Fiskebiologiske undersøkelser i Surna. Årsrapport 2015

Ugedal, O., Jensås, J.G. & Østborg, G. 2016. Fiskebiologiske undersøkelser i Surna. Årsrapport 2015. - NINA Rapport 1246. 27 s. I perioden 2002 - 2015 er det utført årlige undersøkelser i Surna med formål å bedre kunnskapen om bestandsstatus av laks og sjøaure. Kunnskapen skal brukes i vurderinger av relevante kompensasjonstiltak for å bøte på effekter av reguleringen av vassdraget ut over dagens utsettingspålegg av laksunger. Reguleringen ble iverksatt i 1968 og berører vannføringen i omtrent to tredjedeler av den lakseførende strekningen av vassdraget. Vannføringen i de midtre deler av Surna (mellom Trollheim kraftverk og utløpet av Rinna) er bety-delig redusert, mens elva nedstrøms utløpet fra kraftverket er påvirket av kjøringen av kraft-verket. Surna oppstrøms samløpet med Rinna er ikke direkte berørt av reguleringene. I 2015 ble det rapportert om fangst (sum av avlivet og gjenutsatt) av 1098 laks og 261 sjø-aure med en samlet vekt på henholdsvis 3698 kg og 315 kg i Surna. Av fangsten ble 37 % av laksene og 17 % av sjøaurene gjenutsatt. Laksefangstene fordelte seg i 50 % smålaks, 44 % mellomlaks og 6 % storlaks. Gjennomsnittsvekta for laks var 3,4 kg, mens gjennom-snittsvekta for sjøaure var 1,2 kg. For laks var fangsten i 2015 høyere enn i 2014, men under middels sammenlignet med perioden 1993 - 2015. Fangsten av sjøaure i 2015 var den tredje laveste i perioden 1993 - 2015 både i antall og vekt. Det er innført betydelige fangstbegrensninger i sportsfisket etter både laks og sjøaure i Surna, slik at fangstene i de siste årene er vanskelig å sammenlikne med tidligere år uten å ta hensyn til dette forholdet. Analyser av skjellprøver fra sportsfisket tyder på at 80 % av fangsten i 2015 bestod av villlaks. Av dette var 95 % førstegangsgytende laks og 5 % tidligere gytere. Førstegangsgyterne fordelte seg med 40 % 1-sjøvinter, 48 % 2-sjøvinter, 6 % 3-sjøvinter og 1 % 4-sjøvinter laks. Den beregnede fangsten av 1-sjøvinter laks fra smoltårsklassen 2014 var noe lavere enn fangsten av 1-sjøvinter laks fra årsklassen 2013, men likevel vesentlig større enn fangstene av slik fisk i de foregående årene. Samlet kan disse to smoltårsklassene gi forhåpninger om et relativt stort innsig av mellom- og storlaks i Surna i 2016. Andelen fettfinneklippet laks i skjellmaterialet fra sportsfiskefangstene var 5 % i 2015 og disse fiskene stammet fra utsettinger av laksesmolt i perioden 2011, 2013 og 2014, med størsteparten fra utsettingene i 2014 i form av 1-sjøvinter laks i 2015. Tilslaget i form av gjenfanget laks i sportsfisket fra smoltutsettingene i 2009-2013 har vært svært dårlig, mens tilslaget på smoltutsettingene i 2014 synes å bli noe bedre. I 2015 ble det funnet årsyngel av laks på samtlige av de 29 undersøkte lokalitetene i hoved-strengen av Surna. Nedstrøms kraftverket var tettheten av lakseyngel gjennomgående lav og lavere enn i 2014. Den gjennomsnittlige tettheten av yngel var lav til moderat på elvestrekningene oppstrøms kraftverket, men på om lag samme nivå som i 2014. Den gjennomsnittlige tettheten av eldre laksunger i 2015 var vesentlig lavere enn i 2014 i alle undersøkte vassdragsavsnitt. En viktig årsak til dette er at årsklassen som stammer fra gyting høsten 2013 er svak med lave tettheter av 1+ laksunger spesielt i elva oppstrøms kraftverksutløpet. Tettheten av presmolt laks (laksunger større eller lik 10 cm) var i alle de tre hovedavsnittene av vassdraget vesentlig lavere enn i 2014 og lavere enn de fleste andre år i undersøkelsesperioden 2002 - 2015. Dette kan tyde på at smoltutgangen i 2016 kan bli mindre enn den har vært de to siste årene og de fleste andre årene av undersøkelsesperioden. I 2015 ble det funnet årsyngel av aure på 23 av 29 lokaliteter. De høyeste tetthetene ble funnet nedstrøms Trollheim kraftverk, og her var tetthetene høyere enn i 2014. Oppstrøms kraftverket var aureyngel klumpvis fordelt og med gjennomgående svært lave tettheter. Tetthetene av eldre aureunger var lav på alle strekningene, som de har vært i hele undersøkel-sesperioden.© Norsk institutt for naturforskning. Publikasjonen kan siteres fritt med kildeangivelse

