Author(s): Keisuke Yoshida; Hiroshi Yajima; Yasushi Yamashita; Md. Touhidul Islam; Yutaro Hashimoto
Linked Author(s): Keisuke Yoshida, Hiroshi Yajima
Keywords: Rtificial spawning bed Ayu tidal river section spawning habitat suitability sandbar excavation
Abstract: Conservation and expansion of fish habitat are critical for maintaining ecological balance and supporting sustainable fisheries, particularly for species with specific spawning requirements like Amphidromous Ayu (Plecoglossus altivelis). This study addressed the challenge of limited spawning grounds by excavating a sandbar in the tidal zone of the Asahi River in Japan. The objective was to create a sub-current channel and artificially establish a new spawning ground under normal flow conditions. Field observations and numerical calculations were conducted to comprehensively examine the hydro-environmental suitability of the artificial spawning area and investigate potential impacts on the existing natural spawning habitat. Results showed that the suitable spawning area was one where there was no salinity increase at any time, and that the riverbed grain size, water depth during spawning, and flow velocity fell within the suitable ranges proposed by earlier studies. Notably, spawning density in the constructed area showed a more pronounced correlation with sediment grain size characteristics than with flow regime dynamics. Moreover, two-dimensional horizontal flow calculations, based on high-resolution bathymetric data, showed that the creation of the new spawning area did not significantly disrupt the hydraulic environment of the existing natural spawning grounds. Instead, it contributed to the increase in the spawning bed area, which was the primary goal of the project. Finally, the study recommends ongoing monitoring of the excavated area to assess long-term ecological responses, sediment dynamics, and develop adaptive management strategies to enhance fish habitat restoration in similar river ecosystems.
Year: 2025