Boundaries

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.

Topography

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).