Te Arawa Lakes Trust utilising Mātauranga Māori to combat invasive weeds

Mātauranga Māori is being woven together with scientific concepts to combat invasive pest weeds displacing 15 native species in the Rotorua lakes.

The trust in charge of Te Arawa's fourteen lakes, is using uwhi, or harakeke flax mats, to suppress the weeds and improve water quality in Rotorua.

It's the first time Te Arawa Lakes Trust has had the opportunity to create a space for a Māori approach to weed management.

While suiting up to jump in Lake Rotoiti, the trusts lead diver, Cory O'Neill explains the concept.

"The specific pest weed are targeting here with our trial, is lagarosiphon which is commonly known as oxygen weed and originally came from aquariums; and hornwart that is another aquarium type pest weed.

"They are dominant lake weed within Lake Rotoiti and that is the aquatic pest weeds we are looking to suppress with our uwhi, harakeke flax mats."

In the 50s, dumped water from aquariums made its way into the lakes, introducing weeds that squeeze out native plants and animals, he said.

However, by the time anyone noticed it was too late, he said.

"You've got a literal wall of aquatic pest weed which prevents the kōura migrating up to the shallow water to forage for food.

"There are other detrimental effects of those weeds as well. They displace native flora, they also deoxygenate the water and as that biomass dies off it creates a sediment that is detrimental to native growth."

O'Neill said it was possible to spray the weeds, however, the uwhi prevent photosynthesis and stop weeds from rising to the surface again.

And as the harakeke gradually breaks down it provides a nutrient base for the native seed growing water plants.

While the primary purpose is to suppress the weeds, kaumātua of Te Roopu Raranga Ki Rotorua, Jim Schuster, was excited to see kōura return.

"You can walk along in the shallows with a sort of scooper, and sort of scoop them up. You can get a tub full in a night but you don't get a tub full so much anymore because they are not getting through that pest weed."

Schuster said his group was approached by Te Arawa Lakes Trust last November, to combine their skills of weaving and the trusts' knowledge of the pest weed.

"We're using what we call the parakoka, the discard from making flax, when you are preparing flax for whaariki, kete, or even piupiu.

"We didn't want to use the term whaariki, because whaariki is a mat usually indoors and it is very fine weaving. This wasn't going to be like a whaariki and its just a rough weave really, with what is usually regarded as rubbish."

Schuster said there were four different weaving patterns they have tried, and if successful, the group have intellectual property rights to make more for rohe across the country.

He hopes it continues to create jobs for weavers, while also saving the artform from fading.

With support from Toitū Te Whenua Land Information New Zealand, the uwhi will be trialled in Te Arawa lakes as a low cost, native alternative to imported hessian mats.

Biosecurity and Biodiversity manager Tracey Burton says the kaupapa has the potential to change the way lake weeds are managed in the future.

"We're proud to support research which has the potential to change the way we manage lakes weeds in the future, while contributing to positive environmental and cultural outcomes and creating jobs in the region."

She said lake users also play a part in helping to stop lake weed and foster kōura.

"Check, clean and dry remains our best line of defence for preventing the spread of invasive pests between waterways in the region."

Now the uwhi are secured to the lake bed, divers will monitor the sites each month to gauge weed growth and kōura restoration.