Protecting native fish species

In 2007, ACTEW committed to increase the capacity of the Cotter Reservoir from 4 gigalitres (GL) to 78GL as part of a suite of water security measures. Increasing the dam size will also mean raising the potential reservoir level by around 50 metres and lengthening the reservoir’s shoreline from around 10 km to nearly 25 km.

The existing Cotter Reservoir and Cotter River provide critical habitat for several aquatic species that may be affected by the construction and operation of the Enlarged Cotter Dam.

These include:

  Macquarie Perch (Macquaria australasica)
  Endangered (the only sustainable ACT population is in the Cotter Reservoir)

 

  Trout Cod (Maccullochella macquariensis)
  Endangered

  Murray Cod (Maccullochella peelii peelii)
  Vulnerable

  Two-spinned Blackfish (Gadopsis bispinosus)
  Vulnerable

  Murray River Crayfish (Euastacus armatus)
  Vulnerable

ACTEW is committed to addressing issues which may impact on these threatened species in order to comply with the requirements of the ACT’s Nature Conservation Act and the Federal Government’s Environment Protection and Biodiversity Conservation legislation.

Protecting threatened native fish species

ACTEW is committed to the ongoing protection of native fish species and the improvement of aquatic habitats in the vicinity of the dam. Working closely with experts from the University of Canberra, Australian National University and University of Sydney - and addressing the concerns of key stakeholders such as the ACT’s Environmental Protection Authority, Territory and Municipal Services and the Commonwealth Department for Environment, Water, Heritage and the Arts - ACTEW has developed a comprehensive program to ensure environmental and water quality issues are addressed.

A key focus area is the protection of threatened aquatic species.

Establishing artificial fish habitats

When the Enlarged Cotter Dam is complete and the reservoir begins to fill, the macrophyte reed beds that Macquarie Perch currently use as shelter will be inundated. As part of a comprehensive fish management program involving ACTEW Corporation and the University of Canberra, Australian National University and the University of Sydney, ACTEW completed a trial of artificial fish habitats for the endangered Macquarie Perch population in the Cotter Reservoir. Results showed that in the absence of reed beds Macquarie Perch prefer artificial rock reefs over other forms of artificial habitat that were trialled.

Following the submission of a Development Application to the ACT Planning and Land Authority in early 2011, work began on constructing artificial rock reef habitats at carefully selected sites around the Cotter Reservoir for the Macquarie Perch. The habitats will provide new shelter for the fish species when the enlarged reservoir begins to fill and the macrophyte reed beds that they currently shelter in are inundated. Rocks of the right size and quality have been sourced to create the habitats and it is expected construction of them will be complete before the water level starts to rise in the enlarged Cotter Reservoir.

Fish habitats

The rock reef habitats taking shape at the site

Managing risk to aquatic species

A series of studies are being undertaken by various government agencies, university researchers and ACTEW to mitigate potential risks associated with the construction and later operation of the Enlarged Cotter Dam. Results from these studies will enable ACTEW to understand and manage:

  • use of artificial habitats by Macquarie Perch;
  • the impact of fluctuating reservoir levels on Macquarie Perch food sources;
  • the possible recolonisation of the enlarged Cotter Reservoir by Two-spined Blackfish;
  • the ecology and habitat preferences of Murray River Crayfish;
  • measures to protect the Cotter Reservoir from the EHN virus (fatal to some threatened native fish species);
  • native fish access to upstream sections of the Cotter River;
  • establishing other populations of Macquarie Perch and Two-spined Blackfish in locations outside the Cotter River system;
  • the impact of alien fish species on threatened native fish populations;
  • monitoring and evaluation as the basis for adaptive management measures to protect threatened species from predators and competitors within the enlarged Cotter Reservoir.

ACTEW continues to work with our partners to help protect these fish species, and these activities remain integral to the ongoing Enlarged Cotter Dam works.