Amazingly enough, I have to agree with ByWarren on the marine preserve issue. I don't think he is saying there should not be one down there, I think what he is saying is that any such effort must have the approval of the local fishermen who live off the sea.
Parks (whether on land or on the sea) are great but not when they wreak havoc on a local subsistence economy.
There are a lot of people on Ambergris Caye who make their living at least in part by fishing. Many of the dive and snorkel boat operators also fish commercially and supplement their income by fishing (many were fishermen before the tourists came).
In Belize, the fishing activity is manual labor, ordinary guys in little boats. It is not the kind of large scale net-based commercial fishing that can "fish out" a small area quickly.
Also, someone referenced spear-fishing. No area ever lost its fish because people were spear-fishing. It's difficult and you are lucky to get 2 or 3 fish. It's the ultimate in "subsistence fishing."
It may be that the reefs around Long Caye are a great place for a marine reserve. But if so, there will have to be consensus among the community.