Summary: Male turtles are easy to sex because they have long toenails and an indented shell. Learn to identify male and female turtles with tips from the owner of a reptile store in this free pet care video.
"Hi, my name is Tim Cole, I'm with the Austin Reptile Service and I've been keeping reptiles amphibians for over forty years. I'm here to talk to you about sex and turtles. We're going to talk about water turtles, to start off with. If it's an adult, males can be easily identified by looking at their front feet. They have very long toenails that they use to court the females with. They also have a shell that's usually indented more than the female, if we look at the bottom of the shell it's fairly flat and then we look at the tail, they have a much longer tail than the female. The opening to the tail is actually at a point past the shell, whereas, a female has shorter toenails, it has a more convex shell on the bottom, and the tail, which you can barely see, is very short on a female. That's the easiest way to identify the sexes of adult water turtles."
eHow Article: How to Determine the Sex of a Turtle