Like so many unenforced laws in the TCI. It is illegal to remove anything from their National Parks, ...
Ha, I like how you slipped in "
un-enforced...."
As for some genius coming up with that answer, to the question of "detecting in Jamaica?" : I would venture to say that you can probably find such laws/rules for every speck of public land here in the USA too. Yup, even where you and I routinely detect with no problems. It would fall under boiler-plate provisions that forbid "taking", "harvesting", "removing", etc.... of "park features".
If you doubt that, pick any spot you routinely detect, w/o issues. Then go to the administering agency of that place (park, beach, forest, school yard, etc...) and ask the powers-that-be : "Hi, can I remove park and beach features, for my own profit and enjoyment ?". And then sit back and relish in their answer. If it applies to not taking home the park benches, or harvesting the sand for commercial sale, then so-too can the same logic be applied to the type items we find when md'ing. They too can be construed as "park features".
I have a sneaking suspicion that such "silly answers" to "pressing questions" can happen on a national scale too. Ie.: ask enough border consulate lawyer types, and purist archies there, and .... "presto: You can not *remove* items". Then we can all sit around, post the reply we got for our FAQ's, and sit around and gripe about our "lack of freedoms". When odds are, it was just
US IN THE FIRST place that went around swatting hornet's nests !