It's both a focus problem and depth of field problem. Many macro shooters shoot at high ISO because at macro distances depth of field is shallow. Macro shooters shoot at f16 or higher all the time.
With those salamanders, the focus needs to be on the eye. If you find your pointing at the eye but the camera won't focus where you are pointing it, you may have a back or front focus issue with the lens...
Just stop down a little and you will get more depth of field and focus will be more forgiving.