The size of the individual fish stocks constantly change. The Institute of Marine Research issues recommendations on how much fish may be caught. This requires knowledge of fish stocks, how much the stock grows from year to year, how great natural mortality is and how much is caught. Fisheries biologists use data from research expeditions, catch statistics, etc. to recommend quotas that can be harvested by the fishing fleet. More information is available in the article ”Fra målebrett til kvote” (in Norwegian) at the Institute of Marine Research.