A piece of cooked chicken as bait in a turtle trap is very reliable at
picking the turtles off one by one.

The bait attracts the turtle into the cage, the tug on the bait closes
the trap door, kerchunck, one healthy turtle, in the trap, waiting for
room service

Set out two traps, and you can dawdle from trap to trap at a leisurely
pace, collecting turtles. You might want to create an enclosure if you
collect numbers, to separate out the 'nice' turtles like painted
turtles, from the snapping turtles

Turtles are very sensitive critters, a bait of chicken in a trap when
they can here and feel there is nobody hanging is quite effective at
tempting them into a simple cage

Regards, andy
http://www.members.aol.com/abdavisnc/swglist.html

What else would work good in
attracting snapping turtles so that they can be "humanely" disposed of.
It can't be something that falls off the took too easily or be slowly
picked at by small fish.