Biosecurity: Call for community vigilance as new clam species found in Waikato River

Te Awamutu Courier

28 May, 2023 12:00 AM4 mins to read

Close up freshwater gold clams. Photo / NIWA

Biosecurity New Zealand and mana whenua for the Waikato River are urging people who work and play in and around the river to keep a lookout for a new-to-New Zealand clam species that has been found at Bob’s Landing near Lake Karāpiro.

The freshwater gold clam — also known as the Asian clam, or by its scientific name Corbicula fluminea — is native to eastern Asia but is widely established in North America, South America and Europe.

Overseas, these shellfish are a pest species because they reproduce rapidly and can clog water infrastructure such as hydroelectricity plants, municipal water supply and irrigation systems. They are also potentially a threat to native species, because in large populations they consume a lot of plankton.

Biosecurity New Zealand deputy director general Stuart Anderson says it is not known how the freshwater gold clam will behave in New Zealand conditions, but overseas it has proved difficult to control and there has been no documented successful eradication.

“We are partnering with Waikato-Tainui, the Waikato River Authority, Waikato Regional Council, Te Papa Atawhai Department of Conservation and Toitū Te Whenua Land Information New Zealand to understand this incursion and how best to respond to it.

“This includes setting up a panel of technical and mātauranga (traditional Māori knowledge) experts to provide us with management advice,” says Stuart.

Initial checks have found the freshwater gold clam present over a 45km stretch of the Waikato River, from 1.5km upstream of Bob’s Landing, itself just upstream of Lake Karāpiro, and downriver to Hamilton.

Freshwater gold clams from the Waikato River with ruler for scale. Photo / MPI

Stuart says the plan now is to search further, both within the Waikato River and in other rivers and lakes that are linked through human activity.

“This wider surveillance will include using targeted eDNA testing.

“To support this science, we’re asking people who work around the river, or boat, fish or swim there, to keep a lookout and report any sightings of this new-to-New Zealand freshwater clam.

“They are a dirty white to yellow or tan and adult ones are 2-3cm across. They can be found within the water, sitting on top of sandy or muddy surfaces, or buried shallowly within them. They’re quite distinctive — there are no New Zealand species that look like this in the river.”

Freshwater gold clams are not safe to eat from the Waikato River, which is known to have high concentrations of toxins in the water. They filter-feed from the water and accumulate toxins in their gut.

Waikato Regional Council chief executive Chris McLay said: “It is hugely disappointing that this invasive species has been discovered in the river, which is a vital source of life for such a large part of our rohe.”

“It’s been found over an especially popular stretch of the river. Lake Karāpiro alone has 50 days of events every year that attract thousands of competitors, and through summer, our maritime officers can find hundreds of boats, jet skis and kayaks using the lake on any given day. Even in winter, it continues to be heavily used.

“It’s possibly one of the most busy and congested stretches of inland water in New Zealand.

“To protect our precious waterways — not just here in the Waikato region, but right around New Zealand — we strongly urge water users to make sure they’re following the Check Clean Dry approach. It will be vital to stopping the spread of this species elsewhere,” Chris said.

Check

Remove any visible matter, including any clams you can see, along with plant material or mud. Drain all river water.

Clean

Do a washdown of your gear and watercraft with tap water onto grass, beside the waterway or at home and not into a stormwater drainage system. This will flush off clam larvae, which can be too small to be seen.
For gear made of absorbent materials, which will stay wet longer, apply a cleaning treatment.

Dry

Allow gear to dry to the touch, inside and out, then leave it to dry for at least five days.
Dry areas inside the watercraft where water has pooled, for example with an old towel, and then leave the craft to dry for at least five days. The hull of a watercraft will dry when towed.