We saw lobster, or at least some carapace of lobster that has already been eaten or died of other causes, particularly right near the exit of Baureke passage - the one to the south of the Village. Laxton says this in his description of his visit "Crayfish too, abound on the right tides, caught easily by hand in knee-deep water by torchlight.", so if you have a torch, you can catch them on the reef. If not it gets a lot harder. You have to go into the water off the edge of the reef, preferably at night, and dive down to get them. Not exactly something I can imagine AE doing, but who knows.
The pond is a salt water pond, been there, tasted it. But that doesn't mean that the Castaway didn't think it might be fresh and head down that way to check it out. Might help explain how they ended up at the 7 site.
There were some provisions left behind by the NC survivors, and I think some Casks of water were on the list. The corks on chains that were found by Gallager could have come from such casks. See the Ameliapedia
http://tighar.org/wiki/Corks If you haven't spent time on the Ameliapedia, you should as it is full of great info.
Andrew