Forster's or Common Tern?
Black-naped Terns aren't common at Suva Point - up to 4 birds can sometimes be seen resting on the structures off shore. This individual was sitting on a sandbar - allowing reasonably close views. About half the size of the commoner Crested Terns, much whiter overall, with the well-marked black nape rather than the scruffy looking black that you might get on other wintering terns.
Sterna is a genus of terns in the bird family Sternidae. It used to encompass most "white" terns indiscriminately, but mtDNA sequence comparisons have recently determined that this arrangement is paraphyletic (Bridge et al., 2005). It is now restricted to the typical large white terns occurring near-globally in coastal regions.