We don't normally see sting rays like that while diving in Cozumel. I've never seen any besides eagle rays. I'm guessing that they are large southern rays in there.
I wonder if releasing [escaping] non native rays into the local environment will have any impact ?
We don't see many diving in Cozumel, but south of Playa on the mainland we see them just about every dive. Last December we had truly National Geographic momenent. At the end of one of our dives there were two very large southern stingrays mating. My photos just looked like a sand storm (I wasn't going to get too close), but wow, what an amazing site.