Rachel Bowes (RivEM PostDoc) and colleagues have studied the downstream passage of several migrating fish species during spring and fall 2020. Here she writes about their work:

Laxeleratorn at Vattenfall’s Research & Development facility in Älvkarleby

“Dams are like giant road blocks for fish in rivers. It is not always feasible or realistic to remove a dam to restore fish movement throughout rivers, so we need to design detours around them.

When going downstream we call this detour past the dam a bypass. The question we are asking is: How can we design a better bypass for multiple fish species to be able to move downstream past a dam more easily and efficiently? To test this, we are using the Laxeleratorn at Vattenfall’s Research & Development facility in Älvkarleby. We are testing Silver Eels, Salmon, and Roach fish species. Changing the design of the bypass and amount of water flowing through it, we hope to find out what combination creates the optimal bypass for these fish species.”

European eel (Anguilla anguilla)
Florian Stein, Director of Scientific Operations for the Sustainable Eel Group

On Tuesday 13 October (tomorrow), Florian Stein will give the seminar “The illegal trade in European eels from Europe to Asia”. Florian works as Director of Scientific Operations for the European organization Sustainable Eel Group (SEG). His main focus is on the illegal trade in European eels from Europe to Asia. During his seminar, Florian will talk about the global trade with European eel and law enforcement in relation to this trade.

The seminar starts at 13.15 and will be streamed live over Zoom. Contact Olle Calles (olle.calles@kau.se) to receive the zoom link to this seminar.

Read more about the Sustainable eel group here:

European eels, Anguilla anguilla

On Tuesday 26 May Roman Motyka, NRRV PhD student, will give a seminar entitled “The role of behavior and habitat use in conservation biology of the European eel (Anguilla anguilla). During this seminar, Roman will present his plans for his PhD project.

The seminar starts at 13:15 and will be held online and streamed via the video communication system Zoom. Everyone who wants to attend the seminar are welcome to do so. We will not distribute the zoom link to the seminar publicly online. If you want to attend the seminar, contact Roman (roman.motyka@kau.se) or Olle Calles (olle.calles@kau.se), and they will send you a zoom link so that you can participate.

Roman Motyka (right) and Tobias Knieps (left) with some eels in a net.

European eel, Anguilla anguilla

On Tuesday 18 June, Niclas Carlsson, lab/field technician and master student at Karlstad University, will give a seminar titled: “Low-sloping racks and the importance of bar spacing for eel passage”. The seminar starts at 13:15 in room 5F416 at Karlstad University. Everyone who wants to are welcome to attend the seminar.




European eel, Anguilla anguilla. Photo: Jörgen Wiklund

Karlstad University has an opening for a PhD position in aquatic conservation biology. The project will focus on “Resolving production bottlenecks for the European eel”. Conserving biodiversity is one of the major challenges in applied aquatic ecology. The European eel functions as a flagship species in marine and freshwater conservation, and its population collapse is of major concern for ecologists, fishers and managers.

The aim of the PhD project is to identify:

(i) relationships between yellow eel habitat use, growth, behavior and survival.

(ii) effects of habitat characteristics and the surrounding landscape on eel large-scale movements within freshwater systems.

(iii) functioning downstream passage solutions at hydropower plants for a wide range of silver eel phenotypes.

The position is full-time for four years. Doctoral students may also be assigned departmental duties, such as teaching, which will extend the period of employment accordingly.

Read more and apply for the position here.

Last day to apply is 5 June 2019.

Two papers in Animal Conservation

Posted by Karl Filipsson | Papers

Two papers from NRRV were recently published in the journal Animal Conservation. The first paper presents a field study on how sedimentation affects brown trout (Salmo trutta) fry emergence in relation to freshwater pearl mussel (Margaritifera margaritifera) recruitment. The second paper presents a combined field and laboratory study on passage solutions for upstream-migrating eels (Anguilla anguilla).


