En ung öring bland fin ved (foto: Anders Tedeholm)

Den vetenskapliga artikeln “Effect of fine wood on juvenile brown trout behaviour in experimental stream channels” av Åsa Enefalk och Eva Bergman, publicerades nyligen i tidskriften Ecology of Freshwater Fish. Artikeln presenterar en studie där författarna undersökt unga öringars beteende i strömakvarier med olika mängder fin ved. I artikelns abstract sammanfattar författarna studien:

“In-stream wood can increase shelter availability and prey abundance for stream-living fish such as brown trout, Salmo trutta, but the input of wood to streams has decreased in recent years due to harvesting of riparian vegetation. During the last decades, fine wood (FW) has been increasingly used for biofuel, and the input of FW to streams may therefore decrease. Although effects of in-stream FW have not been studied as extensively as those of large wood (LW), it is probably important as shelter for small-sized trout. In a laboratory stream experiment, we tested the behavioural response of young-of-the-year wild brown trout to three densities of FW, with trout tested alone and in groups of four. Video recordings were used to measure the proportion of time allocated to sheltering, cruising and foraging, as well as the number of aggressive interactions and prey attacks. Cruising activity increased with decreasing FW density and was higher in the four-fish groups than when fish were alone. Foraging decreased and time spent sheltering in FW increased with increasing FW density. Our study shows that juvenile trout activity is higher in higher fish densities and that trout response to FW is related to FW density and differs from the response to LW as reported by others.”

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Horrsjöälven där två av försökets lokaler återfinns.

Den vetenskapliga artikeln “Effects of fine wood on macroinvertebrate drift in four boreal forest streams” av Åsa Enefalk och Eva Bergman har publicerats i tidskriften Hydrobiologia. Artikeln presenterar forskning om hur fin ved i skogsvattendragen påverkar mängden driftande macroinverterbrater. I abstraktet skriver författarna:

“Most studies of stream wood have focused on pieces ≥0.1 m diameter. However, this approach may overlook an important feature of small streams, where wood <0.1 m can constitute the majority of wood pieces. We examined the effect of fine wood (FW) on local drift of stream macroinvertebrates. The study was carried out at seven sites in four boreal forest streams, from early June to mid-August 2011. This was done by anchoring bundles of FW at each site and measuring drift upstream and downstream of each bundle. We hypothesized that FW would increase drift density, biomass and diversity of aquatic invertebrates. Ten weeks after FW addition, aquatic drift density was higher downstream than upstream of FW bundles, while drift biomass and drift diversity did not differ significantly downstream and upstream of FW.”

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Kelt framför intagsgaller (foto: Herman Wanningen).

Den vetenskapliga artikeln ”Post-spawning survival and downstream passage of landlocked Atlantic salmon (salmo salar) in a regulated river: is there potential for repeat spawning?”, om efterleksöverlevnad, nedströmsmigration och passage hos lax-kelt i Klarälven, har publicerats i River Research and Applications. Författare är Daniel Nyqvist, Olle Calles, Eva Bergman, Anna Hagelin och Larry Greenberg.

I abstraktet skriver författarna: “Repeat salmonid spawners may make large contributions to total recruitment and long term population stability. Despite their potential importance, relatively little is known about this phase of the life history for anadromous populations, and nothing has been reported for landlocked populations. Here, we studied post-spawning behaviour and survival of landlocked Atlantic salmon in relation to downstream dam passage in the River Klarälven, Sweden. Eight hydropower stations separate the feeding grounds in Lake Vänern from the spawning grounds in the River Klarälven, and no measures to facilitate downstream migration are present in the river. Forty-nine percent of the salmon survived spawning and initiated downstream migration. Females and small fish had higher post-spawning survival than males and large fish. The postspawners migrated downstream in autumn and spring and remained relatively inactive in the river during winter. Downstream migration speed in the free flowing part of the river was highly variable with a median of 9.30 km/day. Most fish passed the first hydropower station via upward-opening spill gates after a median residence time in the forebay of 25 min. However, no tagged fish survived passage of all eight hydropower stations to reach Lake Vänern. This result underscores the need for remedial measures to increase the survival of downstream migrating kelts.”

