Salmon regulation: How should we do it?

A fair point: how do we divide up the world to minimize the issues that cross multiple jurisdictions? In the natural world one great answer is watersheds. Many, but not all, solutions to some specific concern must be addressed within one or more watersheds. Fewer issues cross between them. How far does the watershed extend? For salmon, the issues are narrowest at the top of the watershed and become quite diluted a short distance offshore.