I took my aforementioned Winchester Defender and put pistol grips on it a few years ago--it hurt like h*ll! Even with reduced recoil loads, it hurt.
Shotguns are shoulder arms, and work a lot better that way, IMHO.
If you can swing it take both--a stainless or polymer handgun in .44 Mag or 10mm say, that you wear constantly, for the surprises. That way, you could pack in the wrapped up and protected shotgun or other short rifle to back you up for the real emergencies on land, if you get stuck or attacked.
But, good point on your skill level/experience. If you're not used to it, a .44 or 10 will be a surprise also! Don't go anywhere without practicing first.
Just some thoughts.