Freshwater gold clams (Corbicula fluminea), native to Asia and widespread in North America, South America and Europe, have been discovered along a 45km stretch of the Waikato River, near Hamilton.
Preliminary testing by Biosecurity New Zealand showed the exotic species could now be elsewhere as well, the council said.
The council issued a statement yesterday warning the species posed a risk to southern waterways, native freshwater species and infrastructure.
Council environmental implementation manager Libby Caldwell said she was concerned the clams could hitch a ride on boats, trailers, fishing gear, paddleboards, kayaks, jetskis and the like if they were taken from the North Island down south.
‘‘Fast-spreading’’ freshwater gold clams could proliferate when they attached to boats or were carried in ballast water, used as bait, through the aquarium trade or carried further afield by water currents, she said.
People should thoroughly wash all their equipment in the same manner as they would to prevent the spread of lagarosiphon and didymo, she said.
‘‘These freshwater clams can reproduce rapidly and form large populations which can clog water-based infrastructure such as electric generation plants, irrigation systems and water treatment plants.’’
They were filter feeders and could potentially compete with native species for food.
‘‘In rivers, colonisation downstream is easily achieved as juveniles are transported by currents, or through being attached to floating vegetation.’’
Ms Caldwell said it was not yet known how the clams would respond to New Zealand conditions, but elsewhere they reproduced rapidly.
Studies showed the species could survive in water as cold as 2°C and therefore most Otago waterways were potentially a habitat for the clams.
Despite international evidence the clams would be preyed on by some fish or crayfish, ‘‘eradication has never been achieved’’.
‘‘If there is an incursion of this pest species into the Otago freshwater system, there are likely to be significant environmental and economic impacts.’’
Freshwater gold clams were found in freshwater, near river mouths, sitting on top of sandy or muddy surfaces, or buried within them. They could also be found among debris settled on a riverbed.
- To report sightings: Biosecurity@orc.govt.nz
