Spatial distribution of spawning redds and larvae of Rhinogobius flumineus in relation to hydrogeomorphological characteristics in Kamo River, Japan

Abstract

A freshwater goby, Rhinogobius flumineus, is one of the dominant species in the Kamo River and the Takano River, Kyoto City, Japan. We investigated the spatial distribution of their spawning redds and larval habitats in relation to hydrogeomorphological features at the confluence of the Kamo and Takano Rivers. A total of 78 egg masses were found. The spawning redds were concentrated in the transition area from a pool to a riffle. Most of them were found on the underside of half-embedded stones in the riverbed. The spawning redds were also concentrated at stones aligned in the run. These results indicated that potential sites for spawning redds would be created artificially by putting stones in the transition area from a pool to a riffle. Distribution of larvae showed that the average larval size was smaller in the secondary channel than in the main channel and was also smaller at a shore area with a bare water's edge than with a vegetated water's edge. The statistical model selected by the widely applicable information criterion showed that larval size could be predicted with the highest accuracy by a model that takes both channel type and vegetation into consideration. On the basis of the model selection and observations in the field, we concluded that bare shallow shore areas are more beneficial to larvae of an early stage than vegetated or deeper shore areas, probably because larvae can avoid accidental drifting and predation by predatory fish and aquatic insects.