The 10th IFB Seminar

Presentation Title: Installation and effect verification of stone basket reefs under the Fisheries Agency’s eel habitat improvement support project

Lecturer: Noritaka Mochioka

Affiliation: Specially Appointed Professor, Kyushu University

Date and Time: September 30, 2025, 13:30–15:00

Place: Conference Room, Freshwater Biology Research Institute, 1088 Komaki, Ueda City, Nagano Prefecture

Online streaming available

Registration URL: https://forms.gle/eD7r9CvGKEj39HDr7

Abstract: The Japanese eel was classified as Endangered IB by the Ministry of the Environment in 2013. In response, the Fisheries Agency implemented the Eel Habitat Improvement Support Project from 2016 to 2023, installing stone basket reefs (Ishikura-kago) at 86 sites across 40 rivers and 2 lakes in 19 prefectures, ranging from Iwate to Kagoshima. The project was carried out based on the precautionary principle, with effect verification mainly conducted by Kyushu University. Using eight experimental ponds at the Kagoshima Prefectural Fisheries Technology Development Center, it was demonstrated that stone baskets help reduce damage from birds.

Furthermore, six stone baskets of varying stone sizes (long diameter 10, 20, 30 cm) were installed in the brackish zone of the Saigo River in Fukutsu City, Fukuoka Prefecture. It was revealed that yellow eels prefer stones of 10 cm in diameter, while silver eels prefer 20 cm, and that individuals with high-frequency use of stone baskets had better nutritional conditions compared to those with low-frequency use. Currently, stone baskets have been installed at four sites from the freshwater zone to the estuary of the Saigo River and the Arase River in Kagoshima Prefecture, in an effort to identify effective locations for protecting individuals undergoing silvering metamorphosis.