‘Flow hydrodynamics’, ‘turbulent kinetic energy’, ‘rheotactic behaviour’ – whilst these terms might not mean much to you, they are essential parts of native fish migration in the Murray-Darling Basin.  

The Murray-Darling Basin is one of the most regulated river systems in the world, home to over 10,000 barriers preventing fish from migrating. These barriers include dams and weirs, and whilst important for water supplies, they are increasingly a key threat to Australian native fish. Water managers and scientists over the last decade have been working hard to install fishways – such as the Toorale and Koondrook fishways – which enable fish to move past barriers upstream and downstream.

Water flowing over the Homestead Dam fishway at Toorale. Source: Matthew Gordos, NSW DPI, Fisheries.

Tube Fishway installed at the Water Research Laboratory, providing an 8 metre lift. Photo: I. Suthers.

However, these relatively recent additions to our rivers require more research so they are effective in helping native fish complete essential migration patterns. Different sorts of fishways work better for different types of fish species. Fishways use attraction flows to attract fish, however, it has become apparent that different species require different attraction flow velocities and turbulence. One of these fishways that is being trialled by a research team at the University of New South Wales is the Tube Fishway (pictured above).

Attracting juvenile silver perch into a fishway entrance system at UNSW Water Research Laboratory. Image credit: Maryam Farzadkhoo.

Scientia PhD candidate Maryam Farzadkhoo, conducting systematic experiments to attract freshwater fish species into a fishway entrance system at the UNSW Water Research Laboratory. Image credit: Maryam Farzadkhoo.

Velocity is the speed of the flow, whilst ‘turbulent kinetic energy’ is a measure of turbulence in the water. Fish are attracted by water with sufficient velocity and turbulence, relative to their swimming ability, as they are prone to ‘rheotactic’ behaviour – which is the technical term for how fish turn to face a current, swimming in the fishway’s direction.

Recent experiments by scientists at the University of New South Wales have been investigating what sort of attraction flow hydrodynamics and velocities attract different native fish to fishways. The findings are important and help inform what sort of attraction flows are used to help most native fish migrate past barriers in a river.  

What they found…

The study focused on two species of native fish — juvenile silver perch and Australian bass – and found that higher levels of turbulence and velocity to a certain level were effective in guiding the fish into the entry of the fishway. However, the study found that Australian bass and silver perch required less turbulence than other species, but attraction flows were more effective when directed near a sidewall in the river, as it helps the fish orient themselves.  

Some fish were found preferring less turbulent attraction flows. This may be because they preferred to use less energy following the jet flow than they would with higher flows.  

Where to next?

These initial findings demonstrate that different native fish species react differently to different attraction flows. Future research by the team at UNSW will investigate the reactions of different ages of fish and different species, looking at the effect of attraction flow behaviour and the geometry of the fishway’s entry to find the most efficient entrance style for fish migration. This research is critical to ensure our fishways are as effective as possible in helping native fish species migrate past barriers in Australia’s regulated rivers.  

Resources:

• Read the study here.
• More info on the tube fishway.

This research was led by Maryam Farzadkhoo (Scientia PhD candidate, School of Civil and Environmental Engineering and School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney)

Supervisors: Associate Prof. Stefan Felder; Prof. Richard Kingsford, Prof. Iain Suthers.

Featured image: Hume Dam in Southern NSW. Image credit: Wikimedia Commons.

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