Fish breeding and conservation in traditional and land consolidated paddy water areas

Connectivity and short‐term flood interactively affect fish community composition in drainage ditches of paddy fields in an agricultural landscape

“…Aquatic communities in rivers have been threatened because of the shrinking various waterbodies in floodplain by the modern river alteration (Nagayama et al, 2015) and the increasing intensity and frequency of flood disturbance by ongoing climate changes (Ledger & Milner, 2015). Therefore, drainage ditches in an agricultural landscape can play more important roles as temporary refuges and seasonal habitats for spawning and growth, as the drainage ditches somewhat resemble streamlets that once existed in natural floodplains (Minagawa, 2021; Nakano, 2017). To secure their roles, it is desirable to recover the hydrological connectivity between drainage ditches and downstream rivers by removing vertical gaps (e.g., flap gates) that the modern river alteration and the drainage system construction for agriculture have created (Minagawa, 2021; Nakano, 2017; Tawa et al, 2022).…”

“…Therefore, drainage ditches in an agricultural landscape can play more important roles as temporary refuges and seasonal habitats for spawning and growth, as the drainage ditches somewhat resemble streamlets that once existed in natural floodplains (Minagawa, 2021; Nakano, 2017). To secure their roles, it is desirable to recover the hydrological connectivity between drainage ditches and downstream rivers by removing vertical gaps (e.g., flap gates) that the modern river alteration and the drainage system construction for agriculture have created (Minagawa, 2021; Nakano, 2017; Tawa et al, 2022). Moreover, the structures permitting backflow retention of flood from downstream rivers to paddy fields, such as the floodplain open levee system ( kasumi‐tei ) (Taki et al, 2021; Teramura & Shimatani, 2021; Yamada et al, 2022), should enable drainage ditches and paddy fields to play a greater role as temporary refuges for fish in the event of a more severe flood than that observed in this study.…”

“…The short‐term flood increases water discharge from paddy fields and thus facilitates the fish immigration to ditches, similar to the midsummer drainage practice does. The rise in water level due to the short‐term flood also enables fish species to move to drainage ditches by removing a vertical gap at a confluence with downstream rivers that impedes the connectivity during non‐flood periods (Minagawa, 2021). Hence, it has been suggested that drainage ditches can serve as temporary refuge habitats for fish during short‐term flash floods, playing a crucial role in biodiversity conservation (Tawa et al, 2022).…”

Connectivity and short-term flood interactively affect fish community composition in drainage ditches of paddy fields in an agricultural landscape

“…Aquatic communities in rivers have been threatened because of the shrinking various waterbodies in floodplain by the modern river improvement (Nagayama et al, 2015) and because of increasing intensity and frequency of flood disturbance by ongoing climate changes (Ledger & Milner, 2015). Therefore, drainage ditches in an agricultural landscape can play more important roles as temporary refuges and seasonal habitats for spawning and growth as the drainage ditches somewhat resemble streamlets once existed in natural floodplains (Minagawa, 2021;Nakano, 2017). To secure their roles, it is desirable to recover the hydrological connectivity between drainage ditches and downstream rivers by removing vertical gaps (e.g.…”

“…The rise in water level by the short-term flood enables fish species to move to drainage ditches by removing a vertical gap at a confluence that impedes the connectivity during non-flood periods (Minagawa, 2021). The short-term flood also increases water discharge from paddy fields and thus facilitates the fish immigration to ditches, as the midsummer drainage practice does.…”