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Reintroducing Atlantic salmon to once native areas: Competition between Atlantic salmon, brown trout and grayling
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013).ORCID iD: 0000-0002-9683-8080
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013).ORCID iD: 0000-0003-2220-1615
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Worldwide declines in salmonid populations have generated major interest in conservation and restoration of wild populations and riverine habitats. Plans to re-introduce species to rivers where they previously occurred raises questions as to their potential impact on these systems after so many years. In the River Klarälven, Atlantic salmon (Salmo salar) has been extinct from the upper reaches of its former distribution for more than 50 years due to the construction of hydropower dams. Here we study competitive interactions between Atlantic salmon and two other salmonids, grayling (Thymallus thymallus) and brown trout (Salmo trutta), that presently occur in the upper reaches of the river. We examine foraging rates, aggression and activity of juvenile Atlantic salmon, grayling and brown trout in allopatry at three different densities and in sympatry with one or both potential competitors in laboratory flumes. We found that Atlantic salmon captured prey less frequently in the presence of brown trout and grayling, whereas grayling and brown trout affected each other, but were unaffected by Atlantic salmon. Rates of aggression initiated by salmonids in allopatry versus sympatry revealed differences between fish species, with grayling being the most aggressive and salmon the least. There was also a difference in activity, i.e. time spent cruising or holding position, between the species, with grayling being the most active and salmon the least. These results suggest that re-introduction of Atlantic salmon probably will have little impact on grayling and brown trout, whereas high densities of grayling and brown trout could affect the success of re-introducing Atlantic salmon.

National Category
Ecology
Research subject
Biology
Identifiers
URN: urn:nbn:se:kau:diva-71326OAI: oai:DiVA.org:kau-71326DiVA, id: diva2:1291157
Available from: 2019-02-22 Created: 2019-02-22 Last updated: 2019-02-25Bibliographically approved
In thesis
1. Conservation of landlocked Atlantic salmon in a regulated river: Behaviour of migratory spawners and juveniles
Open this publication in new window or tab >>Conservation of landlocked Atlantic salmon in a regulated river: Behaviour of migratory spawners and juveniles
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Hydropower dams represent one of the major threats to river ecosystems today. The dams block migratory routes in many rivers, which is problematic for migratory fish species. Trap-and-transport may be an alternative to fish passage solutions, as a strategy to compensate for lost river connectivity. Stocking of hatchery fish is another mitigating measure often used to compensate for reduced yields in fisheries, but also as supportive breeders in declining populations.

 

In this thesis, I report the results from radio-telemetry studies where the behavior of migrating Atlantic salmon spawners has been investigated in a regulated river. I also studied the function and success of using hatchery fish as supportive breeders and if there are any effects of migratory timing on migratory success. Further, I evaluated upstream passage performance by Atlantic salmon and brown trout at fishways in rivers Klarälven, Sweden and Gudbrandslågen, Norway. The goal was to determine if prior fishway experience had an effect on passage success. I identified three problems associated with the current river management, namely the high incidence of fallbacks among the early migrating salmon, the negative effects of high river flow and prior experience on fishway efficacy and that the use of hatchery-reared fish as supportive breeders have little, if any, positive effect on reproduction. Finally, I examined the competitive interactions that may occur when reintroducing Atlantic salmon to areas with native grayling and brown trout. I found no evidence of Atlantic salmon affecting grayling or brown trout. Instead, Atlantic salmon were dominated by the other two species, which indicates that reintroduction of salmon may not be successful, especially if habitat diversity is constrained.

 

Conservation and management of migratory salmonids requires an understanding of their ecology and life-histories. In the regulated river Klarälven, populations of landlocked Atlantic salmon and migratory brown trout have declined due to river exploitation. The results presented in this thesis originate from concerns regarding salmonid conservation in regulated rivers, with a focus on the difficulties migratory spawners may face in these altered environments.

Abstract [en]

In this thesis, I report the results from radio-telemetry studies where the behavior and success of migrating Atlantic salmon (Salmo salar) spawners has been investigated in a regulated river. I have also studied the function of using hatchery fish as supportive breeders and evaluated the upstream passage performance by Atlantic salmon and brown trout (Salmo trutta) at fishways in the River Klarälven, Sweden and Gudbrandslågen, Norway.

I identified three problems associated with management in a regulated river, namely the high incidence of fallbacks among the early migrating salmon, the negative effects of high river flow and prior experience on fishway efficacy and that the use of hatchery-reared fish as supportive breeders have little, if any, positive effect on reproduction.

Finally, I examined the competitive interactions that may occur when reintroducing Atlantic salmon to areas with native grayling (Thymallus thymallus) and brown trout.

Conservation and management of migratory salmonids requires an understanding of ecology and life-histories. The results presented in this thesis originate from concerns regarding salmonid conservation in regulated rivers, with a focus on the difficulties migratory spawners may face in these altered environments. The results of my research can be applied to other regulated systems, particularly those with trap and transport solutions.

Place, publisher, year, edition, pages
Karlstad: Karlstads universitet, 2019. p. 51
Series
Karlstad University Studies, ISSN 1403-8099 ; 2019:7
Keywords
Atlantic salmon, conservation, migration, spawning, hydropower, competition, juveniles, brown trout, hatchery reared, fallback, delay
National Category
Biological Sciences
Research subject
Biology
Identifiers
urn:nbn:se:kau:diva-71333 (URN)978-91-7867-002-4 (ISBN)978-91-7867-007-9 (ISBN)
Public defence
2019-04-12, Sjöströmssalen 1B309, Karlstad Universitet, Karlstad, 10:15 (English)
Opponent
Supervisors
Available from: 2019-03-22 Created: 2019-02-22 Last updated: 2019-05-08Bibliographically approved

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