In 2005, there was a drastic change in the ecosystem in the Norwegian Sea, which would prove to have consequences for many Norwegian salmon populations. It is likely that the change also affected salmon populations further south in Europe.
According to the scientists, the supply of nutrient-rich Arctic water, which is usually transported naturally into the Norwegian Sea north of Iceland, was greatly reduced around 2005.
They believe that climate change could be a possible explanation, but also point out that knowledge about what controls the inflow of Arctic water is lacking.
The effect can’t really be compared to turning off a tap at home, because the supply of Arctic water to the Norwegian Sea has increased slightly. However, the change in 2005 is seen as a drastic decline, a regime change in which a large part of the most nutrient-rich source of food disappeared.
It would result in a distinct decline in the growth, and basically the fish grew less the following year at sea.
All of this is documented by NORCE scientist Knut Wiik Vollset and his colleagues in a new study, which has been published in the prestigious Science Advances journal.
Salmon stocks are becoming more vulnerable
The research has been carried out in collaboration with the Institute of Marine Research, Rådgivende Biologer (Advisory Biologists) and the Norwegian Institute for Nature Research – NINA.
The scientists reported a sudden reduction in the growth of wild salmon from 2004 to 2005, in populations from Oslo to Nordland County. In the two most affected regions, Western Norway and Southern Norway, the decrease in growth is 25 percent and 36 percent respectively.
“The basis for strong salmon populations is good growth conditions at sea. When such drastic changes in the ocean occur, our salmon populations become more vulnerable than they have been”, says Vollset, who is the main author of the new study.