Ah, excellent, thanks for the reply. That's good to know. We are going down there later this month and my buddy and I have been spearing them in other places, but were always told no in Cozumel. It gets frustrating to drift past a group of 10-15 lionfish sunbathing on a coral head and not be able to exterminate a couple.
You won't see huge numbers anymore in the marine park thanks to many of the divemasters continuous harvesting of lionfish. Below recreational depths (130ft+) and outside the marine park the numbers are much much higher.
I briefly dropped down on a ledge about 140ft only to see 5 huge ones just sitting there.