Sedimentation affects emergence rate of host fish fry in unionoid mussel streams

Martin Österling


In the abstract, the author writes:

Freshwater pearl mussel, Margaritifera margaritifera

“Free-living, sympatric sedentary life stages of hosts and parasites are often adapted to similar environmental conditions. When the environment where these life stages occur is disturbed, both species can decline, causing strong negative effects on the parasitic species. For the highly threatened unionoid mussels with their larval parasitic life stage on fish, habitat degradation may simultaneously affect the conditions for the sedentary host fish eggs and the juvenile mussels in the sediment. This study provides novel information on the effect of sedimentation on the emergence rate of yolk sac fry, and its relation to mussel recruitment in two drainage basins, and is exemplified by the brown trout Salmo trutta, host fish for the threatened freshwater pearl mussel Margaritifera margaritifera. The results imply that turbidity and sedimentation can reduce the survival of trout eggs and yolk sac fry emergence rate regardless of trout strain and drainage basin. The results further suggest that low yolk sac fry emergence rates reduce the potential for mussel infestation and recruitment. The results indicate a year round negative effect of sedimentation, having strong and combined direct and indirect effects on juvenile mussel recruitment. Conservation measures that reduce anthropogenic sediment transportation into streams are a key factor for the conservation of mussels and their host fish.”

Access the paper here, or contact the author.


Climbing the ladder: an evaluation of three different anguillid eel climbing substrata and placement of upstream passage solutions at migration barriers

Johan Watz, Anders Nilsson, Erik Degerman, Carl Tamario and Olle Calles


European eel, Anguilla anguilla. Photo: Jörgen Wiklund

In the abstract, the authors write:

“Conservation programmes for endangered, long-lived and migratory species often have to target multiple life stages. The bottlenecks associated with the survival of juvenile anguillid eels migrating into inland waters, the survival and growth of the freshwater life stage, as well as the recruitment and survival of silver eels, migrating back to the ocean to spawn, must be resolved. In this study, we focus on the efficiency of passage solutions for upstream-migrating juveniles. Such solutions can consist of inclined ramps lined with wetted climbing substrata. We evaluated different commonly used substrata in a controlled experiment, recorded eel behaviour at the entrance of the ramp with infrared videography and validated the experimental results at a hydropower dam, where we also investigated the effects of ramp placement on performance. In the experiment on eel substratum selection, 40% of the eels passed in lanes with studded substratum, whereas only 21 and 5% passed using open weave and bristle substrata respectively. Video analysis revealed that the studded substratum attracted more approaches and initiated climbs than the other substrata, but once a climb had been initiated, passage success rates did not differ between substrata. Eels using the studded substratum climbed 26% faster than those using the bristle substratum and almost four times as fast as those climbing in the open weave. The superior performance of the studded substratum was supported by data from the field validation. Moreover, ramps positioned by the bank with low water velocities caught the most eels, but proximity to the dam had no effect on performance. To strengthen the European eel population, more juveniles need to reach their freshwater feeding grounds. A critical step to achieve this increase is to equip upstream passage solutions with suitable substrata and to optimize ramp placement at migration obstacles.”

Access the paper here, or contact any of the authors.

Marcell Szabo-Meszaros, Christy Ushanth Navaratnam, Jochen Aberle, Knut Alfredsen (Norwegian University of Science and Technology), Ana T. Silva, Torbjørn Forseth (Norwegian Institute for Nature Research), Olle Calles (Karlstad University) and Hans-Petter Fjeldstad (SINTEF Energy Research) recently published the scientific paper “Experimental hydraulics on fish-friendly trash-racks: an ecological approach” in the journal Ecological Engineering. The study is part of the project SafePass, where methods for safe and efficient migration for salmonids and European eel past hydropower structures are evaluated. SafePass aims to facilitate fish migration in regulated rivers, using perspectives of both the fish and the hydropower industry. Read more about SafePass here.

In the abstract of the paper, the authors write: ”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 fish mortality at a low operational cost. This study presents results from an experimental investigation of head-losses and the hydrodynamic performance of six angled trash-rack types with 15 mm bar spacing, varying bar-setup (vertical-streamwise, vertical-angled and horizontal bars) and bar profiles (rectangular and drop shape) under steady flow conditions. The trash-racks were positioned at 30° to the wall of the flume and combined with a bypass at their downstream end. The impact of the different trash-rack types on the upstream flow field was characterized using Image based Volumetric 3-component Velocimetry (V3V) and at the bypass-entrance using an Acoustic Doppler Velocimeter (ADV). The results show that trash-racks with vertical streamwise and horizontal oriented bars with drop-shape profiles have similar head-losses (13% difference), while trash-racks with vertical-angled bars provide 3–8 times larger head-losses compared to the remaining configurations. The velocity measurements showed that the highest flow velocities occurred for configurations with vertical-angled bars (0.67ms−1 and 0.81ms−1 on average, respectively).Turbulence related parameters (e.g. Reynolds shear stresses and Turbulent kinetic energy) were also investigated to evaluate the performance of the alternative trash-racks from both, engineering and ecological perspectives.”

