OK, relax
Wow, this really got to you, didn’t it? 
First of all, the word “whitewater” was not to be part of the message. What I want to do is to be hunting marine birds and ducks in silent seawater.
I seem to be able to get as near as a few meters from them, so if the kayak is adequately stable, I don’t see any problem…
Poor Old Joseph-
The fact that he’s even thinking about it at his advanced age is worth a round of applause… ;^)
I assume you know your regulations
I bring up the subject of regulations, because in my state, and I think this may be true for all U.S. inland waters, hunting from “open water” (water which is devoid of emergent vegetation) is illegal, except for jump-shooting on rivers. Things may be different on the coast, assuming that’s where you are.
Don’t fret over all the attention you got. The vast majority of the message boards on various other topics that I have checked out usually have posted questions that are many months old with only one or two responses each, if that. This is a good board with good people and lots of action, so you’re going to get a lot of extraneous opinions along the way, some of which may not be so useful, but that’s just how things go. Since your original question didn’t include any details at all, you shouldn’t be surprised that all sorts of issues were raised which are irrelevant. And hey now, if the word whitewater wasn’t part of your message, why did you put it there?
Anyway, now that we know for sure that you are talking about hunting waterfowl, I’d say don’t worry about steadying your aim. People take pictures from kayaks all the time, which requires far steadier support than shooting a shotgun. You’ll do just fine.
speaking of extraneous opinions
I’m having trouble finding that surfski thread. Just curious.
Hunting friend
I know someone who uses an old style whitewater boat for bird hunting. He can stuff a take-apart shotgun and a bunch of decoys inside. Uses the boat to get to where he wants to go (usually alone, in the dark, and often in wind) sets the decoys, but hunts from land. Doesn’t need a retriever since he can paddle out to the birds.