Automated fluvial hydromorphology mapping from airborne remote sensing

Mapping fluvial hydromorphology is an important part of defining river habitat. Mappingvia field sampling or hydraulic modelingis however time consuming, and mappinghydromorphology directly from remote sensing data may offer an efficient solution.Here, we present a system for automated classification of fluvial hydromorphologybased on a deep learning classification scheme applied to aerial orthophotos. Usingselected rivers in Norway, we show how surface flow patterns (smooth or rippled sur-faces vs. standing waves) can be classified in imagery using a trained convolutional neu-ral network (achieving a training and validation accuracy of >95%). We show howintegration of these classified surface flow patterns with information on channel gradi-ent, obtained from airborne topographic LiDAR data, can be used to compartmentalizethe rivers into hydromorphological units(HMUs) that represent the dominant flow fea-tures. Automated classifications were broadly consistent with manual classifications thathad been made in previous ground surveys, with equivalency in automated and manu-ally derived HMU classes ranging from 61.5% to 87.7%, depending on the river stretchconsidered. They were found to be discharge-dependent, showing the temporallydynamic aspect of hydromorphology. The proposed system is quick, flexible, generaliz-able, and provides consistent classifications free from interpretation bias. The deeplearning approach used here can be customized to provide more detailed information onflow features, such as delineating between standing waves and advective diffusion ofair bubbles/foam, to provide a more refined classification of surface flow patterns, andthe classification approach can be furtheradvanced by inclusion of additional remotesensing methods that provide further information on hydromorphological features.publishedVersio

Modelling the effect of hydropeaking‐induced stranding mortality on Atlantic salmon population abundance

Studies of hydropeaking‐induced stranding mortality on fish populations have been confined to analysis of empirical data and/or short‐term hydraulic‐habitat modelling of individual events and are thus limited as to how they may be used to infer long‐term effects in fish populations. In this study, the effects of stranding mortality on an Atlantic salmon population were simulated using an individual‐based Atlantic salmon population model with the objective of determining the sensitivity of population dynamics to stranding. It was found that density‐dependent mortality (an alternative source of mortality in juvenile Atlantic salmon) partially compensated for stranding mortality, acting as a negative feedback mechanism that dampened change in population abundance. Stranding caused a perturbation in population dynamics, and effects of individual stranding events persisted in time across the life stages of the population. Effects on population abundance depended on the time of year when stranding was applied, both because of intra‐annual changes in stranding mortality probability and because of intra‐annual changes in the ability of density‐dependent mortality to compensate for stranding mortality. We concluded that empirical measurements of stranding mortality have limited potential for inference of overall effects on the population, and a more dynamic modelling approach, incorporating system feedback, allows for a better modelling of the impact of stranding. Sensitivity analysis showed that population abundance was highly sensitive to density‐dependent mortality, and we suggest that this area should be prioritized for further research when investigating the effects of hydropeaking on rivers.acceptedVersio

Multi-criteria decision analysis in Bayesian networks-Diagnosing ecosystem service trade-offs in a hydropower regulated river

The paper demonstrates the use of Bayesian networks in multicriteria decision analysis (MCDA) of environmental design alternatives for environmental flows (eflows) and physical habitat remediation measures in the Mandalselva River in Norway. We demonstrate how MCDA using multi-attribute value functions can be implemented in a Bayesian network with decision and utility nodes. An object-oriented Bayesian network is used to integrate impacts computed in quantitative sub-models of hydropower revenues and Atlantic salmon smolt production and qualitative judgement models of mesohabitat fishability and riverscape aesthetics. We show how conditional probability tables are useful for modelling uncertainty in value scaling functions, and variance in criteria weights due to different stakeholder preferences. While the paper demonstrates the technical feasibility of MCDA in a BN, we also discuss the challenge

Bias in estimates of electrofishing capture probability of juvenile Atlantic salmon

We evaluated the effect of the total number of passes used, and the application of block nets, on multi-pass electrofishing removal sampling for estimating juvenile Atlantic salmon (Salmo salar L.) abundance and body size distribution. Sites within selected salmon-bearing Norwegian rivers were enclosed by block nets and electrofished for multiple passes (range: 7–13), and capture probabilities and abundances were estimated using the Carle and Strub removal method. We examined for different body size classes: (1) bias in the estimated capture probability and abundance associated with the number of passes used; (2) the potential for bias to be minimized by the use of block nets; and (3) electrofishing-induced mortality. We found that the capture probability estimate was strongly dependent upon the number of passes used, tending to decline with successive pass, with the effect depending on size class. Thus, estimates made using the traditional three-pass approach would result in underestimates of abundance, and biased estimates of size distribution. Smaller juveniles were both more likely to impinge on the block nets and more likely to experience mortality than larger juveniles. Mortality was greatest when water temperature was high (> 18 °C). Our findings indicate that quantitative electrofishing for small juveniles may be unreliable, and that electrofishing at high temperatures should be avoided due to potential high mortality. Atlantic salmon Electrofishing Multi-pass removal Net capture MortalityBias in estimates of electrofishing capture probability of juvenile Atlantic salmonacceptedVersio

