Sometimes fish don't catch even when they are exactly in the middle of the circle, I think this happens the most in the area where the boat gets spawned on the first island. I wanted to go to the second one on the second session but I accidently hit the "new game" button and there was no popup asking if I'm sure. YOU HAVE TO MAKE THE POPUP, MAN! xD
Good game so far, but I'm not starting it over. I'll probably come back to it when the steam demo get released :D