I've had turtles.. Not to sound like a hick from the boondocks or anything, but when I was a kid, a big thing to do was own a turtle to take to "Turtle Races"... PETA would just love that. Most people will say, that when a turtle latches on, you should cut it's head off.. But that could scar the kid even worse than the bite - which can be pretty bad. You have a few choices, more or less, someone is going to get hurt. The victim, or the Turtle. See, they don't have any teeth, but their beak like thing is kinda like a pair of tin snips, I'm sure if they got a good grip, they'd take a chunk or a part of the finger off. You could just sit.. and wait. Once you leave him alone, he'll probably let go once he doesn't feel dangered anymore.. Try blowing air (o2) in it's face, to make it hide in the shell. or.. Kill it. If you don't have any drugs to sedate it that is. Now the bite. You gotta disinfect the hell out of it, b/c some turtles have toxins; or can pass along some really nasty infections and diseases. Irrigate and carefully scrub at the same time. Yeah, it's gonna hurt, but that's life and the only way to clean a wound.
The people who make those little field guides, Informed, sell an animal version. Maybe you could keep one on hand in the station, near a phone. Doubt it will have anything on turtles. Call a vet; or Dept. of Waters/Streams/Fish Commission/Etc.
http://www.informedguides.com/index.cfm?ev...uide%26trade%3B