Commonwealth Environmental Water Office via Murray- Darling Freshwater Research Centre
Dr Paul Humphries, Dr Stacy Kopf, Luke McPhan and Institute Adjunct Dr Geoff Vietz
ILWS researchers, in collaboration with researchers from the Centre for Freshwater Ecosystems (formerly Murray-Darling Freshwater Research Centre) are undertaking research activities for the third and final phase of the Murray-Darling Basin Environmental Water Knowledge and Research (EWKR) project’s Fish theme. The theme’s main aim is to better understand the important factors affecting the recruitment of riverine fish and how these factors are influenced by water flows.
Photo : Dr Amina Price (CFE) and Dr Paul Humphries collecting samples in the Ovens River. Pic: Jessica Davison.
Building on the outcomes of the Conceptualisation of flow-recruitment relationships for riverine fisheries. Foundation activities for the Fish Theme of Environmental Water Knowledge Research (EWKR) project, a three year on-ground data-collection project Relative importance of key recruitment drivers across multiple spatial scales is underway.
For this project researchers are testing some of the hypotheses that came out of the conceptual synthesis. One hypothesis being tested is that the more complex a river’s structure (snags, macrophytes and geomorphological features), the better the supply of food for fish larvae. While there is good evidence to show that complex reaches have greater retentiveness which leads to more nutrient retention which leads to more growth of plants which leads to more growth of lower order animals, the researchers are testing to see if this percolates up to the young stages of fish.
The Ovens River, in North-East Victoria, is being used as a “test river” as it is relatively unimpacted by flow regulation. Twelve of its reaches have been characterised in terms of their retention capacity. In summer 2017-2018 researchers collected zooplankton (which the juvenile fish feed on) from within those reaches to determine if increasing retentiveness equates to more food.
What the researchers have found, so far, is (as expected) that the complexity of a reach, at higher flows, influences the retentiveness of the reach and that tends to breakdown as the flow decreases. As the flow decreases, all the reaches got slower and more retentive and complexity is not as much an issue.
The next stage of the project is to test another hypothesis which is that fish larvae settle in those reaches that are more retentive and more likely to provide more food. Field work for this component of the project will be undertaken summer 2018-2019.
The research is expected to provide a better understanding of the links between key water flow characteristics and potential fish responses which will assist water managers to develop environmental water regimes around the needs of native fish. The information will also improve predicting the outcomes of proposed water management regimes.
Dr Paul Humphries Email