Open Question: What does ‘Mudhshark’ mean?

My very racist friend said this girl he knew in college had become a "mudshark" but I didn't know what he meant. Does anybody know the meaning of 'mudshark'. I think it has something to do with white women dating men of other races, but I'm not sure. It sounded bad though. Any help is appreciated. Thanks Mrs. Eli. I still don't get where the mud or shark comes from but maybe I don't understand red/neck either so I'm obviously a retard when it comes to racism. Those sayings are so crazy to me.