Innovative fish counter to help monitor fish migration in the Murray

The first Australian trial of an infrared fish counter at Lock 10 (Wentworth) on the Murray will boost scientists’ understanding of native fish migration along the river.

The trial is being conducted and funded under the Murray-Darling Basin Authority’s award winning ‘Sea to Hume Dam’ program which aims to improve fish migration along the full length of the river.

‘Sea to Hume Dam’ is part of the Authority’s Native Fish Strategy, which aims to help restore depleted native fish populations to 60 per cent of their estimated pre-European settlement levels.

A four-state team of Murray River fishways researchers from NSW Department of Primary Industries (DPI), Queensland Department of Employment, Economic Development and Innovation, Victorian Department of Sustainability and Environment, and South Australian Research and Development Institute is undertaking the study, which will provide the first field-based assessment of an infrared fish counting system in Australia.

NSW DPI research scientist based at Narrandera Fisheries Centre, Dr Lee Baumgartner, said current methods of trapping fish within fishways had certain limitations.

"Some fish show a natural shyness to traps, others behave differently after being handled. So scientists are always interested in innovative counting systems that may offer a less invasive alternative to more traditional sampling methods," he said.

Dr Baumgartner said an innovative system developed in Iceland is the Vaki Riverwatcher. The system has been successfully used in Northern Hemisphere rivers, where it has shown greater than 95 per cent accuracy when quantifying upstream migrations of up to 500 fish an hour.

The system counts fish by establishing an infrared grid around a point of known fish migration, such as within a fishway. When fish migrate through the grid they are counted and measured. Information obtained on each fish passing though the infrared scanner includes: date, time, upstream or downstream direction and body depth.

As fish pass through the grid, the system is also able to map an outline of the shape of the fish. This is converted into a picture file as a silhouette diagram, which is being used to help identify different species.

In July 2008, NSW DPI took possession of a Vaki Riverwatcher Infrared Fish Counter. Field trials took place at Lock 10 (Wentworth) in late 2008 and more than 400 hours of data was logged.

Dr Baumgartner said despite particularly turbid water during the study, the Vaki Riverwatcher successfully provided information on hundreds of migratory fish during a five-week period.

Scientists hope that further development of the technology will lead to a long-term method to monitor fish migration in the Murray-Darling system.