not sure if this works were you are but road mortality. more females are hit by cars, picked up etc, crossing the road to lay eggs. males do not cross as much and are therfore more numerous at least here. ex I caught 23 midland painted turtles (chrysemys picta marginata) and 5 females last year in a pond that goes on both sides of the roads. I alos heard about a report done on the same thing
wayne