Helping spotted Salamanders?

My girlfriend lives in the country and has a woods out back. We were walking around back in october and she saw a yellow spotted salamander trudging along. She scooped it up and we went home. It was rather lathargic and had damage to its tail tip. We set up a partial habitat and i brought it home since i had better equipment. It has been in a 20 gallon tank since then with a large fiddler crab that died recently. We were thinking of releasing it by the creek around mating season. If we continue to find them in the fall, would it be good to care for some over the winter? will this help the population at all? Was it a bad idea in the first place? just looking for some advice, thanks.