The Asian species - Anguilla japonica (cf. the European A. anguilla), if not divided into subspecies, is very widespread as far as adult individuals found in freshwater are concerned. We see distribution as far south from Vietnam and the Philippines all the way along coastal rivers in Hainan, Guangxi, Guangdong, HK, Fujian, Zhejiang, NE China, Taiwan, Japan and Korea.
So if the spices is as threatened so suddenly should be left for further fieldwork data. The northen movement of the pacific ocean salinity front which also drives its spawning ground northward is known for many years and if recent development is becoming drastic should be closely followed. The northerly movement is believed to affect the arrival time of juvenile eels to the river mouths. Too early arrival may affect their ability to go through the freshwater transformation stage.