The freshwater fish of the Pilbara are dominated by the relatively few species that can survive the extremes of massive flooding and high-velocity flows after cyclones and the long dry season when rivers contract to isolated pools. But it doesn’t mean that fish are scarce, as Njamal elder Peter Coppin recounted:
See, we come from the De Grey River and …. down Yarrie way. I remember the old people was dancing there, woman and men, for the ceremony for makin’ more fish. … Used to get them with a net. Christ, you couldn’t hardly lift them out of the water! Every year, every year, they used to do that, every year before the rain.
Ten freshwater fish species have been recorded in Pilbara rivers, and another lives in groundwater. The rivers also host 16 fishes that spend most of their lives in the ocean or estuaries, some of which may have a freshwater juvenile phase, including barramundi, mangrove jack and sea mullet. There are also at least 2 introduced species: sailfin molly and mosquito fish.
At least 2 freshwater fishes are thought to be unique to the Pilbara – the Fortescue grunter, found only from the Ashburton River to the upper reaches of the Fortescue, and an undescribed catfish (Neosilurus sp.) in the Robe River that has not been captured for many years. The Fortescue grunter has recently been assessed by the IUCN as endangered. Of concern are recent invasions of exotic fish in its range and declines in habitat quality due to mining.
There are likely to be additional endemic fish in the Pilbara, for there are significant genetic differences between populations in the Pilbara and elsewhere of at least 3 species (bony bream, Hyrtl’s tandan, western rainbowfish) and between Fortescue grunters, indicative of potential new species. This ‘apparent high degree of endemism and genetic divergence’ between populations in the Pilbara and elsewhere warrants investigation. The most unusual fish in the Pilbara is the blind cave eel (Ophisternon candidum) recently discovered in aquifers in the Robe River area and also known from Barrow island and Cape Range Peninsula. This is one of just 3 vertebrate animals in Australia known to live their entire lives underground (the others are gudgeons in the same region). This eel grows up to 400 mm long, lacks eyes and skin pigment, and eats mainly crustaceans. It has recently been assessed by the IUCN as endangered, mainly due to mining. All Pilbara populations occur in mining leases with large-scale open-cut mining and dewatering.
Two threatened sawfish species may migrate between salt and fresh waters in the Pilbara. The north-west region is regarded as ‘a global hotspot’ for sawfish . A likely nursery for green sawfish was recently discovered in the Ashburton estuary and surrounding tidal mangrove creeks . It was the first pupping site recorded in Western Australia and, based on numbers, ‘is potentially the most important globally’ . The only confirmed records of freshwater sawfish are from the Ashburton River below a tidal water barrier, and they have occasionally been reported from the De Grey River . Sawfish are an important food source and ‘cultural and spiritual icon’ for many Traditional Owner groups in northern Australia [196,197].
The main threats to freshwater fish are likely to result from mining (dewatering and impacts on water quality), water extraction and climate change [185,198]. One climate change analysis predicted that fish extinction rates in 6 Pilbara rivers will be amongst the highest in the world by 2090 due to reduced water availability under climate change . Four species are currently listed as threatened or priority species at a state level (Table 2-5, Figure 2-7).