New didymo finds have DOC concerned
Date: 14 November 2008
New didymo finds in the lower Cass and Macaulay rivers have DOC worried about the potential for didymo to be spread further into the upper Tekapo catchment.
Water samples taken from both rivers have tested positive for the invasive algae, confirms Twizel-based Programme Manager - Biodiversity Threats, Dean Nelson.
Didymo
"It is very important that we keep didymo out of the upper Cass, upper Macaulay and Godley Rivers," said Mr Nelson. "These waterways are examples of prime braided river habitats and it would be devastating to see didymo become established in them."
Braided rivers are networks of ever-changing channels weaving between temporary shingle islands and are globally unique to New Zealand's South Island.
"The thick smothering mats that we have seen in other didymo-affected rivers could impact significantly on the habitat and food sources that native birds and fish feed on," said Mr Nelson.
Riverbed birds such as the nationally critical black stilt/kakī and the threatened wrybill/ngutu pare and black-fronted tern/tarapirohe, feed around the shallow river braids of the upper Tekapo catchment waterways.
"These birds have a difficult enough time surviving predators, disturbance from people, dogs and vehicles and the invasion of their nesting habitat by weeds, without the added problem of potentially losing their feeding grounds," Nelson continued.
Nationally threatened native fish species such as the upland longjaw galaxias and bignose galaxias can also be found in waterways within the catchment.
The Upper Tekapo catchment is a popular area for a number of recreational activities such as mountain biking, hunting, fishing, four-wheel driving, boating and tramping. To ensure didymo is not further spread up the catchment, Mr Nelson is encouraging all waterway users to decontaminate for didymo.
"It is crucial we all remember to 'Check, Clean, and Dry' any items that come into contact with waterways, every single time - regardless of whether you think didymo is there or not. This will not only protect our waterways from didymo, but other aquatic pests as well.
"Decontaminating gear, such as fishing equipment, is reasonably easy to do by thoroughly soaking the items in a 5% solution of dishwashing detergent. It is important to ensure that all surfaces are in contact with the solution for at least one minute before it can be rinsed off" said Mr Nelson.
"Items likely to absorb water, such as footwear and waders, need a bit more time set aside for decontamination in the detergent solution. An alternative method is to freeze absorbent items until they are solid as this will kill any didymo cells present".
"Using bridges to cross waterways instead of fords and avoiding driving in riverbeds where you are likely to cross many streams and channels, are other key actions to help prevent the spread of didymo."