Journal of The School of Marine Science and Technology,Vol.9 No.3
Pipe choice by yellow eel stage of Anguilla japonica collected in the
lower reaches of small rivers in Shizuoka Prefecture, Japan
T. ASAKURA, S. KUMAGAI, H.GOTO and I. AKAGAWA
Abstract
Rearing experiments to investigate nest choice of yellow eel stage of Anguilla japonica collected in the lower reaches of the Shinkawa and Ohashi Rivers, Shizuoka, Japan, showed many individuals may prefer the longest available pipes. Most eels tried the several pipes and chose to stay with the head around the tip of the longer pipe than the individual length. The pipe length/eel total length was significantly larger in first chosen pipes than the second, and that of the second chosen pipe was significantly larger than no chosen pipes. A pipe diameter choice experiment showed that the individuals ＞20mm in body depth （＞ca.500mmTL） chose pipe diameters without tendency, while smaller individuals （＜20mm in body depth） never chose pipes larger than 3 times of their body depth, but chose pipes twice of body depth frequently. Nest diameter choice is thought to be essential for small individuals. It is suggested that nest preference thereafter might vary with growth due to competition and predation pressures changing. Artificial enhancement of microhabitat in the lower reaches, utilizing pipes of sufficient length and various diameters as shelters, should permit a free movement and residence of yellow eels, possibly resulting in an increase in individual numbers in suitable riverine systems for eel.