2024 Volume 80 Issue 16 Article ID: 23-16104
We evaluated the function of a tributary as Ayu Plecoglossus altivelis altivelis spawning grounds based on surveys of riverbed materials and spatiotemporal surveys on downstream migration and spawning of the target fish using environmental DNA analysis. The study sites were the mainstream and a tributary Yato River in the lower-Gonokawa River system in Shimane Prefecture, western Japan. Compared to the mainstream, the tributary had higher proportions of small-sized riverbed materials and higher penetration values, both of which are suitable riverbed characteristics for the fish spawning grounds. The downstream migration surveys revealed that the fish uses the tributary as a habitat in the summer and then migrate downstream within a short period in the fall. Multiple surveys on spawning revealed that the fish uses both the mainstream and the tributary as its spawning grounds. Furthermore, the magnitudes of the environmental DNA fluxes (environmental DNA concentrations × discharge) were of the same order between the mainstream and the tributary, especially during the late spawning season, indicating that the tributary is functioning as major spawning grounds of the fish in the Gonokawa River system.
