It is virtually impossible to summarize such rules, since it does not vary only from island to island, but within each country as well. For example, some
marine parks have no diving, some snorkel only, some have guided trips only. Some allow spearfishing, some don't... some allow spear
guns, some Hawaiian slings, some pole spears. etc, etc, etc.
Such
research really isn't hard. Start with the better
cruising guides, and follow up online for
current info.
It's not like you are going to do the entire
Caribbean at a go. Each time you jump off, you'll have two or three alternative destinations, so check those, and pick your spot. You have to do your
research for
ports of entry, and entry requirements anyway, what's an extra
google search on top of that???