Numerical simulation to resolve the issue of downstream migration of the Japanese eel

In 1991 an expedition of a Japanese research vessel discovered that the spawning ground of the Japanese eel is located in the North Equatorial Current (NEC) in the Pacific Ocean. Several unanswered questions about the distribution of the eel and their larvae downstream of the NEC, however, remain and are unlikely to be resolved by observations alone. Three such questions are about (1) previous misdetermination of spawning ground, (2) the large larval catch off the west coast of Taiwan, not off the east coast, and (3) the low abundance of larvae in Korean coastal waters. It had been thought that the physiological behavior of adult and larval eels and their adaptation to different environments determined their distributions. However, we have demonstrated that these issues can be explained by the water circulation in the North Pacific.