Yes, you can eat them. Catching, cleaning and cooking are easy once you learn a few tricks. Be aware that many turtles carry salmonella, and animals that that inhabit sewage polluted water will be infected by it. So watch how you swing the knife while cleaning, wash your hands, keep uncooked meat away from cooked meat and foods served raw, and cook the meat thoroughly.

Be aware that turtles and snakes don't reproduce very fast. They lay a lot of eggs but their early-life mortality rate is quite high. Just about everything out there feeds on baby snakes and turtles. One hunter working a large area isn't much of an issue long-term but it is pretty easy to exceed the carrying capacity. Something you won't know you have done until several years after the fact.

It also has to pointed out that the most effective gun for dealing with snakes is ... a stick. Who in their right mind shoots them from 10 yards away when you can walk up and bag them? A waste of ammunition to even try to shoot them. Besides, snakes and turtles keep longer if you don't kill them. Just pin them, pick them up, and stuff them into a sack.

Using a gun of turtles isn't much better. Shoot one on a log and it will fall off. Good chance it gets lost. Waste of game and ammunition. Use a dip net. Cheaper, faster, surer, less noisy. When they are on the water's edge you step out into the water and pick them up them when they make a run for it. Or sneak the net below them when they are sunning on a log and they dive right in. Did a lot of that when I was a kid.

In the water shuffle your feet. Alligator snappers and gators tend to bite first, and then move, if you step on them. If you bump them they slink off. They are both ambush predators and if they are interrupted, but not threatened, they simply move and set up elsewhere.

Of course in the water you're going to run into water snakes. Most will run from you but water moccasins can get aggressive. They aren't dangerous at a couple of meters away and unless they are standing still, in which case they are harmless, they are close to impossible to reliably hit with a gun because they move fast. Even a shotgun doesn't do much good. At close range the shot doesn't spread enough to hit a significant area. Makes an lot of noise and an impressive splash.

A pistol loaded with rat-shot shells can serve for ranges under ten feet but a stick is simply the better tool for the job. A stick always works, never jams, never runs out of ammunition. Sticks are also free. Whack the water in front of a snake with the flat of the stick swung overhead and most will turn and run. Snakes sense the impact and vibration from the water. Hitting them never fails to back them off or kill them.