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Institute of Marine Research

Ascending Atlantic salmon (Salmo salar) and sea trout (S. trutta) in River Guddalselva, Kvinnherad, 2000-2012.

Recommended citation:
Øystein Skaala (2018) Ascending Atlantic salmon (Salmo salar) and sea trout (S. trutta) in River Guddalselva, Kvinnherad, 2000-2012.
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During the 1990s, there was a rapid expansion of salmon farming in Norway, with observations of escaped farmed salmon in many rivers, and reports of high salmon louse infections in anadromous brown trout. National authorities became increasingly concerned about the potential detrimental impacts of salmon aquaculture on wild populations; there was a growing awareness of the need for greater genetic and ecological knowledge about wild populations and the interaction between aquaculture wild salmonids. A decision was made to use the river Guddalselva, located in the Hardangerfjord, as a “river laboratory”- i.e. as an experimental facility to study the interaction between aquaculture and wild salmonid populations in 2000 as a joint effort between several management authorities, river owners and research institutions. The primary tasks were to a) Establish full control of fish migrations in a natural river system in order to assess the natural production of smolt, the timing of migration and the marine survival of anadromous brown trout, b) Investigate the occurrence of local adaptation in anadromous brown trout and to what extent populations may have different susceptibilities to marine parasites, c) Conduct experimental field research on impacts of genetic introgression on fitness and production in wild salmon populations. Thus far, the results have been published in eight peer reviewed scientific papers. Another four manuscripts are also under preparation. These studies provide new insights into population dynamics, population differentiation, adaptation and marine survival in anadromous brown trout (sea trout). Moreover, survival of wild, hybrid and farmed salmon offspring has been studied in this river laboratory, providing unique insights into the potential consequences of escaped farmed salmon introgression into wild populations. Biological samples from Guddalselva has also contributed to a number of comparative studies on performance of Atlantic salmon families and populations under laboratory conditions, several of which have been conducted at the Institute of Marine Research´s facility at Matre. Data on salmon and trout smolt runs in the river in the period 2001-2016 have contributed to the national working group in modelling smolt migration for the so-called “Traffic Light System” for management of Norwegian aquaculture since 2016. The river, Guddalselva, represents one of only two rivers in Norway with permanent smolt traps where the whole river transect is covered. The data on smolt migration represents one of the longest and most complete timeseries yielding unique empirical data on smolt migration in Europe.
Scientific keywords:
Key words:
Salmon, Trout
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