Background 
Winter mortality probably has a substantial impact on the production of juvenile salmon. Salmon fry burn off more energy than they consume during the winter, and they will die if their bodies’ reserves of stored energy are exhausted. To survive the winter, salmon fry depend on the fat reserves they have built up during the summer season and on an active nutritional intake during the winter.

Climatic conditions vary considerably from north to south in Norway, and it is therefore likely that the relative dependence on stored energy and nutritional intake also varies. Physical factors such as temperature and ice processes affect metabolism and winter survival rates. We know that different salmon populations react differently to changes in physical conditions. For example, the absence of surface ice in connection with the regulation of river systems has a negative impact on northern populations, while southern populations do not seem to be affected.

The duration of the winter varies considerably from north to south in Norway. It is therefore important to study the strategies (relative dependence on fat reserves vs. nutritional intake) which salmon in different climate zones in Norway use to survive the winter. This will also provide both general insight into how salmon are affected by climate change and information about how human intervention affects the winter survival rate of salmon in different parts of the country.

Implementation
The project is organised as part of the Research Council of Norway’s Wild Salmon Programme, and is being carried out by the Norwegian University of Science and Technology (NTNU) and the Norwegian Institute for Nature Research (NINA). 

Results

• To measure, both before and after the winter, the energy reserves stored by salmon fry along a climate gradient from Finnmark in the north to Rogaland in the south
• To carry out detailed studies of the seasonal dynamic in the stored energy of salmon fry in three rivers in Finnmark, Central Norway and Rogaland respectively
• To create a model showing the importance of stored energy relative to nutritional intake under various climatic conditions, using bioenergetic