African rhinoceroses (rhinos) experienced a poaching onslaught since 2008 with the epicentre in South Africa where most of the world’s rhinos occur. South African national parks, under the management of South African National Parks (SANParks), are custodian to 49% of South Africa’s white and 31% of the country’s black rhinos. We collated information on rhino population sizes in seven national parks from 2011 to 2015. We include and report on rhino surveys in Kruger National Park during 2014 and 2015. South-western black rhinos increased over the study period, which allows SANParks to achieve its contribution to South Africa’s 2020 target of 260 individuals. South-central black rhinos declined over the study period because of poaching in the Kruger National Park, making it difficult for SANParks to realise a 9% increase per annum for its expected contribution to the South African target of 2800 individuals. For southern white rhinos, SANParks requires 5% annual growth for its contribution to the South African target of 20 400 individuals. To continue to evaluate the achievement of these targets, SANParks needs annual population estimates relying on total counts, mark-recapture techniques and block-based sample counts to track trends in rhino populations. SANParks’ primary challenge in achieving its contribution to South Africa’s rhino conservation targets is associated with curbing poaching in Kruger National Park.

Conservation implications: The status and trends of rhino species in SANParks highlight key challenges associated with achieving the national targets of South Africa. Conservation managers will need to improve the protection of southern white rhino, while the Department of Environmental Affairs need to be made aware of the challenges specifically associated with not achieving targets for south-central black rhino. Outcomes for south-western black rhino have already realised and the good conservation efforts should continue.

Introduction

Rhinoceroses (rhinos) are under threat worldwide. Of the African rhinos, the southern white rhino Ceratotherium simum simum is the most abundant (Amin et al. 2006a), with its total numbers exceeding that of a minimum viable population (Reed et al. 2003). In contrast, the African black rhino sub-species experienced severe declines with the eastern black rhino Diceros bicornis michaeli and south-western black rhino Diceros bicornis bicornis listed as critically endangered and the south-central black rhino Diceros bicornis minor listed as vulnerable (Amin et al. 2006a). The northern white rhino Ceretatherium simum cottoni is functionally extinct (Groves, Fernando & Robovský 2010) and the western black rhino Diceros bicornis longipes (Emslie 2011) recently went extinct (Travers, Waterland & Stroud 2011). Asian rhinos (greater one-horn rhino Rhinoceros unicornis; Javan rhino Rhinoceros sondaicus and Sumatran rhino Dicerorhinus sumatrensis) all survive only in small numbers, with the Sumatran and Javan rhinos each with less than 100 in the wild. There were 3557 greater one-horn rhino by the end of 2015 (Emslie et al. 2016).

By 2014, South Africa was home to approximately 90% of the global population of southern white rhinos, and 36% of the world’s black rhinos, consisting of south-western, south-central and a small extra-limital population of eastern black rhinos (Emslie et al. 2016). By then, the South African National Parks Board (SANParks) was custodian to roughly half of the white rhinos (49%) and 31% of the black rhinos within South Africa (Emslie et al. 2016). South African national parks are thus home to a substantial proportion of the world’s rhino and play a key role in ensuring their survival.

Rhino conservation efforts, including anti-poaching, range from maximising species protection to restoring ecosystem processes. For instance, African rhino conservation plans typically seek to maximise population growth (e.g. Amin et al. 2006b; Knight, Balfour & Emslie 2013; Milliken, Emslie & Talukdar 2009; Mills et al. 2006), induce meta-population dynamics (Knight et al. 2013) and maintain genetic integrity (Emslie & Brooks 1999; Karstens et al. 2011). Although the most serious threat to rhinos in Africa is poaching (Emslie 2013), intensified anti-poaching alone may not curb the poaching onslaught (Emslie 2013; Ferreira, Pfab & Knight 2014; Ferreira & Okita-Ouma 2012; Kagande & Musarurwa 2014) and broader socio-economic approaches are required (Haas & Ferreira 2016). Hence some plans incorporate social and economic objectives (Knight et al. 2015).

Several regional, national and international rhino conservation strategies and targets thus underpins SANParks’ rhino management. The Black Rhino Biodiversity Management Plan (Knight et al. 2013) aims for a South African black rhino population growth rate of 5% per annum, with 2800 south-central and 260 south-western black rhinos by the end of 2020. The White Rhino Biodiversity Management Plan (Knight et al. 2015) also aims for a white rhino population growth rate of 5% per annum, with 20 400 southern white rhinos by the end of 2020 in South Africa.

