Sadly, I'm having this problem too. Spent a good 40 minutes trying to catch a fish. I've tried all sorts of methods and nothing seems to work. Either I lift the Wiimote too quick and the bobber comes out of the water and I scare the fish away, or by the time there's tension on the line, the fish has already let go of the hook. I'm stumped and it sucks that I can't get past this part of the game.