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:

Johan Watz, doing field work during his PostDoc in Japan.

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.

A forest stream on Hokkaido, northern Japan.

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.

 

The left photographs show Dolly Varden (a) and white‐spotted charr (b). The right photographs show enclosures in a non‐spring‐fed (c) and a spring‐fed (d) tributary.

 

The structurally enriched (left) and barren (right) tanks used in the study on how structural complexity in the hatchery environment affects juvenile brown trout.

 

River Rottnan in winter.

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:

A juvenile brown trout (Salmo trutta) hiding in fine stream wood.

“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 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.

Burbot, Lota lota

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.

Nedre Dalälven.

Projekt LIV – laxfisk i nedre Dalälven, som doktorand Anna Hagelin vid Karlstads universitet har varit projektledare för, uppmärksammades nyligen av svt nyheter i och med publiceringen av projektets slutrapport. Målet med projektet har varit att undersöka nedre Dalälvens potential att återfå livskraftiga och självreproducerande bestånd av havsvandrande lax och öring. Projektet är ett samarbete mellan länsstyrelserna i Gävleborg och Uppsala samt kraftverksägarna Fortum och Vattenfall, och finansierades till störst del genom Fortums och Vattenfalls miljöfond samt naturskyddsföreningens miljömärkning Bra Miljöval.

Restaurering av lekplatser för lax och öring i nedre Dalälven.

Det finns många vandringshinder för lax och öring i nedre Dalälven. Trots detta kan det finnas goda förutsättningar att få tillbaka självreproducerande bestånd av båda arterna. För att fiskens lekvandring ska fungera krävs det stora investeringar i form av alternativa vandringsvägar (så kallade omlöp) förbi vandringshinder som till exempel kraftverk. För tillfället kommer fisken till Älvkarleby, men länsstyrelsen Gävleborg vill göra det möjligt för fisken att själva vandra upp till sina lekområden.

Läs nyhetsartikeln på svt här, eller mer om LIV-projektet på länsstyrelsen Gävleborgs hemsida.