Comment by perrygeo

The salmon populations has been dropping for a century and have reached critical levels in the last few decades. This is not a recent phenomemon. There are many causes and they are understood quite well: dams block spawning habitat, water temperature increases, food web collapse, overfishing, habitat destruction, and algae blooms from pollution are all extensively documented in the literature. Where do you get the idea that scientists are flummoxed by this?