The Indo-Pacific eel, Anguilla marmorata Quoy & Gaimard, has the widest geographic distribution of anguillid eels. At least four populations (North Pacific, Micronesia, Indian Ocean and South Pacific) of this species were estimated to exist by previous morphological and molecular genetic studies. Recent mitochondrial control region haplotype analysis of A. marmorata eels from the eastern Caroline Islands and Guam grouped them in two separated lineages with eels from the South Pacific and western Indian Ocean. To examine the composition and possible distribution of the Micronesia population of A. marmorata that may mostly be found in the Mariana (Guam) and Caroline (Palau, Yap, Chuuk, Pohnpei, Kosrae) islands in relation to other populations in the Indo-Pacific region, we statistically compared the total number of vertebrae (TV) of specimens collected from throughout most of the range of A. marmorata including 32 specimens from Kosrae and Pohnpei islands. The TV for 1298 specimens of A. marmorata in combined data from 15 localities ranged from 100 to 110. The mean TV (107.95, 108.03) and range (105–110) of eels from the Mariana and Caroline islands were clearly higher than other localities. The post hoc multiple pairwise comparisons of the 105 pairs of single localities showed that there were 57 significant TV differences between each locality. The most significant differences were between Mariana and Caroline eels and all the other 13 localities. The statistical differences of pooled regional TV data, various genetic studies, and general geography indicate that there are likely six spawning populations of A. marmorata. This study indicates that the Caroline Islands are included in the Micronesia population, but further research is needed to understand the spawning area and life history of the Micronesia population of A. marmorata that seems to live on a relatively small number of islands in Oceania.
