Peter Unmack



Major Habitat Type

Xeric freshwaters and endorheic (closed) basins

Drainages flowing into

Indian Ocean.

Main rivers to other water bodies

The major drainages from south to north are the Murchison, Gascoyne, Ashburton, Fortescue, and De Grey rivers. All rivers are largely ephemeral.



The ecoregion extends from and includes the Greenough drainage in the south to the DeGrey in the north. It is bordered by the Great Sandy Desert in the north and east.


The Pilbara Province occurs over a large ancient Precambrian block from which most rivers drain. The highest elevation is 1,253 (Mt Meharry), and most of the ecoregion is over 200 m with rivers rising in rugged mountains. Many of the rivers have carved deep spectacular canyons as they drain towards the coast. These canyons contain much of the permanent water in the region.

Freshwater habitats

This ecoregion is moderately sized, covering 570,000 square kilometers or 7.3% of Australia. Due to the extreme aridity of the region all rivers are intermittent and are reduced to a series of isolated pools during extended dry periods. Due to weather patterns (including cyclones) the area occasionally receives heavy rainfall resulting in massive flooding. During dry periods, southern rivers tend to become quite saline, > 32 ppt (Morgan & Gill 2004). No major dams exist within this ecoregion.

Terrestrial habitats

Open shrublands dominate the vegetative cover and are interspersed with closed shrublands and grasslands.

Description of endemic fishes

The species Milyeringa veritas (blind gudgeon) represents an endemic genus. That species, plus Ophisternon candidum (blind cave eel) are endemic to cave systems on North West Cape (Morgan & Gill). There are three additional endemic species: Craterocephalus cuneiceps (Murchison River hardyhead), Hypseleotris aurea (golden gudgeon), and Leiopotherapon aheneus (Fortescue grunter). The first two are mostly found only in rivers from the Gascoyne south, while the latter is found between the Ashburton and Fortescue rivers. Overall five out of 20 species are endemic (25%).

Other noteworthy fishes

Several of the more abundant fishes within this ecoregion have the broadest distributions within Australia (Nematalosa erebi, bony bream; Neosilurus hyrtlii, Hyrtl’s catfish; Amniataba percoides, banded grunter; and Leiopotherapon unicolor, spangled perch). These species have broad environmental tolerances and do well under harsh conditions.

Justification for delineation

A total of 10 strictly freshwater fishes are present, three of which are endemic. Addition of the brackish cave fauna brings endemism up to five species. The region is apparently strongly isolated from other parts of Australia by the Great Sandy Desert, which has no surface runoff, lacks significant river channels, and is quite arid. This isolation has presumably facilitated the evolution of the five endemic fishes, and resulted in at least four of the widespread species having distinctive populations in the Pilbara (Leiopotherapon unicolor (Bostock et al. 2006), Nematalosa erebi (M. Adams pers. comm.), Melanotaenia australis (Unmack 2005), and Neosilurus hyrtlii (P. Unmack unpub. data).

Level of taxonomic exploration

Taxonomic exploration is good, with the exception that Morgan & Gill (2004) suggested there may be an additional undescribed catfish present in the Robe River. Neosilurus hyrtlii inhabiting this ecoregion may also be sufficiently different to be separated into a distinct species (P. Unmack unpub. data). Populations of Melanotaenia australis may also be separable into a different taxon relative to more northerly populations (Unmack 2005).


  • Allen, M. G.,Morgan, D. L.;Gill, H. S. (2005). "Distribution, zoogeography and biology of the Murchison River hardyhead (Craterocephalus cuneiceps Whitley, 1944), an atherinid endemic to the Indian Ocean (Pilbara) Drainage Division of Western Australia" Ecology of Freshwater Fish
  • Bostock, B. M., Adams, M., Laurenson, L. J. B., et al. (2006). "The molecular systematics of Leiopotherapon unicolor (Gunther, 1859): testing for cryptic speciation in Australia's most widespread freshwater fish" Biological Journal of the Linnean Society 87 pp. 537–552.
  • Knott, B. (1993). "Stygofauna from Cape Range peninsula, Western Australia: Tethyan relicts" Records of the Western Australian Museum 45 pp. 109-127.
  • Morgan, D. L. and Gill, H. S. (2004). "Fish fauna in inland waters of the Pilbara (Indian Ocean) Drainage Division of Western Australia -- evidence for three subprovinces" Zootaxa 636 pp. 1-43.
  • Proudlove, G. S. (2006). "Subterranean fishes of the world. An account of the subterranean (hypogean) fishes described to 2003 with a bibliography 1541–2004" Moulis: International Society for Subterranean Biology.
  • Unmack, P. J. (2001). "Biogeography of Australian freshwater fishes" Journal of Biogeography 28 (9) pp. 1053-1089.
  • Unmack, P. J. (2005). "Historical biogeography and a priori hypotheses based on freshwater fishes" Unpublished Thesis. Arizona State University .
  • Allen, G. R.,Midgley, S. H.;Allen, M. (2002). "Field guide to the freshwater fishes of Australia" Perth: Western Australian Museum.