cheers guys, yep atiu is a good place, i have been there twice already and i am going to go back. not for everyone but it is a place that i really enjoy and cannot get enough of.
seamower, do both i reckon. fish off the shore, some good fish to be had there in aitutaki in the lagoon and off the reef edge, big gts and blue fin trevally. also go on a charter, lots of options, plenty of different fishing also like trolling for tuna, wahoo etc, jigging for dogs or casting lures for gts. google search a few options like aitutaki charters, black pearl charters, baxter fishing etc. all charter boats have game gear, not many if any have quality jigging/casting gear so take your own.
one of the best things you can take is a softbait set, unreal fishing for all sorts in the lagoon, the blue trevally pull string really hard and are great fun, also good for the smaller mahimahi at fads on occasion.
landlocked, yes you are correct on the second one, the coconut crabs burrow deep underground and sort of hibernate in the winter months, some guys dig them out, lots of effort and often they are in poor shape/condition at that time of year. locals are not known for their "no taking", more a case of if it is alive, eat it!!!!

(all in good nature)