抄録
To clarify the foraging microhabitat of the Japanese charr, Salvelinus leucomaenis, I investigated focal point depths and velocities in a 730-m reach of a typical mountain stream in central Japan in the spring and summer of 2004. The water depths and velocities of focal points used by 123 fish (>9-cm fork length) were compared to data for random points in the stream. The charr utilized focal points with depths>10 cm and velocities<60 cm/s. The preferred habitat was comparatively deeper (21-60 cm) and moving at a slower velocity (11-20 cm/s). The proportion of favorable foraging habitat in the study reach was calculated to be 15% in July and 18% in August based on focal points. This habitat was dispersed in small patches and distributed randomly throughout the reach. In small mountain streams such as the one studied here, there are repeated small steps and pools. Most of the favorable foraging habitat was in the pools. Therefore, charr density may be affected by river morphology, such as the number of pools or steps in a reach.
