You're making a lot of assumptions with that. The velocity, range, and accuracy of bullets drops sharply underwater due to the drastically increased atmospheric pressure, But at that distance, yeah, that should still be enough to kill one of those little bastards.

A Barrett might be a bit much for fish, but it might be perfect for gators.

They'll still fold like a lawn chair when hit in the brain stem with a round or two of 7.62 NATO.

Where there's smoke, they pinch back.

Those were the good ol' days.