| Summary: | A study of the growth of Atlantic salmon and sea trout during two different periods. Changes in growth between the two periods are related to ongoing changes in the ecosystems of the different life stages. The populations of Atlantic salmon (Salmo salar) and sea trout (Salmo trutta) are declining in Europe. For both species the key seems to be found in the saltwater stage of their life cycle. Two major changes have occurred in this stage over the last thirty years; the rise of aquaculture and climate change. For sea trout the main problem is believed to be aquaculture, with associated epizootics of salmon lice (Lepeophtheirus salmonis). For Atlantic salmon the problem seems to be a changing ecosystem in the North Atlantic, probably due to climate change. The focus of this study is growth of Atlantic salmon and sea trout caught in the river Etneelva, Western Norway, in 1983 and 2008. The growth of 1+ Atlantic salmon parr was positively correlated with river temperature. In the river, Atlantic salmon displayed a slight increase in growth between 1978-1981 and 2003-2005, but it was marginally not significant. The growth of sea trout parr was not significantly different between 1976-1981 and 2000-2006. There was a significant negative correlation between the size of 1+ Atlantic salmon parr at the beginning of the growing season and the growth of the 1+ sea trout parr. In the fjord, the sea trout post smolt growth has been reduced from 1979-1982 to 2002-2007. The growth during the second sea summer was also reduced for the sea trout, as was Fulton’s condition factor when the fish were caught. For the Atlantic salmon post smolt the growth was increased from 1979-1982 to 2004-2007, while the growth was significantly reduced for the 2 SW. Fulton’s condition factor for the spawners was also reduced. The weight of the MSW caught in 2008 was lower than expected. 65 % of the Atlantic salmon caught in 2008 displayed summer growth checks during their first year at sea, whereas only 4.5% of the fish caught in 1983 had this. ...
|
|---|