Environmental terrorism fears have led an iwi trust to hire security for a Rotorua lake after online threats to introduce invasive clams that could “obliterate” its “delicate ecosystem”.
It comes as Biosecurity New Zealand announces Lake Ōkataina, a culturally significant and popular trout fishing spot, will be closed to boating and fishing for a month to install protections against the freshwater gold clams.
The announcement was made just days before the trout fishing season was set to open on Sunday. Fish & Game issued a media statement calling the decision a “blow to anglers”.
The decision was in response to Ngāti Tarāwhai Iwi Trust’s urgent bid to protect the lake, fearing if the clams reached its waters they would cause “irreparable and irreversible damage” to native flora and fauna.
Gold clams, also known as Asian clams, were found in the Waikato River in May and have multiplied to cover a 99km stretch. Surveillance had not found them anywhere else.
The clams can reproduce 400 fully formed clams a day. They feed on plankton — what most native species survive on — and can clog infrastructure in the water.
Eradication overseas has never been achieved.
Prior to the closure decision, iwi trust chairman Cyrus Hingston said that as the lake’s traditional owners and kaitiaki (guardians), it asked the Ministry for Primary Industries to publish a Controlled Area Notice (CAN) to temporarily close the lake to boats.
This was the first line of defence against the “hard-to-eradicate monster” that would “obliterate the delicate ecosystem” in the lake.
“We can no longer wait for the invasive species … to hitch a ride on a boat that has come from the Waikato River and enter our precious lake.”
The trust was developing a prevention and control strategy with MPI, environmental specialists and Te Arawa Lakes Trust to try to stop the spread of the clams to the lake.
Hingston told the Rotorua Daily Post the trust had hired a private security guard after threats were made online to drop clams into the lake.
“We take every threat seriously.”
He agreed the threats could be described as environmental terrorism. The trust was assessing them and getting regular updates.
“If these golden clams get into our taonga, they’ll have a “long-term destructive impact on fishing and everything else we hold dear about Lake Ōkataina”.
He said the iwi took its guardianship responsibilities seriously. It had focused on Lake Ōkataina because the surrounding land was owned by Ngāti Tarāwhai people or the Crown.
“Even if we have interests in other lakes and waterways that are shared by other iwi, we cannot speak for them.”
Te Arawa Lakes Strategy Group, which includes the Bay of Plenty Regional Council, Rotorua Lakes Council, Te Arawa Lakes Trust and local community groups supported the closure request in principle.
Te Arawa Lakes Trust biosecurity manager William Anaru said the clams were a risk to all Te Arawa lakes and rivers and must be contained to Waikato.
“If we leave the lakes open for all to come through without proper procedures, we will get [the clams] unfortunately.”
Lakes Trust chief executive Daryn Bean said it supported Ngāti Tarāwhai’s efforts and was exploring further protective measures, including establishing a customary rāhui.
Rāhui are temporary prohibitions and are customary, not legally enforced.
Prior to the closure being confirmed, Fish & Game chief executive Corina Jordan said it was “deeply concerned about discussions to close the lake”, particularly given the Waikato River system and Lake Karapiro had “next to no restrictions”.
She said clams were mainly spread by boats with a ballast system. Anglers and other Lake Ōkataina users who posed little risk were “worried about the situation” ahead of the angling season.
She said “stronger measures” should be taken to prevent the clams from spreading to other regions and the organisation was “disappointed” there had not been more investment in isolating the clams to the Waikato River.
Steps such as boat-ramp wash stations should have been installed as soon as the clams were discovered, she said.
“We are now in a race against time to stop the spread.”
Jordan said Fish & Game was working with mana whenua, Te Arawa Lakes Trust and MPI to understand the risks and looking at the science to better understand the implications. She urged anglers to continue with biosecurity practices.
She said Rotorua lakes attracted 120,000-150,000 angler days per season. Lake Ōkataina, renowned for “trophy” rainbow trout, recorded 6000 to 7000 angler days each season in Fish & Game’s National Angler Survey.
Biosecurity New Zealand deputy director general Stuart Anderson said in Thursday’s media statement the lake would be closed to boating and fishing from October 1 to 31 under the Biosecurity Act to reduce the risk of an “incursion”.
The temporary biosecurity rules were “part of a precautionary and balanced approach” to reduce the risk of the clams spreading.
“Lake Ōkataina holds special cultural significance to Ngāti Tarāwhai because it contains a drowned pa site and other submerged Māori archaeological features.
“It is also a popular trout fishing lake and its popularity with fishers, many who travel from Waikato, makes it vulnerable.”
During the closure period, boat cleaning facilities would be installed to ensure boats entering Lake Ōkataina were clam-free.
“We appreciate people want to get on Lake Ōkataina at the start of the trout fishing season, but a small sacrifice this month goes a long way towards preserving it for generations to come.”
Cleaning stations would also be installed in Waikato to help users meet “check, clean and dry” requirements already in place for moving between waterways. The first station would be at Lake Karāpiro and it was exploring having them at all major boat ramps.
Anderson said the agency planned to expand its national surveillance programme to 80 sites and run trials to see if suppressing the clams to the Waikato River was feasible.
Prior to the closure decision, he told the Rotorua Daily Post scientists had advised elimination was “extremely unlikely” and had not been achieved overseas but a containment and suppression strategy was possible.
The “complex response” was progressing urgently. In Waikato, it was working to contain the clams while allowing continued public use and believed it had struck the right balance.
As well as check, clean, and dry requirements, it had awareness campaigns, signage by Waikato and Bay of Plenty waterways and was providing washdown equipment for events such as regattas. It was exploring further measures.
Bay of Plenty Regional Council biosecurity manager Greg Corbett said juvenile clams drifted on the current, pulled along by a sticky mucous thread that can attach to boats and gear, which was why check, clean and dry procedures were crucial.
Corbett said the Regional Pest Management Plan (RPMP) 2020-2030 could require all boat ramp users to certify their vessel, craft and trailer were clean.
Te Arawa Lakes Trust and Biosecurity NZ hosted an open-forum discussion about gold clams at the Millenium Hotel on Wednesday night and about 150 people attended.
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 from gear and leave it at the site (the river or lake bank), or put it in the rubbish. Don’t wash plant material down any drain.
Use 10 per cent dishwashing detergent mixed with water and leave the item wet for 10 minutes.
Ensure gear is completely dry to touch, inside and out, then leave to dry for at least another 48 hours before you use it.
Cira Olivier is a social issues and breaking news reporter for NZME Bay of Plenty. She has been a journalist since 2019.
Additional reporting Samantha Motion