The Murray cod, the apex predator of Australia’s inland waterways, is making a significant return to the Murray-Darling Basin. Capable of reaching 1.8 metres in length and weighing more than 50 kilograms, the fish is regaining its hold on rivers and creeks from the Condamine in Queensland to the Campaspe in central Victoria.
A History of Decline
The Murray cod (Maccullochella peelii) and its relatives, including the trout cod, Mary River cod, and eastern freshwater cod, once dominated the region. However, the population suffered a drastic decline, nearly disappearing from much of its range during the 1970s.
This collapse was driven by habitat degradation and the construction of vast dams, such as Lake Hume, which altered natural water flows. Overfishing also played a critical role, particularly commercial fishing activities that spanned from the late 19th century into the mid-20th century.
Taylor Hunt, a recreational fisheries manager with the Victorian Fisheries Authority (VFA), noted that recreational fishers reported the species was very hard to come by from the 1970s through the 1990s. While the species remains classified as vulnerable under the Australian Environment Protection Biodiversity Conservation Act, current trends are positive.
pondiin the Ngarrindjeri language.
Signs of Resurgence
Recent scientific surveys and angler feedback indicate an amazing resurgence
in population numbers. In Victoria, some rivers have seen two-to-five-fold increases in Murray cod since the 1990s, including the Goulburn, Ovens, Campaspe, Broken River, Broken Creek, and Gunbower Creek.
Lake Eildon has emerged as a premier fishery for trophy fish over a metre long and up to 30kg. Between 2014 and 2019, the lake saw an 81 per cent increase in overall numbers, supported by the VFA stocking more than 6.3 million Murray cod since 1990.
Other recovery highlights include the Ovens River, where an electrofishing survey found more than 110 Murray cod per kilometre. Populations in Mullaroo Creek and the Lindsay River have returned to pre-2021 levels following devastating blackwater fish kills in 2022.
The Battle Against Invasive Carp
The presence of the Murray cod is vital for ecological balance, as they feed on juvenile European carp. When the cod disappears, carp populations often explode, which can drastically alter aquatic flora and lead to toxic blue-green algae blooms.
The VFA estimates that European carp populations are now 30 times higher than record levels seen before the 2022 floods in Victoria. While Murray cod are better equipped to handle this pressure because they grow larger than carp, other native fish like yellowbelly (golden perch), Macquarie perch, and trout are still seeing their numbers pushed down by the overabundance of carp.
Ecological Crisis in the Darling River
Despite successes elsewhere, Stuart Rowland, a retired research scientist with NSW Fisheries known as The Codfather
, describes the Darling River as an ecological disaster. He states that the river has been neglected while other streams were restored.
According to Rowland, the disappearance of the top predator in the Darling River has damaged the entire food chain. He emphasizes that the top predator is perhaps the most crucial species in an ecosystem because it shapes the entire environment.
Conservation and Regulations
The recovery is attributed to a mix of habitat restoration, fish production, and stricter regulations. In New South Wales and Victoria, the legal catch limit is set between 55cm and 75cm; fish outside this range must be released.
Bag limits are strictly enforced, allowing one fish per person in Victorian rivers and two in New South Wales and specific Victorian lakes. A VFA survey of more than 3,500 respondents found that more than 90 per cent support these conservation efforts, including voluntary catch-and-release practices.
Future Outlook
If current conservation trends continue, other small-bodied native fish may see a recovery similar to that of the Murray cod. The implementation of carp control programs, similar to those used for foxes and rabbits, could potentially further stabilize these ecosystems.
Future success in neglected areas like the Darling River may depend on whether restoration efforts are expanded to match those seen in the Ovens and Goulburn rivers. Continued adherence to size limits and improved fish-handling practices are likely to remain central to maintaining these population gains.
Frequently Asked Questions
What are the current legal catch limits for Murray cod?
In Victoria and New South Wales, the legal catch limit is between 55cm and 75cm. Fish that are smaller or larger than this range must be released.
How do researchers count fish populations using electrofishing?
Researchers run up to 1,000 volts of direct current through the water, which stuns fish within a 5m radius without harming them. The fish are then caught, counted, and released back into the wild.
Why is the loss of Murray cod dangerous for the river ecosystem?
As the top predator, the Murray cod shapes the entire ecosystem. In its absence, European carp populations can explode, which damages the food chain, alters aquatic flora, and can lead to toxic blue-green algae blooms.
Do you believe voluntary catch-and-release programs are the most effective way to protect native species?