Net-biting and escape behaviour in farmed Atlantic cod Gadus morhua: effects of feed stimulants and net traits

Preventing farmed fish from escaping sea cages is a major challenge for developing sustainable aquaculture practices. In this study, the individual behaviour of Atlantic cod Gadus morhua to inspect and bite the net was investigated in 4 replicate multi-patch experiments, using underwater video techniques and behavioural event recording. The experimental system included a tank enclosure where cod were presented with 6 separate net panels: duplicate pairs of plain control nets and 2 different treatment panels. Four holes were made in the treatment panels, 3 of which were mended with different repair techniques including short and loose thread ends and contrasting colour repair threads. Behavioural effects of feed stimulants were studied before, during and after a feed source was placed outside the net. The cod inspected and bit the net systematically, significantly focusing on loose threads or minor damage on the net, and the fish were capable of causing severe net damage within a few days. The observed behaviours were related to hunger level and feed stimulation, and increased significantly during times when a feed source was present outside the net wall. Few bites were observed, and almost no measureable damage was recorded to plain control panels and the area around unrepaired holes during the treatment. Repairs made with white and black threads, and loose, long ends were significantly more damaged than repairs made with short thread ends and threads of similar colour as the net. The experiments demonstrated how a behavioural approach might be used in interpretation of a practical problem in aquaculture, and the results will be useful in the development of technology and escape mitigation strategies.Financial support for this study was provided by the EU project Prevent Escape, the Norwegian Research Council through the strategic research project Acoma (AS31649), and the project SECURE 184974/S40

Revealing the full ocean migration of individual Atlantic salmon

Knowledge of the complete horizontal migration and vertical movements of Atlantic salmon (Salmo salar L.) during the marine phase is important for understanding the link between individual processes and population recruitment. We studied the detailed migration behaviour of six post-spawned adult Atlantic salmon from a North Norwegian river, during the entire ocean migration, by using high-resolution light-based geolocation archival tags. The fish performed long-distance migrations and utilized Arctic areas from the eastern Barents Sea, to areas of Jan Mayen Island, and north to Svalbard. Four of six individuals exhibited a strong fidelity towards Jan Mayen Island, particularly during winter, which may suggest that the ecological conditions in these waters may be important for overwintering. One fish displayed exclusive utilization of the Barents Sea, indicating that growth and survival of some individuals are entirely dependent on these waters. The fish displayed a pelagic behaviour and all individuals spent more than 83% of the time in the uppermost 10 m of the water column. There was a strong seasonal trend in diving intensity, with the number of dives increasing with day length, independent of individuals’ spatial distribution. Diving depth was positively correlated with the depth of the mixed layer. The Atlantic salmon displayed large individual variation in horizontal migrations, utilizing different ocean areas north of the Arctic Circle. This means that, despite the overall fidelity towards northern latitudes, individuals from the same population may experience highly different ecological conditions, potentially contributing to within-population variation in growth and survival. The seasonal correlation between diving intensity and day length, and spatial correlation between diving depth and depth of the mixed layer, indicate that the overall depth use of the Atlantic salmon depends on both spatially independent seasonal factors, and dynamic oceanographic conditions that facilitate food aggregations. This is the first study of Atlantic salmon to present detailed information about individuals’ continuous horizontal migration and simultaneous vertical movements during the entire ocean migration, thus providing novel information on how habitat use change throughout the ocean residency

Automatisk posisjonering av akustisk merket smolt i tre dimensjoner – utprøving og evaluering i Mandalsvassdraget.

