Didymo in Von River mouth - investigation needed

DATE 21 October 2005

Didymo cells found in Von River mouth, but further investigation needed.

A sample from the mouth of the Von River near Queenstown has been found to contain Didymo cells, but further work is required to determine the extent of its presence in the river, Biosecurity New Zealand announced today.

Biosecurity New Zealand Manager Surveillance and Incursion Response David Hayes said the sample, taken earlier this week during the nationwide Didymo survey, detected three live and one dead Didymo cell. The sample was analysed yesterday.

The result is the first confirmation of Didymo in any river since the nationwide survey began on 3 October, though analysis of all samples is not yet complete. River patrols and signs warning of the find are being organised today.

“This find reiterates the importance of this national issue. No alga of any sort was visible at the sample site, but Didymo was present. People should already be taking precautions and cleaning their equipment in between using any New Zealand freshwater. Those precautions need to continue.

“From here we need to work to determine the extent of Didymo in the river. It could be that it’s blooming somewhere upstream, or that testing has detected very low levels of Didymo,” David Hayes says.

The Von River was surveyed in December 2004 along with the upper Waiau, Oreti, Aparima, and Mataura after Didymo was identified in Southland’s Mararoa and lower Waiau Rivers (in October 2004). About 550 samples from 62 sites showed no evidence of Didymo.

The latest national survey has been guided by a NIWA study which rates every New Zealand river reach on its suitability as an environment for Didymo. Information about river values and local knowledge on use rates was included during sample site selection.

Surveying in the Southern third of the South Island has been completed apart from four sites unable to be sampled due to high water levels. Testing in the Central third is likely to be completed today. The final nationwide results should be available late next week, weather permitting.

Results from the Northern third of the South Island as far south as Kaikoura have already been announced. No Didymo was found other than in the Buller River, the first confirmation of Didymo outside of Southland.

Didymo has been found in seven rivers: The Mararoa, the upper and lower Waiau and Oreti Rivers in Southland, the Von, Hawea and upper Clutha Rivers in Otago, and the Buller River in the Tasman District.

ENDS

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