Corbicula fluminae, commonly know as gold clams.

Invasive clams may not be causing everyone sleepless nights, but they have for Kids Greening Taupō lead education co-ordinator Rachel Thompson.

By Chris Marshall

Accompanying a school camp to Lake Karapiro and realising there was no information presented to the students about how to clean their togs and gear afterwards was a real source of concern.

Corbicula fluminea was found in the Bob’s Landing area of the Waikato River near Lake Karāpiro in May 2023. Later, it was also found in the Waikato River from Lake Maraetai Landing to Tuakau.

“I ended up talking to the kids about it, then when I came home I had a sleepless night because those 62 children from a local school… had been swimming, paddle boarding, they had been in the water in their clothes, shoes, everything and they were coming back on the Friday to do the Ironkids Triathlon on the Saturday.”
Knowing a pair of damp togs would be enough to inadvertently transfer the pest from the Waikato River to Lake Taupō was “a terrifying moment”.

Other parents on the camp had been asking her ‘How how come we don't know about this?’ Rachel says.

“‘There needs to be more education’, and I was saying ‘yeah there needs to be more education’ and then I realised I’m the environmental educator so came back and had a bit of a realisation that actually someone needs to be going around the schools.

“The Kids Greening Taupō kaupapa is that if we can get the messaging to the kids, then they will get the messaging to their families which is the easiest way to get it to the community.”

Work with organisations including Tūwharetoa Māori Trust Board, Waikato Regional Council and Biosecurity New Zealand resulted in the creation of a series of student-friendly resources including printable wordfinds, crosswords and worksheets and an online information resource on the KGT website.

That has been followed by visits to as many schools as possible in Tūrangi and Taupō.

“All it would take is for one person to go swimming at Mangakino or boating or paddleboarding… and then come back without cleaning their gear appropriately or without drying their togs or their wetsuit.”

The juvenile clams are invisible to the naked eye and once the self-fertile molluscs reach a reproductive stage, they can produce 400-500 babies a day.
“So it's quite terrifying when you think about it. It's that drying things for 48 hours that's the most important.”

And she is still noticing plenty of adult helpers at her sessions surprised they don’t know more themselves.
“They come up afterwards to say ‘Oh my gosh I didn’t know about that, I'm going home to tell my family.’”
Part of Thompson’s presentations involve stressing the difference between the freshwater native mussel kākahi (Echyridella menziesi) and the invasive clam.

“We've got people removing kākahi from the lakes at Whakamaru and Taupō because they think that they're invasive clams and reporting them and putting messaging out there on Facebook… so that’s led to quite a lot of false news. A lot of people think we have clams in the lake which we don't – they’ve seen kākahi.”
Thompson will make a presentation on recent KGT educational initiatives to the Thursday, June 19 meeting of the Taupō Lakes and Waterways Trust alongside presentations from scientists working for the Ministry of Primary Industries.

The meeting of the Taupō Lakes and Waterways Trust at Waiora House on June 19 begins at 5.15pm.

Important updates

It will include an update on the control of invasive clams as well as a presentation on recent educational initiatives being undertaken by Kids Greening Taupō.

Presentations on the clam (Corbicula fluminea) from scientists working for the Ministry of Primary Industries will update information presented at the Trust’s November forum including more detail on a collaborative long-term management plan.

This includes a national surveillance strategy, and the development of a rapid assessment plan for new incursions as well as research to better understand the clam’s impact on waterways and expanding public awareness of Corbicula.

Overall, the focus of the long-term management plan is to contain the clam to the current known areas in the Waikato catchment, reduce its impact where feasible, and develop tools to achieve this.

Key recommendations in the Biosecurity New Zealand aquatic readiness team surveillance plan include a substantial increase in the number of eDNA samples collected, and the use of visual sampling techniques, such as benthic dredge tows.

Early detection, says MPI, will allow for timely management and intervention, significantly increasing the chances of successful containment.

More information will also be presented on a treatment to eliminate Corbicula australis from a lagoon at Wairakei which began in March.

This has had a positive response with many dead clams surfacing following initial application. Treatment will take up to 10 weeks and includes monitoring to provide confidence that the clam has been eliminated from the lagoon.

New clam treatment

In other updates on clam control Biosecurity New Zealand has collaborated with Waikato Regional Council and the New Zealand Water Ski Racing Association to conduct trials of a hot-water treatment for ballast tanks.

The one-off trial used a system developed by the council to treat the tanks with water heated to 50-55 degrees for five minutes, a treatment scientifically proven to kill juvenile Corbicula.

The hot water trolley system was successfully tested on 22 boats with hard ballast tanks.

A pilot ballast-tank treatment service is now planned as an option for boaties who use Waikato waters. Work is underway to develop service specifications, a verification system, and to identify a suitable Waikato-based service provider.

The meeting at Waiora House on Thursday June 19 begins at 5.15pm.