Indicator: IW-31 Fish - Abundance and distribution


2002 NSW freshwater fish report


  • 82 native, introduced and estuarine fish species recorded from NSW rivers
  • Five large-scale communities identified in Montane rivers, and in Murray, Darling, North Coast and South Coast rivers

Current Status:

Native Fish

  • 22% of species expected to occur were not recorded in recent surveys
  • Fish communities in the Murray region are in poor condition
  • Many species now have reduced abundance or distribution
  • High incidence of abnormalities in some areas

Threatened species

  • Eleven species recognised internationally as threatened
  • Ten freshwater species (including 3 invertebrates), 2 populations and 1 ecological community listed under NSW legislation
  • Four key threatening processes listed under NSW legislation
  • Several other species are of concern
  • Trout cod stocking program continuing

Alien species

  • Thirteen introduced species recorded from NSW freshwaters
  • Carp, goldfish, redfin perch, Gambusia, rainbow trout, brown trout most common
  • Greatest numbers recorded from rivers in the Murray region

Fisheries-related uses:

  • Commercial fishery for native species (except yabbies) closed
  • Carp fishery expanding
  • Recreational fisheries for freshwater species are significant
  • Widespread stocking of native fish into impoundments


  • River flow alteration
  • Habitat loss
  • Water quality
  • Introduced species
  • Stocking and translocation

Recent trends:

  • Continued decline of native species
  • Continued spread of carp, Gambusia and oriental weatherloach
  • Increased recruitment of many native species in wet years
  • Increased recruitment of carp in wet years
  • Increased construction of fishways on barriers


  • Government policy initiatives to rehabilitate rivers, including State Weirs Policy, State Fishway Program, and NSW Water Reforms
  • General angling license continues to support freshwater recreational fishing, as well as fishing restrictions
  • Habitat policy and guidelines
  • Threatened species and Biodiversity Program Plan

NSW Fisheries research:

  • Fish passage, fishways and migration
  • Benefits of environmental flows
  • Methods for carp control
  • Threatened species research
  • Sustainable Rivers Audit
  • Habitat rehabilitation

Source: NSW Fisheries 2003, Status of Fisheries Resources 2001-2002, NSW Fisheries, Cronulla, NSW, viewed 15 Nov 2005,

Murray Darling Basin

It has been estimated that only 10% of pre-European fish populations are left within the Murray Darling Basin and without intervention this is likely to fall to 5% in the next 40 to 50 years

Source: Murray-Darling Basin Commission, 2003. Native Fish Strategy for the Murray-Darling Basin 2003-2013. Murray-Darling Basin Commission, Canberra

Ten of the 22 native species which are known or suspected to have previously existed in the Lower Murray-Darling catchment are either locally extinct or survive at very low abundances. In addition the biomass of the fish community is quite low, with 56% of the total biomass being introduced fish.

Murray cod and golden perch stocks increased in the Lower Murray-Darling catchment between 1984 and 1994, partly due to stocking programs. These increases stabilised between 1994 and 2005. Catfish, Macquarie perch and tench populations in the same area declined to the point of local extinction by 1990, carp-gudgeon abundance has been increasing significantly since at least 1994, Australian smelt abundance has been increasing significantly in the Murray River since 1994, and carp abundance has declined significantly since 1994 in some parts of the catchment.

Source: Gilligan, D. M 2005, Fish communities of the Lower Murray-Darling catchment: Status and trends, NSW Department of Primary Industries, Sydney, viewed 15 May 2006,

What the data mean

In NSW surveys reveal that condition of fish communities continues to decline, with reduced abundance or distribution. Pressures include river flow alteration, habitat loss, water quality, introduced species and stocking and translocation.

Data Limitations

The only data available are from NSW.

Issues for which this is an indicator and why

Inland Waters - Response of biota - Fish 

Declines in abundance and distribution are indicative of declines in the overall viability of a species. A decline in fish communities also provides a warning that the natural ecological functioning of the aquatic system is at risk.

Other indicators for this issue:

Biodiversity - Species, habitats and ecological communities - Conservation status of species and ecological communities 

Pressures on fish species include significant changes to water flow, damage to riparian zones, removal of in-stream habitats, sedimentation, lowered water quality, thermal pollution, barriers to fish passage, and competition with and / or predation by introduced fish species. Changes in distribution and abundance of some fish species may be indicative of changes in environmental condition more broadly.

Other indicators for this issue:

Biodiversity - Species, habitats and ecological communities - Condition of freshwater biodiversity 

The health of populations and communities of native fish species is an indicator of the overall condition of the aquatic ecosystem. A decline in fish communities provides a warning that the natural ecological functioning of the aquatic system is at risk.

Other indicators for this issue:

Further Information

Queensland long term monitoring program