環境

A survey was conducted to understand the ecology of the Japanese eel in the Tama River water system, a typical urban river flowing through densely populated areas near the Tokyo Metropolitan.

A total of 73 individuals were collected during a two-year survey, with eels frequently being caught in the summer.

The ages of these individuals ranged from one to six years old.

Stomach contents analysis showed that the eels consumed different organisms depending on their habitat, although most of the eels had empty stomachs.

Otolith stable isotope ratio analyses revealed that all but one individual were identified as being wild eels.

One male eel was determined to be of aquaculture origin, which was collected a short distance downstream of a stocking site, and it had stayed near the release site for at least several months.

Furthermore, environmental DNA metabarcoding analysis detected the DNA of Japanese eels at 15 sites in the Tama River system.

These results indicate that wild individuals of the Japanese eel were well adapted to this urban river near the Tokyo Metropolitan, although their density was not high.

Takashi YAMAKAWA
Fuki MIZUTA
Shunya KITAMI
Seiya KUDO