Re: Seaswirl decking attaching
You may not be able to tell even with the glue removed. They fastened the decking down and then fiberglass over the decking and screws if it was screwed.
I would guess that they screwed the decking down because that is the quickest and easiest way.
You can set a skil saw for 1/8" deep and run it on each side of the stringer and then pry the fiberglass up with a wood chisel or small flat bar to find the screws if they're there and you know where your stringers are.
How much of the decking are you removing?