Slow might be a decent thing, to give fishermen time to reel their lines out
of the way, or even deal with a fish on the hook,

These regulations seem to be for the draw span where fishing is prohibited.
BTW I have never seen a fisherman on a bridge give the least consideration for
a boater. You are lucky if they don't try to hit you. It reminds me of rednecks
shooting at signs on the side of the road.
You are certainly a target if you fish near a bridge from a boat.