Salmon eat insects when they are young and eventually eat other fish when they are older. In the Pacific Northwest, salmon populations are doing very poorly. There are many reasons for this. Logging an area around a stream reduces the shade and nutrients available to the stream and increases the amount of silt or dirt in the water which can choke out developing eggs. Dams cause fish to die from the shock of going through the turbines and from predators which eat the disoriented fish as they emerge from the dam.
Fishing is another source of death that can contribute to the decline of salmon.
The weather also affects the amount of food that is available to salmon in the ocean. Some things we can do to save salmon are to protect their stream habitat, help restore streams that have been damaged, reduce fishing, and help find ways to increase salmon survival through the dams.