AWA: Academic Writing at Auckland

Sodium fluoroacetate: considering the evidence surrounding New Zealand’s most contentious Poison

Abstract

In the last 800 years, the introduction of mammals into New Zealand has played a critical role in the destruction of native biodiversity, shaping the ecosystems we see today (Craig et al. 2016; Russell et al. 2015). Loss of biodiversity is accompanied by impacts to primary production and human health in the wake of mammalian pests, invasive species costing around NZ$3.3 billion annually from control and losses (Byrom et al. 2016). Native flora and fauna show few adaptations to deal with this threat, compounded by the explosive nature of alien mammals and their capacity to spread disease (Byrom et al. 2016; ERMA 2007).

Aside from humans, the mammals that pose the most significant threat to native biodiversity include Possums (Trichosurus Vulpecula), ship rats (Rattus rattus) and stoats (Mustela erminea) (Wright 2011). The varied and intricate impacts of these species on native ecosystems and primary industry is beyond the scope of this report. However important points include they all detrimentally impact native species populations, ecosystem functions, human health and are widespread and difficult to control. Moreover, Possums are major vectors of Bovine Tuberculosis (TB), one of the greatest threats faced by the agriculture industry (Nugent et al. 2001; Byrom et al. 2016). The use of poison in pest control is the topic of long-standing debate (ERMA 2007). Despite a growing body of evidence concerning the effectiveness of aerially based operations for pest control and its relative safety, public opinion regarding poisons such as sodium fluoroacetate (henceforth referred to as 1080) have only gotten worse (Russell 2014). By investigating the evidence surrounding 1080, regarding both its use as a ‘tool’ to significantly control mammalian pests and the risks/adverse impacts of its use, we can gain a clear understanding of the practicality of 1080 and justification for further treatment.

Evidence of significant conservation gains through 1080

As New Zealand’s most applied pest control method, 1080 causes mortality by interfering with energy metabolism in animal. Application is administered through laced cereal bait pellets both in ground based and aerially based operations. The largest sectors involved in mammalian pest control are the Department of Conservation (DOC), OSPRI (under the TBfree programme, previously known as the Animal Health Board) and local governments. On average, 635,000ha of New Zealand’s 27M ha is aerially treated with 1080 every year, with a further 4-5M ha being applied in ground control programmes (Wright 2013). However, these figures vary annually, with a trend showing an increase in the use of aerially applied 1080 over larger areas in smaller quantities (Elliott & Kemp 2016).

Reports published in 2011 and 2013 by the Parliamentary Commissioner for the Environment (PCE) presented and compelling case for the continued use of 1080, heavily promoting the increased usage of the poison as New Zealand’s only viable option. These reports assessed both the effectiveness and concerns regarding 1080, constructing a framework of questions used to compare 1080 to an ‘optimum pest control tool’ (Wright 2011).

This framework is an effective way to assess the research concerning the pros and cons of 1080, providing evidence-based answers to fundamental questions regarding the its impacts, and whether it has significant conservation benefits. Since a large amount of literature was critically evaluated in the 2011/2013 PCE report, this report will use the PCE’s framework to evaluate the impacts of 1080, only using research conducted after the release of the 2011 report.

Can 1080 decrease populations of pests, do natives increase afterwards?

A 2018 study using BACI sampling design and paired treatments sites over the course of four years, showed possums decreased to negligible levels in one-off 1080 treatment sites, whereas non-treatment sites had substantial increases. Rats and Stoats also showed significant reductions but rebounded in following years. This study also showed that the longer-term effects on nine bird species were all neutral or positive post-1080, showing negative effects on non-treatment sites (Burge et al. 2018).

Several other recent studies have demonstrated the susceptibility of pest mammals to 1080, with an increase in average kill rates for possums (75-100% in 2011 to 90-100% now), with less 1080/ha than previous studies (Byrom et al. 2016). Associated with greater pest control, evidence has demonstrated a significant, positive response in previously understudied species to 1080 treatments, such as common forest birds (i.e.  Zosterops lateralis, Gerygone igata, Fringilla coelebs, etc.), and native bats (Mystacina tuberculata) (Schadewinkel et al. 2014; Veltman et al. 2014).

Can 1080 stop Irrupting pest populations?

