Turbid water induces refuge behaviour of a commercially important ayu: A field experiment for interstream movement using multiple artificial streams

Abstract

Riverine systems are inherently dendritic in nature, and turbid water may not necessarily flow equally throughout an entire catchment. Tributaries have the potential to serve as refugia from temporarily turbid water in the main stem. As ayu (Plecoglossus altivelis) are one of the important species for the inland fisheries industry and recreational fishing, their behaviour in a branched river network is a primary concern. We released ayu with radio‐transmitting tags into two experimental streams that joined at a downstream pool. Turbid water was released into one of the streams, and we identified whether avoidance movement of ayu between the two experimental streams was triggered by flowing turbid water. The suspended solid concentration elevated rapidly after adding the turbid water and was maintained at more than 400 mg/L for 3 hr. Avoidance movement of ayu was triggered when the suspended solid concentration exceeded approximately 200 mg/L. Then, most ayu moved from the turbid stream to the nonturbid one, leading to a difference in ayu density between the two streams. Therefore, we demonstrated that turbid water induced interstream movement of a commercially important ayu as refuge behaviour, suggesting that river connectivity is important for the persistence of the ayu.

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

“…Many fish species used the temporary underwater path to actively immigrate to drainage ditches that serve as spawning and nursery habitats (Nakano, 2017). Additionally, fish species could evacuate from the disturbed downstream rivers during a flood, as previous studies showed that fish species inhabiting a mainstream actively move into tributaries or backwaters for refuge when a flood increases flow discharge and turbidity in the mainstream (Koizumi et al, 2013; Mori et al, 2018; Sumida et al, 2019; Tawa et al, 2022). Also, some fish species were likely to be passively swept away to drainage ditches by backflow of water from downstream rivers.…”

“…We would also have failed to observe fish species that evacuated from a mainstream because our sampling of fish was done not during but several days after the flood for safety and practical reasons. Indeed, previous studies showed that some fish species that once moved to tributaries during a flood returned to a mainstream as soon as the flood settled (Koizumi et al, 2013; Mori et al, 2018).…”

“…They found that community structures were highly influenced by stochastic processes of dispersal shortly after flash floods and then affected by deterministic processes of species sorting during the stable hydrological period. In contrast to these taxonomic groups, different groups such as fish can actively migrate in response to flood, not only between habitats within a river floodplain but also between multiple rivers, such as between a mainstream and tributaries (Koizumi et al, 2013; Mori et al, 2018). It is thus expected that the short‐term flood can change fish community structures of tributaries at a short time scale, depending on the degree of changes in connectivity between a mainstream and tributaries.…”

Impacts of Flood Disturbance on the Dynamics of Basin-Scale Swimming Fish Migration in Mountainous Streams

“…The response to floods may differ among fish species based on their ecology and biological characteristics. Plecoglossus altivelis is known to avoid turbid water and evacuate turbid sections [30]. The Yoshida River, which had the lowest eDNA concentration after Flood Event 1, showed high turbidity during the flood (Figure 4).…”

Impulsive fishery resource transporting strategies based on an open‐ended stochastic growth model having a latent variable

“…The fish P. altivelis is a major fishery resource of inland fisheries in Japan; Hii River is not an exception. Fish catches of the fish has been steadily decreasing during 2000s due not only to aging and population decrease of members of inland fisheries cooperatives, but also to degradation of river environment serving as habitats, which was triggered by the flow regulations by operating huge hydraulic structures like dams [61][62]. Especially, Obara Dam is completely fragmenting habitats of aquatic species including P. altivelis because of its heigh 90 (m) as well as the lack of fish ladders.…”