In addition to these rhino Biodiversity Management Plans (BMPs), South Africa’s cabinet adopted an integrated four-pronged approach to curb rhino poaching during 2014 (Department of Environmental Affairs 2014). These are: (1) compulsory interventions to protect rhinos by implementing widespread and intensive anti-poaching programmes as well as creating particular zones of management using technology and intelligence, (2) game-changing interventions, targeted simultaneously at disrupting organised crime and creating opportunities for more equitable benefit-sharing of ecosystem services with all South Africans, (3) long-term sustainability interventions to explore the development of a legal and sustainable rhino trade system and (4) biological management interventions that focus on strategic removals from areas of high poaching risk to create rhino strongholds elsewhere. Biological management historically served as the core of South Africa’s rhino conservation approach and successes (Knight et al. 2015).

As an identified implementing agency of the rhino BMPs, SANParks should contribute 22% (538–676) and 65% (169) of the individuals to the south-central and south-western black rhino targets for 2020, respectively, based on population estimates during 2014. For the southern white rhino, SANParks needs to contribute 49% (9854–10 232 individuals) of the 2020 targets.

As rhino conservation targets are set around rhino population sizes and growth rates, it is important to survey populations frequently to detect statistical changes. Estimates and trends allow for evaluating progress towards the targets, and assessing the effectiveness of current management interventions. Conservation authorities, however, face several challenges when counting and detecting trends in rhinos and other large animal population sizes. These relate to the feasibility of techniques at different population sizes and densities (Table 1), and sources of bias or error (e.g. Caughley 1974) linked to different methods and habitats. Optimal survey designs and intervals are thus context-specific, influencing the precision and accuracy of counts (e.g. Ferreira & Van Aarde 2009).

Although authorities recognise the effect of rhino poaching on southern white rhinos in Kruger National Park (Ferreira et al. 2015), there was no previous published attempt to quantify SANParks’ overall progress towards the national rhino conservation targets across the SANParks estate. Moreover, SANParks have not yet assessed whether the techniques employed to count rhinos are optimal at current population sizes or densities. This study therefore aims to collate all SANParks’ data on rhino population estimates for the period 2011–2015, across the range of methodologies employed to (1) evaluate the population status of southern white rhino, south-western and south-central black rhino populations in SANParks, (2) assess whether the techniques employed to count rhinos are optimal within park-specific contexts and (3) recommend optimal survey designs for the three sub-species in various National Parks. For south-central black and southern white rhinos in Kruger National Park we also derive estimates of recruitment rates (i.e. proportion of rhinos less than 1 year old reflect rhinos born and that survived the first year after birth) between two surveys and compare these to estimates of poaching rates. The results will allow us to evaluate SANParks’ progress in achieving South Africa’s rhino conservation targets and help inform management interventions.

Material and methods

Study populations, data collection and collation

The study populations include all rhinos in SANParks’ protected areas from 2011 to 2015 (Appendix 1). Seven National Parks contain rhinos in a single management unit. Addo Elephant National Park has rhinos in three separate sections, but for analytical purposes we consider these combined. Rhinos experience different features and management histories in the various National Parks (Appendix 1). We collated data from all rhino census surveys that took place in these Parks during our study period.

South-western black rhinos occur in four National Parks: Addo Elephant, Mountain Zebra, Karoo and Mokala National Parks. In the Kuzuko Section of Addo Elephant National Park, field ranger patrols and game guides record daily sightings of individually recognisable rhinos, through ear notch patterns (Greaver, Ferreira & Slotow 2014; Ngene et al. 2011). The Nyathi Section has low visibility in the mesic thicket vegetation and requires ground or camera-trap observations of individually marked rhinos. However, the presence of several un-notched rhinos that are not individually recognisable, challenges the maintenance of an up-to-date rhino register. Regular patrols, however, allow rangers to identify individuals by sex and age occurring in a specific area. Rangers monitor rhinos in the Colchester-Main Camp Section through individual observation from the ground or using aerial surveys. The populations of black rhino in Karoo, Mountain Zebra and Mokala National Parks are small enough to maintain a register of all individuals through observations of individually notched rhinos. We collated data on south-western black rhino from SANParks records (SANParks Unpublished data¹) for Addo Elephant, Mountain Zebra, Karoo and Mokala National Park annually from 2011 to 2015.

