In my experience, very few perch float when they die. I lost all but one 12”+ YP this year (about 20 of original stockers) due to them being really old. I only found one dead one. I still have a lot of smaller YP, but the old ones clearly died this year as they no longer came for food.

It is possible they died and floated to shore where something ate them in the night, as it is unlikely they died all at once.