A search of Google Maps will show the geographically impaired that the Kingdom of Tonga lies northeast of New Zealand, about halfway to the equator - a long way to go to catch a sailfish, but some of the world's biggest reputedly prowl these waters. Effort for the species remains minimal.
Why You Should Go: Not a bad place to look for a world record; the men's 50-pound line-class record of 210 1/2 pounds was taken here, with sails larger than the world-record 221 pounds probably caught but never weighed. The run to start fishing can be fairly short and often begins working along steep reef edges - but beware of big yellowfin and wahoo as well (and of course closer to the reefs, dogtooth tuna and giant trevally).
But... During the best sailfish season (winter in the southern hemisphere), 15- to 20knot trade winds blow constantly. Figure on 30 to 40 hours traveling each way and dropping two to three grand for the privilege.