INTRODUCTION
South Africa currently accounts for 75% of Africa’s rhino population (Emslie et al. 2019), and despite an upward trend in numbers of South Africa’s black rhino (Diceros bicornis), the species remains critically endangered on the IUCN Redlist (Emslie, 2020b) while the white rhino (Ceratotherium simum), currently decreasing in numbers, remains near threatened (Emslie, 2020a). The IUCN reports that poaching is a major threat to both rhino species; in South Africa alone, a total of 6,151 rhino were lost to poaching between 2008 and 2016 (an increase from 68 to 1,054 individuals poached per year) (Knight, 2017). Despite an international ban on trading of rhino horn by CITES since 1977, the major spike in poaching since 2008 has been driven by increased demand in Asian markets, primarily China (Cheung et al., 2021) and Vietnam (Dang Vu & Nielsen, 2018). The use of rhino horn in traditional medicine, displays of wealth and gifting, and more recently claims for its cancer curing properties form the basis of this demand (Eloff & Lemiuex, 2014; Nguyen et al., 2020). Strategies to successfully prevent rhino poaching in South Africa national parks and private game reserves have primarily involved field patrol rangers and law enforcement approaches (Haas & Ferreira, 2018) but these do not consistently deter poachers (Lindsey & Taylor, 2011; Challender & MacMillan, 2014; Barichievy et al., 2017) and can be financially unviable to maintain, particularly for privately owned reserves (Chapman & White, 2020; Clements et al., 2020). Consequently, dehorning is an increasingly common practice adopted by rhino owners in South Africa (Lindsey & Taylor, 2011), namely Kruger National Park and private reserve partners in the Greater Kruger area (SANParks, 2019; 50/50, 2020), as well as Pilansberg National Park (Sisha & Cocks, 2020) and a number of other private reserves (Lindsey & Taylor, 2011; Phelan, 2018), to add to the arsenal of anti-poaching strategies.
Dehorning is a veterinary procedure involving the trimming and removal of horn above the growth plate while rhino are chemically and safely immobilised (Badenhurst et al., 2016). The use of the procedure, in addition to other field strategies, is not consistently documented as an effective strategy for protecting rhinos from poachers (Lindsey & Taylor, 2011; Milner-Gulland et al., 1994), there are concerns in the long term strategy against poaching and considerations around legalizing the trade of rhino horn as a necessary approach (Challender & MacMillan, 2014; Ferreira et al., 2014; Rubino & Pienaar, 2020).
EFFECTIVENESS OF DEHORNING IN THE ARSENAL OF ANTI-POACHING MEASURES
The use of dehorning as a last resort anti-poaching strategy is apparent in the literature by means of removing the part of the rhino which is most valuable, thus reducing their attractiveness to poachers (Kagande & Musarurwa, 2014). Lindsey & Taylor (2011) report that only 1 in the 33 rhinos poached in reserves in Mpumalanga (excluding Kruger National Park) between 2009-2011 were dehorned, suggesting that dehorned rhino are less attractive to poachers. Similarly, 78 rhinos in Klaserie Private Nature Reserve were dehorned in 2019 with a follow up dehorning in 2020 and the reserve has since reported no losses to poaching (Lars, 2021). Consistent with this, South African private reserve managers and associates in Balule anecdotally agree that dehorning their rhinos has significantly reduced losses to poaching (50/50, 2020; Albert, 2021). However, dehorning alone may not be an effective strategy against poaching without working synergistically with other anti-poaching efforts (Kagande & Musarurwa, 2014; Mukwazvure & Magadza, 2014; Alberts, 2021), particularly patrol, security and law enforcement measures (Martin et al., 2013; Eloff, 2014; Barichievy et al., 2017) as well as translocation to safer areas (Penny et al., 2019), an approach recently implemented by Kruger National Park (Maron, 2021). Equally, these measures have their own challenges e.g. extensive security patrol resources can be ineffective without monitoring poaching patterns and ensuring rangers are in the right place at the right time (Eloff, 2014; Barichievy et al., 2017) and translocation may simply attract poachers to new areas (Lindeque, 1990).