South-central black rhinos occur in two National Parks: Marakele and Kruger National Parks. We extracted data for 2015 for Marakele from Ferreira and Greaver (2016). This study made use of a mark-recapture approach to estimate population size.

For Kruger National Park, we collated south-central black rhino data from Ferreira, Greaver and Knight (2011) as well as Ferreira et al. (2015). These publications provided estimates with 95% confidence intervals for 2009 and 2013, respectively. To obtain estimates for 2011 and 2012, we used Monte-Carlo simulation techniques (Fishman 1995) to randomly draw from the probability distributions of the estimates collated for 2009 and 2013, and calculated an annual exponential growth rate (Caughley 1977).

Our study also made use of surveys targeting the southern parts of Kruger National Park during September 2014 and 2015 using block count techniques (Ferreira et al. 2011, 2015). The technique focused on surveying 470 and 487 randomly placed blocks 3 km × 3 km in size during 2014 and 2015, respectively. Surveyors systematically completed transects comprising a 200 m observation strip on each side of a helicopter within each block with flights 45 m above ground at 65 knots. The survey team comprised a pilot, a data recorder and two observers. Using the block count data with an estimator (Jolly 1969) during 2014 and 2015 allowed landscape-specific estimates and overall estimates for Kruger National Park after accounting for the following biases: availability bias came from relationships between vegetation cover and rhino visibility (Ferreira et al. 2015), and observer bias came from estimates made during a previous survey (Ferreira et al. 2011). Detectability bias was minimal as the size of observation strips was narrower than it was in previous studies when detectability was noted as negligible (Kruger, Reilly & Whyte 2008).

Using the observed age distribution and sex ratios, we could derive recruitment rates for Kruger National Park between the surveys of 2013 and 2014, as well as 2014 and 2015. This allowed us to compare the number of rhinos recruited through birth and first year survival in the total black rhino population with the number of rhinos poached between the two surveys. We thus collated poaching data in Kruger National Park for those periods (SANParks Unpublished records²).

Southern white rhinos occur in four National Parks – Kruger, Marakele, Mapungubwe and Mokala National Parks. We collated all southern white rhino observation data for these parks from 2011 to 2015.³ Annual and bi-annual helicopter surveys flying at a height of 50 m at a speed of 50–60 knots used 200 m wide transects to systematically cover a Park. This provided total counts of southern white rhinos at Mokala National Park and Marakele National Parks, respectively. Southern white rhinos in Kruger National Park also occur mostly south of the Olifants River. We collated estimates for 2011, 2012 and 2013 (Ferreira et al. 2012, 2015). During September 2014 and September 2015 we made use of the same survey and analytical approaches as used for south-central black rhinos in Kruger National Park. Rangers have a full record of every individual in Mapungubwe National Park based on regular observations.

Analysis of trends in population estimates and growth rates

We calculated sub-species-specific exponential growth rates for each park using an exponential model (Caughley 1977). For parks and species that included sample-based estimates with associated 95% confidence intervals in any particular year we made use of Monte Carlo simulations (Fishman 1995) to define exponential population growth rates and their associated 95% confidence intervals. For each year when a sample-based estimate was available, we extracted a value of the population size from the probability distribution defined by the estimate and its 95% confidence interval of that specific population estimate, and calculated exponential growth. We repeated this process 100 000 times and calculated the median, as well as 2.5% and 97.5% percentiles as a definition of the 95% confidence interval. If the confidence intervals of exponential growth rates excluded zero, we concluded that a population is changing. This allowed us to identify the National Parks that play an important role in SANParks’ ability to achieve contributions to national rhino objectives.

In order to evaluate SANParks’ requirements to meet national targets by 2020, we calculated the annual rhino population growth rate required for each sub-species to reach the stipulated targets, given the population status during 2015 (see the ‘Results’ section). These evaluations allowed us to assess whether authorities require revised conservation interventions.

Determining optimal survey requirements

Surveying populations living at low densities present similar statistical challenges as surveying populations with few individuals. We generated a two-way matrix that describes the population sizes and densities of all rhino species in SANParks (Table 2). For ease of classification we defined population density categories on exponential scales. This allowed us to place a population in the smallest category based on size or density and identify the most suitable techniques given the category (Table 3).

