I will start with yes, it's real. I'm not the only one saying that. I will start with that.
The impact of climate change on salmon can happen in different aspects. Fish are ectothermic, which means they use the temperature of the surrounding environment to.... They have the same temperature as their environment. When you have all those fish coming up through a river, and the temperature of the river is 20°C to 25°C, which is not the optimal temperature for those fish to live at, they are overstressed. That will be the first impact.
On the other hand, if you have higher temperatures in the ocean, the whole trophic chain is out there, so algae and phytoplankton bloom and therefore the shrimp that feed on them proliferate. Therefore, what amount of food is available for salmon? It's all a chain.
Unfortunately, these changes happen even with a minimal change in temperature. We're talking about even a couple of degrees Celsius being able to trigger this big change in productivity.