Waikato Regional Council invests $414k to fight invasive gold clam Dec 2024 - more information here:
Monday November 25th Taupō Lakes & Waterways co-hosted an Aquatic Biodiversity Forum with REAP outlining threats to our waterways including the Freshwater Gold Clam. WRC to invest in fight against invasive gold clam.
Waikato Regional Council invests $414k to fight invasive gold clam
Taupō Turangi Herald article - Chris Marshall:
‘Scientific measures to monitor and target the freshwater gold clam’s invasion of the Waikato River are about to enter a new phase.
But vigilance from the community in following ‘check, clean, dry’ requirements and in reporting any potential sightings in new areas will also be crucial in stopping the spread of Corbicula fluminea.
Those were the messages delivered at Monday night’s (November 25) Taupō Lakes and Waterway’s aquatic biosecurity forum, in presentations and discussions that explored both the response so far but also the enormity of the task ahead.
Well-known conservation advocate Didymo Dave Cade didn’t mince words at the end of the forum on the difficulty of ensuring public compliance with the ‘check, clean, dry’ message, first developed to limit the spread of didymo (Didymosphenia geminata, a microscopic alga that can be spread in a single drop of water) but now amended to combat the invasive clam (whose microscopic specimens can survive out of water for several days).
“Controlled Area Notices are a wonderful tool, but they only work for people with high biosecurity IQ... They don’t work for the ones that don’t care. We are throwing everything at this check clean dry programme for years, decade after decade and man we’re having some problems,” he said.
Department of Conservation fishery rangers and he had enough trouble getting people to clean their gear with a five per cent solution of dishwashing liquid, said Cade.
“How the hell are we going to do it with 55 degrees hot water for five minutes. It’s what needs to be done, I’m not denying it, but... We’ve got to sit down and encourage all of you to come up with as many ways as possible to look after our lake, to back this team of scientists here.”
The forum earlier heard presentations from Ministry of Primary Industry partnerships lead-aquatic programme/pest management Jackie Bedford and Dr Deborah Hofstra, NIWA principal scientist freshwater ecology.
Corbicula fulminea’s arrival – noticed in Lake Karapiro in May 2023 – marked the first time New Zealand had had an exotic invasive freshwater mollusc, said Bedford.
“That’s quite significant for us. We’ve got algae, weeds, pests like catfish and koi carp but we haven’t had molluscs before.”
By September last year as part of the first research response, delimiting work had been done to find the extent of its spread on the Waikato River, she said.
“At that point we knew they were from Lake Maraetai down. And that has not changed.”
(Plans were in place to eradicate another species, Corbicula australis, found in March this year, in a lagoon in an aqua park near Taupō, she said.)
The self-fertile clams were a problem due to their incredible ability to reproduce, said Bedford, about 400 almost fully formed young a day for about half the year, in two breeding periods.
“Somebody has cranked out the number 70,000 a year which is incredible fertility.”
Overseas where populations had reached 10,000 – 20,000 clams per square metre, mass die offs resulted in shell banks or ‘concrete bottom’ to a lake or waterway with an accompanying foul smell, said Bedford.
The filter feeder clams competed with native mussels (kākahi) and other species for nutrients, light and space, though the full impact of this competition was still being researched.
“They cause problems for power generation, irrigation and town water supply,” she said.
The clams generally spread downstream and while there was potential for spread by domestic pets and waterfowl, distribution patterns didn’t point to this as likely.
It was far more likely they would be spread by human activity, said Bedford.
A sticky mucus thread, or byssal, they used to sail downstream on the current were what people had to keep in mind when cleaning gear and togs, especially as young clams could be as little as a quarter of a millimetre across.
“They are like zooplankton. They are just in the water, and you wouldn’t even know they are there.”
The current strategy was to contain the clam, native to East and Southeast Asia, to the known infested area and exclude it from others.
“It has not been eradicated from any country overseas where it has arrived - North and South America and Europe. There aren’t known tools right now. Research is going to be really important.
“We do know they can’t survive extremes of heat and cold, temperature shock. Basically, bleach type treatments, low oxygen and extended periods of dry.”
However large specimens could clam up for quite a while to survive out of water.
As well as the pest’s potential impacts on waterway ecology and causing issues with infrastructure, it could also impact how people enjoyed our waterways, said Dr Hofstra in her presentation.
“There is a difference between how you might engage recreationally with a sandy lake or stream bed and one covered in clam shells.”
A new study at five sites had been completed in May/June this year, said Hofstra, which gathered data to understand how the clams could be contained to current sites and how to supress any new invasion.
Most of the individuals were found in the top 10cm of substrate, she said, but core samples also revealed some as deep as 15cm.
“You could just be seeing white spots, as the bulk of the clam body is buried and you’re just seeing the siphons.”
As well as in sand, the clams were found among weed beds and at depths from one metre down to 15 m in a dive survey. Dredge and grab samples showed them deeper as well.
Early research tests on how best to kill the gold clams had not revealed a golden bullet, said Hofstra.
“The key message here is they are really hard to kill as they clam up and withstand things they don’t like for a very long time, even copper and zinc which you think in an aquatic environment is often going to kill stuff.”
However, a newly announced MBIE funded research programme would see a NIWA-led programme develop effective and culturally attuned strategies for managing the invasive clam.
The research aimed to:
Better understand the impact in an Aotearoa/NZ context (ecological, economic and cultural),
Better predict their dispersal and likely future establishment, to enable the prioritisation of locations for monitoring and early intervention,
Develop better ways to kill them.
In the meantime, everyone could keep a look out for anything new and let Biosecurity NZ know, said Hofstra.
“For all of us the best thing we can do is make sure our gear is clean. This is super important to me as a scientist. Because Corbicula is not the worst thing we can have here. There are actually two other invasive bi-valves that are in the rest of the world with worse impacts than this. I feel we really need to be getting this right just for our nation.
“In biosecurity and invasive species management, early detection is fundamental to give us the best chance of eradication or just control to manage impacts.”
Information on reporting sightings can be found at www.biosecurity.govt.nz/clam
Information on the NIWA research is at www.niwa.co.nz/freshwater/stopping-gold-clam-its-now-or-never