Torbjørn Forseth

Norwegian Institute for Nature Research | NINA · Department of Aquatic Ecology

Hydropower is an important source of renewable energy, yet dams and other facilities can represent a real threat to migrating fish like salmon and eels, with millions killed in turbines every year. Researchers in the FishPath project aim to exploit the innate response of fish to turbulence to develop an innovative system to guide fish away from tur...

Temperature is a key driver in determining species distribution and abundance across climatic and geographical gradients. This occurs through direct physiological effects of temperature on performance, but may also result from temperature effects on species interactions. In the current study we experimentally test for temperature‐dependent competit...

Hydropower plants commonly impede the downstream migration of Atlantic salmon (Salmo salar) kelts. Thus, understanding the effects of hydraulic conditions on kelt behaviour and passage performance at dams is crucial for developing effective mitigation measures. In this study, we investigated the influence of hydraulic conditions on kelt passage per...

The state of sea trout in 1251 Norwegian watercourses was assessed based on a scoring system for human pressures, abundance data, and local knowledge. Over 16,000 km of rivers and lakes were available to sea trout in these watercourses, spanning from the temperate to Arctic regions. Sea trout were classified to be in a good or very good state in fe...

Given the limited information on prey use during the marine residency period for Atlantic salmon, scales were collected from salmon at return to the River Namsen (Norway) for spawning after 1 year at sea, and scale material from the first and second summer marine feeding periods was analysed using stable isotope methods to understand dynamics of th...

Managers and stakeholders increasingly ask whether predation is a driving force behind the poor status of many species, and whether predator control is likely to be a successful management action to intervene. We review existing literature on Atlantic salmon Salmo salar predation and predator control, as well as general ecological theory on the rol...

The global population of European eel (Anguilla anguilla) is rapidly declining, and migration barriers in rivers are believed to be one of several key causes. While progress has been made in the development of bypass solutions, they are often constructed based on a limited knowledge of swimming behaviour. A bypass close to the stream bed is often r...

The precise homing of Atlantic salmon to their natal river and spawning grounds is the foundation for locally adapted genetically differentiated populations across rivers or across river sections. A sequential imprinting hypothesis states that salmon smolts may imprint on environmental clues along the outward migration route and then use this in re...

While many studies provide microscale relationships between fish and habitat characteristics, studies covering longer river reaches are scarce. Modern remote sensing techniques may enable new and effective ways of mapping and assessing mesoscale habitat characteristics. Using green LIDAR-derived bathymetry and hydraulic modelling, we tested how mes...

This article proposes and demonstrates a new classification system of fish population level effects of hydropeaking operations in rivers. The classification of impacts is developed along two axes; first, the hydromorphological effect axis assesses the ecohydraulic alterations in rivers introduced by rapid and frequent variations in flow and water l...

Atlantic salmon is often a focal species of restoration efforts throughout the north Atlantic and it is therefore an excellent case study for how best to design programmes to address and mitigate threats and correct population declines. This perspective is written to promote the work that has been accomplished towards restoration of Atlantic salmon...

Renewable energy projects such as hydropower facilities contribute towards meeting the world`s growing energy demands and urgent need for mitigating climate change. However, such infrastructure has the potential to substantially alter the environment which, in turn, can induce new challenges related to for instance fish migration conditions. As a c...

Fish swimming performance is strongly influenced by flow hydrodynamics, but little is known about the relation between fine-scale fish movements and hydrodynamics based on in-situ investigations. In the presented study, we validated the etho-hydraulic fish swimming direction model presented in the River Mandal from Southern Norway, using similar be...

Genetic methods for the estimation of population size can be powerful alternatives to conventional methods. Close‐kin mark–recapture (CKMR) is based on the principles of conventional mark–recapture, but instead of being physically marked, individuals are marked through their close kin. The aim of this study was to evaluate the potential of CKMR for...