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Den vetenskapliga artikeln “Spawning migration of wild and supplementary stocked landlocked Atlantic salmon (Salmo salar)”, om laxens lekvandring i Klarälven, har publicerats i River Research and Applications. Författare är Anna Hagelin, Olle Calles, John Piccolo, Larry Greenberg och Eva Bergman från NRRV, Karlstads Universitet. I artikelns abstrakt skriver de:

“Upstream migration by adult salmonids is impeded by dams in many regulated rivers, as is the case for landlocked Atlantic salmon, Salmo salar, in the River Klarälven, Sweden. There, the salmon cannot reach the spawning grounds due to the presence of eight dams. Hence, hatchery-reared smolts are released downstream of the dams, and upstream migrating spawners are caught in a trap at the lowermost dam before transported by truck to the spawning grounds past the dams. To identify the spawning grounds and compare the behavior of wild and hatchery-reared Atlantic salmon during upstream migration and spawning, 34 wild and 28 hatchery-reared, radio-tagged Atlantic salmon were followed during their spawning migration from August to October 2011. Half (50%) of the hatchery fish, but only 11,8% of the wild fish ended up as fallbacks, i.e. they migrated past the first downstream power station, and did not spawn. A significantly higher proportion (21.4%) of hatchery- reared salmon moved in an erratic way, with several up and down stream movements, when compared to the wild salmon (5.9%). When looking at the salmon that stayed in the river (exc. fallbacks), wild individuals exhibited a holding behavior (little or no movements before presumed spawning) more often (86.7%) than the reared ones (50%). The wild salmon also held position (and presumably spawned) for longer time (25.4 days) than the reared salmon (16.1 days). Reared salmon held position, on average, 10 km further upstream than wild salmon, passing the presumed best-quality spawning habitat. The migration speed (average 17.4 km/day) between two logger stations did not differ between wild and reared fish or between sexes. Our results suggest that the reproductive success of hatchery-reared Atlantic salmon is relatively low and their capacity as supplementary spawners to the wild population in the Klarälven, is probably small.”

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Finns på…

“Norges Jeger- og Fiskerforbund”

… och…

NIVA:s hemsida

Tack Frode och Lars-Åke!

Läs artikel i “The Independent” på nätet om ålarbetet i Storbritannien



Ålen får hjälp nedströms på flera håll, nu även i Göta älv, vilket beskrivs i en artikel på Expressens hemsida. Håkan Wickström vid Fiskeriverket m.fl. uttalar sig om ålen, den svenska ålförvaltningplanen och kraftbolagens avsiktsförklaring för att ge fler ålar möjlighet att nå havet. Man undrar dock över kommentaren från “Författaren och naturexperten Tommy Hammarström, ledarskribent på Expressen” som inte tycks inse att det är viss skillnad på hur mycket vuxen ål man kan fiska i dag och hur många glasålar som kommer in. Kommer det inte någon glasål i dag kommer det inte heller produceras någon vuxen ål i framtiden, oavsett hur mycket ål vi kan fiska i dag…?

Det har alstrats en del rapporter från arbetet i Ätran och ni får gärna ta del av dem om ni hör av er till oss:

Bergdahl, D. 2007. Nedströmsmigration av atlantlax och havsöring vid Hertings vattenkraftverk. Biology, Göteborgs Universitet. 14 sidor.

Bergdahl, D. 2008. Downstream migrating silver eels confronting a hydropower station in southern Sweden. Biology, Göteborgs Universitet. 11 pages.

Calles, O. (2009) Redovisning av åtgärds funktion för nedströms vandrande fisk i Ätran. Slutrapport till Naturvårdsverket No. 3 sidor.

Calles, O. & Bergdahl, D. (2009) Ålens nedströmspassage av vattenkraftverk – Före och efter åtgärd. Karlstad University Studies No. 2009:19. 37 sidor.

Calles, O., Kläppe, S., Österling, M. & Alenäs, I. (2009) Återställning av vandringsväg för fisk vid Hertings kraftstation i Ätran. Årsrapport till Naturvårdsverket. 5 sidor.

Calles, O., Olsson, I.C., Comoglio, C., Kemp, P., Blunden, L., Schmitz, M. & Greenberg, L.A. (2010) Size-dependent mortality of migratory silver eels at a hydropower plant, and implications for escapement to the sea. Freshwater Biology, 55, 2167-2180.

Karlsson, S. 2008. Hydro-electric power and downstream migration of  Atlantic salmon and Sea trout – Evaluation of mortality and movement using telemetry in the river Ätran. Biology, Göteborgs Universitet. 21 pages.

Monsén, J. 2010. Laxens biologi i ett reglerat vattendrag (arbetstitel). Naturresurs rinnande vatten, Karlstads universitet. 10 sidor.

I dag kom vårt vetenskapliga artikel på ålens passageproblem i Ätran ut på tidsskriften Freshwater biologys hemsida. I artikeln utgör den fångstdata vi fått ta del av från Möllers i Nydala en mycket viktig del. Ni kan läsa abstract (sammanfattning) om du klickar här och vill ni ha en kopia på hela artikeln får ni kontakta mig olle.calles snabel-a kau.se

Stora tack till…

… Möllers i Nydala för värdefull information om ålfångsternas utveckling under femtio år!

… alla som hjälpt oss att få tag på studieålar: Lennströms i Östra Frölunda, Anderssons vid Skärshultsbäcken, Jacobsons i Vessigebro och Möllers i Nydala!