belize-
There are places (like
New York even!) that define a "firearm" as anything that fires a projectile by means of stored energy, in intentionally broad terms. So, yes, a speargun can easily be caught up in
regulations, even if officials recognize that it is normally sporting
equipment and they normally ignore it.
Something the OP may not be aware of. Even in Northport, if you go spearfishing for blackfish? You'll find they magically know the reach of a spear, any spear. You buy a gun with a four foot range, they keep six feet away. You buy a gun with an eight foot range, somehow they know to keep ten feet away.(G)
And if you go someplace warmer and plan to look for livestock (like 400# groupers) a big speargun, line spool, and thicker spear start to become advisable. Northport? Hawiian sling just might suffice.(G)