Use of rocks as refuges by Japanese eel, Anguilla japonica, in artificial pond, revealed by acoustic telemetry.

Abstract

The Japanese eel, Anguilla japonica, is one of the most important fishery species in Japan, however, population of this species has been decreased, with the species listed as endangered (EN) on the International Union for Conservation of Nature (UCN) Red List of Threatened Species. To understand use of stone piles as refuge by Japanese eel, behavior of 8 individuals in an experimental pond was monitored using acoustic biotelemetry. The sediment of the pond was sand and mud, and 6 stone piles with about 1 m diameter and 0.7 m height were made as refuge. According to the results of two-dimensions Kernel density estimate, some eels stayed at stone piles and others stayed places without stone piles （sand-mud sediment）. When stone piles were filled with sand, eels did not stay at the filled stone piles. Burrowing behaviors were sometimes observed in this experiment. Although Japanese eels might prefer stone piles as refuge, they can also use sand-mud sediment as refuge by burrowing themselves.