The Ovens River in north-eastern Victoria is home to two large-bodied native freshwater predators: Murray cod and Trout cod. These iconic fish are top order piscivores (carnivorous animals that primarily feed on fish), helping to regulate the structure and functioning of their aquatic environments. While threatened Murray cod are highly sought after by anglers, the endangered Trout cod, which was reintroduced into the Ovens River in the 1990s, remains free from harvest.  

Murray cod. Source: Scott Raymond
Trout cod. Source: Scott Raymond

Both species of cod have high ecological, cultural and economic importance, and have suffered severe declines in abundance and distribution throughout the rivers of the Murray-Darling Basin. Threats are often attributed to poor river regulation, habitat removal and invasive species, all of which have potential adverse impacts on riverine health.  

To reverse the declining trend in fish numbers, the Murray Darling Basin Authority established a series of river rehabilitation programs known as Demonstration Reaches, with the aim of improving native fish stocks to 60% of pre-European levels by 2050. The Demonstration Reach program combines multiple rehabilitation strategies on a river reach to demonstrate the cumulative benefits of rehabilitating in-stream and riparian habitat for improving river health and native fish. Engaging the community in all aspects of the project is an important project outcome. 

Fish hotels being submerged. Source: Scott Raymond

The Ovens River Demonstration Reach program (2008-2022) was designed to quantify the ecological benefits of the restoration efforts. Throughout the duration of the program, the North East Catchment Management Authority has added more than 300 large snags to the river to enhance cod habitat, fenced off 20km of river frontage from livestock access to reduce sedimentation, planted 100s of native trees along the riverbank to promote shading and bank stability, removed a barrier to fish passage, and assisted in the removal of introduced willow trees and invasive carp. 

Over the study, Murray cod and Trout cod numbers increased by 300%. The preference of Murray cod for woody habitat resulted in higher fish numbers in areas where wood was added while Trout cod increased throughout the reach. After 10-years since restoration actions were completed, Arthur Rylah Institute scientists surveyed the fish community and found similar numbers of both cod species, highlighting the ongoing success of the demonstration reach program. In addition, numbers of Golden perch increased within the reach, showing benefits for other native fish species. A healthy self-sustaining population of Macquarie perch was sampled in the reach, following a recent reintroduction program.  

Murray cod (bottom) and Trout cod (top) on a fish measuring mat. Source: Scott Raymond

While the legacy of the Ovens River Demonstration Reach is intact, there are plans to further enhance the reach for native fish. These plans include the continued removal of introduced carp and invasive plant species and to strengthen the health of the river to promote positive outcomes for native fish. 

More on the Ovens River:

Main photo: Murray Cod.
Source: Scott Raymond.

Subscribe now for quarterly updates on Finterest articles