Answer:
There are distinct shapes for each the male and female dungeness crab on the underside (abdominal) of the body and it takes up about half of the underside. The male's looks more elongated (triangular) and the female's is wider in shape. Check out the Oregon Department of Fish and Wildlife web site for more info including videos of how to crab. Here's a link (copy and paste it into your browser's address bar) to a flier for more details: http://www.dfw.state.or.us/resources/fishing/docs/CrabbingFlyer.pdf