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 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.

Johan Watz, Assistant Professor at Karlstad University, recently published two papers on juvenile salmonid ecology:

 

Temperature‐dependent competition between juvenile salmonids in small streams

By Johan Watz, Yasuhiko Otsuki, Kenta Nagatsuka, Koh Hasegawa & Itsuro Koizumi, published in the journal Freshwater Biology.

In the abstract, the authors write:

1) Biotic interactions affect species distributions, and environmental factors that influence these interactions can play a key role when range shifts in response to environmental change are modelled.

2) In a field experiment using enclosures, we studied the effects of the thermal habitat on intra‐ versus inter‐specific competition of juvenile Dolly Varden Salvelinus malma and white‐spotted charr Salvelinus leucomaenis, as measured by differences in specific growth rates during summer in allopatric and sympatric treatments. Previous laboratory experiments have shown mixed results regarding the importance of temperature‐dependent competitive abilities as a main driver for spatial segregation in stream fishes, and no study so far has confirmed its existence in natural streams.

3) Under natural conditions in areas where the two species occur in sympatry, Dolly Varden dominate spring‐fed tributaries (cold, stable thermal regime), whereas both species often coexist in non‐spring‐fed tributaries (warm, unstable thermal regime). Enclosures (charr density = 6 per m²) were placed in non‐spring‐fed (10–14°C) and spring‐fed (7–8°C) tributaries.

4) In enclosures placed in non‐spring‐fed tributaries, Dolly Varden grew 0.81% per day in allopatry and had negative growth (−0.33% per day) in sympatry, whereas growth rates were similar in allopatry and sympatry in spring‐fed tributaries (0.68 and 0.58% per day). White‐spotted charr grew better in sympatry than in allopatry in both thermal habitats. In non‐spring‐fed tributaries, they grew 0.17 and 0.79% per day and in spring‐fed tributaries 0.46 and 0.75% per day in allopatry and sympatry, respectively.

5) The negative effect of inter‐specific competition from white‐spotted charr on Dolly Varden thus depended on the thermal habitat. However, there was no strong evidence of a temperature‐dependent effect of intra‐ and inter‐specific competition on white‐spotted charr growth.

6) Multiple factors may shape species distribution patterns, and we show that temperature may mediate competitive outcomes and thus coexistence in stream fish. These effects of temperature will be important to incorporate into mechanistic and dynamic species distribution models.

 

Read more about the Koizumi lab at Hokkaido University (where Johan did his PostDoc) on their website!

 

Structural complexity in the hatchery rearing environment affects activity, resting metabolic rate and post‐release behaviour in brown trout Salmo trutta

By Johan Watz, published in the Journal of Fish Biology

In the abstract, Johan writes:

The effects of structural enrichment in the hatchery rearing environment of brown trout Salmo trutta was linked to post‐release performance. Enrichment resulted in reduced swimming activity scored in an open field test and reduced movement in a natural river after release. Also, enrichment increased resting metabolic rates, which correlated positively with overwinter growth.

 

Contact the author to access the papers.

 

 

 

Åsa Enefalk, Ari Huusko, Pauliina Louhi and Eva Bergman recently published the paper “Fine stream wood decreases growth of juvenile brown trout (Salmo trutta L.)” in the journal Environmental Biology of Fishes. In the abstract, the authors write:

“In this study, the growth rate, gut fullness, diet composition and spatial distribution of brown trout was compared between artificial channels with and without fine wood (FW). Access to FW resulted in significantly lower brown trout growth rates over the study period from late summer to early winter as water temperatures declined from 17 °C to 1 °C. Access to FW resulted in minor differences in occurrence of the most common taxa found in brown trout diets, except for chironomid larvae which were found in c. 60% of the brown trout guts from control treatments but in only 30% of the guts from FW treatments in early winter. Diet consisted primarily of case-bearing and free-living Trichoptera larvae, Asellus, chironomid and Ephemeroptera larvae. Brown trout gut fullness was not significantly affected by access to FW bundles. Brown trout aggregated among FW but were more evenly distributed in channels lacking it. Our results suggest that juvenile brown trout use FW as a shelter at a wide range of water temperatures, and that this behaviour may result in reduced growth rates during their first fall and the onset of their first winter. We also show that prey availability and the composition of brown trout diet changes from late summer to early winter and that FW has a small but significant effect on brown trout diet composition.”

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

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:

“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

 

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.

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.

On Tuesday 3 April 2018, Karl Filipsson, PhD student at Karlstad University, will give a talk titled “The effects of temperature and light conditions during winter on antipredator responses of juvenile brown trout against burbot”. The seminar will start at 13:15 in room 5F416 at Karlstad University. Everyone is welcome to attend the seminar.