Too many wild boar? Modelling fertility control and culling to reduce wild boar numbers in isolated populations.

Simon Croft,Barbara Franzetti,Giovanna Massei,Robin Gill,Emmanuel Serrano

doi:10.1371/journal.pone.0238429

Abstract

Wild boar and feral swine number and range are increasing worldwide in parallel with their impact on biodiversity and human activities. The ecological and economic impact of this species include spread of diseases, vehicle collisions, damage to crops, amenities and infrastructures and reduction in plant and animal abundance and richness. As traditional methods such as culling have not contained the growth and spread of wild boar and feral pigs, alternative methods such as fertility control are now advocated. We used empirical data on two isolated wild boar populations to model and compare the effects of different regimes of culling and fertility control on population trends. We built a Bayesian population model and applied it to explore the implications for population control of various management options combining culling and/or contraception. The results showed that, whilst fertility control on its own was not sufficient to achieve the target reduction in wild boar number, adding fertility control to culling was more effective than culling alone. In particular, using contraceptives on 40% of the population to complement the culling of 60% of the animals, halved the time to achieve our target reduction compared with culling only. We conclude that, assuming the effort of adding fertility control to culling was found to be cost-effective in terms of population reduction, these two methods should be used simultaneously if a rapid decrease in wild boar number is required for a closed population.

Highlights

Wild boar and feral swine belong to the same species Sus scrofa and are among the most widely distributed large mammals in the world, where they occur as native or introduced [1,2,3]
We examined the effects of culling and fertility control on wild boar numbers, as these methods are most likely to be considered for reducing wild boar numbers in contexts where toxicants are not registered or allowed
For the Castelporziano Preserve, we adopted post-breeding, pre-removal population sizes, i.e. we used the total number of wild boar estimated through nocturnal line transect sampling (NLTS) in autumn each year, between 2001 and 2016. This number indicates the density of wild boar post-breeding and post-live cage trapping but pre-cull, adjusted using data from cage trapping in late summer to account for pre-survey removals. We considered these population estimates to be more reliable than those based on data from early summer Capture Mark Recapture (CMR), which better match the requirement of the model

Summary

Introduction

Wild boar and feral swine belong to the same species Sus scrofa and are among the most widely distributed large mammals in the world, where they occur as native or introduced [1,2,3]. The environmental and economic impacts of this species include spread of diseases to livestock and people, vehicle collisions, damage to crops, amenities and infrastructures and reduction in plant and animal abundance and richness Wild boar have colonised urban areas, where their impact include extensive damage to private gardens, public parks, sport grounds and cemeteries, as well as transmission of diseases to humans and companion animals [18, 19]), have catalysed discussions on options to reduce local wild boar numbers Reducing local densities is generally assumed to decrease the species’ impacts (e.g. [17]) and in recent years, outbreaks of diseases such as African swine fever (ASF) and classical swine fever (CSF), which may cost affected countries billions of euros (e.g. [18, 19]), have catalysed discussions on options to reduce local wild boar numbers

Methods

Results

Conclusion