Migration

I'n confused. Stripers show up in the warmer rivers of Maine before they appear on the beaches. Don't they have to go through the colder waters near the beaches in order to reach these rivers? The rats will be showing up any day now in the Kennebunk River which is 30 miles north of me. It's only logical that they have to pass me to get there, but I can't catch fish until they start coming out of the rivers. This makes no sense. Can someone clarify this for me? Thanks.