A summary of 20 years (1998-2017) of scientific work on genetics and survival in anadromous brown trout (Salmo trutta L) and Atlantic salmon (S. salar L) in the river Guddalselva western Norway

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Betydninga av lange tidsseriar i forvaltningsrelatert havbruksforsking: Sjøaure i Hardangerfjorden - Årlege svingingar i antal og vekst hos parr og vekst hos postsmolt

The report includes studies on numbers, growth and survival of seatrout and salmon par in River Øyre, Kvinnherad from 1988 to 1998. The abundance o

Atlantic salmon and sea trout display synchronised smolt migration relative to linked environmental cues

Anadromous salmon and sea trout smolts face challenging migrations from freshwater to the marine environment characterised by high mortality. Therefore, the timing of smolt migration is likely to be critical for survival. Time-series comparing migration of Atlantic salmon and sea trout smolts in the same river, and their response to the same environmental cues, are scarce. Here, we analysed migration timing of ~41 000 Atlantic salmon and sea trout smolts over a 19-year period from the river Guddalselva, western Norway. Trout displayed a longer migration window in earlier years, which decreased over time to become more similar to the salmon migration window. On average, salmon migrated out of the river earlier than trout. Migration of both species was significantly influenced by river water temperature and water discharge, but their relative influence varied across the years. On average, body-length of smolts of both species overlapped, however, size differences were observed within the migration period and among the years. We conclude that salmon and trout smolts in this river are highly synchronised and migrate in response to the same range of linked environmental cues.publishedVersio

Cryptic introgression: evidence that selection and plasticity mask the full phenotypic potential of domesticated Atlantic salmon in the wild

Domesticated Atlantic salmon grow much faster than wild salmon when reared together in fish tanks under farming conditions (size ratios typically 1:2–3). In contrast, domesticated salmon only display marginally higher growth than wild salmon when reared together in rivers (size ratios typically 1:1–1.2). This begs the question why? Is this a difference in the plastic response driven by divergent energy budgets between the two environments, or is it a result of selection, whereby domesticated salmon that display the greatest growth-potential are those at greatest risk of mortality in the wild? We reared domesticated, hybrid and wild salmon in a river until they smoltified at age 2 or 4, and thereafter in fish tanks for a further 2 years. In the river, there was no difference in the mean size between the groups. In contrast, after being transferred from the river to fish tanks, the domesticated salmon significantly outgrew the wild salmon (maximum size ratio of ~1:1.8). This demonstrates that selection alone cannot be responsible for the lack of growth differences observed between domesticated and wild salmon in rivers. Nevertheless, the final size ratios observed after rearing in tanks were lower than expected in that environment, thus suggesting that plasticity, as for selection, cannot be the sole mechanism. We therefore conclude that a combination of energy-budget plasticity, and selection via growth-potential mortality, cause the differences in growth reaction norms between domesticated and wild salmon across these contrasting environments. Our results imply that if phenotypic changes are not observed in wild populations following introgression of domesticated conspecifics, it does not mean that functional genetic changes have not occurred in the admixed population. Clearly, under the right environmental conditions, the underlying genetic changes will manifest themselves in the phenotype.publishedVersio

Rømt og vill fisk i Etneelva 2017

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Rapport frå det nasjonale elvelaboratoriet i Guddalselva 2021 - Elvemiljø, smoltutvandring og gytebestandar av laks (Salmo salar) og sjøaure (Salmo trutta)

I Guddalselva er det installert ei heildekkande smoltfelle (Wolf type) som fangar smolten på veg ut i sjøen. Dette gjer at vi får representative uttak av mengde smolt produsert i elva. Elva har også ei fisketrapp som vert brukt til å registrera all oppvandrande fisk. I 2021 vart smoltfella opna 7. april og demontert 17. juni. Fyste aure- og laksesmolt vart begge registrert 9. april. Hovudmengda av laksesmoltane vandra ut mellom 11. og 18. mai. For auresmoltane vandra store delar ut mellom 11. og 16. mai, men der var òg ei stor utvandring mellom 25. mai og 4. juni. Siste laksesmolt vart registrert i smoltfella 14. juni, medan siste auresmolt vart registrert 17. juni. Til saman passerte 1091 laksesmolt og 2362 auresmolt fella. Registrering av oppvandrande fisk vart i år starta 22. mai, og avslutta 5. november. I løpet av desse månadane vart det registrert 114 laksar og 267 aurar. Ingen av laksane viste seg å vere rømlingar (oppdrettsfisk). Den første sjøauren var i fisketrappa 31. mai, mens den siste kom 29. oktober. Oppvandringa av sjøaure var på det høgaste i første halvdel av juli. Det meste av auren som gjekk opp var under 1,4 kg, med ei snittvekt på 0,95 kg. Biomassen for hofisk var på 168 kg. Den første laksen kom i fisketrappa 28. juni, medan den siste kom 8. oktober. Så å seie all laks kom i juli, august og september, med størst oppvandring i veke 37 og 39. Snittvekta var på 2,6 kg, men store delar låg i vektklassa 1 – 2 kg. Biomassen for hofisk var på 150 kg.publishedVersio