A recent study has found that toxin-based predator control on Banks Peninsula is having a positive impact on the presence of our endemic tree wētā.
The report, entitled Effects of Possum Focused Predator Control on Terrestrial Macroinvertebrates in Banks Peninsula, was undertaken by researcher, Erin Marshall, using data collected by Pest Free Banks Peninsula (PFBP) and Lincoln University. Marshall analysed the abundance of Banks Peninsula tree wētā (Hemideina ricta), using data from wētā motels and wooden discs installed at 12 sites – within and outside the PFBP Extended Wildside area. Data was collected in 2021 as a baseline prior to the commencement of the PFBP elimination programme, and in 2024 after mammalian predator control had been undertaken at some locations.
The report’s findings suggest that while predator control was associated with an increase in wētā abundance, further monitoring was required to gain a true understanding of the biodiversity outcomes resulting from PFBP’s possum elimination programme.
“Biodiversity outcome monitoring is a priority for Pest Free Banks Peninsula,” said Operations Manager, Tim Sjoberg. “Whilst we can see the immediate impact of our predator control programmes in things like forest and bush regeneration and positive feedback from landowners and communities, the impact on biodiversity can sometimes take time to see and understand. This study provides an important baseline for our work – it says, yes, we are having an impact, but more needs to be done to evaluate our progress and ensure that PFBP’s efforts towards biodiversity outcomes are effective.”
Sjoberg says multiple factors impact the health and regeneration of plant and animal species post-predator control. Studying invertebrates, like tree wētā, which are sensitive to changes in the environment, makes them useful for indicating the health of ecosystems. It also brings in the ‘community element’ of PFBP’s work – as the tools used to help biodiversity monitoring – the wētā motels and wooden discs – were made by members of the Akaroa Men’s Shed and a local arborist.
“We all play a part. Whether creating practical tools to support biodiversity on the peninsula or undertaking academic research to guide our predator control programmes, each of us can make a positive difference to biodiversity outcomes.”
To date, few studies have examined the impacts of predator control on wētā abundance. Previous studies have revealed marked increases in the abundance of wētā after rodent eradication, however, the impact that possums have is less well understood.
“This study highlights the importance of effective monitoring. We know possums consume invertebrates, so the opportunity now is to implement more frequent monitoring, given we have baseline invertebrate values. Looking ahead, this study will form the basis of a deep understanding of the value our predator control programme has on biodiversity.”