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Report, 2012

Populationsgenetisk kartläggning av Vänerlax.

Palm, Stefan; Dannewitz, Johan; Johansson, David; Frida, Laursen; Norrgård, Johnny; Prestegaard, Tore; Sandström, Alfred

Abstract

In Lake Vänern, Sweden, two of the world's few land-locked and large-sized Atlantic salmon (Salmo salar) populations exist. The lake also is home for fast growing, lake-migrating populations of brown trout (Salmo trutta). Since the 1800s, widespread human exploitation of spawning and nursery areas in rivers has severely affected the migratory salmonids in the Lake Vänern area, and a large number of local populations have gone extinct. To compensate for lost natural production caused by the hydropower development, extensive compensatory stocking has been going on for many decades using local salmon and trout originating from Rivers Klarälven and Gullspångsälven. In these two rivers wild production of salmon still exists, and they are also the most important reproduction and nursery areas for the wild lake-migratory trout. The salmon and trout from Klarälven and Gullspångsälven are considered unique with a high conservation value. At the same time, they constitute valuable biological resources for the fishery. A prolonged history of weak populations in the wild, use of few parental fish in hatchery production, stock-crosses, and interbreeding of farmed and wild fish has undoubtedly altered the genetic population structure. So far, however, it has remained largely unclear how large genetic changes that have taken place. This report contains a comprehensive population genetic survey of salmon and trout (wild and hatchery produced) originating from Gullspångsälven and Klarälven. By comparing contemporary genetic data with historic material (microsatellite DNA) extracted from scale samples collected during past decades, it has been possible to assess levels of genetic change since the 1960s. It has also been possible to estimate genetically effective population sizes, levels of gene flow and population admixture. Our results show that clear genetic changes have occurred due to a combination of genetic admixture and random allele frequency fluctuations in small populations (genetic drift). Despite significant genetic changes in several cases, current levels of genetic differentiation among the stocks are nevertheless marked. Hence, it is still justified to regard these as genetically unique and worthy of protection. At the same time there are reasons for serious concern. For example, the estimated proportion of "native genes" in current Gullspångsälven salmon (both wild and hatchery) is only about 70 %, corresponding to a gene flow from Klarälven salmon since the 1960s of about 6-9 % per generation - an alarmingly high level. To prevent continued erosion of the genetic population structure, a set of recommendations is provided. A more successful genetic conservation work will be needed to safeguard long-term survival and productivity of the Lake Vänern (wild and hatchery) stocks, and is a basic condition for a sustainable salmonid fishery.

Published in

Aqua reports
2012, number: 2012:4
ISBN: 978-91-576-9071-5
Publisher: SLU, Institutionen för akvatiska resurser

Authors' information

Swedish University of Agricultural Sciences, Department of Aquatic Resources
Swedish University of Agricultural Sciences, Department of Aquatic Resources
Johansson, David
County Administrative Board of Västra Götaland
Frida, Laursen
County Administrative Board of Västra Götaland
Norrgård, Johnny
Karlstad University
Prestegaard, Tore
Swedish University of Agricultural Sciences, Department of Aquatic Resources
Swedish University of Agricultural Sciences, Department of Aquatic Resources

Associated SLU-program

Lakes and watercourses
Biodiversity

UKÄ Subject classification

Genetics

URI (permanent link to this page)

https://res.slu.se/id/publ/43239