Electrofishing: Scientists Gather More Fish Data

Scientists from the Queensland Government have recently been undertaking fish surveys in several Wet Tropics basins to add to future Wet Tropics Report Cards.

The fish index is one of three key indices required to properly assess waterway health in the Wet Tropics basins. In the report card, our annual assessment of waterway health uses water quality, habitat and hydrology indices to provide ‘multiple lines of evidence’ for a comprehensive understanding of waterway condition. The inclusion of a fish indicator is considered necessary to give a robust assessment of waterway health.

The number and type of fish present in a waterway can tell us a lot about the overall health of the system that can’t be determined by the other indicators in isolation, and provides a tangible link between physical, chemical and biological processes in waterways.

Basin-wide fish surveys across the Wet Tropics region were first conducted around 27 years ago. Since then fish surveys and monitoring have been project based and focused upon specific issues and fish communities.

This gap in basin-wide species diversity fish monitoring was first identified in the 2016 Pilot Report Card and since then funding through Cairns Regional Council and the Queensland Department of Environment and Science (DES) has allowed basin-wide species diversity surveys to be conducted for the Russell and Mulgrave in 2017-18.

The funding through DES has now allowed the surveys to be expanded to the Mossman, Barron, Johnstone, Tully and Murray basins in 2019 with repeat surveys and the Herbert to be conducted in 2020.

The surveys are assessing how many species are present and the proportion of native vs. exotic or translocated species.

Over the last few weeks scientists have been using a technique called Electrofishing to sample fish communities at randomly chosen sites across the Wet Tropics basins. This non-destructive technique puts fish within a 3-metre radius into a trance allowing them to be caught, identified and returned to the water unharmed.

In the 2019 Report Card, fish diversity at the majority of sites in the Russell and Mulgrave basins was rated as good or very good but the scientists have noticed an increase in the number of sites with exotic species compared to earlier surveys.

Electrofishing is only viable in fresh water, so the Partnership are looking at other methods for assessing fish in estuaries. This has traditionally been a challenge in northern Australia where estuarine waters are often turbid and where the presence of crocodiles can hamper sampling efforts.

Emerging technologies such as bioacoustics, advanced video techniques and eDNA are being considered, along with the use of commercial and recreational catch data.
Stay tuned for the 2020 report card, where the results of the fish indicators will be revealed!

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