The Current Status of Predators on New Zealand Offshore Islands

Posted by Zach Carter

New Zealand is committed to preserving its uniquely rich biological heritage with Predator-Free New Zealand (PFNZ). This audacious programme is focused on ridding the country of the three most biologically and economically harmful mammalian taxa by the year 2050 (Innes, Kelly, Overton, & Gillies, 2010). Pests targeted for eradication include rodents (Rattus rattus, R. norvegicus, R. exulans), mustelids (Mustela furo, M. ermine, M. nivalis) and the common brushtail possum (Trichosurus vulpecula). These mammals predate upon native biota and threaten to undermine New Zealand’s most lucrative industries, including tourism and the primary industries. There is unilateral support for PFNZ, but how close are we to actually achieving this goal on New Zealand’s offshore islands?

If we exclude large islands that are source to substantial pest populations, including Stewart Island (Rakiura) and Great Barrier Island (Aotea), and islands that cannot support mammalian life for extended periods (islands < 5 hectares, ha), 85 offshore islands (islands ≤ 50 kilometres from the mainland) currently host PFNZ mammal pests. Insofar, 87 offshore islands have been eradicated of mammals since New Zealand began systematic removals in 1980 (Figure 1). This means that over half (50.5%) of the islands with a historical pest presence have been eradicated!

Figure 1: PFNZ mammal eradications that have occurred on New Zealand offshore islands from 1980 through present.

If we investigate the total amount of island area eradicated in this dataset, we paint a slightly different picture; 84,300 ha of island area currently host mammal pests, and 24,200 ha have been eradicated. This means that only 22.3% of island area historically hosting mammals have been eradicated. Note, this dataset includes only cases of confirmed pest presence (islands with an unknown status were excluded) and excludes incursions as being considered confirmation of pest presence. Moreover, these numbers do not coincide with other eradication estimates that use different geographical boundaries or different pest species (e.g.(Towns, West, & Broome, 2013).

Admittedly, there is much work left to accomplish. This does not mean that PFNZ is impossible, though, only that it will be an uphill battle. In order to keep with the designated timeline, multiple government agencies and private groups have come together seeking creation of new (or “future”) control technologies that can address issues of ethical and technical concern. Transformative genetic control tools (including virus-vectored immunocontraception, RNA interference, and transgenic ‘Trojan’ approaches), and novel takes on current-day technology (including automated self-resetting traps, remote monitoring, and highly attractive lures) are being designed to target specific species in a manner that is cost-effective, environmentally benign, and exceeds the public conception of humaneness (Campbell et al., 2015). Such tools will be essential to the success of PFNZ. If they can be implemented in a timely manner, New Zealand will be well on its way to being the first nationwide endemic sanctuary.

Zach Carter is a PhD student at the University of Auckland in the School of Biological Sciences. He works with Dr. James Russell prioritising eradications of mammal pest species throughout New Zealand.

References

Campbell, K. J., Beek, J., Eason, C. T., Glen, A. S., Godwin, J., Gould, F., . . . Ponder, J. B. (2015). The next generation of rodent eradications: innovative technologies and tools to improve species specificity and increase their feasibility on islands. Biological Conservation, 185, 47-58.

Campbell, K. J., Beek, J., Eason, C. T., Glen, A. S., Godwin, J., Gould, F., . . . Ponder, J. B. (2015). The next generation of rodent eradications: innovative technologies and tools to improve species specificity and increase their feasibility on islands. Biological Conservation, 185, 47-58.

Innes, J., Kelly, D., Overton, J. M., & Gillies, C. (2010). Predation and other factors currently limiting New Zealand forest birds. New Zealand Journal of Ecology, 34(1), 86.

Towns, D. R., West, C., & Broome, K. (2013). Purposes, outcomes and challenges of eradicating invasive mammals from New Zealand islands: an historical perspective. Wildlife Research, 40(2), 94. 10.1071/wr12064

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