Low flows could affect trout

A decision by the Otago Regional Council to set a minimum flow rate of 900 litres per second for...
The Lindis River at low flow. Photo: Supplied.
A low-flowing Lindis River could be worse for trout than periods of no flow, University of Otago zoology department head Prof Gerry Closs says.

Yesterday, on behalf of the Otago Fish & Game Council, Prof Closs provided his peer review of some evidence given at an Environment Court appeal in Cromwell.

Judge Jon Jackson and two commissioners are considering what minimum flow rate irrigators should be required to maintain in the Lindis River to ensure it no longer dries up during summer.

Prof Closs, in the conclusion to his written evidence, said as flow reduced, the passage of juvenile trout became blocked.

"As shown by [Fish and Game officer Morgan Trotter] significant losses of fish occur as surface continuity is broken or becomes increasingly tenuous.

"Low levels of flow can be worse than no flow, with a low discharge tempting fish downstream, then trapping them between shallow riffles by day as the water warms to stressful or even lethal levels."

Fish & Game is supporting the minimum flow rate of 900 litres per second set by the Otago Regional Council in its plan change 5A, while the Lindis Catchment Group (LCG) and the ORC are arguing for a minimum flow of 550 litres per second.

Mr Trotter said a minimum flow of 550 litres per second was "insufficient to protect the ecological functioning of the lower Lindis River".

"If the river was held at this level for an extended period (weeks to months), it is likely fish trying to out-migrate would become stranded and experience high levels of predation."

Mr Trotter considered a minimum flow of 900 litres per second was "also far from ideal from an ecological point of view but it would see significant improvements for fish habitat and survival".

Prof Closs said the LCG's proposed "galleries" scenario, replacing water races with bores and with the 550 litres per second minimum flow, would result in "a tenuous level of surface continuity" along the lower part of the river "with severe impacts on habitat quality" while the ORC's plan change 5A decision would "ensure continuity of flow".

Judge Jackson cancelled today's hearing to allow him time to consider the evidence already presented.

The hearing will resume on January 28.

 

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