Boundaries

The ecoregion encompasses the relatively wet, temperate region at the tip of southwestern Australia. The boundaries of this ecoregion were determined based on aridity. To the north, northeast, and east all drainages lack fishes due to a lack of water. Most fishes are found in areas with >700 mm of annual rainfall (Unmack 2001). The specific boundaries are from slightly east of Albany north to the Arrowsmith River.

Topography

Rivers descend from the edge of the interior plateau (at an elevation of between 300-400 m) to the coastal plain. The Darling Range is located at the edge of the Western Plateau and extends about 320 km parallel with the west coast. The highest elevation is 1096 m (Bluff Knoll), with most of the ecoregion’s fishes occurring below 200 m.

Freshwater habitats

This ecoregion is relatively small, covering 125,000 square kilometers or 1.6% of Australia. Freshwater habitats include coastal rivers and estuaries of varying salinity. River flows tend to be strongly seasonal and highly predictable with generally low variability each month. Many waters tended to be naturally slightly more saline, but increasing salinity in some rivers is becoming a major impact, as are exotic species such as Perca fluviatilis (European perch) and Gambusia holbrooki (Eastern mosquitofish).

Terrestrial habitats

eucalypt woodlands dominate the terrestrial vegetation. Along the southwestern coast, heath, swamp, and dune vegetation also occur.

Description of endemic fishes

This ecoregion has one endemic family (Lepidogalaxiidae, Lepidogalaxias salamandroides, salamanderfish) and two endemic genera: Bostockia porosa (nightfish) and Nannatherina balstoni (Balston’s pygmy perch). Of the total fauna, 10 out of 15 species are endemic. All strictly freshwater fishes are endemic (nine species) as are two of the three estuarine atherinids, while the three diadromous species are also found in eastern Australia (Morgan et al. 1998).

Other noteworthy fishes

Lepidogalaxias salamandroides

is exceptional in that it can aestivate during the dry summer period (Berra & Allen 1989; Pusey 1989; 1990). While research is lacking, it appears as if Galaxiella munda (western mud minnow) and G. nigrostriata (black-striped minnow) may also be capable of aestivation. Lepidogalaxias salamandroides is also the only Australian freshwater fish known to have internal fertilization (Pusey & Stewart 1989). Two normally diadromous species (Galaxias maculatus, common galaxias, and G. truttaceus, spotted galaxias) have adapted alternative life history strategies to enable them to reproduce totally within freshwater (Morgan 2003; Chapman et al. 2006).

Justification for delineation

This ecoregion hosts a rich biota with high endemism within most flora and fauna, as shown by its ranking in the top 25 hotspots for endemism globally (Myers et al., 2000). Fishes from this ecoregion typically have relationships to other fishes in southeastern Australia (Unmack 2001). Dry areas to the north and east clearly separate this region and its fish fauna from adjacent regions, i.e., no fishes are known north of the region until the Greenough drainage in Pilbara Province [802] nor east until southern Eyre Peninsula (in Paleo Province [810]) and the South Australian Gulf (in Murray-Darling Province [808]) (Unmack 2001). Most fishes and other biota have probably remained isolated from southeastern Australia since formation of the Eucla Basin (Nullabor Plain) 14-16 million years ago (Unmack 2001).

Level of taxonomic exploration

Taxonomic exploration is generally fairly good, and while most of the species are well documented, there is some recently recognized cryptic diversity within Nannoperca vittata (Western Pygmy Perch, Unmack 2005) and Galaxias occidentalis (Western Galaxias, Watts et al. 1995). More studies are needed to confirm the taxonomic status of the other species.