Autumn microhabitat for larvae of endangered arctic lamprey（Lethenteron japonicum） in Noto Penisula, Ishikawa Prefecture

Abstract

The critical habitat for the larvae of endangered arctic lamprey dwelling in southern limited of habituation was studied by field environmental survey and laboratory rearing experiment. The study site was selected in the middle reach of the Machino River in Noto Peninsula, Ishikawa Prefecture. The eight sections （inside side cavity and outside side cavity） were established laterally along river shore. The bored larvae in fine substrate were captured using electric fisher, and environmental variables were measured in each section. Density of larvae in the side cavity section was consistently larger than control sites. Very fine sand （under 0.125 mm） and organic matter in the side cavity were significantly higher than the control sites. Velocity in the side cavity were slower than the control sites. However, there was a wide variation of larvae density among the side cavities. Toreveal the critical environment factor for larvae in the side cavity, lamprey larvae were reared in the tank where three different particles （under 0.25 mm, 0.25 mm~1 mm and gravel） and organic matter containing ratio （8%, 2% and 0%） were prepared. Larvae mostly preferred the finer particle （under 0.25 mm） and no organic matter where ORP value was the lowest. It is concluded that the aerobic condition with fine particle in the substrate is mostly significant for creating a favorable lamprey larvae habitat.