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Big trouble for little fish: The 22 freshwater fishes at risk of extinction

Mark Lintermans (The University of Canberra) and Hayley Geyle (Charles Darwin University)

Australian freshwater fish are in trouble. Many species have declined sharply in recent decades, and as many as 90 of our approximately 315 freshwater fish species may now meet criteria as threatened. No Australian fish species is yet listed officially as Extinct but some have almost certainly been lost before scientists ever knowing they existed. With so many fishes at risk, understanding which species are in greatest peril is a vital first step in preventing extinctions. 

In collaboration with the Australian Society for Fish Biology, our team of freshwater fish experts evaluated population sizes and trends, and current and looming threats to identify species at high extinction risk. The project was funded by the Australian Government’s National Environmental Science Program through the Threatened Species Recovery Hub and has been published in Pacific Conservation Biology. 

We identified 20 species that have a 50% or greater probability of extinction within the next two decades unless there is new targeted conservation action, and further two with a greater that 40% chance of extinction in that period. 

Twelve of the species identified have only been formally described in the past decade, and seven are still awaiting description. This highlights the need to act before species are listed under legislation and even before they are formally described. These formal processes can take many years, at which point it may be too late for some species. 

Drought, trout and fires 

More than half of the species on the list are galaxiids, small-bodied, scaleless fish that live in cooler, upland streams and lakes. These habitats are also favoured by trout, much larger predatory species which were introduced to Australia for recreational fishing. Trout have taken a heavy toll on galaxiids and many other small bodied species in southern Australia. 

For example, Victorian Shaw galaxias (Galaxias gunaikurnai) have been eaten out from much of their former range. Now just 80 individuals survive, protected by a waterfall from the trout below. We estimate that the Shaw galaxias has more than an 80% probability of extinction within the next 20 years unless we do something soon to save the species. 

Many galaxiids do not thrive or readily breed in captivity, so suitable trout-free streams are essential for their survival. Urgent, sustained effort is needed to improve trout management, including collaborations with recreational fishers, increased awareness, and changing values among government and key sectors of society. Without this, trout will almost certainly cause extinctions of native galaxiids. 

Native fish out of place can also be a problem. For example, sooty and khaki grunters (Hephaestus fuliginosus and Hephaestus tulliensis), favoured native fishing species that have been widely translocated in Northern Australia, threaten the ancient Bloomfield River cod (Guyu wujalwujalensis). Tiny Malanda and Running River rainbowfishes (Melanotaenia sp.) are being displaced or hybridised out of existence by larger Eastern Rainbowfish (Melanotaenia splendida) that have been released from aquaria. 

Victoria’s Shaw galaxias is one of 14 species of galaxias identified as at high risk of extinction. Predation by intro-duced trout is a major threat to these small-bodied native species. Credit: Tarmo Raadik.

All our eggs in one basket 

All of the most imperilled species are now highly localised, with ranges of between only 4 and 44 km2. 

These species could now be wiped out by a single catastrophic event, like a large bushfire that fills their streams with ash and robs them of oxygen. One of the key management steps that can be taken to reduce this risk is carefully considered translocations to safe sites. 

Climate change is another threat to all identified species, as it is likely to cause reduced flows and water quality, or increased fires, cyclones and flooding. Many species have already been forced to the edge of their range and a prolonged drought could dry their remaining habitat. 

The Malanda rainbowfish is at risk from hybridisation with the larger and more common eastern rainbowfish. Credit: Michael Hammer/Museum and Art Gallery of the Northern Territory.

Action needed 

Only three of the highly imperilled fish species are currently listed as threatened under national environmental legislation (the EPBC Act). Listing species under legislation is important to provide some protection to the last remaining survivors and can prompt recovery action. Given our assessment of extinction risk, we consider 19 fish species should urgently be added to the national list of threatened species. 

Understanding which species are at highest risk is a critical first step, but must be followed by targeted action, investment and collaboration among governments and non-government organisations to mitigate threats and support recovery. 

Small native freshwater fishes are worth saving; they play a vital role in our aquatic ecosystems and are part of our natural heritage. By identifying and drawing attention to the plight of these highly imperilled species we are aiming to change their fates. We cannot continue with business as usual if we want to prevent their extinctions. 

For further information, see the list of 22 freshwater fish species at risk of extinction in this research findings factsheet, or contact Mark Lintermans or Hayley Geyle: 

mark.lintermans@canberra.edu.au 

hayley.geyle@cdu.edu.au 

The main threat to the Daintree rainbowfish is loss of stream flow due to drought, climate change and water extraction. Credit: Michael Hammer / Museum and Art Gallery of the Northern Territory.

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