Source: Radio New Zealand
The invasive gold clam. NIWA
Lake Rotomanu in New Plymouth will be emptied this week to allow scientists to get a full picture of the extent of a freshwater gold clam infestation.
The invasive clam Corbicula fluminea was found in the lake on 8 November, the first discovery in New Zealand outside the Waikato River.
The lake was closed to motorised watercraft days later.
The Taranaki Regional Council said the Lake Rotomanu outlet would be opened 11 December and it would take about four days for the lake to drain.
During this time the fish population would be harvested in partnership with local hapū, who would utilise as many fish recovered as possible.
Taranaki Regional Council (TRC) leads the newly established Regional Corbicula Coordination Group (RCCG) alongside New Plymouth District Council (NPDC), Ngāti Te Whiti hapū, Biosecurity New Zealand, Fish & Game, Earth Sciences NZ and others.
TRC Environment Services Manager Steve Ellis said before draining the lake the RCCG had to ensure the clams would not spread to the Waiwhakaiho River.
“Over the last few weeks we’ve carried out testing and obtained advice on the salinity and flow of the river. We are confident any clams or larvae will be quickly washed the short distance out to sea.
“Given that assurance the RCCG has asked lake owners NPDC to now empty the lake so we can get a good look at exactly what we are dealing with.”
A team from Earth Sciences NZ would next week carry out a detailed survey of the whole lakebed to determine where and how widespread the clams were, how deep they had burrowed and estimate the age of the clams present.
That information would help inform the next steps in the response. In particular, whether an elimination attempt was feasible and if so, what the treatment options were and how much they would cost.
Ellis said the financial cost of elimination was likely to be significant and at this point it was unclear how it would be funded and by whom.
“To be clear, there is no guarantee we will attempt to treat or eliminate the clams, even if it is technically feasible.
“We all want the best for the region and we’re all aware of the massive economic damage these clams can do, so we’re having those conversations as a matter of urgency. In the meantime, we’re looking forward to seeing what the lakebed survey uncovers.”
The recreational lake would need to stay empty for the summer, which Ellis said was not a decision made lightly.
“We know it’s a popular summer spot and that locals and visitors will be disappointed, but we hope they understand the reasons for it.
“The invasive clam Corbicula is a massive threat to our infrastructure, economy, ecosystems and recreational use of all the region’s waterways, so we need to act now to give ourselves the best chance of preventing long-term damage or recreational restrictions.”
Ellis said testing at Lakes Rotokare, Ratapiko, Rotorangi and the Waiwhakaiho River had not found any clams, while eDNA testing of the water had also been clear. While encouraging, that did not mean they were not present.
Boaties, jet skiers, kayakers and other lake users were asked to be extra vigilant this summer, so as not to unknowingly spread the clam or other freshwater pests. Juvenile clams produced an invisible sticky thread of mucus which attached to surfaces, like boats and recreational gear.
Lake users were encouraged to always follow the Check, Clean, Dry procedure when moving between waterways and if possible, wake boats should be kept to just one lake.
A washdown trailer was on its way to Taranaki, courtesy of Biosecurity New Zealand, and would be set up at popular lakes over the summer.
Two dedicated Check, Clean, Dry ambassadors would also be in the region to spread the message, supported by new signage, direct education with clubs and organisations and a social media campaign.
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– Published by EveningReport.nz and AsiaPacificReport.nz, see: MIL OSI in partnership with Radio New Zealand
