PPM pour la localisation a echelle fine a des distances moderees d'installations hydroelectriques. [Traduit par la Redaction], Introduction High-resolution data on fish behaviour and migration are becoming increasingly important in fisheries management and research (Hussey et al. 2015), as well as in aquatic ecotoxicology and conservation (Crossin [...]

Human‐mediated dispersal of non‐native earthworms can cause substantial changes to the functioning and composition of ecosystems previously earthworm‐free. Some of these earthworm species have the potential to "geoengineer" soils and increase plant nitrogen (N) uptake. Yet the possible consequences of increased plant N concentrations on rodent grazing remains poorly understood. In this study, we present findings from a common garden experiment with two tundra communities, meadow (forb dominated) and heath (shrub dominated), half of them subjected to 4 years of earthworm presence (Lumbricus spp. and Aporrectodea spp.). Within four summers, our earthworm treatment changed plant community composition by increasing graminoid density by, on average, 94% in the heath vegetation and by 49% in the meadow. Rodent winter grazing was more intense on plants growing in soils with earthworms, an effect that coincided with higher N concentrations in plants, indicating a higher palatability. Even though earthworms reduced soil moisture, plant community productivity, as indicated by vegetation greenness (normalized difference vegetation index), was not negatively impacted. We conclude that earthworm‐induced changes in plant composition and trophic interactions may fundamentally alter the functioning of tundra ecosystems. [ABSTRACT FROM AUTHOR]

Salmonid repeat spawners are precious individuals for wild populations due to their high fecundity and previous spawning experience, making them important in environmental policy. However, repeat spawners rarely exist above hydropower dams in regulated rivers as the mortality of post‐spawners (kelts) when passing through turbines during downstream migration is very high. To mitigate this problem, there are different technical solutions that potentially guide fish toward available fishways. Bubble barriers represent one alternative to costly physical guiding structures, but the efficiency of bubbles for guiding downstream migrating kelts has not been tested. In this study, we evaluate a 100 m long bubble barrier in guiding salmonids—both smolts and kelts—away from the main current and toward an alternative fishway in Ume River, a large regulated river in northern Sweden. We used both acoustic telemetry and sonar to measure the guiding effect of the bubble barrier for downstream migrating fish. We found that more than twice as many salmonids chose the alternative fishway when the bubble barrier was turned on. This was true both for smolts and kelts, suggesting that bubble barriers can be used to guide salmonids of different life stages in rivers with flow rates over 500 m3 s−1. Indeed, our study indicates that bubble barriers are low‐cost structures that could be rapidly applied in many regulated rivers to support salmonid migration. [ABSTRACT FROM AUTHOR]

Northern soils play an important role in Earth’s climate system as they store large amounts of carbon that, if released, could strongly increase greenhouse gas levels in our atmosphere. Most research to date has focused on how the turnover of organic matter in these soils is regulated by abiotic factors and few studies have considered the potential role of biotic regulation. Here, we claim that soil organisms’ presence or absence is key to understanding and predicting future climate feedbacks from northern soils. We propose that the arrival of soil organisms with currently ‘missing traits’, i.e., properties that the present community does not have, can alleviate functional limitation and result in greatly enhanced decomposition rates, in parity with effects predicted due to increasing temperatures. We base this argument on a series of emerging evidence suggesting that the dispersal of until-then absent micro-, meso- and macro-organisms (i.e., microbes and invertebrate soil fauna) into new regions and newly-thawed soil layers can drastically affect soil functioning. These new observations make us question the current view that neglects organism driven ‘alleviation effects’ when predicting the future feedbacks between northern ecosystems and our planets’ climate. We therefore advocate for an updated framework in which soil biota and their traits become essential when predicting the fate of soil functions in warming northern ecosystems. [ABSTRACT FROM AUTHOR]