There is a documentary about this as well (
https://youtu.be/XdNJ0JAwT7I), which I thought was fascinating. I learned from this and one other (I’ve forgotten the name) that the salmon likely suffer far less from overfishing than most people believe. Perhaps what happened is the primary population pressures occurred until fishing pressure became noticeable. At that point people pointed their fingers to the most obvious cause of salmon deaths and missed the ones we’re only recently becoming more broadly aware of.
Not to say fishing doesn’t make a difference. It’s just not the only problem. Fish farm research was suppressed by the Canadian government which showed that the farms were spreading vast amounts of disease very consistently, for example. One disease acted so quickly that the fish would die before they could spawn. Fortunately the research surfaced eventually and farms are largely being shut down, but these farms have been operating for decades.
It’s a very complex and frightening problem. I’m glad we’re making progress in understanding it better.