Fish movement and sensitivity to contaminated mine water

Flowing through the Ranger uranium mine lease and into Kakadu National Park, Magela Creek is home to important populations of native fish species that need to be able to move between the river, floodplain and escarpment country at different times of the year.

Weathering of waste rock from the mine releases contaminants, including magnesium sulfate, a salt. These contaminants are washed out by the rain and are predicted to move through the local groundwater towards Magela Creek. Depending on the concentration, the magnesium sulfate has the potential to affect fish, trees and other freshwater ecosystems in and near Magela Creek downstream from the Ranger mine site.

There were two main parts of the project.

  • Acoustic tracking was used to examine the how fish moved up and down the sand channels of Magela Creek past the mine site. With the help of the Djurrubu Rangers, we tagged large-bodied fish (saratoga, sooty grunter and sharp-nose grunter) from Mudginberri and Bowerbird billabongs to track their movements over two wet–dry cycles, and mid-bodied fish (spangled perch, barred grunter and black catfish) from around Mudginberri Billabong to see how they moved upstream at the end of the wet season as the flood flows receded. Ten acoustic receivers were deployed across the study area to track movement of the tagged fish.
  • We used high-resolution sonar video surveys to identify and measure individual fish in Mudginberri and Bowerbird billabongs, allowing us to estimate the abundance and sizes of fish species in the dry, build-up and wet seasons. We combined this information with the acoustic tracking data to develop an understanding of the movements, distribution and population structure of fish across the study area.

Location of Kakadu National Park, Magela Creek, Ranger uranium mine and the four billabongs where fish were collected, tagged and detected.

Location of Kakadu National Park, Magela Creek, Ranger uranium mine and the four billabongs where fish were collected, tagged and detected.

  • An upstream monitoring site in Magela Creek, Kakadu. Photo: Supervising Scientist Branch (Commonwealth of Australia).
  • Researchers will investigate fish migration around the mine site to provide understanding on aquatic impacts. Photo: NESP NAERH.
  • A monitoring site in Magela Creek, Kakadu. Photo: Supervising Scientist Branch (Commonwealth of Australia).
  • Researchers will investigate fish migration around the mine site to provide understanding on aquatic impacts. Photo: NESP NAERH.
  • Researchers will be investigating fish movement to determine mining runoff on fish migration. Photo: NESP NAERH.
  • The researchers will use different methods of tracking fish movement to see the effects of surface groundwater runoff. Photo: NESP NAERH.
  • Gulungul creek floodplain between Baralil and Magela. Photo: Supervising Scientist Branch (Commonwealth of Australia).
  • Magela Creek in Kakadu. Photo: Supervising Scientist Branch (Commonwealth of Australia).

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