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Published: 2014-05-09 00:00:00

Hundreds of native fish have been removed from a Waikato stream tributary and then returned safely as part of an operation to clear the stream with minimal impact on aquatic life.

The recent operation at Gordonton by Waikato Regional Council showed the benefits of taking a planned and careful approach to such clearance operations which go on regularly throughout the region.

“Unblocking waterway channels helps reduce flood risk and maintain the productivity of land near the waterways. But we also need to strike a balance and ensure ecological values are maintained and avoid damaging aquatic life wherever possible,” said river and catchment services group manager Scott Fowlds.

The Gordonton operation, which used a mechanical excavator to clear sediment in a tributary of the ecologically sensitive Komakorau Stream, followed a fish survey carried out in December. The survey had confirmed the presence of giant kokopu and longfin eels, both species listed as at risk by the Department of Conservation.

“Giant kokopu are one of six native fish species that make up whitebait. They are found in lowland streams but do not have a very wide distribution compared to other native fish. Interestingly, the Komakorau Stream catchment appears to support good numbers of this unique species,” said the council’s freshwater ecologist Mike Lake.

“Giant kokopu are known to be very sensitive to the disturbance caused by mechanical excavators taking out sediment. So staff followed behind the excavator scooping the fish out of the stream as they struggled at the surface. After being held for a while in a large tank the fish were then released back into the stream again when the water quality had improved. Eels were not removed because they can tolerate very poor water quality for short periods of time,” Mr Lake said.

All up some 1.3 kilometres of stream were cleared at Gordonton, with a total of 227 fish removed and then returned. Just over three quarters of the fish were giant kokopu, while other species collected included banded kokopu, inanga and common smelt. No exotic species were found.