Marine food consumption by adult Atlantic salmon and energetic impacts of increased ocean temperatures caused by climate change

Atlantic salmon Salmo salar are experiencing widespread population declines, and reductions in growth and survival in the marine environment are contributing factors. Our aims were to estimate marine food consumption of adult salmon and to determine how energetics would be directly afected by the increased ocean temperatures associated with climate change. We tagged previous spawners on outward migration (body size 76–119 cm) with archival tags and used a bioenergetic model to combine in situ temperature recordings with individual data on body growth. Average energy consumption was estimated to be 331–813 kJ per day, which is equivalent to 5–11 prey fsh with an average body mass of ca. 15 g. Energy content of prey was the most important factor determining food consumption required to maintain growth. Conversely, the increases in ocean temperatures expected with climate change were predicted to have limited physiological efects on energy budgets and limited impact on the food consumption needed to maintain growth. We conclude that climatic warming will impact Atlantic salmon primarily through changes in prey availability and ecosystem structure rather than the direct efects of temperature on physiological performance

Modelling the effect of hydropeaking‐induced stranding mortality on Atlantic salmon population abundance

Studies of hydropeaking‐induced stranding mortality on fish populations have been confined to analysis of empirical data and/or short‐term hydraulic‐habitat modelling of individual events and are thus limited as to how they may be used to infer long‐term effects in fish populations. In this study, the effects of stranding mortality on an Atlantic salmon population were simulated using an individual‐based Atlantic salmon population model with the objective of determining the sensitivity of population dynamics to stranding. It was found that density‐dependent mortality (an alternative source of mortality in juvenile Atlantic salmon) partially compensated for stranding mortality, acting as a negative feedback mechanism that dampened change in population abundance. Stranding caused a perturbation in population dynamics, and effects of individual stranding events persisted in time across the life stages of the population. Effects on population abundance depended on the time of year when stranding was applied, both because of intra‐annual changes in stranding mortality probability and because of intra‐annual changes in the ability of density‐dependent mortality to compensate for stranding mortality. We concluded that empirical measurements of stranding mortality have limited potential for inference of overall effects on the population, and a more dynamic modelling approach, incorporating system feedback, allows for a better modelling of the impact of stranding. Sensitivity analysis showed that population abundance was highly sensitive to density‐dependent mortality, and we suggest that this area should be prioritized for further research when investigating the effects of hydropeaking on rivers.acceptedVersio

Iteroparity and its contribution to life-history variation in Atlantic salmon

Evolution of iteroparity is shaped by the trade-off between current and future reproduction.We studied variation in iteroparity among 205 050 individual Atlantic salmon caught in 179 rivers spanning 14◦ of latitude. The proportion of repeat spawners (iteroparous individuals) averaged 3.8% and ranged from 0% to 26% across rivers. Females were more often repeat spawners than males and had lower cost of reproduction in terms of lost body mass between spawning events. Proportion of repeat spawners for a given sea age at maturity, and the ratio of alternate to consecutive repeat spawners, increased with increasing population mean sea age at maturity. By combining smolt age, sea age at maturity, and age at additional spawning events, we identified 141 unique life-history types, and repeat spawners contributed 75% of that variation. Our results show that repeat spawners are important for life-history variation and suggest that the association between mean sea age and the frequency of repeat spawning is adaptive rather than a pleiotropic side effect arising from selection on sea age. age at maturity, life-history evolution, local adaptation, repeat spawning, trade-offpublishedVersio

Salmon lice-induced mortality of Atlantic salmon during post-smolt migration in Norway

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Evaluation of genetic effects on wild salmon populations from stock enhancement

