Abstract
Population control of invasive mammal pests is an ongoing process in many conservation projects. In New Zealand, introduced wild domestic cats and mustelids have a severe impact on biodiversity, and methods to reduce and maintain predator populations to low levels have been developed involving poisoning and trapping. Such conservation efforts often run on limited funds, so ways to minimize costs while not compromising their effectiveness are constantly being sought. Here we report on a case example in a 150 km2 area in the North Island, New Zealand, where high predator numbers were reduced by 70-80% in an initial ‘knockdown’ trapping program, using the full set of traps available in the fixed network and frequent checks, and then maintained at low density using maintenance trapping with less frequent checking. We developed and applied a simulation model of predator captures, based on trapping data, to investigate the effect on control efficacy of varying numbers of trap sites and numbers of traps per site. Included in the simulations were captures of other, non-target, introduced mammals. Simulations indicated that there are potentially significant savings to be made, at least in the maintenance phase of a long-term predator control programme, by first reducing the number of traps in large-scale networks without dramatically reducing efficacy, and then, possibly, re-locating traps according to spatial heterogeneity in observed captures of the target species.
Highlights
Invasive mammalian pests continue to have significant negative impacts on biodiversity values internationally [1,2,3]
The predator capture rate in the initial knockdown phase, during the first year after commencement of trapping, declined significantly over successive years: an average of 19.2 predators were trapped per month between December 2011 and May 2012, and the trap rate declined by 54% over the 12 months (June 2012 to May 2013), and by 66% over the subsequent 12 months (June 2013 to May 2014) relative to the first six months
Strategies for increasing the cost-effectiveness of mammalian pest-control trapping operations, which often run on very limited budgets, include improving accessibility to real-time trap-site information from the trap network,either through logistical improvements in physical access or by facilitating remote-sensing of trap sites [16], and/or by optimizing the spatial arrangement of the trapping network [15, 32]
Summary
Invasive mammalian pests continue to have significant negative impacts on biodiversity values internationally [1,2,3]. Some invasive mammals have been successfully eradicated from islands [4, 5], eradication is often not an option on large mainland areas (>100 km2), especially where the broadcast application of toxic baits for pest control is socially or politically unacceptable [6]. In such cases the alternative strategic choice is often sustained ‘maintenance‘ control, which attempts to reduce and hold populations of pests below a threshold density at which their impacts are either eliminated or at least reduced to a level deemed acceptable by stakeholders [7, 8].
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