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.
Horizons Regional Council environmental manager Craig Davey said the Whanganui River Clam Response Group is 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 is 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, reinforcing 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 jet skis and move around the motu.
“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.
Corbicula fluminea, known by its common name freshwater gold clam, was found in the Waikato region in May 2023 and is currently under management by Biosecurity New Zealand.
The clams are prolific breeders and can reach extremely high densities when the conditions are right, producing up to 400 juveniles a day or up to 70,000 a year.
This means they can 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 to 3cm in length. It is dirty white, yellow or tan and has a ribbed texture on the shell.
Ministry for Primary Industries’ cleaning advice includes 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 100ppt (parts per thousand) (5-litre mix = 500g salt in 5 litres 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 spot freshwater gold clams are 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 is found.
LDR is local body journalism co-funded by RNZ and NZ On Air
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