Gold clams from Waikato River. Photo / Tracey Burton, Toitū Te Whenua Land Information New Zealand
Gold clams from Waikato River. Photo / Tracey Burton, Toitū Te Whenua Land Information New Zealand
Authorities are ramping up prevention and detection efforts in the Whanganui River after the invasive freshwater gold clam – already established in Waikato – was confirmed in Taranaki.
Corbicula fluminea, known as the freshwater gold clam, was found in the Waikato region in May 2023 and is under management byBiosecurity New Zealand.
Horizons Regional Council environmental manager Craig Davey said the Whanganui River Clam Response Group was already working to stop the destructive species from reaching local waterways.
“Everything that touches the water, that includes fishing and boating gear and equipment, swimwear, even the dog, needs to be checked, cleaned and dried,” he said.
Ngā Tāngata Tiaki o Whanganui kaihautū/chief executive Nancy Tuaine said immediate action was needed.
“We all have a role in keeping the clams out of our waterways, and we need to take this seriously,” she said.
Davey warned the species was notoriously difficult to control.
“Eradication has never been achieved overseas. The clams reproduce really fast, forming massive populations which can turn river and lake edges into ‘clam pavements’.
“Clams less than a millimetre in size can move between waterways in or on wet equipment.”
He said human activity was the most likely reason gold clams were introduced to Lake Rotomanu in New Plymouth recently, which reinforced the council’s emphasis on strict cleaning protocols.
“With the weather warming up, we know that people will be gearing up to get out on their boats and jetskis and move around the motu [region].
“This is why we are urging people to use the ‘check, clean, dry’ method to ensure they’re not transferring any clams across waterways.
“Check for what is visible, clean for what is not visible, and dry to be sure,” he said.
River users are being asked to take extra care to keep the invasive freshwater gold clam from Whanganui. Photo / Moana Ellis
The clams are prolific breeders and could reach extremely high densities when the conditions are right, producing up to 400 juveniles a day or up to 70,000 a year.
This meant they could clog water-based infrastructure, such as electricity generation plants, irrigation systems and water treatment plants.
The clam is native to eastern Asia and is small, with adults growing between 2cm and 3cm in length. It is dirty white, yellow or tan and has a ribbed texture on the shell.
Ministry for Primary Industries cleaning advice included blasting equipment with tap water onto grass and, for absorbent materials, using one of the following:
Soak in hot tap water (50-55°C) for at least five minutes
Soak in a 5% bleach solution (5-litre mix = 250ml bleach in 4.75 litres water) for an hour
Freeze until solid overnight
Soak in a salt solution at 100 parts per thousand (5 litre mix = 500g salt in 5 litres of warm water) for four hours
Both gear and watercraft must then be dry to the touch – inside and out – for 48 hours.
“Following this advice ensures any equipment or boats that have been in water don’t bring these clams or other freshwater pests into our region’s waterways,” Davey said.
Horizons has already begun surveillance to detect any new incursions early.
“We really hope to minimise the impact for our region by not only prevention, but also early detection,” Davey said.
“Early detection provides a greater opportunity of controlling the spread further.”
People who spotted freshwater gold clams were urged to take a photo and report it to Biosecurity New Zealand on 0800 80 99 66 or via report.mpi.govt.nz, and to leave the clam where it was found.
– LDR is local body journalism co-funded by RNZ and NZ On Air.
