Counting of spawning stocks in rivers in Western Norway

Project Department: Uni Research Environment (group: LFI - freshwater biology) period: 14.07.04 - 31.12.17

About the project

 

In the period 2004-2010 LFI-Uni Environment has counted spawing stocks of Atlantic salmon and sea trout in many rivers in Western Norway.

 

The studies aimed to characterise the current situation of the stocks and to estimate the number of escaped farmed salmon in the different rivers.

The work has been financed by several sources. The Directorate for Nature Management and the County Governor of Hordaland has contributed financially in limed rivers and national salmon rivers and the Institute of Marine Research and LFI has cooperated through NFR-projects TRACES and EPIGRAPH to study several unregulated rivers in the Hardanger region. Waterpower companies Statkraft, Lyse energi and BKK have financed counting of spawning stocks in several regulated rivers. LFI has contributed with own means in the accomplishment of field work and data analyses.

Counting of spawning stocks gives a good overview of the total spawning stock of Atlantic salmon and sea trout. These studies will give important information of the long term management of salmon and sea trout in the study rivers, although sources of error should be pointed out. Even though the divers usually could get a good view of the river, it is almost impossible to count the whole spawning stock. This because some fish will avoid the divers by laying under big rocks and in big pools. The counting of spawning stocks therefore represents a minimum estimate. The results must be analysed with these sources of error in mind.

Farmed salmon was recognized by morphological appearances like body shape, pigmentation and wear and tear of the fins. In many cases it is not possible to identify escaped farmed salmon by the appearance of fish. Therefore it is likely that some escaped farmed salmon have been classified as wild salmon. Our experience shows that it is seldom that wild salmon is classified as escaped farmed salmon. This implies that the amount of wild salmon is overestimated and the amount of escaped farmed salmon is underestimated.

Results of the counting for spawning stocks in the counties Sogn og Fjordane, Hordaland and Rogaland in the autumn 2010

Development in the period 2004-2010:

Sogn og Fjordane 2004-2010

Hordaland 2004-2010

Rogaland 2007-2010

Results of the counting in Sogn og Fjordane, Hordaland og Rogaland fall 2009

For more information about the results and the process of counting of spawning stocks see LFI-report No. 163 Gytefisktellinger i elver i Nordhordland, Hardanger og Ryfylke 2004-2008 – bestandsstatus for villfisk og innslag av rømt oppdrettslaks.

cp: 2019-10-17 12:17:13