In the 1990s Hwange National Park, Zimbabwe dehorned and translocated their rhinos with an initial 29.1% increase in chance of survival against poaching, but a lack of security resulted in the eventual poaching of all dehorned rhinos 12-18 months after dehorning (Cheteni, 2014; Mukwazvure & Magadza, 2014; Lindsey & Taylor, 2014). Lindsey & Taylor (2011) also report that multiple other parks which dehorned their rhinos, suffered severe poaching losses due to inadequate security. Multiple cases highlight that dehorning alone does not effectively deter poachers. Furthermore, though dehorning is an apparently increasing and last resort anti-poaching strategy, there continues to be a lack of scientific documentation which supports its effectiveness (Milner-Gulland et al., 1994; Lindsey & Taylor 2011; Penny et al., 2020).
BIOLOGICAL IMPACTS OF DEHORNING
Rhino horns grow continuously throughout their life (Pienaar & Hall-Martin, 1991), requiring that continuous dehorning be conducted in order to prevent horns reaching a size of profitability for poachers (Milner-Gulland et al., 1994). The growth rate of rhino horn varies with species, age and sex (Pienaar & Hall-Martin, 1991; Taylor et al., 2017; Ververs, 2018) but it is recommended that dehorning as many individuals in a population and as regularly (every 12-36 months) as possible, is optimal for anti-poaching objectives, depending on the level of threat (Milner-Gulland, 1999; Lindsey & Taylor, 2011). With this come concerns over the long-term viability of repeated dehorning regarding the biological wellbeing of rhinos.
The limited amount of research addressing the dehorning procedure as a stressor for rhinos primarily addresses the chemical immobilisation process and its potential to induce physiological stress responses and reproductive implications. For example, Badenhorst et al. (2016) found that routine dehorning significantly increased short term (48 hours after procedure) stress levels in female white rhinos. Intensive immobilisation regimes in female black rhinos for dehorning, radio-collaring and other procedures at Sinamatella Intensive Protection Zone, Zimbabwe, also negatively impacted female fertility, specifically inter-calf-intervals (Alibhai et al., 2001). Contrary to this, Penny et al. (2020a), found that there were no significant long-term difference in stress hormone levels between rhinos which were dehorned and those which weren’t and that the effects of procedure did not lead to chronic stress. A lack of changes in progesterone levels from the same study also supported that dehorning does not compromise reproductive performance, as further evidenced by no change in inter-calf-interval (Penny et al., 2020b) and no change in birth sex ratio of calves (Ververs, 2018) following dehorning of white rhinos. Furthermore, Penny et al., (2021) show that dehorning is unlikely to have effects on aspects of behaviour related to the horn use in free-ranging white rhinos. Due to the unusual intensity of embolization regimes in Sinamatella (Alibhai et al., 2001), and the more recent findings that the dehorning procedure has little physiological or behavioural consequences (Penny et all, 2020a; Penny et al., 2021), the current literature supports that dehorning as a routine anti-poaching strategy has minimal effects on rhino physiology or behaviour, though the extent of this remains thinly documented.
