Macquarie perch is listed as a nationally endangered species and holds significance for the upper Murrumbidgee River. Once widespread throughout the region, populations have experienced significant declines due to habitat degradation, barriers to movement and reduced genetic diversity. The species is an important part of the upper Murrumbidgee River ecosystem and represents the health, history and resilience of the river itself.
Recent research has shown that the upper Murrumbidgee River supports one of the largest remaining populations of Macquarie perch, with breeding occurring along more than 91 kilometres of river. While this population remains critically important to the species’ recovery, investigations have revealed declining genetic diversity, reduced breeding population size and increasing levels of inbreeding. Without intervention, these genetic challenges could reduce the population’s ability to adapt to future threats such as climate change, disease and environmental disturbance.
Improving genetic diversity through genetic rescue
A genetic rescue program has been developed to improve the genetic diversity and long-term viability of Macquarie perch in the upper Murrumbidgee River.
The project is delivered by Associate Professor Mark Lintermans, a highly respected threatened fish researcher and manager with more than 40 years of experience working with Australian freshwater fish. Associate Professor Lintermans has played a leading role in Macquarie perch conservation, including developing survey and monitoring techniques, undertaking long-term research in the upper Murrumbidgee River and contributing to the genetic studies that identified the need for intervention.
Genetic rescue is a recognised conservation technique used to restore genetic diversity within declining populations. Increasing genetic diversity can improve population health, reduce the impacts of inbreeding and enhance the species’ ability to adapt to changing water temperatures and quality.
Translocating fish to restore population health
The project involves manually mixing Macquarie perch from different sections of the recovery reach by carefully translocating juvenile and sub-adult fish between sites.
Fish from downstream areas, where genetic diversity is higher and levels of inbreeding are lower, are being moved to upstream locations. This process creates new breeding opportunities between fish that would otherwise remain genetically isolated, helping to strengthen the overall population. Between five and eight sub-adult Macquarie perch per site are being translocated between selected sites throughout the river system as part of this targeted conservation effort.
Monitoring and fish collection
Eight monitoring sites were established across the lower, middle and upper sections of the species’ distribution within the upper Murrumbidgee River.
Sampling focused on collecting juvenile and sub-adult Macquarie perch suitable for translocation. Fyke nets (12 mm stretch-mesh) were used to capture fish, as this method has proven highly effective for targeting smaller size classes of the species while minimising impacts on the fish and non-target animals. The fyke nets were secured to the riverbank and positioned at an angle facing downstream, with weights used to keep the nets stable and effective during operation.
Fish processing and tracking
All captured fish were carefully measured and assessed before release or selection for translocation. Fish chosen for the genetic rescue program underwent additional processing, including:
- measuring and weighing
- collection of a small fin clip for genetic analysis
- implantation of a Passive Integrated Transponder (PIT) tag containing a unique identification number.
These procedures allow researchers to monitor individual fish over time and evaluate the success of the translocation program.
Looking to the future
The outcomes of the genetic rescue program will take time to measure. Translocated fish must first reach sexual maturity and successfully reproduce before the benefits can be assessed.
Future monitoring programs will sample the offspring of these fish to determine whether genetic diversity has increased and whether inbreeding levels have declined. The results will provide valuable information about the effectiveness of genetic rescue as a conservation tool and help guide future recovery efforts for the species.
Project outcomes
The Macquarie perch genetic rescue project aims to:
- increase genetic diversity within the upper Murrumbidgee population
- reduce the impacts of inbreeding
- improve the long-term resilience of the species
- enhance the population’s ability to adapt to environmental change and climate pressures
- support the recovery of one of Australia’s most endangered native freshwater fish
- contribute to the long-term ecological health of the upper Murrumbidgee River.
This project is helping to secure a future for the Macquarie perch and ensuring that this iconic native fish remains an important part of the upper Murrumbidgee River for generations to come.