I'm heading there this Saturday and will take an expandable spear just in case.
I would advise not to. You'll get in trouble with either customs at the airport or the Marina Park authorities.
As a matter of fact STINAPA (National Park Authorities) is implementing a program right now to distribute specially designed hand spears to dive professionals and island residents under very strict rules (a personal contract with STINAPA allowing a person to hunt lionfish with a numbered weapon that remains property of STINAPA). All other types of spears will be strictly forbidden.