Habitat evaluation for the endangered fish species Lefua echigonia in the Yagawa River, Japan

Abstract

Spring-fed streams in Tokyo are important habitats for various aquatic species, whereas urbanization as well as introduction of invasive species is threatening the sustainability of such aquatic ecosystems. This study applies the System for Environmental Flow Analysis (SEFA) in a small urban river in Tokyo to assess the dynamics of the suitable habitats for the endangered freshwater fish Lefua echigonia (Jordan and Richardson 1907). A set of Habitat Suitability Curves (HSCs) for water depth, velocity and substrate was developed to evaluate the suitable habitats. The habitat assessment indicated that the Area Weighted Suitability (AWS) reached the maximum at 0.02 m3/s, which is close to the base flow of the target river; a gradual decrease in AWS was observed for higher flows. The temporal distribution of AWS, during forty-one consecutive months, showed that, on average, the best habitat conditions for adult L. echigonia occur during the period between January and July, whereas the worst situation occurs during the period between August and December. This work presents information and tools for instream habitat analysis that should help managers to conserve this aquatic species and prioritize actions to further rehabilitate urban rivers, using L. echigonia as a case study.