Sorry, but that arrow will pull out. The broadhead needs barbs. If you kill the gator with the shot, Great, But, you still have to keep it from sinking. If you use a detachable head you still have to get good penetration with the line you are using, that's where good spyder wire comes in handy, It is thin. Even if it gets shot in the tail and is pulling the float it will tire after awhile, and then you can stick it with a killing shot or harpoon.
We're not shooting off of a reel. And you might have to make a 10 to 15 yard shot. I'd rig up an arrow that will penetrate at that distance, with a line attached at the back. With a line attached at the front it gets real exciting when you are shooting off a dark boat with everyone holding lights and someone steps on the line coiled on the deck when you shoot.
A simple stone point on a cane arrow will work, it did for thousands of years.