ASSESSMENT OF THE SPAWNING ENVIRONMENT FOR CHUM SALMON AT THE MIDDLE REACHES OF THE TOYOHIRA RIVER BY USING PHABSIM

Abstract

We surveyed the cross-sectional profile, bed materials, water permeability of the substrate, temperature of permeable water flow and distribution of spawning beds in the Toyohira River. Based on the survey results, two suitability criteria for salmon spawning habitat were developed for use in PHABSIM. One criterion, called "the 2nd suitability criterion," depends only on the use frequency of spawning beds. The other criterion, called "the 3rd suitability criterion," focuses on environmental bias. Also, normalized composite suitability index and selectivity index were used to examine physical factors for the spawning habitat in the areas surveyed. The results show that the 3rd suitability criterion was more effective in evaluating the distribution of the spawning beds than the other criterion. Additionally, 90% fine-particle size, water permeability of the substrate, temperature of permeable water flow and water depth were considered to be physical factors influencing the spawning habitats in the areas.