The damage of the shark to the player is too low.. at least 6 or 7 bites should kill you
Agree with the too low damage but if you are dead, everything you have built in many many hours is gone and you have to start at the beginning.
So first the system of saving your game has to change. You can continue from your last save when dying and not at the world´s first beginning.
Makes more sense, if the game has some kind of dangerous stuff like diving for treasures, so you can risk a bit and not lose everything.