Te Arawa Lakes Biosecurity

April 2023

The rewarding work of controlling invasive plant and fish pests in Te Arawa Lakes.

Te Arawa Lakes Trust was awarded a Biosecurity Award in 2022 for work the organisation is undertaking in a number of areas within its rohe. Among the invasive species being tackled are fresh water ‘oxygen weeds’, and catfish. A combination of management and volunteer programmes, using both conventional and traditional techniques, are being used to contain and control these plant and fish pests. But the work is far from over.


In 2018, Rural Delivery looked at research and work on the control of catfish that had been discovered in Lake Rotoiti in 2016. Prior to that time, catfish had been confirmed in Lake Taupo and throughout Waikato rivers, but not in the Rotorua catchment. Catfish are a highly successful coloniser of New Zealand waterways and a big threat to the populations of koura (freshwater crayfish) that are a traditional food source for Te Arawa.


When Rural Delivery last connected with this work, control efforts included cordoning off Te Weta Bay (which had presented the heaviest infestation in the Lake) and a programme of fyke netting (using fine cylindrical-shaped nets) for capture and population counts. Also being considered were pheromone baits to attempt to increase the catch rates using pheromone attractants. There is a feasibility study currently underway looking at the impact of using sterile males to disrupt the breeding cycles. This project is in its early stages and has a masters project aligned to it. The use of acoustic tags is being looked at, to help determine movement patterns and the spread of fish populations.


In 2023 the catfish work is continuing, as more people are being made aware of and engaged with the massive and ongoing undertaking to protect our native species and local environments. Twenty nets are set daily on Lakes Rotorua and Rotoiti and are monitored by volunteers overseen by the Te Arawa Biosecurity team.


William Anaru is Operations Manager, Biosecurity & Taiao Restoration for Te Arawa Lakes Trust. One of the stated roles of the Trust is to maintain and establish areas of spiritual and cultural significance to Te Arawa, of which the region’s 14 lakes and associated wetlands form a critical part. William explains that a combination of contract and volunteer workers have been organised to net and undertake monitoring and surveillance work, as well as run a programme of public awareness, engagement, and education.


William says they are also contracted through Ministry for Primary Industries (MPI) to perform ‘check, clean, and dry’ surveys with fishers and boat owners, as there is a very real threat of pests spread via boat trailers, winches and weed left on anchors. Catfish are able to survive up to four days out of water and can crawl on dry land for short distances to new water bodies, and as noted previously, there are many of these under Te Arawa’s rohe. The other, more problematic area to address is the occasional intentional spread of pest fish from aficionados of what is known as ‘coarse’ fishing.


While the task is immense and multi-factored, William believes there is much to be optimistic about. He describes the upcoming generation as being more aware of the needs of the environment, and readily embracing the knowledge and actions required to remediate damaged environments and protect those that are currently in good condition. William cites the work of a local school (Lynmore Primary) that was a finalist in the Kura (School) Award for the 2020 New Zealand Biosecurity Awards, and the winner of the same award in 2021.


There are currently 36 schools in the biosecurity programme. In 2018, a group known as the ‘Catfish Killas’ had 2,500 volunteers on their books. William notes while there will always be some who are stuck in a particular way of thinking about their right to do as they please in our environment, he and his teams are often thanked by members of the public for the work they are doing.


In addition to the catfish work, another group of pest plants are impacting on waterways. They are described as ‘oxygen weeds’ – the main culprits of which are elodea, egeria, hornwort, and lagarosiphon. They were introduced through the dumping of fish acquaria and the like and have made themselves very much at home in the Bay of Plenty’s water bodies. The plants grow fast at the edges of lakes in about 1.5 to 6 metres of water. They form dense weed mats that interfere with the life cycles and natural behaviour of species such as koura, inhibiting migration to the shallows to feed. In spring and autumn, spraying operations re carried out to minimise their spread. But an additional approach is being taken by the Trust.


At Lakes Rotoma, Rotoiti, and Tarawera, and in the Kaikaitahuna Stream (that flows into Lake Rotorua), trials are underway using woven harakeke (flax) mats, called uwhi, to suppress weed growth and spread. The work has been partially funded by Jobs for Nature, and as of January 2023, the mats have been in the water for about a year. 


William says the results so far are encouraging, with good suppression of weed growth and little decay of the uwhi. Local weavers from Te Roopu Raranga ki Rotorua created the uwhi, work which has partly helped to fill the gap created by Covid and the resultant drop in tourist numbers to Rotorua. Monitoring of the uwhi is done by a specially trained scientific dive team working for Te Arawa Lakes Trust.


Wetland restoration and pest control is also a feature of the work by the Trust. At the intersection of state highways 30 and 33 on the approach to Rotorua airport, Te Pohue wetland has been under the care of Te Arawa Lakes Trust and hapu members from Ngati Rangiteaorere since midway through 2021. Work here has involved planting, water sampling, weed control and pest animal and plant control.


All this recognised mahi of Te Arawa Lakes Trust is part of a greater picture of environmental care and restoration and clearly need to continue for years to come. The biosecurity threats to these environments are already spread throughout the region, and it is only with community commitment and innovative approaches combining conventional scientific technologies, in partnership with mātauranga Māori, that real and lasting progress will be made.

For the 2018 Rural Delivery catfish story, see: https://www.ruraldelivery.net.nz/posts/Catfish