Fairly simply they take native salmon, in this case chum salmon native to the area, the rivers and creeks where they originally spawned, and they take the eggs and implant them into every river and creek that they want those fish to return to. When the salmon get to a certain stage, they go out to the ocean, and they come back to those same rivers and streams when they return to their systems. It's hugely successful.
On November 21st, 2017. See this statement in context.