How the river runs. The plight of and solutions for native fish in our inland rivers with Dr Martin Mallen-Cooper

In this episode, we chat with Dr Martin Mallen-Cooper about the problems facing the Murray Darling Basin, in particular, the effect of weir pools on flow in the river and the knock-on effect this has on our native fish. 

Martin takes us through a step-by-step summary of the demise of the Murray Darling Basin. He identifies five major practices that have incrementally killed fish and aquatic life in the last 100 years, which include; cold water pollution, fish barriers, weir pools, desnagging and the introduction of carp. Martin takes a particular interest in the effect of weir pools on flow and fish passage within the Murray Darling Basin and highlights that without flow, aquatic life simply cannot thrive.

This episode was recorded before the 2023 Menindee Fish Kills

Dr Martin Mallen-Cooper is an internationally respected fisheries scientist. He has advised on over 100 projects across the Murray-Darling Basin, and worked in advising governments of the Mekong River on fish ecology and fish migration. Martin is considered to be one of Australia's top experts in the management and conservation of freshwater resources.

Challenging accepted thinking has been a hallmark of his career. A good example is the accepted view that historically the Murray River dried to a series of pools in droughts. Contemporary scientists interpreted this as natural and therefore fish and other river animals are adapted to life in still pools, as well as a flowing river.

However, using archival data and research in old library files and books, Dr Mallen-Cooper and colleagues found that it was an exaggerated myth. In fact, early irrigation by numerous small pumps had caused the river to stop flowing historically. Moreover, it not only flowed but the Murray River had a big spring pulse of flow every year, even in droughts. Significantly, this meant a flowing river is the norm and that the fish are actually adapted to these conditions; this is now becoming a major theme (ecohydraulics) in environmental flow management. The finding also showed that weirs change a flowing river to pools, which has severely impacted fish and other aquatic animals. It also revealed a huge opportunity – that removing weirs can recreate the original flowing river and bring back native fish.

Along with fishways, Dr Mallen-Cooper did research on freshwater fish migration in the Murray-Darling Basin. In the 1990s he changed the predominant view that it was only adults of golden perch and silver perch migrating upstream to spawn; in fact, 95% of the migratory population were immature fish. This finding changed the primary objectives of fish passage to include these smaller fish.

With a career that has stretched over 50 years, Martin has had numerous breakthroughs that have been well-documented in academic literature. In this episode, Martin runs us through each of these achievements and the story behind how they were achieved. One of the highlights of the episode was Martin’s take on how cultural science can be an invaluable tool for the recovery of the Murray Darling Basin. He provides anecdotes of working alongside first nations people, and sheds light on the knowledge they possess that could be the key to unlocking future management systems within Australian Rivers.

Throughout his career, Dr Mallen-Cooper has been a vocal advocate for the sustainable management of freshwater ecosystems. He has played a key role in the development of numerous policies and regulations aimed at protecting and sustaining these ecosystems. In recognition of his contribution to the field, Dr Mallen-Cooper received the prestigious 2018 International Career Achievement Award in Fish Passage. Dr Mallen-Cooper’s work is widely recognized in the scientific community, and he has been invited to speak at numerous conferences and symposia on fish ecology and river rehabilitation

Join us, as we take a look below the surface.