Et nytt system som kan gi tredimensjonal (3D) posisjonering av smolt ved hjelp av trådløs akustisk telemetri ble utprøvd og evaluert i Mandalsvassdraget sommeren 2014. I forsøkene ble signaler fra akustiske merker logget i et system med fastmonterte trådløse hydrofoner i ku-biske arrangement. Det ble gjennomført forsøk både i Mannflåvann (optimalt oppsett) og to forsøk ved inntaket til Laudal kraftverk (et mer utfordrende oppsett). Merkene ble i begge oppsettene 3D-posisjonert med høy presisjon (verifisert med høyoppløse-lig GPS) og effektivitet (andel signal som ga en posisjon). Bevegelsen til merker som ble slept gjennom oppsettene ble også 3D-lokalisert med høy presisjon. Det utviklede analyseverktøyet (YAPS, skrevet i statistikkprogrammet R) var godt egnet til tredimensjonal posisjonering, og fungerte bedre enn kommersielt tilgjengelig programvare for todimensjonal posisjonering. Resultatene fra utprøvingen viste at 3D posisjonering av smolt merket med små akustiske sendere kan gjennomføres ved hjelp av frittstående, trådløse akustiske loggere. Dette har tidli-gere ikke vært mulig, fordi akustiske merker med dybdesensorer er for store til å brukes på smolt. Med det utviklede verktøyet er det mulig å spore merket fisk med høy presisjon (<1 m) i tre dimensjoner ved inntaksrista til Laudal kraftverk og i andre lignende lokaliteter. 3D-metodikken kan kombineres med 2D-sporing som kan dekke et mye større areal. For framtidig sporing av nedvandrende smolt i Mandalselva anbefales det derfor en kombinasjon av detaljert 3D sporing rett foran tunnelinntaket og 2D-sporing som dekker hele elvetverrsnittet. Mandalsvassdraget, Marnardal, Vest-Agder, laksefisk, smolt, metodeutvikling, programvareutvikling, telemetri, hydroakustikk, River Mandal, Vest-Agder county, Salmonid fishes, smolts, method development, programming, telemetry, hydroacousticsA new system developed for three-dimensional tracking of salmonid smolts using wireless acoustic telemetry was tested and evaluated in the River Mandal watercourse in southern Norway during summer 2014. Signals from acoustic tags were monitored on an array of wireless hydrophones in cubic arrangements in two localities - in an ideal setting (in terms of turbulence and potential echoes from the surroundings) in the lake Mannflå and a more challenging setting in front of the hydropower intake to Laudal hydropower plant (with dynamic velocity patterns and concrete walls). At both sites tags were 3D-positioned with high precision (verified with high resolution GPS positioning) and high efficiency (the percentage of transmitted signals that resulted in successful positioning). The trajectories of tags dragged through the setups were also recorded accurately. The developed data analysis system (YAPS, scripted in the statistical software R) showed successful performance for 3D-positioning and outperformed the commercially available software for 2D-positioning. The present study showed that salmonid smolts can be tracked with sub meter accuracy by a wireless acoustic telemetry system in 3D. Previous systems needed depth sensors in the tag making the tags too large to be attached to wild salmon smolts. The study also showed that detailed 3D-tracking in the vicinity of hydropower structures (e.g. hydropower intakes and trashracks) can be combined with 2D-tracking covering the whole river transect.© Norsk institutt for naturforskning. Publikasjonen kan siteres fritt med kildeangivelse

Identification of salmon population bottlenecks from low flows in a hydro-regulated river

Flow regime alterations from hydropower regulation may impact fish populations. Impacts can be characterized using methods for mapping bottlenecks for different species life stages. Improving the understanding of such bottlenecks could provide a basis for mitigation measures. An integrated modelling approach coupling a salmon population model (IB-salmon), a hydraulic 1D model (HEC-RAS) and a temperature model (Air2Stream) was used to identify the bottlenecks constraining the salmon population in a hydro-regulated river (Ljungan River, Sweden). This integrated approach evaluated changes in the salmon population under different low flow scenarios, involving potential dewatering of spawning sites, and the effect of restored spawning sites. Model results demonstrated that low discharges in winter and summer were potential hydrological bottlenecks for the salmon population, particularly in winter due to potential dewatering of spawning sites. Restoration of spawning sites increased salmon production under all scenarios, posing a potential counter measure against low flows

Identification of salmon population bottlenecks from low flows in a hydro-regulated river

Flow regime alterations from hydropower regulation may impact fish populations. Impacts can be characterized using methods for mapping bottlenecks for different species life stages. Improving the understanding of such bottlenecks could provide a basis for mitigation measures. An integrated modelling approach coupling a salmon population model (IB-salmon), a hydraulic 1D model (HEC-RAS) and a temperature model (Air2Stream) was used to identify the bottlenecks constraining the salmon population in a hydro-regulated river (Ljungan River, Sweden). This integrated approach evaluated changes in the salmon population under different low flow scenarios, involving potential dewatering of spawning sites, and the effect of restored spawning sites. Model results demonstrated that low discharges in winter and summer were potential hydrological bottlenecks for the salmon population, particularly in winter due to potential dewatering of spawning sites. Restoration of spawning sites increased salmon production under all scenarios, posing a potential counter measure against low flows