Chris,
Rivers, especially the Mississippi are a totally different scenario than an enclosed lake, and how do you know there has been no ill effects of our fishing from what it was years ago, say before the influx of electronic technology into the fishing world? I know Dick Sternberg would be glad to go toe to toe with any individual that thinks that. He is an old river rat from way back before he became the famous biologist and writer he is today. As you well know, rivers are always in a state of flux. A walleye caught in Red Wing could have been down by Winona 2 days ago, and some where down in Iowa the week before. That same fish could have originated in some lake and washed over a dam in the spring and swam down some small feeder river many miles before it got to the Mississippi. The point is, the all famous P4 is stocked daily by any one of many different means with fish that are catchable the day they arrive there. There is no way to truly say that any fish is a P4 fish, because the day before they might have been in P2, or last week in P12. There was a telemetry study done several years ago by the Wisconsin DNR studing the movements of walleyes in P4. It is amazing just how far those fish would move in a day. The only constant was that there were 3 spots on Pepin that always held at least 1 fish during that study.
Bottomline is this, 2 lines is not an issue on P4, but you can not compare what happens there with any other body of water in the state. There is no constant to the river to set a base line for the study.