New rules in force as concerns mount over invasive clams

Boaties and other watercraft users must be extra vigilant about cleaning their vessels and gear before transporting them around the country this summer.

The warning from the Ministry for Primary Industries (MPI) comes as concerns mount over the threat of spreading the invasive freshwater gold clam, which has now established itself in a lengthy stretch of the Waikato River.

The pest species, first found in the Bob’s Landing area of the Waikato River near Lake Karāpiro in early May this year can “harm everything we love about the water”, MPI said.

“It can disrupt our recreation, clog water pipes, and threaten other freshwater species.”

It’s been declared an Unwanted Organism under the Biosecurity Act and penalties apply for boaties and other watercraft users who don’t follow new rules.

“The clam can only spread if humans move it between lakes and rivers with boats and gear, the MPI said.

Native to eastern Asia, the freshwater gold clam (Corbicula fluminea) is widely established in North and South America and Europe.

It can survive a wide range of temperatures in fresh or brackish water.

A prolific breeder, gold clams are able to produce 400 juveniles a day and up to 70,000 juveniles a year.

Because freshwater gold clams reproduce so rapidly and form large populations, they can clog water-based infrastructure, such as electricity generation plants, irrigation systems, and water treatment plants, MPI said.

They are filter feeders that can potentially compete with native species for food.

“Overseas, this clam has proved difficult to control and eradication has never been achieved.” MPI said.

Initial surveillance, using visual checks and environmental DNA (eDNA) testing, determined the spread of the clam. It focused on the Waikato River and its key tributaries (prioritising the Waipā River), as well as Lake Taupō.

The clam has been detected from Lake Maraetai down to the river mouth at Port Waikato. There is no evidence of clams outside the Waikato River but they are easily spread and usual cleaning regimes are not enough to prevent it.

After the discovery of the clam in the Waikato, Biosecurity New Zealand immediately established a partnership with river iwi and other stakeholders,

A technical advisory team, made up of national and international scientists, said there were not currently any technologies to eradicate gold clams in the Waikato River but a strategy of containment and suppression was possible. Environmental DNA testing of high-risk water bodies linked to the affected Waikato River areas was ongoing. It was surveillance work that would also allow for a rapid response if the pest was detected in other regions.

“This means that people must not knowingly move or spread the freshwater gold clam or water that may contain it. To do so would be an offence under the Biosecurity Act. People can still use the Waikato River for recreation, including boating and fishing, or gathering of kai (food) as long as they follow the requirements of the controlled area notices, including clam-specific Check-Clean-Dry procedures, before moving their equipment or craft,” MPI said.

Most people who hold consents to take water from the Waikato River under the Resource Management Act (RMA) — such as for irrigation, municipal water supply or other commercial uses — will notice no impact although some will require special permits.

Biosecurity rules are in place to stop the spread of the clam through a mechanism under the Biosecurity Act called a Controlled Area Notice (CAN).

Two CANs are in force — one for the Waikato River and another for the Te Arawa lakes with additional protections for Lake Ōkataina.

A CAN with specific rules for all wake boats applies to the Waikato River from the Whakamaru Dam to the river mouth at Port Waikato. This came into effect on November 24 and will remain in place until further notice. Wake boats are any craft with an internal tank or bladder that cannot be completely drained.

All wake boats that have been in the controlled stretch of the Waikato river must not be used in any other waterways, including parts of the river outside the controlled area, MPI says.

Recreational river users that have been in the controlled stretch of the river must continue to follow Check-Clean-Dry requirements for any craft, gear (such as fishing and other equipment used to gather kai) and equipment (including water skis, wakeboards, and inflatable pool toys).

For Lake Okataina, all boats must be cleaned at a designated wash station in Rotorua before entering the lake. This is in addition to the Check-Clean-Dry requirements.

For all 14 Te Arawa lakes, any boat that has been in the Waikato River in the previous 30 days must also be cleaned at a designated wash station before entering the water — also in addition to the Check-Clean-Dry requirements.

• More information can be found on the MPI website.

Check-clean-dry process

Freshwater boaties and other water users must follow a new check-clean-dry process:

Check  for what is visible.  Remove any visible matter, including any plant material, mud, or clams. Drain all river or lake water.

Clean for what is not visible.  Use tap water to wash down your watercraft, gear, vehicle, and trailer that has been in contact with river or lake water and do it on to grass, beside the waterway, or at home. Do not wash anything where potentially contaminated water could run into a stormwater drain system.

For absorbent surfaces and materials (including wetsuits and carpet on trailers), use one of these treatments: Soak items in hot tap water (55ºC) for at least five minutes; soak items in diluted household bleach (10 percent, or 1 in 10 ratio) for an hour; freeze items until solid (eg overnight).  Refer to the manufacturer’s instructions if needed.

Dry to be sure. Allow potentially contaminated gear to dry to touch, inside and out, then leave it to dry for at least 48 hours (two days) before using again. Dry areas inside the watercraft where water has pooled, for example with an old towel, and then leave the craft to dry for at least 48 hours (two days).