The current distribution of the Japanese eel Anguilla japonica and giant mottled eel A. marmorata were surveyed in 1120 inland water bodies on mainland Kyushu and the Nansei Islands, southern Japan. Anguilla japonica occurred at 8 and 2 sites on Kyushu and the Nansei Islands, respectively, the low catch rate apparently reflecting its cryptic life style. The likelihood of occurrence of A. japonica in stream habitats on the Nansei Islands was significantly lower than on mainland Kyushu. Anguilla marmorata occurred at 46 sites (mostly streams) on the Nansei Islands. Accordingly, low stream occurrence of A. japonica on the Nansei Islands may have resulted from interspecific competition. An informal verbal survey of 359 local respondents indicated that A. japonica had formerly been plentiful in Nansei Islands paddy fields, although a similar survey on mainland Kyushu found the habitat of A. japonica to be streams, rivers and/or estuaries. Local names of A. japonica on the Nansei Islands, including “paddy-dwelling eel” and “mud-dwelling eel”, also indicated adaptation of A. japonica to a paddy environment, the use of “stream-dwelling eel” for A. marmorata further suggesting habitat segregation of the two species. The paddy environment appears to be the primary habitat of A. japonica on the Nansei Islands. However, such paddy fields have decreased significantly in extent due to a recent crop change to millet. Restoration of the paddy environment is essential for future A. japonica conservation on the Nansei Islands.
