The Environment Agency is tagging more than 4,000 salmon and 900 sea trout smolts to understand how climate change is impacting the environment.
The fish are set to be monitored to gauge how changes to the environment are shaping their biology, specifically being tracked in their migration from the River Tamar out to sea.
Marine survival rates are also being counted, to understand the likelihood of growth to adult salmon in current natural conditions.
Paul Elsmere from the Environment Agency said: “Salmon are key indicators of climate change and are considered by many to be the perfect barometer for measuring the health of our oceans and rivers as they have life stages in both environments.
“Since the Tamar index river programme started in 2004 we have recorded significant changes in run timing, stock structure, body size and condition, juvenile recruitment and the emergence of new diseases and conditions, all of which can be linked to climate change.”