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Predation by northern pike Esox lucius on migrating hatchery-reared salmonid smolts
Karlstad University, Faculty of Social and Life Sciences, Department of Biology. (Naturresurs rinnande vatten)
Länsstyrelsen i Västra Götalands län, Vänersborg, Sverige.
Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Supplementary stocking of hatchery-reared smolts is the main method used to mitigate and compensate for lost production of Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) populations in rivers. The survival of hatchery reared smolts in nature is generally low, and predation is one explanation for this. In the River Klarälven, Sweden, approximately 175 000 hatchery reared salmon and trout smolts are annually released into the rivr approximately 25 km upstream of Lake Vänern, to where they migrate and remain until maturity. During 2006-2010 half of the released hatchery reared smolts tagged with telemetry transmitters did not reach Lake Vänern. The loss rate of smolts was higher in river reaches with shallow vegetated areas and in reaches with deep pool areas than in the dominant habitat type, consisting of intermediate depths and sandy, uniform bottom substrates. Similarly, average CPUE of northern pike (Esox Lucius) was high in the same habitats as where smolts were lost. Gut content analyses of pike showed that they fed chiefly on European smelt (Osmerus eperlanus) in April, hatchery-reared salmonid smolts in May and European river lamprey (Lampetra fluviatilis) in June. We argue that when these different energy and lipid rich alternative prey occur at high densities during their spawning periods they are probably an easily caught energetically favorable prey. Our results indicate that there may be ecological windows of opportunity for stocking hatchery-reared smolts that could increase survival in the River Klarälven.

Keyword [en]
ecological window; habitat-specific predation; migration; opportunistic predator; salmonid management
National Category
Ecology
Research subject
Biology
Identifiers
URN: urn:nbn:se:kau:diva-31979OAI: oai:DiVA.org:kau-31979DiVA: diva2:714120
Available from: 2014-04-25 Created: 2014-04-25 Last updated: 2014-05-15Bibliographically approved
In thesis
1. Migration and quality of landlocked Atlantic salmon smolt: Implications for conservation and management
Open this publication in new window or tab >>Migration and quality of landlocked Atlantic salmon smolt: Implications for conservation and management
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Atlantic salmon Salmo salar has a complex life cycle, including long migrations and habitat shifts for both juveniles and adults. As such, salmon populations are vulnerable to habitat degradation and fragmentation along their migratory routes. This makes management and conservation a complex task requiring knowledge of salmon ecology at different temporal and spatial scales. In this thesis I highlight the use of a holistic life-history based approach in the conservation and management of wild and hatchery-reared salmon in regulated rivers and lakes.

Small populations of wild-reproducing landlocked salmon and trout Salmo trutta exist in the regulated River Klarälven, Sweden. Since the 1930s, transportation of adult spawners upstream of eight dams has given the fish access to spawning grounds. The number of returning wild spawners became critically low in the 1960s, but stocking of hatchery smolts resulted in an increase in spawners that continues today. My data show that wild smolt may suffer high mortality due to multiple dam passages. To ensure viable populations of wild populations, future management should include both up- and downstream solutions that ensure connectivity in the system.

The recreational and commercial salmonid fishery are maintained by compensatory stockings, yielding annual catches of about 75 tons, and a river return rate of hatchery fish of about 1%. As a large portion of the stocked smolts does not survive downstream migration to the lake, there has been discussion about the quality of the stocked smolt and about stocking strategies. Based on my studies, producing hatchery smolts more closely resembling wild-born conspecifics should result in reduced loss rates. I suggest changes in the hatchery and stocking procedures to increase the survival of stocked smolts. The results of my research should be applicable to other regulated systems, particularly those with mixed stocks of wild and hatchery salmonid populations.

Abstract [en]

Atlantic salmon Salmo salar has a complex life cycle, including long migrations and habitat shifts for both juveniles and adults. As such, salmon populations are vulnerable to habitat degradation and fragmentation along their migratory routes, which make management and conservation a complex task requiring knowledge of salmon ecology at different temporal and spatial scales. In this thesis, I highlight the use of a holistic approach in the conservation and management of wild and hatchery-reared salmon in regulated rivers and lakes.

Small populations of wild-reproducing landlocked salmon and trout Salmo trutta exist in the regulated River Klarälven, Sweden. Since 1930, transportation of adult spawners upstream of eight dams has been done to give the fish access to the spawning grounds. My data indicate that a large proportion of the wild smolts are lost due to multiple dam passages, and future management should include both up- and downstream solutions, ensuring connectivity in the system. The fishery in Klarälven and Lake Vänern is maintained by compensatory stockings, yielding catches of about 75 metric tons and a river return rate of stocked fish of about 1%. I suggest changes in the hatchery and stocking procedures to increase the survival of stocked smolts.

Place, publisher, year, edition, pages
Karlstad: Karlstads universitet, 2014. 43 p.
Series
Karlstad University Studies, ISSN 1403-8099 ; 2014:29
Keyword
acoustic telemetry, hatchery, life history, migration mortality, regulated rivers, Salmo salar, salmon, smolt, trout
National Category
Ecology
Research subject
Biology
Identifiers
urn:nbn:se:kau:diva-31980 (URN)978-91-7063-561-8 (ISBN)
Public defence
2014-06-05, Erlandersalen, Universitetsgatan 2, Karlstad, 10:15 (English)
Opponent
Supervisors
Available from: 2014-05-15 Created: 2014-04-25 Last updated: 2016-08-16Bibliographically approved

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