As the survey techniques employed to estimate south-central black and southern white rhinos had estimates of confidence intervals, and thus precision (i.e. the likely spread of estimates given the uncertainties introduced by biases such as availability, observer and detectability biases, see Caughley 1974 and Thompson 1992), these values allowed us to define optimal monitoring intervals directed at detecting required population growth. We used the required growth rates to achieve targets along with recorded confidence intervals to define optimal survey requirements using power analyses to detect trends (Gerrodette 1987). When designing optimal survey requirements, authorities need to trade-off the magnitude of change to detect, survey intervals, the number of surveys required and the total change by the time a trend is detected. This results in authorities deciding how many surveys and intervals are needed to obtain reliable data for detecting trends.

Results

Contribution of various subpopulations to rhino population size targets

Addo Elephant National Park makes the largest contribution towards south-western black rhino populations, with the combined numbers in Kuzuko, Nyathi and Colchester-Main Camp Sections comprising a minimum of 120 individuals (Table 4). Over half of the south-central black rhinos within SANParks occur in Kruger National Park (Table 4). Between the 2013 and 2014 surveys, the number of south-central black rhinos born that survived the first year in Kruger National Park was similar to the number of rhinos poached (Table 5). More south-central black rhinos were poached between the 2014 and 2015 surveys than what were born and survived the first year.

The block count of southern white rhinos in Kruger National Park produced an estimate of 8821 (95% CI: 8335–9307) south of the Olifants River during 2015. This figure increased to a total of 8875 (95% CI: 8365–9337) after including field ranger observations north of the Olifants River (Table 5). Elsewhere, an additional 252 individuals occur in Mapungubwe, Mokala and Marakele National Parks combined. More southern white rhinos were born and survived the first year than what were poached between the 2013 and 2014 surveys (Table 5). Between the 2014 and 2015 surveys, the number of rhinos born and surviving the first year were similar to that poached. This result confirms that, despite significant numbers of southern white rhino poached, Kruger National Park remains the most important contributor towards the conservation of wild free-ranging individuals of this species within its natural range in South Africa.

Contemporary trends and requirements to meet conservation targets

South-western black rhinos increased at a rate of 0.17 (95% CI: 0.10–0.25) per annum from 2011 to 2015, based on annual exponential growth calculated using observed total population estimates. During 2015, SANParks was already contributing 166 individuals of the 169 that SANParks must contribute to the 260 south-central black rhino required by 2020. If SANParks maintain trends noted from 2011 to 2015, 388 (95% CI: 186–810) south-western black rhinos will reside in South African National Parks by 2020. The SANParks target is achievable assuming that the current constraints on SANParks south-western black rhinos do not change substantially.

SANParks’ south-central black rhinos declined overall at an annual exponential rate of −0.11 (95% CI: −0.03 to −0.18). In Kruger National Park from 2011 to 2015 there was an exponential decline of −0.15 (95% CI: −0.05 to −0.25), largely as a result of rhino poaching, which overrode the exponential annual rate of 0.48 (95% CI: 0.26–0.69), because of management introductions, at Marakele National Park. If SANParks is to contribute 538–676 individuals to meet the South African target of 2800 south-central black rhinos by 2020, this will require SANParks’ south-central black rhinos to reach an annual exponential growth rate of 0.09 (95% CI: 0.02–0.18) from 2016 to 2020.

Southern white rhino populations occurring in the parks outside of Kruger National Park increased at a rate of 0.14 (95% CI: 0.10–0.19), partly because of introductions from Kruger. However, these populations contributed only 3% to the total number of southern white rhinos occurring in South African National Parks (Table 4). Within Kruger National Park, southern white rhinos may be declining at an exponential rate of −0.05 (95% CI: 0.01 to −0.09) from 2011 to 2015, because of rhino poaching. As a result, SANParks’ southern white rhinos exhibited at best a fluctuating population overall. If SANParks is to contribute the required 9854–10 232 individuals to the 20 400 target of southern white rhinos in South Africa, their populations will need to increase at an annual exponential rate of 0.03 (95% CI: 0.01–0.05) from 2016 to 2020. This is unlikely if the current rates of poaching are sustained.

Optimal survey intervals and requirements

Survey methods for south-western black rhinos (Table 4) do not allow for estimates of confidence intervals and hence do not allow definition of optimal surveys through trade-offs (Gerrodette 1987). Consequently, south-western black rhino numbers require estimation on an annual basis making use of total counts as before and mark-recapture techniques in future using ear-notching (Greaver et al. 2014; Ngene et al. 2011) and or genetic marking (Brook et al. 2012).

