Thanks for the current replies.

I'll look at air rifles, but I'll also just try to convince Old John that a .22 in the country won't attract much attention.

It's a U-shaped driveway with a few houses within 100 yards of the ponds.

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My Ruger precision with a can and subsonic is a lot quieter than my Gammo pellet gun...and more effective

i have a winchster wild cat 16" barrel and they are loud my western auto 20" barrel they are quiet.

I bough whatever Hop told me to buy. Shoots great.!!!!!!!

Make three of these with chicken wire for the netting.

.22 Super Colibri

Pretty much silent, a pellet on a .22 shell with little or no powder. Won't cycle in a semi auto though unless it's rated for .22 long, short, LR. Works great in bolts and levers though.

I was able to load them in a 10/22 by leaving out the mag and chambering them from the magwell with my thumb.

Same here, Benjamin with a 3X9 scope. Quite accurate too

Trapping is more effective than shooting.

Catching turtles is pretty easy,

Game Viper in 177 caliber comes with a quality 4X scope that is very accurate and powerful for what it is.

This, and a good bolt action...............

One of the things I noticed when looking is the .177 seems to have more velocity in a given model but once you reach about 1100fps, you get the sonic boom and it sounds like a .22LR. Because the .22 pellet is heavier, it'll do the same damage with less speed...and less noise.

Air pistols are significantly less powerful than the rifles. Also accuracy gets much more difficult the shorter you make the barrel. I've tried shooting water snakes with a BB pistol from a kayak. Shooting from a moving position at a snake that's moving on water that's also moving with the BB gun is quite a bit more challenging than you might think.

If the real goal is to reduce the number of turtles then trapping is definitely the best option. Turtles don't seem particularly bright to me I don't think it would be very hard to do.

I suppose you could use an air rifle to supplement the trapping if you just happen to stumble across a couple. In that case there's been several good suggestions made. I would just say I would favor the 22 (air rifle round) over the .177 for a reasons mentioned above.

4th or 5th vote for a subsonic .22 round. They are no louder than an air rifle.

When I was a kid, we caught and shot more turtles than I could count. Just google turtle trap and there's all kinds of designs. Ours had a ramp they'd climb up, then the board across the top would twist and they'd fall in, you don't even have to bait it.

A pellet gun will 100% shoot through a shell, but a head shot is 100% effective. I've got the same gun Hop posted a pic of, I think it sacrifices speed over accuracy, but it'd sure work if you're close enough.

Another vote for the Benjamin air rifle.
Had one as a kid. Could put up to 10 pumps in it and it dropped everything I shot. We had a pond and it's amazing how turtles will just show up and continue to show up.

Aim for the head for sport.
Aim for the body for an easy kill.