By Louis Addo, Lise Meneboo, Mahboobeh Hajiesmaeili, John J. Piccolo & Johan Watz

In the world of riverine fish, life isn’t always calm and flowing. In fact, for young Atlantic salmon and brown trout, the river can sometimes feel like a wild rollercoaster ride—especially in areas impacted by hydropeaking, where dam operations cause rapid and frequent changes in water flow.

A new peer-reviewed study led by Louis Addo and colleagues at Karlstad University investigates how sudden shifts in flow affect the foraging behavior, social dynamics, and habitat use of young salmon and trout. The study’s twist is that it examines whether it matters whether the two species were raised together (sympatric) or separately (allopatric).

What Did They Find?

Contrary to what many ecologists might expect, the study found that:

• Rapid flow fluctuations did not impact how well the fish could forage for drifting food.
• Group composition, not flow, was the big game-changer when it came to social spacing (nearest neighbor distance) and microhabitat selection.
• Salmon stayed closer to the bottom of the tank regardless of conditions, suggesting a preference for stable positions, while trout were more mobile, especially when raised with salmon.

So, does hydropeaking make life harder for juvenile salmonids? Not necessarily. The findings suggest that as long as the water stays within a certain range of temperatures and flows, the fish adapt surprisingly well.

Why does this matter?

Many environmental models that simulate salmon and trout populations often leave out behavioral details like social spacing and microhabitat selection under changing flow. This study provides encouraging news: those simplifications may not lead to big errors, at least when it comes to modeling energy intake and growth.

In other words, salmon and trout parr seem to hold their own in fast-changing rivers, using different strategies to navigate their environment—some stick together, some spread out, some hug the substrate—depending on who they’re with.

Big Picture

As river managers, ecologists, and hydroelectric developers look for ways to balance renewable energy with aquatic biodiversity, studies like this are crucial. They remind us that behavioral flexibility in fish may be a powerful buffer against environmental change—though we shouldn’t assume they’re invincible.

This paper is open access and can be downloaded on https://onlinelibrary-wiley-com.bibproxy.kau.se/doi/epdf/10.1002/rra.4464

Louis Addo (a Ph.D. student in Biology at Karlstad University) will be giving a talk about the interaction of salmonids fry with changing flows. The talk will be a presentation of a recently published article entitled “Growth and mortality of sympatric Atlantic salmon and brown trout fry in fluctuating and stable flows” by Louis and others from the River Ecology and Management Research group working with salmonids ecology and IBM’s.

You are invited to join this seminar live on zoom and at the biology department at Karlstad University (5F416) at 13:15 CET on 6th December 2022. To join in via zoom use the link: https://kau-se.zoom.us/my/kaubiology

Watch Part 2 of the epic aquatic documentary (part of a trilogy) this Sunday, 24 October, 19.00-20.00 on Swedish National TV (SVT2). This epic aquatic trilogy (the first of its kind on Swedish TV) covers three years of filming work by a team of experts. The team while making this documentary in 2019 spent two days with the University of Karlstads’ master course in river Ätran. Find out more on: https://www.svtplay.se/fiskarnas-rike ¨ https://fiskarnasrike.se/

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In addition to that, there’s another documentary broadcasted on SVT’s “Kalla fakta” next week (Part 3 THE SEA is broadcast on Sunday 31 October, 19.00-20.00 on SVT2) on “eel conservation”. Watch out for Professor Olle Calles (a lecturer at the University of Karlstad and a member of the River Ecology and management research group) answering very important questions concerning eels.

On Tuesday 8 December Kalle Filipsson, RivEM PhD student, will present his work on how elevated temperatures and predator presence during egg incubation affect development and behaviour of brown trout. The seminar starts at 13:15 and will be streamed live on Zoom. Contact Kalle (karl.filipsson@kau.se) if you are interested in attending the seminar, and he will send you a link.

On tuesday 27 October (tomorrow) Patrik Andreasson (Adjunct Professor, Luleå University of Technology; Specialist, Vattenfall AB) will give a seminar titled “Fish diagnostics by image recognition using machine learning (AI)”.

The seminar starts at 13:15 and will be held via zoom. Everyone who wants to are welcome to attend the seminar. Contact Olle Calles (olle.calles@kau.se) to receive a zoom link to the seminar.

Image recognition using AI, as a tool for fish identification, was mentioned on the Swedish news earlier this year. Follow this link to svt.se to watch a short video and to read more about the project (in Swedish).

On Tuesday 10 March, Kristine Lund Bjørnås, PhD student at Karlstad University, will give a seminar entitled “Modeling Atlantic salmon and brown trout responses to river habitat alteration”. The seminar starts at 13.15 in room 5F416, everyone who wants to is welcome to attend the seminar.

This seminar is a practice seminar in preparation for Kristine’s licentiate defense, which will be held Thursday 26 March at 10:00. More information about the licentiate seminar will be provided closer to the defense.

Anna Hagelin successfully defended her PhD thesis with the title “Conservation of landlocked Atlantic salmon in a regulated river: Behaviour of migratory spawners and juveniles” 12 April this year.

Anna also presented her research at “forskningspodden” (the research podcast), which is a popular science podcast at Karlstad University. Here you can listen to Anna talk about her research on salmon conservation in river Klarälven (in Swedish).

PhD-defense: Conservation of landlocked Atlantic salmon in a regulated river

On Friday 12 April, Anna Hagelin will defend her PhD-thesis “Conservation of landlocked Atlantic salmon in a regulated river – Behaviour of migratory spawners and juveniles”. The defense will take place at 10:00 in room 1B309 (Sjöströmssalen) at Karlstad University. Everyone is welcome to attend the defense.

Ian Fleming (Memorial University of Newfoundland (Canada) will be the opponent and Jaakko Erkinaro (Natural Resources Institute, Finland), Eva Thorstad (Norwegian institute for Nature Research, Norway) and John Armstrong (Marine Scotland Science Freshwater Fisheries Laboratory, Scotland) constitute the grading committee.

 

Mini-symposium on Atlantic salmon

On Thursday 11 April, a mini-symposium on Atlantic salmon will be held in room 5F322 at Karlstad University, where the visiting researchers will give presentations:

 

14:00-14:30: Ian Fleming, Memorial University of Newfoundland. Life-history dependent migration strategies in Atlantic salmon 

14:30-15:00: Jaakko Erkinaro, Natural Resources Institute Finland. Diversity in Atlantic salmon – evolutionary ecology and management implications 

15:00-15:30: Coffee break

15:30-16:00: Eva Thorstad, Norwegian Institute for Nature Research. Status of salmon in Norway and importance of the ocean phase 

16:00-16:30: John Armstrong, Marine Scotland Science Freshwater Fisheries Laboratory. Current and future applications of science for management of salmon in Scotland

On Tuesday 5 March (tomorrow) Anna Hagelin, PhD student at Karlstad University, will give a pre-dissertation talk titled “Conservation of landlocked Atlantic salmon in a regulated river: behaviour of migratory spawners and juveniles”. The seminar starts at 13:15 in room 5F416. Everyone is welcome to attend the seminar.

Anna will defend her doctoral thesis on 12 April at 10:00 in room 1B309 at Karlstad University. More information will come closer to the dissertation.

För några veckor sedan, 8 mars, publicerades ett inlägg på nrrv.se om projekt LIV – laxfisk i nedre Dalälven. I projektet undersöktes nedre Dalälvens potential att återfå livskraftiga och självreproducerande bestånd av havsvandrande lax och öring. Nu är slutrapporten för projektet publicerad, och kan nås via länsstyrelsen Gävleborgs hemsida.