The need for fast, effective pest control has become increasing apparently as we learn more about how introduced pests interact with native ecosystems, with special regards to ‘mast’ events. Rats are identified as particularly problematic, with populations returning to viable densities 16 months following a successful 1080 treatment (Griffiths et al. 2015). Recent studies have shown quick, tactical control is effective, especially when coupled with recently advanced field methodologies. These include pre-feeding non-toxic bait, modern survey technologies, multispecies approach, land-bridges, pre/post-detection methods such as chew-cards and tracking tunnels (Griffiths et al. 2015).

Can 1080 be used on a large scale/cost effective?

In 2014 DOC treated more than 600,000ha, with a following 900,00ha treated in 2016. Much of the treatment area being difficult, inaccessible terrain and the average cost per hectare for this operation reported at $17. Costs are often less in routine OSPRI treatments. The average cost for ground-based treatment can be as low $5/ha in lowland but often exceed $80/ha in rugged terrain, alongside ongoing monitoring costs (Burge et al. 2018).

Considered risks and adverse impacts of using 1080

Like all pest control methods, 1080 presents drawbacks. Whilst being the tightest regulated pest toxin in New Zealand, and deemed by the EPA ‘comparatively safe’, these adverse impacts continue to contribute to negative public opinions regarding 1080 (ERMA 2007; Farnworth et al. 2014). Ongoing research since its 2011 review have helped minimise these impacts as well as identify new potential risks.

All pest control methods exhibit by-kill. 1080’s non-specific versatility has lead to concerns regarding the potential damage to native fauna. Since greater management regulations and advances in bait techniques since 2011, studies have either found no effect, or reduced effects of non-target mortality, with the small numbers of affected individuals offset by the subsequent increase in survivorship with removed pests (Katzenberger & Ross 2016; Schadewinkel et al. 2014).

The PCE’s report justifiably raised the issue 1080’s humaneness in comparison to the ‘ideal tool’. However, 1080 causes considerably less stress/pain compared to the majority of the other fifteen poisons sanctioned for pest management in New Zealand (Wright 2011).

‘Competitive release’ release is one recently considered risk, post-1080 treatment. Demonstrated in several studies where population eradication has targeted single species objectives, ‘meso-predator release’ has shown to be a real threat to conservation goals (Ruscoe et al. 2011). Another indirect effect of pest control is prey switching. While becoming less threatening due to multi-species approaches, the consequences of prey switching are presented in various recent studies (Burge et al. 2018).

Gaps in knowledge and future research

Increasing interest in the idea of a ‘Predator Free New Zealand’ demands greater research into continuous large-scale pest management. Several areas in this field exist where knowledge is lacking, or systems could be optimised (Nugent et al. 2001; Russell et al. 2015). Recent social surveys/studies have evaluated ongoing attitudes towards 1080 and overall pest management and have highlighted the need for more representative future studies. Social data is crucial in estimating public response to pest management, helping inform governments, policymakers, conservation estates, Iwi, economists and more (Farnworth et al. 2014; Russel 2014).

Further Research is necessary regarding the indirect effects resulting from 1080. These effects include both positive and negative, with special interest in historically unexplored systems. Reviewing the literature shows an ecosystem and taxonomical bias, with majority of focus on Broad-leaf forests and Native, rare birds respectively (Byrom et al. 2016; Elliot & Kemp 206).

From a design stand point, future studies would benefit from the coordination surrounding the undertaking of 1080 research (Craig et al. 2016). Standardisation of biodiversity indices and experimental design would allow the contribution of data to greater pest control meta-analyses and would present a better picture of native success (as opposed to immediate population response) (Byrom et al. 2016). Furthermore, studies accessing long-term effects on biodiversity would focus goals surrounding desired ecosystem outcomes.

Recommendation of 1080 in future conservation efforts

Despite compelling evidence for 1080’s effectiveness and safety, its implementation by DOC and OSPRI continues to be a contentious issue (Russell 2014). Since the PCE’s report in 2011, further evidence has been accrued that 1080 and aerial treatments can result in substantial positive effects to a variety of non-pest species (Burge et al. 2018; Nugent et al. 2012). I strongly advocate for the continued use of 1080, and without these tools, New Zealand’s biodiversity would be under far greater threat. Continued efforts to find new pest control tools, bridge gaps in knowledge, inform the public and enhance treatment design are still necessary if New Zealand is to become pest-free by 2050.

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