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Searching for fish – CSI style

​A female scientist stands in a creek sampling the water​

We all know the risk of a criminal leaving behind their DNA at a crime scene.

We’ve all watched enough true crime to know how easily a single hair or flake of skin can be used to identify a culprit.

But did you know our scientists are now using very similar DNA technology to find out what fish are in an area?

They can do this without ever spotting a single fish, simply by collecting water samples containing tiny DNA fragments shed by fish through their skin or excrement.

Environmental DNA (or eDNA) sampling now enables scientists to determine the types of fish (or other species) occurring in a water-catchment area by analysing a water sample for DNA fragments.

DPI Fisheries are using eDNA technology to identify the fish present at Everlasting and Tuckean swamps, in northern NSW before, during and after proposed remediation works.

This technology is suitable for the non-invasive detection of rare species in swamp environments, which can be difficult to sample using conventional methods.

DPI Fisheries Max Osborne has been leading the project to rehabilitate several heavily impacted coastal wetland sites including these areas.

He said using eDNA to monitor fish communities will be a great way to track the health of these wetland sites.

“Fish are good indicators of aquatic ecosystem health, as they provide evidence that the water quality at that location can support life over extended periods,” he said.

“We’ve already collected the water samples at these swamps and had them analysed to identify fish species that are present now.  We will repeat this sampling in a few years as the swamps are rehabilitated and see what we find.”

“It is amazing to think how the kind of fish present will change after we rehabilitate these wetlands. This eDNA sampling gives us a tool to see what is going on in these areas,” he said.

Mr Osborne said the water quality of Everlasting and Tuckean swamps can be poor due to historic drainage projects.

“In the past tidal-barrages, floodgates and drains were installed to restrict tidal saltwater flows, lower floodplain groundwater and wetland water-levels to create farmlands. These drained creeks, swamps and floodplains now periodically produce large volumes of highly acidic and/or deoxygenated water (also known as blackwater) which impacts fish, the health of these wetlands and the estuaries they flow into,” he said.

“We are currently working with landholders, traditional owners, government agencies, partner organisations and expert consultants to develop wetland remediation projects at these wetlands and start to reverse these problems,” Mr Osborne said.

Mr Osborne said he’s looking forward to seeing the results of these eDNA surveys in future years.

“Now we have used eDNA techniques to assess the fish community across all aquatic habitats within the two swamps we have a baseline against which the success of any future large-scale wetland remediation activities can be evaluated,” he said.

The Coastal Wetland Rehabilitation program is conducted by DPI Fisheries and funded via the NSW Marine Estate Management Strategy.

You can read the report here.

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