We're all a little confused also :-)
Lionfish invasion has relaxed the rules a little. Divers are carrying spear guns nowadays and killing as many as possible while on dives.
We have specially designed small guns for that special purpose.
In theory tourist snorkellers should not be shooting fish however no one seems to enforce the rule and you'll find operators that send tourist out for the purpose of spearfishing on the reef.
You can purchase a spear gun at Captain Sharks Supply but if you bring one with you your probably get nabbed at the airport.
Your sure to find tour guides that will take you and some Hotel/Resort front desks will book you on a spearfishing trip.
Spearfishing is a sport and regulated in some countrys, sadly not here.
I personally would like to see the ban on shooting tourist with spearguns lifted.:-)

White Sands Dive Shop
https://whitesandsdiveshop.com/