Repeat spawners constitute an important component of Atlantic salmon populations, but survival of post-spawning individuals (kelts) are often compromised by anthropogenic structures such as hydropower plants (HPPs). Potential effects of HPPs include migration delays and associated increased energy depletion, which potentially results in increased o...

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 Man-dalselva River in Norway. We demonstrate how MCDA using multi-attribute value functions can be implemented in a Bayesian network with...

Dear Colleagues, Habitat fragmentation of watercourses, river impoundment, and construction of large reservoirs are major threats to worldwide aquatic biodiversity (Winemiller et al., 2016, Silva et al., 2018). On one hand, hydropower is a renewable source of energy and an important part of the worldwide effort to reduce emissions of climate gasse...

We implement a multicriteria decision analysis (MCDA) on environmental design alternatives for environmental flows (eflows) and physical habitat remediation measures in the Mandalselva River in Norway. This methods paper provides further documentation of the ecosystem service sub-models and their implementation in Hugin Expert software. We demonstr...

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 Man-dalselva River in Norway. We demonstrate how MCDA using multi-attribute value functions can be implemented in a Bayesian network with...

Anthropogenic structures in rivers are major threats for fish migration and effective mitigation is imperative given the worldwide expansion of such structures. Fish behaviour is strongly influenced by hydrodynamics, but little is known on the relation between hydraulics and fish fine scale-movement. We combined 3D Computational fluid dynamics mode...

This paper presents results from an ongoing research project on extreme upgrading of existing hydropower systems. The project, AlternaFuture, studies how an existing hydropower system can be upgraded with a tripling or more of the installed capacity including pumped storage and at the same time improving the environmental conditions in the river ba...

There is no generic solution to establish safe passage of downstream migrating fish passed hydropower facilities and mitigation measures are species‐ and site‐specific. Development of solutions is thus often based on “trial and error” and modelling based approaches may significantly reduce cost and time to arrive at successful mitigation. Here we e...

In 2017, Norway experienced an invasion of the Pacific salmonid pink salmon (Oncorhynchus gorbuscha) in numbers never before seen in rivers all along the coast. Significant numbers were also caught in other parts of northwestern Europe. Pink salmon has been observed in variable numbers in Norwegian waters in the summer and autumn of most years sinc...

This review provides a summary of knowledge on two-way fish migration of salmonids and eels past hydroelectric plants in Europe. On the basis of a summary of international literature, general designs and recommendations for best practices for fish-pass facilities are provided. The review is part of the Norwegian SafePass project, which focuses on A...

The cover image is based on the Research Article Common mechanisms for guidance efficiency of descending Atlantic salmon smolts in small and large hydroelectric power plants, by Tormod Haraldstad et al., https://doi.org/10.1002/rra.3360. Photo credit: Tormod Haraldstad.

Dams and turbines associated with hydroelectric power plants (HEP) disrupt connectivity by affecting fish movement and survival. There has been an increasing focus on measures to facilitate downstream migration at HEPs. The fish guidance efficacy (FGE) of downstream mitigation measures largely remains suboptimal and calls for development of knowled...

Habitat use of aquatic organisms is essential to evaluate effects of many environmental challenges like effects of hydropower regulation, where stranding may occur under hydropeaking (rapid dewatering of shallow river areas). Experimental studies as well as observations from nature with juvenile Atlantic salmon (Salmo salar) show that the proportio...

The spawning migration of Atlantic salmon has been characterized by tracking salmon carrying electronic tags as they ascend rivers, but still little is known about how natural obstacles such as waterfalls influence migratory behaviour and how such behaviours are mediated by various biotic (e.g., fish size) and abiotic (e.g., discharge, water temper...

The obstruction of fish migratory routes by hydroelectric facilities is worldwide one of the major threats to freshwater fishes. During downstream migration, fish may be injured or killed on the trash-racks or in the hydropower turbines. Fish-friendly trash-racks that combine both ecological and technical requirements are a solution to mitigate fis...

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...

