The salmon lifecycle

The Atlantic salmon needs both access to rivers and the Atlantic ocean to complete their lifecycle. After hatching and living in a river for 1-3 years the baby salmon journey out to the ocean where they grow into adult salmon.

Then they return from the ocean to the same river where they were hatched to lay eggs and start the cycle again. Most salmon die after laying eggs, but some do this more than once.

This means that if we are not careful, changes to their breeding rivers can wipe out whole salmon populations.

Major salmon populations that have disappeared

• The river Rhine in Germany, once Europe’s biggest salmon river
• The river Gudenaa, once Denmark’s biggest salmon river

Data spike in 2015

In the year 2015 something happened to the Atlantic salmons growth rate out in the ocean, it spiked down. Both female and male salmon now grow slower and as they need to reach a minimum weight before returning to their river to breed, more and more salmon stay out in the ocean for longer, slowing down the breeding rate.

Several of the research presentations touched on this phenomenon. The researchers are looking into multiple factors for why this change occurred, one of the major ones being ocean temperature changes.

Some of the threats to the Norwegian salmon

Power dams

Power dams can block the salmons migration in and out of the rivers and also affect the salmon mortality during these journeys. Several presentation were given on the their impact on the salmon migration.

Increased gas saturation in the water caused by the power turbines and change of water flow, has been proven to damage and even kill salmon and its prey in the river. This was first discovered in Canada but is now confirmed to affect river fish in Europe, and the European council has initiated a monitoring program.

Humpback salmon invasion

Researchers are monitoring more and more humpback salmon in several Norwegian rivers. They can displace the local salmon species and drive them extinct with their aggressive breeding strategy.

Genetic contamination by farmed salmon

Escaped farmed salmon can interbreed with wild salmon. Farmed salmon genes makes them grow much faster than wild salmon, but also reduce their survival rate in the wild. By interbreeding this reduction carries over to the wild salmon population.