I've seen divers on many occasions with small pneumatic spear guns hunting lion fish in the park. Some dive shops turn a blind eye to their customers....pneumatics are illegal and only authorized persons by parque marino are allowed to spear fish lion fish in the marine park.
For what it is worth, I have never seen a pneumatic spear gun in use in Cozumel. 25 years here. Rubber only and Hawaiian sling types in the park, yes. And no, they don't show up in droves at night.
Dave Dillehay
Aldora Divers