‘Full didymo mode’ needed to combat invasive clam

Invasive gold clams could be a ‘‘massive problem’’ for the Waikato awa, according to Endangered Species Foundation chair Stu Muir.

The Ministry for Primary Industries announced the discovery of the invasive species on Thursday, news that has ‘‘mortified’’ kaitiaki, who fear it could further disrupt the river’s already fragile ecosystems.

Muir, who also farms along the Waikato River, said one of the issues with the clam was its ‘‘phenomenal’’ reproductive rate.

He said one clam alone can produce 400 offspring in a single day, and as many as 70,000 per year. ‘‘At this stage, based on what we’ve seen overseas, it could be a massive problem,’’ Muir said.

The clams contribute to numerous problems in waterways, including the excretion of significant amounts of inorganic nutrients, including nitrogen, which promote the growth of algae and contribute to pollution.

They can also clog water-based infrastructure, and consume large amounts of plankton, threatening native species.

And they pose a threat to other taonga species such as tuna (longfin eel – already an endangered species) and kā kahi (a freshwater mussel also known as kāeo and torewai). Muir wasn’t aware of any successful eradication programmes overseas, but was clear that ‘‘doing nothing is not an option’’.

He said further research was already under way to ascertain how far the species has spread, and that they were ‘‘already covering 45km’’. He said combating the clam would need cooperation between iwi, MPI, Fish & Game and river users.

He said ‘‘full didymo mode’’ is needed, with anglers and boaties urged to make sure they clean their equipment – and not wash off into stormwater drains.

The gold clam has a ribbed shell, which Muir said is typically dirty white, yellow or tan and can be found in freshwater and brackish water, on sandy or muddy surfaces, and amongst debris on the riverbed. Adult clams are between 2 and 3cm long

Muir also asked anyone who sees partly exposed gold clam shells, or their syphons (breathing tubes) should report the sightings, and location, to the MPI hotline on 0800 80 99 66.

Muir also said there may be what he described as a ‘‘small window’’ to combat the species’ spread as he was unsure exactly how they would fare as water temperatures dropped over the winter months.