I have 2 games going 1 in nature and 1 in magic , in the nature the sharks went away and never came back , in the magic the sharks never went away and are still there but fishing is working , is this a _bug_ or the way the game was made? thanks

I think that's the way the game was made -- the guide says that the "nature" potion acts like a shark repellant (sharks go away) and the "magic" potion works like a charm (sharks stay but won't attack villagers).

That's exactly how it works!