Didymo found in Arahura River
Date: 05 February 2008
The invasive algae didymo has been found in the Arahura River north of Hokitika.
The Department of Conservation says it is concerned it could be spread to more rivers and might impact on endangered native whio/blue ducks.
The didymo cells have been found in samples taken near the mouth of the Arahura River in a DOC didymo survey. Didymo has previously been confirmed in the Buller, Haast and Kakapotahi Rivers, bringing the number of rivers infected on the West Coast to four.
The department and MAF Biosecurity New Zealand are reminding people to 'Check, Clean, and Dry' their gear between waterways to prevent the spread of didymo to other rivers and areas in the catchment.
DOC Acting Hokitika Area Manager, Judy Brennan, said the find of didymo in the Arahura River was very disappointing and concerning.
"While the long term effect on invertebrates and whio is unknown, didymo can form dense mats which may affect invertebrate populations. Invertebrates are a food source for whio".
Follow these steps to help prevent the
spread of didymo
The Arahura is a popular recreational river, as well as having significant cultural importance to Maori. We are appealing to people kayaking, fishing or carrying out other activities in the area, particularly the Arahura, to make sure they 'Check, Clean and Dry' their gear between waterways.
"Trampers are asked to avoid contact with Arahura River water and as the track runs alongside it they won't need to cross it. If any boots, socks or other gear are put in the river then these should be cleaned afterwards using 'Check, Clean and Dry' procedures before being put in any other waterway. Wherever possible, trampers should use bridges to cross waterways.
"People recreating in the Arahura river have an essential role to play in preventing the spread of didymo within area and helping to protect the areas' pristine rivers, freshwater biodiversity and native blue ducks. Kayakers need to be very vigilant with following procedures for cleaning gear, especially when they are kayaking different catchments.
MAF Biosecurity New Zealand didymo response manager Chris Bicknell said the find highlighted the need for every fresh waterway user, no matter where they are, to 'Check, Clean and Dry' their gear between waterways.
"Individual water way users have a crucial role in slowing the spread of didymo and other aquatic pests. 'Check, Clean, and Dry' is our best defence.
Information on didymo and approved cleaning methods can be found on the MAF Biosecurity New Zealand website: www.biosecurity.govt.nz
The DOC didymo survey on the West Coast, in conjunction with a MAF Biosecurity New Zealand didymo survey, is testing for didymo in about 20 rivers. Rivers being surveyed include those considered to be at high risk of didymo infestation or which have high biodiversity values.
Didymo is tested for using conical shaped drift nets that are placed in a river. Water is filtered through the net and material is collected at the end of the net in a small plastic jar. Samples are examined using a compound microscope at 40 and 100 x magnification. Didymo cells are a distinctive shape and can be readily distinguished from other diatom species. Any samples identified as having didymo in them are sent to NIWA for verification.