The agency says it has no plans to close other lakes but would consider requests, as it did the Lake Ōkataina application from Ngāti Tarāwhai Iwi Trust, which feared the clams could “obliterate” the lake’s “delicate ecosystem” if they reached its waters.
Gold clams, also known as Asian clams, were believed to have been in the Waikato River for at least two or three years but were discovered in May. Fast reproducers, they have multiplied to be found in a 99km stretch, but have not been found elsewhere in New Zealand.
The clams feed on plankton most native species survive on, and can clog infrastructure in the water. Eradication overseas has never been achieved.
Te Arawa Lakes Trust chairman Geoff Rolleston said the trust was considering implementing a rāhui as an “interim measure,” to raise awareness and uphold kaitiakitanga (guardianship) responsibilities.
A rāhui is a customary and temporary prohibition, and not legally enforced. Its details would depend on “the evidence being built to encompass a rāhui whakarauora taiao, to allow for conservation, and a rāhui aukati mōreareatanga, to address the biosecurity risk”.
Rolleston said the need for more wash stations for vessels around the lakes was “of paramount importance” to preserve the Rotomoana environment.
Te Arawa Lakes Trust chairman Geoff Rolleston. Photo / Kelly Makiha
There was also a “pressing” need for stations along the Waikato and a comprehensive education and awareness campaign.
He said the “Check, Clean, Dry” biosecurity measures — instructions for cleaning vessels and gear of pests before moving between waterways — were well-recognised by locals and visitors also needed to adhere to them.
“To safeguard our Rotomoana, a comprehensive plan must be developed.”
He said preparations should also account for other potential future freshwater biosecurity risks.
“It is our shared responsibility to collaborate in the best interest of all our lakes and their enduring health.”
“The discovery of these clams may necessitate further closures to our Rotomoana.”
Freshwater gold clams.
The trust was exploring ways to bolster the presence of biosecurity officers on the lakes.
It was also calling for increased resource investment towards clam eradication and believed containing the clams to the Waikato was “an obligation”.
“We emphasise that this threat should be addressed with the same gravity as other biosecurity threats, akin to agricultural and horticultural concerns.”
He said the trust continued to “charter a collective path forward to strengthen our communities to activate further our kaitiakitanga principles for the protection of our cherished Te Arawa Rotomoana”.
Biosecurity New Zealand director of readiness and response John Walsh said it had “no plans to close other lakes”, but would work collaboratively and consider any requests, as it did for Lake Ōkataina.
He said measures taken to keep the clams out of Rotorua included a national surveillance plan, a public awareness campaign promoting Check, Clean, Dry including a Waikato-based version, and making the clam an unwanted organism under the Biosecurity Act.
Biosecurity New Zealand director of readiness and response John Walsh at a public meeting about the gold clams last week. Photo / Andrew Warner.
He said the best tool to prevent the spread, without closing lakes and rivers, was ensuring river users followed Check, Clean, Dry guidelines before moving to another part of the river or a different waterway.
A Waikato coordinator had been contracted to educate users on preventing the spread, and ambassadors were present at events, such as rowing regattas.
He said it had worked with Fish & Game NZ, with “excellent reach”, to make sure fishers knew about the clam situation and the new guidelines, including cleaning with very hot water rather than just detergent.
The agency believed water users were taking all precautions and adhering to the guidelines.
Walsh said Fish & Game Eastern Region staff were at main boat ramps this weekend for enforcement and education purposes, and looking out for Waikato anglers.
Boat cleaning facilities will be installed at Lake Ōkataina while it is closed.
They will also be installed in the Waikato, the first at Lake Karāpiro in about three weeks, and options to have them at all major boat ramps are being explored.
It planned to expand its national surveillance programme to 80 sites and to start trials in November testing the feasibility of suppressing the clams to the Waikato River.
He said its response to the clams was informed by expert advice that found eradication “extremely unlikely” but containment and suppression feasible.
He said Biosecurity NZ was taking “a cautious and balanced approach” so people could enjoy the waters while protecting them.
Fish & Game chief executive Corina Jordan said it had staff at Lake Rotoiti and Lake Tarawera over the weekend, as usual for the trout fishing season opening day.
She said it did not have staff at Lake Ōkataina as it was closed but understood it was quiet. She said Eastern region chairman Ngahi Bidois stopped by and was pleased to see anglers were respecting “the wishes of the local community” and fishing elsewhere.
“We share iwi concerns that this clam will spread across the country and understand why they sought the closure,” Jordan said.
Check, clean and dry
Before moving between waterways you must do the following for all gear that comes into contact with water:
Remove any plant matter and leave it at the site (the river or lake bank), or put it in the rubbish. Don’t wash it down any drain.
Clean
Dishwashing detergent is not effective against gold clams, but hot water is.
For absorbent material, such as lifejackets or clothing, wash with hot water above 60C for at least 1 minute; between 50-54C (hot household tap water) for at least 5 minutes; or above 45C for at least 20 minutes. Alternatively, soak items in a 10 per cent bleach solution.
Dry
Ensure gear is completely dry to touch, inside and out, then leave to dry for at least another 48 hours before using it.
