Invasive clam found in Waikato River could decimate native species, infest Lake Taupō and clog hydro dams

An invasive freshwater clam discovered in the Waikato River has the potential to destroy native habitats, clog water supplies and hydro dams, and infest Lake Taupō if not properly contained.

Researchers have found the specimens of the freshwater gold clam, (also known as the Asian clam) in the Waikato River near Lake Karapiro, the Ministry for Primary Industries revealed on Thursday morning.

According to a Biosecurity New Zealand report, both live and dead clams were found by investigators on May 5, “indicating an established breeding population”.

At this stage MPI officials have no idea where the clams came from, but hold serious concerns for the health of the Waikato River, its tributaries, and Lake Taupō if the clams take hold.

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“C. fluminea has high reproductive potential (400 juveniles a day and up to 70,000 juveniles per year),” the report states.

“The extent of the spread is currently unknown, however the clam has been detected from Horahora Domain through to Wellington Beach in Hamilton (a 45km stretch of river).

“The remaining 409km of the river has not yet been surveyed.

“The organism could have significant potential impacts on taonga species within the Waikato River and Lake Taupō. It has caused serious issues overseas where it has outcompeted and replaced native bivalves in areas where it establishes.”

BNZ deputy director general Stuart Anderson said the organisation, along with mana whenua for the Waikato River, were urging people who work and play in and around the river to keep a lookout for the clam species and report it to authorities.

“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,” he said.

“We are partnering with Waikato-Tainui, the Waikato River Authority, the 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.”

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

Anderson said the plan was 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.”

The clams are a dirty white to yellow or tan colour and grow up to two to three centimetres 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.”

Anderson said the clams were not safe to eat from the Waikato River, which was known to have high concentrations of toxins.

“They filter-feed from the water and accumulate toxins in their gut.”

Suspected sightings should be reported to Biosecurity New Zealand on 0800 80 99 66 or online at report.mpi.govt.nz.

People are being asked to note the precise location and provide a close-up photo of the clam as well as its surroundings.

“Please do not disturb the organism.

“This situation is a reminder of the need to prevent the spread of invasive species like this clam between rivers and lakes and following ‘Check Clean Dry’ guidance is the best approach.”