A case-study evaluating river rehabilitation alternatives and habitat heterogeneity using the hydromorphological index of diversity

Nakai²,

Asaeda

et al. 2023

River Research & Apps

In 2012, the fishway in the Miyanaka Intake Dam in Niigata Prefecture, Japan, was reconstructed and divided into three fishways (ice‐harbor‐, stair‐, and rock‐ramp‐type) with different flow velocities and water depths. We conducted an adaptive monitoring survey in these fishways from 2012 to 2020, and 33 fish types were found, including migratory, swimming, small swimming, and benthic fishes. Many species displayed a preference for specific fishways. The run‐up for Tribolodon hakonensis was studied to determine the effects of physical parameters such as body length, rush speed for instantaneous swimming, water temperature, and presence/absence of nuptial coloration on fishway preference. T. hakonensis with nuptial coloration had greater body length and higher rush speeds than those without it. They also preferred the ice‐harbor fishway, whereas their shorter, uncolored counterparts preferred the stair and rock‐ramp alternatives. The environmental conditions selected by T. hakonensis changed according to their growth stage, as did fishway preference. Changes in fishway environmental conditions may have influenced the observed differences in fishway populations. It was thus confirmed that developing fishways with different flow velocities and water depths is effective in supporting the various life stages of T. hakonensis.

Section: Introductionmentioning

confidence: 99%

Preferential behavior of Tribolodon hakonensis for fishways according to biological characteristics

Nakai²,

Asaeda

et al. 2023

River Research & Apps

“…River channel continuity is an essential requirement for migrating fish [1][2][3][4][5], but is threatened by the modification of rivers, such as the construction of dams and weirs [6][7][8][9][10][11][12][13][14][15]. A fishway is one of the solutions to these problems [3,[16][17][18][19][20][21][22][23].…”

Section: Introductionmentioning

confidence: 99%

Quantifying Vegetation on a Rock-Ramp Fishway for Fish Run-Up and Habitat Enhancement: The Case of the Miyanaka Intake Dam in Japan

Nakai²,

Aoki

et al. 2023

Water

The Miyanaka Intake Dam fishway underwent improvements in 2012, and we established a new rock-ramp fishway called the Seseragi Fishway, cognizant of its utility as a passage and a habitat for bottom-dwelling and small fish with weak swimming ability. However, the fishway is occasionally submerged by floods, causing sediment accumulation that leads to changes in the vegetation composition. In addition, the arrival and inflow of seeds from upstream and the surrounding areas result in vegetation changes. In this study, the inside and outside of the rock-ramp fishway were divided into eight areas, and the vegetation succession after 2012 was determined. A correlation was observed between the results of fish catch surveys during the same period and the vegetation. Based on these results, we reported on the process of steadily operating the rock-ramp fishway while devising and improving specific management methods. Changes in vegetation, such as an increase in upright vegetation and a decrease in flow-obstructing vegetation, contributed to an increase in the population of bottom-dwellers, weak swimmers, and juvenile fish. The existence and management of appropriate vegetation are important for maintaining fishways inhabited by a variety of fish species.

“…Dams and other human-made barriers create obstacles in aquatic ecosystems by altering habitats and fragmenting the lotic system [6]. Restoring continuity is therefore particularly important for rivers disrupted by dams [4,[7][8][9][10][11][12]. Fishways have been developed for this purpose [4,[13][14][15][16][17][18], and the effects of fishways on large varieties of fish have been tested vis adaptive management based on biological, hydraulic, and other physical parameters [19][20][21][22].…”

Section: Introductionmentioning

confidence: 99%

“…However, riverbed materials are essential for bottom-dwelling fish species and other benthic organisms [7,[42][43][44][45][46]. Thus, installing other types of fishways with gentle slopes and riverbed materials is crucial for preserving the biodiversity of the river channel [3,10].…”

Section: Introductionmentioning

confidence: 99%

Effectiveness of New Rock-Ramp Fishway at Miyanaka Intake Dam Compared with Existing Large and Small Stair-Type Fishways

Nakai²,

Asaeda

et al. 2022

Water

The migration of fish is influenced by the unique environmental characteristics of the destination and migratory habitat preferences. There are three fishways in Miyanaka Intake Dam. The rock-ramp fishway was newly established in 2012, creating an environment with different flow velocities and water depths. The purpose of this study was to investigate the effectiveness of the new rock-ramp fishway for native fish through two surveys. In the first survey, traps were installed during the survey period in all three fishways and all fish were caught. The run-up environment was quantified by measuring the flow velocity. In the second survey, fish were caught by spectrum methods upstream and downstream from the dam. It was found that bottom-dwelling fish and swimming fish not bound to the bottom with low migration abilities used the rock-ramp fishway for migration and as a habitat. After the new rock-ramp fishway was built, catches increased upstream from the dam. Further, the rock-ramp fishway is a potential habitat for certain species, such as Cottus pollux. As this is the first study to demonstrate the effectiveness of rock-ramp fishways, the research results are expected to be valuable to fishery managers and those planning river engineering projects.