So after playing the paid version, I have to say this is a pretty good starting point. It was a little frustrating to control at first, but once I realized you're supposed to move in an arc like a dolphin, it became a lot easier. I was able to reach up to 300 so far.
One thing I would suggest is that once the sharks reach the range where they become edible, maybe have the ones that can be eaten approach the player from the opposite side of the screen? While the current situation does allow for a bit of a risk/reward dynamic, it's a bit awkward to gauge whether to avoid them when you have so little time to react, so it usually ends up with the sharks being eaten by accident. It would also make things more consistent, with anything on the left side being dangerous while the right side being food.