Denne rapporten gir en oppsummering av kunnskap om toveis fiskevandring forbi vannkraftverk. Basert på oppsummeringen og internasjonal praksis anbefales mønsterpraksis for fiskepassasjer. Rapporten er en del av SafePass-prosjektet, som primært omhandler fiskeartene laks, ørret, harr og ål, og fokuserer spesielt på oppvandring hos harr og innlandsør...

Much effort has been devoted to developing, constructing and refining fish passage facilities to enable target species to pass barriers on fluvial systems, and yet, fishway science, engineering and practice remain imperfect. In this review, 17 experts from different fish passage research fields (i.e., biology, ecology, physiology, ecohydraulics, en...

Atlantic salmon (Salmo salar) is an economically and culturally important species. Norway has more than 400 watercourses with Atlantic salmon and supports a large proportion of the world's wild Atlantic salmon. Atlantic salmon are structured into numerous genetically differentiated populations, and are therefore managed at the population level. Lon...

This study found empirical evidence supporting the “growth–survival” paradigm in the marine phase of Arctic char (Salvelinus alpinus) and brown trout (Salmo trutta). The paradigm postulates that larger or faster-growing individuals are more likely to survive than smaller or slower-growing conspecifics. The study employed long-term (25 year) capture...

Centre for Environmental Design of Renewable Energy (CEDREN) is a research centre focusing on hydropower production and environmental impacts of hydropower. The main objective of CEDREN is to develop and communicate design solutions for renewable energy production that address environmental and societal challenges at local, regional, national and g...

Competition for limited resources and the resulting density-dependent processes are key factors in driving stream salmonid population dynamics. Here we test for the combined effects of density and shelter availability on the movement of juvenile Atlantic salmon (Salmo salar) in a Norwegian river. Individually marked, hatchery-reared salmon juvenile...

An effect of hydropower and hydropeaking regulation in rivers is stranding of fish. Those fishes that survive stranding may experience stranding as a stressful situation. In four experimental stranding experiments (each with 6 individuals in 10 control and 10 treatment replicates), the energetic consequences of two forms of stranding (i.e . trappin...

Utløpet av Bjelland kraftverk befinner seg på den lakseførende delen av Mandalselva, og vannføringen gjennom kraftverket påvirker leveområdene for laks på den 8 km lange strekningen fra utløpet og ned til Mannflåvatn. I denne rapporten identifiseres forskjellige driftssituasjoner for Bjelland kraftverk, og rapporten har som mål å foreslå en drift s...

This book summarises state-of-the art about environmental impacts from hydro-peaking operations in rivers, introducing rapid and frequent changes in discharge and water level. The book is considered relevant also for other types of abrupt changes in the operation of hydropower plants such as fallouts, or other controlled or non-controlled operation...

While fine mesh trash racks constitute a safe barrier for downstream migrating smolts, such racks can be expensive and technically difficult to retrofit at hydropower intakes. Alternatively, a combination of attraction and repulsion measures can successfully pass fish by the intake and into safe corridors. At the Laudal hydropower plant in the rive...

The status of all 344 Norwegian Atlantic salmon fishways were explored, combining an existing national inventory with collection of additional information from local river authorities and onsite inspections of 89 selected sites to provide more detailed information on design and functionality.

The performance and movements of juvenile Atlantic salmon Salmo salar exposed to variable water discharge (simulating hydropeaking) but with a stable water-covered area were studied in six experimental stream channels, both during the winter and summer. Thirty fish were stocked into each channel, and the growth, body fat and movements of the fish w...

While management according to biological reference points is well established for many commercial marine fisheries, similar systems for more leisure based fisheries for freshwater fishes are less common. This paper describes the scientific foundation for management according to conservation limits and management targets for Norwegian populations of...

Theoretical considerations suggest that the relative abundance of age-specific limiting resources determines the ontogenetic timing of density dependence. Structural shelters may represent one such resource which can become increasingly scarce with increasing body size. Here we use a time series of juvenile Atlantic salmon (Salmo salar) densities a...