LONG TERM AND SHIFTING ROLES OF DEHORNING
The implementation of repeated dehorning, continued monitoring and security involves extensive costs to rhino owners and may not be a financially viable strategy, especially for owners in the private sector (Child, 2012; Collins et al., 2016; Rubino & Pienaar, 2020), which is estimated to account for 33% of South Africa’s total rhino population (Rademeyer, 2016). Private owners also conserve almost as many white rhino as the State (49.3% in 2017) (Emslie et al., 2019) and play an integral part in South African rhino conservation (Child, 2012; Emslie et al., 2019). However, private owners struggle to balance diminishing returns and increasing costs associated with rhino ownership (Child, 2012; Wright et al., 2018) with outgoings almost always exceeding revenues generated (Rubino & Pienaar, 2020). Specifically, the cost of dehorning operations may be substantial for smaller properties while larger properties consider dehorning costs to be insignificant compared to security (Rubino & Pienaar, 2020). However as suggested by the literature, dehorning still requires subsequent security and should be implemented as such for effectiveness (Lindsey & Taylor, 2011). Given the reactive nature of dehorning and security as responses to the poaching threat in South Africa, they will inevitably become more demanding, expensive and complex for rhino owners to implement in order to make the risk to poachers higher than the increasing reward incentive increasing with demand (Challender & MacMillan, 2014; Ferreira et al., 2014). Adding to this, the increasingly sophisticated manner in which rhinos are poached further drives pressure on security required e.g. in Eastern Cape, poachers are reported to use more professional tactics such as dart guns (Wright et al., 2016). This highlights how the organization of poachers has the capacity to operate even under increased enforcement (Challander & MacMillan, 2014). As a result, many rhino owners in the private sector frequently consider removing rhinos from their property (Ferreira et al., 2014; Wright et al., 2018; Rubino & Pienaar, 2020), which would greatly undermine South African rhino conservation (Child, 2012; Rubino & Pienaar, 2020).
One effort prevent this was the 2017 lift on domestic rhino horn trade within South Africa, after legal action by the private sector (Rubino et al., 2018). Consistent with the sustainable use approach already rooted in South Africa’s private wildlife sector (Child, 2012), this decision has potential to incentivise private rhino ownership by providing rhino owners with an additional form of income to cover management and security costs associated with rhino ownership, while also advocating dehorning as an anti-poaching measure (Jakins, 2018; Rubino & Pienaar, 2020). One issue here is the mismatch in the objectives of dehorning practices which though are synergistic in their overall aim to conserve rhinos, may negate each other individually e.g. the interval between repeated dehorning to maximise profits will always exceed that which would be optimal for preventing poaching (Milner-Gulland et al., 1994). It also has the potential to add new demand and escalate rhino-poaching (Collins et al., 2020) or other means of rhino exploitation such as pseudo-conservation (Eloff & Lemieux, 2014), and in fact was passed with little evidence that there is any domestic demand for rhino horn in South Africa that would supplement the cost of rhino ownership (Jakins, 2018; Collins et al., 2020). Because of this, there is support for the reinstitution of the rhino horn trade moratorium in South Africa (Jakins, 2018; Collins et al., 2020) and a calling for the legalization of global trade which private rhino owners believe would benefit rhino owners, rhino conservation and reduce poaching (Rubino & Pienaar, 2020) by allowing sustainable export to and income from the primary source of demand in Asian markets (Wright et al., 2018; Taylor et al., 2017). This is however a controversial issue with a large concern over whether sustainable horn production in South Africa would satisfy the demand overseas and eliminate the incentive for poaching (Taylor et al., 2017), as well as the possible contradictions in economic and conservation interests (Crookes & Blignaute, 2015). Equally, it has potential drive down market prices enough that, with combined effective security and dehorning, the risk to poaching outweighs its benefits, thus reducing its frequency (Ferriera et al., 2014; Challender & MacMillan, 2015).
CONCLUSION
It is argued that the conservation of rhinos in South Africa, specifically the threat of poaching, is addressed by dehorning as a crisis field-based management tool and may be effective in the short term when implemented with sufficient security and law enforcement measures. However, solutions which approach the drivers of this threat, primarily the demand for rhino horn, are needed before reactive strategies become unviable in effectiveness and implementation in the long term (Ferreira et al., 2014; Challender & MacMillan, 2014). The legalization of global trade may shift the role of dehorning in South African rhino conservation; given that the literature currently suggests the success of dehorning relies on effective security and law enforcement to prevent poaching, this shift may give dehorning a more significant role than it currently has in rhino conservation. This role may shift the dynamics of demand and supply of rhino horn towards lower market prices and sustainable supply which supports conservation, and consequently outweighs the risk over benefit to the poaching activity which so greatly undermines rhino conservation in South Africa.
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