Native fish

Why are native fish so important?

The Murray–Darling Basin has over 60 native fish species – including freshwater, estuarine, marine and migratory fish. Many of these freshwater species are unique to Australia, with a number living only in the Basin.

Native fish play many important roles in ecosystems - as a predator, as prey and in nutrient cycling. Recreational fishing is a major pastime throughout the Basin and generates $1.3 billion annually. All of these values depend upon healthy native fish populations.

Flow has a major influence on the life cycles of native fish,  and different species respond differently to different flows. Human water use has changed flow volumes and patterns. This has degraded native fish habitat and reduced connectivity across the Basin, leading to major declines in fish numbers and the area they occupy. Nearly half of the Basin’s native freshwater fish are now listed as under threat.

 

life cycle of fish flow chart
Life cycle of fish
Life cycle of fish and why they need flows

Improving the outlook for threatened and recreational fish are key outcomes sought from the Basin-wide environmental watering strategy. Returning suitable flow conditions is a key action that can help native fish. In some areas, simply returning flows can create a positive fish response. Elsewhere, other factors are also affecting fish and these can be addressed alongside water management.

Getting the scales right – local, regional and Basin-scale flows for fish needs

Spatial scales of flows are very important for fish populations. Some fish populations can do well when we get flows right for a single river or even a river reach. However, the life cycle of other species can operate over many hundreds of kilometres and across different river systems. The impacts of reduced flows and connectivity between rivers are particularly severe on the species that rely on Basin-scale flows - such as golden perch, silver perch, pouched lamprey and short-headed lamprey. 

For these fish, key ecological processes need to work across large scales and multiple rivers. These processes support all parts of the life cycle - such as movement, spawning, egg/larval development, juvenile growth phases and maturation into adults. To meet these life-cycle needs, river systems need to connect at important times and in particular sequences. This needs active coordination of flows across catchments and administrative boundaries, and spanning multiple water years.

Basin annual environmental watering priorities for fish

To achieve the outcomes in the Bain-wide environmental watering strategy that are expected for fish, we need to provide flows that improve fish habitats and allow fish to complete their life-cycles. Flows are also an important measure to protect and improve populations of threatened fish species.

These priorities for native fish provide guidance on how flows can support outcomes for native fish, particularly to meet Basin-scale needs.

Connect southern Basin rivers to recover native fish populations

This priority encourages coordination and linking of flows in different rivers. It aims to restore system-scale ecological processes that promote population recovery of silver perch, golden perch and two lamprey species in the southern connected basin. Flows that improve recruitment of Murray cod and trout cod are also supported by this priority.  The outcomes described here can be achieved without widespread inundation of floodplains and wetlands.

Four flow components that are ecologically significant for native fish, throughout the southern connected Basin are the focus of this priority:

  • end-of-system flows through the barrage fishways and the barrages
  • winter flows that provide habitat in anabranches and tributaries, and connectivity between these habitats
  • flows that support breeding activity in spring
  • flows that support dispersal movements in spring, summer and autumn

Each of the target fish species have different requirements and different flow objectives

Species Specific objectives to recover native fish populations

Murray cod and trout cod

Support regular local recruitment in:

  • the main channel of the River Murray (for both cod) and lower Darling River (for Murray cod only) ; and
  • regulated anabranches and tributaries
Silver perch
  • support annual system-scale recruitment in the mid-Murray
  • support regular local recruitment in the lower River Murray, lower Darling River, tributaries and anabranches
  • promote movement and dispersal, particularly of juveniles, into tributaries and anabranches
Golden perch
  • capitalise on episodic system-scale recruitment from the Darling River (including the Menindee Lakes and lower Darling River)
  • support regular system-scale recruitment in the mid-Murray
  • support regular local recruitment in the lower River Murray, lower Darling River, tributaries and anabranches
  • promote movement and dispersal, particularly of juveniles, into tributaries and anabranches
Short-headed and pouched lamprey

Support system-scale migrations of lamprey:

  • from the ocean, through the estuary and into the River Murray
  • to upstream breeding grounds
  • return to the ocean

Connect river flows to improve outcomes for native fish throughout the Barwon─Darling and into the southern and northern basins

The Barwon─Darling river system is particularly important for the recovery of native fish populations in the Murray─Darling Basin. The system supports a diverse native fish assemblage, comprising at least 15 native fish species, including a number of threatened species.

Fish bred in the Barwon-Darling system contribute substantially to golden perch, silver perch and Murray cod populations in river systems in both the northern and southern Basin.

Water use has resulted in major reductions in the frequency and duration of flow and flood events in the Barwon─Darling. These changes to flows have reduced native fish populations. Returning suitable flow regimes is vital to ensure the Barwon─Darling is able to deliver its key functions and support native fish populations. 

Key focus areas of this priority

Focus area Flow supporting fish outcomes

Improve flow variability in the Barwon─Darling River to support native fish

Better fish outcomes achieved by reducing the frequency and duration of cease-to-flow events and through improved flow variability with base flows, low flows, and small, medium and (if possible) large freshes.

Natural floods also provide essential functions for fish.

Capitalise on natural recruitment flows through the Barwon─Darling River to boost native fish populations

Natural recruitment is an important trigger. A range of flows can capitalise on this recruitment to improve fish outcomes by :

  • boosting food supply, particularly for young fish
  • enabling adult fish to move to and from spawning areas
  • improving survival of eggs, larvae and young fish
  • promoting dispersal of young fish into northern rivers and into the southern basin
Increase flow connections between the Barwon─Darling River and its tributaries Connecting tributaries to the Barwon─Darling to promote the exchange of fish, nutrients and other biota between systems. In particular, to promote the movement of native fish into tributaries to boost resident fish numbers, particularly juvenile and sub-adult golden perch, Murray cod and silver perch.

Support and improve threatened fish populations

Almost half of the native fish species in the Murray─Darling Basin are of conservation concern. Environmental watering, alongside other measures, is a key action to improve outcomes for threatened fish. This priority seeks to protect remaining populations of threatened species and to increase the area(s) they occupy. This process can span multiple years and is important to reduce the risk of populations going extinct. Where populations are disconnected from each other, or locally extinct, stocking will be needed to support threatened fish. Water managers are encouraged to work with threatened species recovery agencies to achieve the outcomes for this priority.

 

Steps to re-introduction Flow management actions

Protect and boost key source populations

Create suitable habitat for adult and young fish to co-exist.

Provide a suitable flow regime to encourage recruitment.

Support temporary surrogate sites and populations that can then start new permanent populations

Maintain habitat including suitable conditions (salinity, turbidity) and food sources, and to ensure that refuges are available during dry conditions.

Provide a suitable flow regime to encourage recruitment.

Identify and prepare sites to establish permanent populations

Restore a suitable flow regime for the fish species to be reintroduced and the habitat and food sources they require.

Support fish stocked into reintroduction sites and secure their long-term future

Maintain the established flow regime and provide flows that support recruitment and, when sufficient numbers exist, dispersal.