I also vote small thresher. Those things usually get tail hooked with minnow plugs and when that happens, you can't stop 'em on 50# string. I've caught white seabass up to 52# from my kayak and they don't fight much for their size so I'd be surprised if it was one of those. Then again there's always the bat ray scenario. In any case, it's a great story and sounds like great fun. Go get 'em next time.
Tight lines,
Adam