"June 2006"

Includes bibliographic references.

The introduced invasive diatom Didymosphenia geminata (didymo) was first identified in the Mararoa and lower Waiau Rivers, Southland, in October 2004. An initial delimiting survey in December 2004 found no evidence of D. geminata in adjacent rivers. 2. Ongoing passive surveillance by Fish and Game Councils, Regional/District Councils, Department of Conservation and Crown Research Institutes who had been provided D. geminata identification sheets by Biosecurity New Zealand in December 2004 have resulted in the submission of multiple suspect samples from around New Zealand. All of these suspect samples had been negative until 27 September 2005, when a NIWA - Fish & Game team discovered D. geminata blooming in the Buller River. This spurred the rapid discovery of further occurrences reported within days from the Hawea and upper Clutha Rivers in Otago and the upper Waiau and Oreti Rivers in Southland. 3. Given the wide geographical spread of the new infestations, priority was given to determine quickly whether the distribution of D. geminata had extended to elsewhere in New Zealand. A second delimiting survey, originally planned for spring 2005 in Otago and Southland, was expanded to cover high-risk sites nationwide. 4. The objective of the October 2005 nationwide survey was to detect the presence of D. geminata in high-risk sites where it was likely to have been introduced by human activity and where it was likely to have established due to environmental suitability. That survey of 492 sites found D. geminata in samples from seven sites from four rivers in the nationwide survey. The Von River, Southland, was the only one from which D. geminata had not been previously identified from the ongoing passive surveillance.. ... - Executive summary.

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