Press Release

April 16, 2015

Fisheries Research Agency

Adult Japanese eels can sense sunrise and sunset at depth
- Periodic vertical migration behavior may be a key to elucidate their enigmatic spawning migration routes -

  • It has been shown that adult Japanese eels stay subsurface (150-300 m) during nighttime, start to descend approximately one hour before sunrise, spend the daytime at a depth of 500-800 m, and start to ascend upon sunset.
  • This daily behavioral pattern is very punctual, allowing us to estimate eel’s position (latitude and longitude) based on sunrise and sunset times deduced from the eels’ depth data. It is expected that this behavior can be used to determine the eels’ spawning migration route from Japan to the Mariana Ridge

The Fisheries Research Agency (FRA) has performed ecological survey of the Japanese eel. To investigate their oceanic migration, we attached ultrasonic transmitters to adult eels and tracked them in their spawning areas in the Mariana Ridge and waters near Japan. The eels represented periodic vertical migration behavior associated with sunrise and sunset, which allowed us to determine sunrise and sunset times based on depth data alone. Eels’ geographic location (latitude and longitude) can be deduced from the local sunrise and sunset times. This procedure can be applied to pop-up satellite archival tag (PSAT) which transmit recorded depth data via satellite. Oceanic migration routes of eels may be identified, if we could obtain depth data several months after release of eels with PSAT.

The findings will serve as a foundation for revealing the migration ecology of Japanese eels in the sea and are also expected to be used to identify their mysterious migration routes. This research used data obtained by the Fisheries Agency’s research vessel Shoyo-Maru. The details were published in the open-access international scientific journal PLOS ONE issued on April 16, 2015 (http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0121801).



Fig. One-week vertical movement profile of a Japanese eel

The eel was observed to stay in shallower water during the nighttime (150-300 m) and in deeper water during the daytime (500-700 m), exhibiting a regular pattern of descending at sunrise and ascending at sunset. The background colors indicate water temperatures.