Cotton Research & Development Corporation (CRDC) has been supporting researchers from QLD Department of Agriculture and Fish (DAF) in developing best management practices for minimising the impacts of irrigation infrastructure on fish.
The team, led by Michael Hutchison has been at Emerald in Central Queensland (Gayiri country) to examine the effect of flow type (natural or allocated), pump size and pump inlet location on fish entrainment rates.
The results of this study will help to guide the configuration of future irrigation intakes to minimise the impacts on fish.
“We chose the Emerald region to do this work because the fish fauna in this area contains a mix of tropical and temperate freshwater fish, so the results can be applied to both northern tropical rivers and southern rivers such as those in the Murray-Darling Basin,” Michael said.
“There is a lot of data we need to capture to identify what best practice looks like.
“Our aim is ultimately to lessen the effect of irrigation infrastructure on fish.”
Some preliminary findings have shown that pump intake location seems to be a better predictor of fish entrainment rates than pump size. Larger pumps do not necessarily entrain the most fish per megalitre.
QLD DAF biologist David Nixon is leading much of the fieldwork and said there can be very large differences in fish entrained per megalitre for any given species, depending on intake location (bankside, mid-river channel or from within a short constructed channel perpendicular to the river).
“For example, the number of golden perch larvae entrained per megalitre is up to 20 times greater in some pumps than in others, depending on intake location,” David said. “This means that a reduction in entrainment rates for this species may be achievable by changing the positioning of pump intakes. “This can also help guide positioning of new irrigation infrastructure.”
To mitigate fish impacts on fish from existing infrastructure (as opposed to a new installation), this study will help to prioritise the intakes where works, such as screening, should be undertaken. Significant reduction in fish/larvae entrainment may be achieved by adjusting intake configurations, without the need for screens in some locations.
Some fish species are more susceptible to entrainment than others. Not all fish species present in the river are being entrained through pumps.
“Some species, like saratoga, are yet to be detected passing through pumps while juvenile bony bream are regularly observed, however they are highly abundant in the river so tend to have relatively low susceptibility scores,” David said.
“In contrast, olive perchlet (glassfish) seem quite susceptible to entrainment, being over-represented in pump samples when compared to the number of fish sampled in the river. For most species of fish, allocated flows and overbank natural flows seem to result in less fish entrainment than within-bank natural flows.”
Meanwhile, Michael says, self-cleaning screening technologies are continuing to evolve with robust options available for flowing environments. “These may be adopted in future at some locations to help protect fish stocks, with the added benefit of maintaining good flow rate by minimising the impacts of debris, reducing maintenance costs and prolonging the life of pumping equipment,” Michael said.
The research in ongoing, with sampling continued over summer 2021/22.
Main photo: A sample of fish caught from an irrigation outlet, which includes olive perchlets.