Key words: vertical slot, fishway, fish passage, innovation, Native Fish Strategy
A major goal of the Murray Darling Basin Commission’s (MDBC) Native Fish Strategy is restoring fish passage, and one of the most successful mechanisms of doing this is to construct vertical-slot fishways. The vertical-slot fishways built for locks 7, 8, 9 & 10 on the Murray River are world-class in functionality, passing a diversity of migratory species and a wide size range. However, their construction cost precludes their broad-scale application across the thousands of other barriers in the Basin. A major factor in the construction cost is the gradient (slope) of the fishway channel, which determines the total length and cost of the fishway. There is a need to develop new approaches to enable fishways to be constructed for lower cost.
Broad aim and methods: The aim of this project was to improve the passage of small-bodied fish in a fishway design known to pass large-bodied fish, and develop knowledge that could be extrapolated to other fishway designs. The study focused on improving the passage of small-bodied fish (< 60 mm long), as these have poor swimming ability and are often the biologically limiting factor in increasing the gradient of fishways.
This project tested two methods of increasing slope and improving fish passage by reducing turbulence within the pools of vertical slot fishway designs. Methods trialled were a) improving energy dissipation with wall roughness (Fig 1) and b) reducing fishway discharge using middle sills placed in each vertical-slot baffle (Fig 2). A top control treatment was used to assess what fish could ascend an unmodified fishway, and an entrance control treatment was used to assess what fish were moving upstream and entering the fishway from the river.
Fish traps were installed upstream of the experimental treatment (or downstream for the entrance control). After 30 minutes of operation, fish species and lengths were recorded.
Findings: The experiments yielded four major findings that are likely to lead to reduced cost and improved performance of fishways throughout the Basin:
- The baffle in the vertical-slot design has significant potential to improve fish passage.
- Turbulence in the fishway pool may be more limiting for the passage of small fish than the high water velocity in the slot of the vertical-slot baffle.
- The sharp-edged narrow-slot appeared to provide improved velocity distribution.
- The number of small migrating fish was much greater than expected.
Lessons learned and future directions: The results show that refining the vertical slot design can improve fish passage performance, but further research is needed before design changes can be applied with confidence to new fishways. Significantly, the design approach with the most potential to reduce cost is to separate the function of passing small fish and large fish, as well as allowing for differential passage in high and low flows as has already been applied with cost savings to the Lock 10 fishway.
The passage of carp gudgeons (Hypseleotris spp.), which are very poor in ascending fishways, is an indication that a range of small-bodied fishes can ascend modified fishways, including small threatened species such as Olive Perchlet (Ambassis agassizii) and Murray Hardyhead (Craterocephalus fluviatilis) (Fig 3). Restoring the ecological processes of dispersal and recolonisation through effective fishways will be an important part of recovering the populations of these species.
Stakeholders and Funding bodies:This project was funded through the Murray-Darling Basin Authority’s Native Fish Strategy, and conducted by a collaborative team from Fishway Consulting Services, Kingfisher Research, South Australian Research and Development Institute, NSW Department of Primary Industries and the Arthur Rylah Institute for Environmental Research.
Contact: Dr Martin Mallen-Cooper, Fishway Consulting Services, (02) 9449 9638, email@example.com.