I spin for pike a lot and all the hooks on my spinners are singles as I have cut off the trebles. I still catch plenty of fish, yes I lose a few now and then but I am not to bothered. Treble hooks can be difficult to remove even worse if the barbs are left on, they are not good for the fish in my opinion.
Have you ever seen some of the big lures on sale with rows of big scary trebles!
I often catch pike on the fly accidently, and they are so much easier to unhook on a single, and no damage is done to the fish.
Keep using singles on your flys far better than trebles, we must look after our fish