Access the paper here, or e-mail any of the authors.

The Volumetric 3-component Velocimetry (V3V) system used in the study.

Illegal eels

Posted by Daniel Nyqvist | Nyheter

Two articles on the eel fishery and illegal trade of glass eels have been published on the Guardian Environmental Blogs. Despite fishing quotas and trade restrictions tons of European eels are illegally exported to lucrative Asian markets.

Read the articles about the illegal eel trade theguardian.com:

Part I – Illegal eel: black market continues to taint Europe’s eel fishery

Part II – Illegal eel: who is pilfering Europe’s catch?

Glass eels. Photo from The Guardian.

In the second article, NRRV (eng. River Ecology and Management Research Group at Karlstad University) collaborator Florian Stein‘s work in Hong Kong is cited.

Niklas B. Sjöberg, Stockholms Universitet, försvarade förra veckan sin doktorsavhandling “Eel migration – results from tagging studies with relevance to management”. Olle Calles närvarade som medlem i betygsnämnden och rapporterar att “Niklas gjorde en stabil insats och gav ett samlat intryck. Med 5 av 6 papper redan publicerade var det hög kvalitet på avhandlingen som spände från simblåsemask till ålar fast  i Mälaren (blankålar som återfångsas i sjön år efter år och således inte verkar hitta ut till havet) och spårningsförsök av ål i Atlanten mot Sargasso havet. Eftersom hälften av ålarna med satellitsändare var från Kau:s arbete i Ätran, var det kul att just de nådde längst!”

Handledare var Sture Hansson, Håkan Wickström och Erik Petersson medan Alan Walker från CEFAS (Centre for Environment, Fisheries and Aquaculture Science, UK) var opponent.

Avhandlingen abstract och en lista på inkluderade publikationer kan läsas här.



eelmigrationThe report – Understanding downstream migration timing of European eel (Anguilla anguilla) – is finally available to DOWNLOAD.

Summary: The European eel stock has long been in decline. Consequently, the species has been added to the IUCN Red List of Threatened Species. One threat that has been identified as one possibly having an impact on the stock is mortality caused by hydroelectric power plant turbines. Turbine management, which is adapted to preferable migration conditions, might reduce the risk of this threat. Our study, conducted at five locations in southern Sweden, aimed at learning about the migratory behaviour of European silver eels paying special attention to preferable environmental conditions for migration by using advanced statistical modelling.

Results indicated that downstream migration triggers can be reliably described using hydrological variables (discharge, precipitation or one of their dynamic derivations), water temperature and moon. Spring and autumn migrations seemed to be triggered differently. In spring, rising water temperatures seemed to be the key trigger, quite independently of hydrological variables and the moon. In the autumn, the importance of the moon and hydrological variables on downstream migration increased. In addition, migration triggers differed depending upon the size of the body of water and/or its location in the river system. In smaller/upstream tributaries, hydrological variables seemed to be the key trigger. In larger/downstream waters, the importance of water temperature and the moon increased.

The transferability of models was limited. Moreover, models indicated that in some cases, the dynamics of water temperature and hydrological variables (precipitation, discharge) provided more explanatory power than the measured, absolute values. Transferability among time series from the same location delivered some reliable results. Success of transferability between locations was limited to sites which originated from the same river catchment. In spring, migration activity did not occur until water temperatures exceeded 6.5 °C in a tributary and 9 °C in the Kävlingeån River. Eels showed significant nocturnal migration behaviour (98.5 %; n = 205) and migration activity became very unlikely in autumn if water temperatures dropped below 5 °C.

Our data on spring migration is limited to one site in a tributary and one site in a lower mainstream. Furthermore, spatial transferability among catchments has not been tested in previous studies. Therefore, we recommend that future studies be performed during the spring and autumn migrations in tributaries as well as lower mainstreams.

Moreover, previous studies indicate that some eels hesitate for several days or even reverse upstream instead of entering the traps the same night that they arrive. Additional visual techniques such as hydroacoustic cameras should be applied upstream of catch facilities in order monitor eel migration activity of unharmed eels. This enables the validation of trap catchability and consequently the response of our models.

Our results clearly show that turbine induced mortality could be minimized if turbine operation focuses on daytime periods, when water temperature is below 5 ° C and when the discharge not is stable or decreasing. Moreover, local adaptive turbine management should be accompanied by studies to determine the local constellation of environmental triggers. In addition, it will be crucial, that later applications (e.g. turbine management, early warning systems etc.) consider the temporal dynamic of water temperature and hydrological variables.