The release of pet herps is a major problem not just for that animal, but more importantly, the native herps in that area. You have no idea what diseases/parasites that turtle may be harboring. It may look healthy to you, but releasing it could potentially wipe out an entire herp population and I am not just talking turtles; snakes can also be killed by a disease carried by apparently healthy looking turtles.
Even if a pet turtle is 100% healthy, it may very well be from another locality altogether. This poses another serious problem: the transfer of foreign genes into the gene pool of a wild population. Most turtle species have an expansive natural range covering a variety of habitats, anywhere from sandy, coastal areas to rocky, cool mountaintops and many areas in between. Wild populations have adapted to their local conditions (soil, climate, vegetation, etc.) for millennia. Research has even shown that turtles of the exact same species inhabiting different areas of their range prefer entirely different temperatures. Releasing a pet turtle into an area where it may breed with wild turtles is like throwing a monkey wrench into the gears of a finely tuned machine.
As a wildlife biologist conducting herpetological research for the National Park Service, I feel I am very qualified to make the above statements. I certainly hope you will follow my advice and that of the others here that feel the same way about releasing pets.
Will Brown
BlueRidgeBiological.com / Rare Natural History Prints
BlueRidgeBiological.com / Rare Natural History Prints