All right, here's the wrap-up. I just want to finish by saying of course I really enjoyed your game and the quality of elegance it offers. It can be really great to think about these things as a mental exercise if nothing else.
Now wrapping up the theory I offered here... above I described a way of reframing your game as a maze... but one thing is still left out: how do we handle the remaining turtles? Well, I don't have a general solution thought up yet, but as a practical one - if you wanted to make more levels without thinking too hard - you could reuse the motif you have in the first level of releasing the remaining turtles all at the end in one move.