nobody cares...Now I'm not even joking I was the first one to say you have ninja turtles (WHICH ARE MALE!) so I have won with a clever word choice.
You cannot assume that just because they are using foreclaw displays that they are both males or even displaying for dominance or breeding. That was long considered the reasons but a few researchers have been doing some long term work on this turtle communication and coming up with some new information. I got to work with Dr. Thomas for a year and this guy knows what he is talking about. Here is a link to one of his papers on the subject. Several of his other papers on the topic can be found on google scholar. Well worth it if you are into turtles.
http://www.bioone.org/doi/pdf/10.1656/1528-7092(2006)5[227:COTFDB]2.0.CO;2
You cannot assume that just because they are using foreclaw displays that they are both males or even displaying for dominance or breeding. That was long considered the reasons but a few researchers have been doing some long term work on this turtle communication and coming up with some new information. I got to work with Dr. Thomas for a year and this guy knows what he is talking about. Here is a link to one of his papers on the subject. Several of his other papers on the topic can be found on google scholar. Well worth it if you are into turtles.
http://www.bioone.org/doi/pdf/10.1656/1528-7092(2006)5[227:COTFDB]2.0.CO;2
As mentioned, any long-term keeper should be able to tell you that both males and females will do this, and it's ALWAYS a sign of dominance. Either they're trying to show dominance for the purpose of courtship, or they're trying to show dominance purely as a sign of aggression. I've personally seen this behavior followed by successful mating and by one turtle killing the other. As they're too small to sex, you can't really know which it is.
Josh H
Unfortunately, the latest research does not support your statement. Neither does the observations that we have made in the wild and captivity over the past 30+ years. The display can be displaying much more than just dominance.