Do surfers mainly use their abs to surf?

I can surf for 6+ hours at times and the muscles that get the most tired on a day like that are the top and back of my shoulders, the muscles between my shoulder blades, my lower back and my abs. In general, your pecks, triceps, lats, all the muscles from your neck through your shoulders, back and butt get worked out from paddling - which is 95% of the effort.