Many salmonid populations are of conservation concern, and the release of hatchery-produced juveniles is a frequently used measure to alleviate declines and increase harvest opportunities. While such releases may be of conservation value for some populations, stocking may also decrease the effective population size and subsequently impose additional strain on already threatened populations. In this study, we assessed how the cohort-wise effective number of breeders in five populations of Atlantic salmon (Salmo salar) were affected by supplementation. Altogether, 19 cohorts were studied (2–7 cohorts per population) by estimating the proportion hatchery-released individuals and the effective number of wild and captive breeders in each cohort of the respective populations. We show that the effect of releasing captive-bred individuals varies both between populations and between years within the same population. A Ryman–Laikre effect—where the effective number of breeders has decreased as a consequence of supplementation—was observed for 11 cohorts. We discuss how supplementation can be adapted to optimize the effective population size, demonstrate that evaluation of supplementation can be reliably achieved, and show that supplementation programmes that lead to high proportions of hatchery-origin fish on spawning grounds are more likely to induce a Ryman–Laikre effect. Atlantic salmon, effective population size, population genetics, Ryman–Laikre effect, Salmo salar, stockingpublishedVersio

Can variation in standard metabolic rate explain context-dependent performance of farmed Atlantic salmon offspring?

Escaped farmed Atlantic salmon interbreed with wild Atlantic salmon, leaving offspring that often have lower success in nature than pure wild salmon. On top of this, presence of farmed salmon descendants can impair production of wild‐type recruits. We hypothesize that both these effects connect with farmed salmon having acquired higher standard metabolic rates (SMR, the energetic cost of self‐maintenance) during domestication. Fitness‐related advantages of phenotypic traits associated with both high SMR and farmed salmon (e.g., social dominance) depend on environmental conditions, such as food availability. We hypothesize that farmed offspring have an advantage at high food availability due to, for example, dominance behavior but suffer increased risks of starvation when food is scarce because this behavior is energy‐demanding. To test these hypotheses, we first compare embryo SMR of pure farmed, farmed‐wild hybrids and pure wild offspring. Next, we test early‐life performance (in terms of survival and growth) of hybrids relative to that of their wild half‐siblings, as well as their competitive abilities, in semi‐natural conditions of high and low food availability. Finally, we test how SMR affects early‐life performance at high and low food availability. We find inconclusive support for the hypothesis that domestication has induced increased SMR. Further, wild and hybrid juveniles had similar survival and growth in the semi‐natural streams. Yet, the presence of hybrids led to decreased survival of their wild half‐siblings. Contrary to our hypothesis about context‐dependency, these effects were not modified by food availability. However, wild juveniles with high SMR had decreased survival when food was scarce, but there was no such effect at high food availability. This study provides further proof that farmed salmon introgression may compromise the viability of wild salmon populations. We cannot, however, conclude that this is connected to alterations in the metabolic phenotype of farmed salmon

Prospects for the future of pink salmon in three oceans: From the native Pacific to the novel Arctic and Atlantic

While populations of other migratory salmonids suffer in the Anthropocene, pink salmon (Oncorhynchus gorbusca Salmonidae) are thriving, and their distribution is expanding both within their natural range and in the Atlantic and Arctic following introduction of the species to the White Sea in the 1950s. Pink salmon are now rapidly spreading in Europe and even across the ocean to North America. Large numbers of pink salmon breed in Norwegian rivers and small numbers of individuals have been captured throughout the North Atlantic since 2017. Although little is known about the biology and ecology of the pink salmon in its novel distribution, the impacts of the species' introduction are potentially highly significant for native species and watershed productivity. Contrasts between pink salmon in the native and extended ranges will be key to navigating management strategies for Atlantic nations where the pink salmon is entrenching itself among the fish fauna, posing potential threats to native fish communities. One key conclusion of this paper is that the species' heritable traits are rapidly selected and drive local adaptation and evolution. Within the Atlantic region, this may facilitate further establishment and spread. The invasion of pink salmon in the Atlantic basin is ultimately a massive ecological experiment and one of the first examples of a major faunal change in the North Atlantic Ocean that is already undergoing rapid changes due to other anthropogenic stressors. New research is urgently needed to understand the role and potential future impacts of pink salmon in Atlantic ecosystems. Atlantification, biological invasions, climate adaptation, Pacific Ocean, regime shiftpublishedVersio

Predicting the nationwide outmigration timing of Atlantic salmon (Salmo salar) smolts along 12 degrees of latitude in Norway

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