The world’s second largest freshwater crayfish was once plentiful in Australia’s longest river – we’re bringing it back

Murray crayfish once thrived in the southern Murray-Darling Basin. The species was found everywhere from the headwaters of the Murray and Murrumbidgee Rivers in the Australian Alps all the way down to Wellington in South Australia.

For thousands of years, First Nations people managed harvesting sustainably. But crayfish stocks crashed after European settlement. This was partly due to commercial and recreational harvest, which began in the late 1860s. At its peak in 1955, 15 tonnes of Murray crayfish were taken from the river in New South Wales and sent to markets in Melbourne and Sydney.

In South Australia, the commercial fishery was unsustainable by the 1960s and the species was no longer targeted. In the 1980s, Murray crayfish became a protected species in the state. But the damage was done.

Over-harvesting was not the only problem. Murray crayfish prefer free-flowing, oxygen-rich water, so they suffered from efforts to regulate river flows using dams and weirs. Poor water quality, including pollution from pesticides and other agricultural chemicals, made matters worse.

Murray crayfish disappeared from South Australia sometime in the past 40 years. Targeted surveys over a five-year period couldn’t find them anywhere in the state.

But that all changed in the winter of 2023 when our reintroduction program began. Now we’re preparing for the third release of crayfish and there are positive signs many crays from earlier releases are still going strong.

A species in need of support

Like many species from the highly threatened Euastacus genus, Murray crayfish grow slowly. It takes almost ten years for a female to reach sexual maturity, and she only produces a small number of eggs. Dispersal is also limited. This makes it hard for the population to recover in both number and range.

Following a recent assessment, the species Euastacus armatus is expected to soon be listed as vulnerable to extinction under Australia’s conservation laws.

Conservation actions such as reintroductions will be necessary to aid recovery of the species.

A long time coming, shaped by adversity

The idea of returning Murray crayfish to the river in South Australia is not new.

Two University of Adelaide ecologists, the late Keith Walker and Mike Geddes, first suggested it in the 1990s. They even conducted trials involving crayfish in cages to show sections of the river would be suitable for the species.

Then in 2007, the reintroduction idea was floated again. It was one of the main recommendations in a report identifying gaps in knowledge of the species.

But the idea really gathered momentum after disaster struck. Widespread flooding across the southern Murray-Darling Basin in 2010–11 led to a “hypoxic blackwater” event. This is where leaf litter and debris from the floodplain wash into the river, depleting levels of oxygen and causing mass deaths of both fish and crayfish.

This inspired further research into crayfish genetics, recovery potential and preferred habitat. It guided a 2019 strategy outlining how the species could be successfully reintroduced. A trial five-year reintroduction program in the New South Wales range of the species helped refine the strategy.

Then another Murray blackwater event in 2022–23, in NSW and Victoria, forced crayfish out of the water and up the riverbanks.

Vision of dying crayfish leaving the water, only to be consumed by predators or poached by people, prompted the community to respond. Guided by fisheries agencies and a fishing conservation charity, they rescued crays and held them safely in aquaculture facilities until they could be released back into the wild.

Many of these crayfish were later returned to the river where they came from. But a small number were held for release into SA as part of our new reintroduction program.

In a truly collaborative effort, a small environmental not-for-profit organisation, Nature Glenelg Trust, worked in partnership with a natural resource management agency, First Nations community, fisheries agencies from three states and a private aquaculture facility to turn the idea into reality.