I've not made it past 42 points in the newest update the shark will follow where I go after some time passes. (Well in the demo version, downloaded the wrong zip.) Even after getting the right download, I can't make it past 750 because the shark keep coming every 5 seconds. And even though I hadn't eaten a single shark it's usually bigger than me. It starts off with the smallest and then it gets right to the biggest after a minute. Also I've been able to eat Eels when they are shocking and still get the power up (sometimes).
I think the Cajun fish power up should work on the shark, at the very least the smaller ones. I don't think any other suggestion is needed for the power up.
I feel that eel power up is rather lackluster because it only helps horizontally not vertically and I end up using it accidently more than purposely and either way get eaten. Possibly instead of double clicking it could be assigned to a different command, possibly the right mouse click or a letter key. I would suggest that the eel could stun the character for a second if not eaten at the right moment. But I don't know what else you have planned for power ups so it may interfere with ideas you're having.