We predict an increase in parr recruitment and smolt production of Atlantic salmon (Salmo salar) populations along a climate gradient from the subarctic to the Arctic in western and northern Norway in response to future climate change. Firstly, we predicted local stream temperature and discharge from downscaled data obtained from Global Climate Mod...

In this paper, we present a spatially explicit individual-based mechanistic model for predicting the freshwater population abundance of Atlantic salmon (Salmo salar L.). The model simulates the complete life-cycle at small spatial (∼50 m) and temporal (weekly) scales. Processes such as spawning, recruitment, mortality and movements are predicted us...

The status of all 344 Norwegian Atlantic salmon fishways were explored, combining an existing national inventory with collection of additional information from local river authorities and onsite inspections of 89 selected sites to provide more detailed information on design and functionality. Inspections of 89 fishways indicated that nearly 70 % we...

We explored the mechanisms of density-dependent growth in Arctic char (Salvelinus alpinus) by comparing the energetics of growth, consumption, and activity obtained under three replicated density treatments in a large-scale enclosure (90 m² surface area) experiment. The enclosures permitted the entry of zooplankton and allowed char to feed on the b...

This study investigated the importance of competition with brown trout Salmo trutta as a driver of the morphological and behavioural divergence of two morphs of Arctic charr Salvelinus alpinus. The morphs originated from two lakes differing in absence or presence of the competitor. The bioenergetics and behaviour of S. alpinus were quantified in re...

The spatial distribution of Atlantic salmon Salmo salar young-of-the-year (0+) and 1 year old parr (1+) from the 2006 spawning cohort in a 5125 m reach of the River Skauga in central Norway was documented. A high degree of similarity was found between the distribution of 0+ and 1+ parr based on catches at 205 transects sampled in both years. Cross-...

In this study, cost effective (in terms of reducing loss of power production) measures for increasing bypass migration of Atlantic salmon Salmo salar were developed and tested by establishing statistical models for timing of smolt migration and favourable diversion of water to the bypass. Initial tracking of radio-tagged smolts showed very low bypa...

1. The intensity of intraspecific competition may influence the growth of differently sized individuals to different extents. Measures of among‐individual variation in growth and body size are commonly applied to assess such effects. The measure chosen is then supposed to control for the effect of mean (also influenced by competition) on variance [...

1. Timing of offspring arrival (i.e. hatching, birth or emergence from nests) is commonly shown to have strong effects on their performance through body size and prior residency effects, but less is known about how such effects differ among species. The strength of such effects tends to be related to competitive intensity (e.g. population density)....

There has been a growing recognition that single species responses to climate change often mainly are driven by interaction with other organisms and single species studies therefore not are sufficient to recognize and project ecological climate change impacts. Here, we study how performance, relative abundance and the distribution of two common Arc...

We tested the importance of thermal adaptations and energy efficiency in relation to the geographical distribution of two competing freshwater salmonid fish species. Presence–absence data for Arctic char and brown trout were obtained from 1502 Norwegian lakes embracing both temperature and productivity gradients. The distributions were contrasted w...

Successful transitions from relying on yolk to exogenous feeding may be strongly influenced by temperature conditions experienced both during embryonic development, through effects on juvenile phenotype, and during initiation of feeding. Here we simultaneously assess these two effects of temperature treatments (2, 5, 8, and 12 °C) in Atlantic salmo...

By comparing the population frequency distributions for specific somatic energy between samplings using quantile–quantile (QQ) plots, we tested for energy-related mortality of juvenile (2- and 3-year-old) Atlantic salmon (Salmo salar) sampled at monthly intervals throughout three consecutive winters in a Norwegian river located at 70°N. Between sev...

We test whether the spatial distribution of spawning sites in a natural population is related to the density and individual growth rate of juvenile stream-dwelling salmonids. For this purpose, fine-scale data on the spatial distribution of Atlantic salmon (Salmo salar) nest sites, juvenile densities and body size, and habitat characteristics were c...