I have a theory about the game too... I'm making the assumption the sharks are there as part of a puzzle. I'm guessing the villagers may have to make some kind of shark-net or something to put in the water before they can swim/fish.
Or I might be right off
It's so hard waiting. I just happened to come by the site THE DAY Plant Tycoon was released. So there was no waiting, no anticipation, no coming here several times a day to see if there's been any progress in the last hour. No wonder I'm going grey