Fishing net is the best thing that will enable you to catch a turtle without hurting it. However, there is a special Turtle net, which is strong enough to hold the turtle and it available in the store if one is not capable of making it. Get detailed tips on how to catch it on http://www.ehow.com/how_2222595_catch-turtle.html.
It really just depends, what type of turtle is it? Snapping turtles are tough animals. A hook wouldn't harm them too much. Just put a hot dog on a hook and leave it there for the night. You have to use a big hook and a large chunk of meat big enough or a smaller fish will seize the opportunity.