Te Arawa Lakes Trust is running a project called ‘Koura’ to try to stamp out an exotic weed introduced 50 years ago into Rotorua lakes, which has caused a serious decline in native species such as the koura (freshwater crayfish).
“The exotic weed upset the ecosystem, so koura are unable to cohabitate and flourish in their natural environment, ”lead diver and tau koura researcher Cory O’Neill says.
The Koura project is a team of local divers/ biosecurity personnel who motor on to the 14 lakes surrounding Rotorua in a new 90 horse powered 5.5-meter Stabicraft, also named Koura in striking red tā moko, to monitor and manage koura counts and conditions.
The team uses the traditional method of tau koura or rope and fern crayfish fishing both for biomarkers and knowledge gathering and to help families in the areas to reestablish this fading practice as a food source.
O’Neill led the team out today on to Rotoiti to pull up a tau koura to check for koura that have settled into the shelters of the fern bracken connected to the tau or rope, which has been sitting there for 12 weeks.
Unfortunately, the numbers today were upsetting for O’Neil who wept on seeing what the exotic weed has done to his whānau food source, which he used to gather with his parents and grandparents when it was abundant many years ago.
“The tau koura is a link to our mana and it was a food source for our hapū and our marae and our whānau.
Not enough for one whanau
“Sadly, that has not happened for decades because now we don’t have enough koura to support one family, let alone marae or hakari kai,” O’Neil says.
O'Neil says the labrasiphin weed starts to dominate the water column from 1.5 meters depth and they replace native species at 4-8 metres. Hornwort takes over at 4-6 metres and they dominate the water column down to approximately 11 metres and are surface-reaching. These are both weed barriers that grow six meters thick, which koura cannot migrate through from the deeper cooler waters up to the shallows where they forage for food and mate in the evenings.
These exotic weeds were introduced from aquariums, which were popular during the 1980s. People emptied out these aquatic species into waterways and they slowly made their way into the lakes over the decades to become the dominant weed in the lakes of Rotorua.
Last year in December Te Arawa Lakes worked in partnership with local rāranga or flax weavers to weave mats (uwhi) that would be placed at the bottom of the lake beds by O’Neil and his divers to help suppress the weeds and allow koura to have access to the shallower areas of the lakes.
Big ambitions
“It is proving itself effective as an aquatic pest weed management tool. Other iwi organisations and government organisations can look at the trends we have established and agree uwhi are affecting the weeds and not just anecdotally but scientifically,” O'Neil says.
Te Arawa Lakes Trust environment manager Nicki Douglas says she has a strong team to thank for the progress taking place and is well supported by “renowned” catfish killer William Anaru. But she says, without the support of Toitū Te Whenua Land Information New Zealand and the government's Jobs for Nature programme, none of this would have been possible.
“We know that if our crayfish are healthy in numbers it is a sign that our waters are well, our food is plentiful, and the land and people of Te Arawa are thriving,” Douglas says.
The National Institute of Water and Atmospheric Research (NIWA) says there has been a depletion in crayfish over the past 50 years. This is due to exotic weeds, eutrophication (over-enriched nutrients) and the introduction of exotic fish. NIWA also supports the use of traditional cray lines as a means of successful monitoring.
“And it is actually these relationships that strengthen our foundations and do provide us a pathway to future solutions,” O’Neil says.
Te Arawa Lakes Trust's ambition is for the koura to become 100% healthy, the waters are rejuvenated, and fostering the lakes of Te Arawa remains intact.