Actually, the first move should be the complete elimination of all marine mixed stock fisheries on Chinook. Allow the fish to grow to adulthood, achieving full age and size. That would immediately provide the whales with food. Habitat restoration will take many years to provide relief.
Doing so will cost some harvest. Only those fish that are actually eaten by the predators are lost. The rest will be available in the terminal fisheries. They will also be larger and they will require less fuel per pound harvested to capture.
If we actually want to recover the whales, that is likely the only way to do it as habitat recovery will take too long and more will starve/abort.