Silver Perch. Illustration thanks to NSW Government.
Listed as a vulnerable species in the ACT in 2001, the Silver Perch is listed as critically endangered nationally, vulnerable in NSW, threatened in Victoria and protected in South Australia and parts of Queensland.
Silver Perch used to be widespread through the Murray–Darling Basin, including the Murrumbidgee and Molonglo rivers, but have not been recorded in the ACT since 1988. They are artificially bred in commercial hatcheries for the NSW fish stocking and market and are stocked into Googong Reservoir.
In the wild, Silver Perch are usually around 30–40 centimetres long, weigh around 0.5-1.5 kilograms, and can live more than 15 years. As omnivores they consume aquatic plants, algae, molluscs, crustaceans and aquatic insect larvae.
Juveniles and adults are known to migrate more than 200 kilometres. Historical observations show upstream migrations of large schools of fish were often associated with spawning, which starts in spring to early summer.
Before new populations can re-establish in the ACT, major threats need to be addressed or mitigated. Threats include habitat destruction or modification, barriers to passage, river regulation, overfishing, alien species, disease and climate change.
Alteration or destruction of fish habitat is one of the most important causes of native fish decline. Silver Perch habitats have been impacted by sedimentation of streams, cold water pollution downstream of dams and riparian degradation along the Murrumbidgee River.
Barriers to fish passage impact Silver Perch isolating habitat and fragment population and, limiting breeding migrations. Barriers can be structural (e.g. dams, weirs, road crossings) or chemical (e.g. discharge of effluents, pollutants, contaminants) and can be partial or total. . Dams can also impact flows downstream, hindering fish passage including spawning migration. Dams create large areas of still water, which may impact on egg and early larval development of Silver Perch.
Introduced species, such as Carp and Redfin, may compete for food and prey on juvenile Silver Perch. They can introduce or spread diseases and parasites to native fish. Silver Perch is extremely susceptible Epizootic Haematopoietic Necrosis Virus, which has regular seasonal outbreaks and is easily transmitted from one location to another.
Climate change also puts fish at risk. Fish can’t regulate their body temperature; given Silver Perch are thought to spawnin response to day length and water temperature, there is a risk that spawning cues can become decoupled with earlier seasonal warming. With more fires and increased rainfall intensity predicted, more sediment may end up in streams.
It has been prohibited to take Silver Perch from ACT waters since 2001.
The major conservation objective of the action plan is to assist, where possible, the re-establishment of Silver Perch in the upper Murrumbidgee Catchment by providing suitable habitat and working with other states to re-establish the species, should resources become available. These actions will be driven by the Silver Perch Action Plan (2018) and the ACT Aquatic and Riparian Conservation Strategy (2018).
To create conditions where Silver Perch and other native fish may thrive, the ACT Government is already:
- replanting on the Murrumbidgee River as part of the Million Trees program
- improving the fishways on the Murrumbidgee River
- improving the fish habitat in the Upper Murrumbidgee Demonstration Reach (the 100 kilometre stretch of river from Bredbo to Casuarina Sands)
- establishing rock groynes and engineered log jams to rehabilitate fish habitat and improve fish passage in the Murrumbidgee River through the sand slug past Tharwa
- regular monitoring of the fish to inform fish management actions.
The action plan outlines how we can:
- support projects aimed at improving understanding of the biology and ecology of the species as the basis for managing its habitat
- protect sites and habitats that are critical to the survival of the species
- support research that may lead to the successful re-establishment and management of Silver Perch in the upper Murrumbidgee River
- continue to monitor the Murrumbidgee River for a re-established population
- manage activities in the Murrumbidgee Catchment in the ACT to minimise or eliminate threats to fish population, for example:
- maintain riverine habitats with appropriate seasonal environmental flows, intact riparian zones, pool depths, and minimal sediment inputs from roads and surrounding land use.
- protect and revegetate riparian zones to increase organic matter, provide shade (which buffers water temperatures, provides cover, prevents erosion and filters sediment from run-off)
- minimise sediment addition
- facilitate fish passage to connect habitats and help migration
- increase community awareness of the need to protect fish and their habitats.
- Silver Perch Action Plan, 2018
- Aquatic and Riparian Conservation Strategy, 2018
- Australian Government’s Conservation Advice
Epsddcomms@act.gov.au or call Access Canberra on 13 22 81