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Certain spawning areas of the critically endangered Lake Saimaa landlocked Atlantic salmon (Salmo salar m. sebago) have been recently restored by excavator- and helicopter-scattered gravel, but the success of applied methodologies has remained open. Here, we monitored the spawning-related movements and redds occurrence of transported semi-wild and hatchery-reared salmon in the restored River Ala-Koitajoki, eastern Finland, using radiotelemetry and snorkeling. Nearly all fish accepted the newly restored spawning habitats in the river that maintains a low flow rate (only 4 [m.sup.3] * [s.sup.-1]). The movements of females released up to 2 weeks before spawning time were restricted mainly to the closest rapids from the release site, and most of the movements were directed downstream. Semi-wild and hatchery background fish exhibited similar mobility, which was more variable among males. A majority of redds were found in restored areas, and both helicopter- and excavator-scattered gravels were accepted as spawning substrates. Our results indicate that natural reproduction of the studied landlocked salmon population can be successfully returned to its original spawning river by restoration of habitats and transfer of spawners. Resume : Certains lieux de frai du saumon atlantique de lac (Salmo salar m. sebago) du lac Saimaa, qui est en voie de disparition, ont ete restaures a l'aide de gravier repandu par excavatrice et par helicoptere, mais le succes des methodes employees n'est pas encore etabli. Nous avons surveille les deplacements associes au frai et la presence de nids de frai de saumons semi-sauvages et eleves en ecloserie transportes dans la riviere Ala-Koitajoki, une riviere restauree de l'est de la Finlande, en utilisant la radiotelemetrie et la plongee avec tuba. Presque tous les poissons ont accepte les habitats de frai nouvellement restaures dans cette riviere qui maintient un faible debit (seulement 4 [m.sup.3] * [s.sup.-1]). Les deplacements des femelles relachees jusqu'a 2 semaines avant le moment du frai se sont principalement limites aux rapides les plus proches du site de lacher, et la plupart des deplacements etaient vers l'aval. Les poissons semi-sauvages et issus d'ecloseries presentaient une mobilite semblable, qui etait plus variable parmi les males. La majorite des nids de frai trouves etaient dans des zones restaurees, et tant les graviers repandus par helicoptere que par excavatrice etaient acceptes comme substrats de frai. Nos resultats indiquent que la restauration d'habitats et le transfert de geniteurs peuvent permettre le retour de la reproduction naturelle dans la riviere de frai d'origine pour la population de saumons de lac etudiee. [Traduit par la Redaction], Introduction Restorations of the spawning and nursery habitats are widely applied to enhance ecological state of regulated and degraded rivers (Pennell et al. 2007; Marttila et al. 2019; Pulg et [...]

Several Finnish populations of salmonids have been maintained exclusively by stocking hatchery-reared fish for several generations, and it is crucial to know whether domestication has affected fitness-related traits and to assess how the developmental environment influences fish phenotypes. Here, we focused on Lake Saimaa landlocked salmon (Salmo salar m. sebago) and studied the role of the early rearing environment in trait formation by comparing juveniles (fingerlings) from three backgrounds: (i) semi-wild (stocked as alevins), (ii) standard hatchery, and (iii) enriched hatchery conditions We compared juvenile morphology, swimming performance, and capability of feeding on natural prey in early winter. We found no differences between standard and enriched hatchery conditions. Semi-wild fish consumed more prey items, but wet mass of stomach contents did not differ among backgrounds. Swimming endurance was comparable among backgrounds. Semi-wild fish had slenderer body shape and longer fins than hatchery-reared fish. The lack of performance differences between hatchery juveniles and their semi-wild conspecifics is possibly due to reduced phenotypic plasticity caused by extremely low levels of genetic diversity in this population. Comme plusieurs populations finlandaises de salmonides ont ete maintenues exclusivement grace a l'ensemencement de poissons eleves en ecloserie pendant plusieurs generations, il importe de savoir si la domestication a eu une incidence sur des caracteres associes a l'aptitude et d'evaluer l'influence du milieu de developpement sur les phenotypes des poissons. Nous nous penchons sur les saumons d'eaux interieures du lac Saimaa (Salmo salar m. sebago) et etudions le role du milieu de l'elevage precoce dans la formation de caracteres en comparant de jeunes saumons (alevins d'un an) de trois origines distinctes, a savoir (i) des individus semi-sauvages (alevins vesicules au moment de l'ensemencement), (ii) eleves en ecloserie dans des conditions normales et (iii) eleves en ecloserie dans des conditions enrichies. Nous comparons la morphologie des jeunes saumons, leur performance de nage et leur capacite a se nourrir de proies naturelles au debut de l'hiver. Nous ne relevons aucune difference entre les individus issus d'ecloseries dans des conditions normales et enrichies. Les poissons semi-sauvages consomment un plus grand nombre de proies, mais la masse humide des contenus stomacaux ne varie pas selon l'origine des poissons. Les poissons semi-sauvages ont des corps plus elances et des nageoires plus longues que les poissons eleves en ecloserie. L'absence de differences sur le plan de la performance entre les jeunes poissons issus d'ecloseries et leurs congeneres semi-sauvages est possiblement due a une plasticite phenotypique reduite causee par des degres extremement faibles de diversite genetique dans cette population. [Traduit par la Redaction], Introduction Many natural salmonid populations are threatened by various human activities, such as overharvesting and construction of hydropower dams. Dams often severely block the movements of migratory fishes and thus [...]