In contrast, estimates for SANParks’ south-central black rhinos made it possible to generate coefficients of variance (8% during the study period) with which optimal survey intervals could be calculated. Two surveys between 1 and 4 years apart are needed to detect the required annual increase from 2016 to 2020. At this survey interval, there is a trade-off with the total amount of change detected at the time of the second survey’s completion. If declining trends continue as at present, a total reduction of 11% south-central black rhinos will be detected during two surveys 1 year apart. In contrast, a total reduction of 44.2% individuals will be detected with surveys every 4 years (e.g. 2016–2020). Optimal survey intervals for south-central black rhinos should also be annual. Techniques should focus on block counts and mark-recapture estimates in Kruger National Park and mark-recapture approaches elsewhere.

Estimates of southern white rhinos living in South African national parks had a coefficient of variance of 5% at the end of 2015. To detect an annual decline of −0.05 as well as the required annual exponential increase of 0.05 from 2016 to 2020, SANParks can estimate southern white rhinos twice with surveys 1–4 years apart. The total change after 1 year, if potential declining trends realise (i.e. 5% decline in numbers), carries less risk than the total change after 4 years (i.e. 22.6% decline in numbers). Southern white rhinos thus also require annual estimates. Techniques should focus on block counts in Kruger National Park and total counts elsewhere.

Discussion

SANParks play a key role in the conservation of three sub-species of rhino within free-ranging conditions in South Africa. For south-central black rhinos and southern white rhinos, however, contemporary trends predict that SANParks will not be able to meet contributions to South Africa’s rhino population targets if observed annual population growth rates remain the same.

Encouraging is the significant increases noted for south-western black rhinos living in Addo Elephant, Mountain Zebra, Karoo and Mokala National Parks. The observed annual growth exceeds the physiological capability of south-western black rhinos – having their first calf at 5–11 years of age, and at best, a calf every 2 years thereafter (Hitchins & Anderson 1983). The high observed annual growth can result from small population effects on accuracy and precision of population estimates (Gerrodette 1987), accentuating estimated vital rates (Akςakaya 2002). High population growth can also result from conservation husbandry seeking to maximise population growth, including skewing sex ratios (Holand et al. 2003) and moving rhinos to maximise the social requirements of individuals (Reid et al. 2007). Over the past 5 years, SANParks moved three south-western black rhinos between four National Parks, placed five under custodianship and introduced an additional seven individuals from elsewhere into National Parks. The overall growth comes from having a female sex skew resulting from the initial introductions and high female calving rate in the initial years after introduction.

The trends noted for the numbers of south-central black rhinos in Marakele and Kruger National Parks significantly contrasts numbers noted for south-western black rhinos. Overall, south-central black rhinos occurring in South African National Parks declined from 2011 to 2015. Even so, the numbers of south-central black rhinos in Marakele National Park increased significantly over a 5-year period. Similar factors influence this trend as for the south-western black rhino population. Importantly the introduction of a robust mark-recapture estimate during 2015 (Ferreira & Greaver 2016) compared to the records on individual rhinos used for the previous year’s may also contribute. Even so, the 2015 survey highlights that Marakele National Park performs well (Ferreira & Greaver 2016). The trends in numbers of south-central black rhinos in Kruger National Park dominate in South African National Parks. At Kruger, south-central black rhino numbers declined significantly over a 5-year period.

Southern white rhinos occurring in South African National Parks followed similar trends to south-central black rhinos where combined numbers, in the three small populations, in Mokala, Marakele and Mapungubwe National Parks increased from 2011 to 2015. In Kruger National Park confidence intervals of estimates from 2011 to 2015 overlapped, but point estimates suggest 1% increase to a potential 9% decline. Kruger National Park is thus a key park that influence SANParks’ ability to contribute to South Africa’s rhino conservation objectives by 2020.

Many of these patterns across South African National Parks result from disruptive effects of poaching on rhinos, particularly in Kruger National Park (Ferreira et al. 2015). From 2011 to 2015, poachers killed one rhino in Mapungubwe, five in Marakele and a staggering 2936 in Kruger National Park (SANParks Unpublished data⁴). A key question is: what would have been the rhino losses if SANParks had not implemented an integrated approach through the rhino protection in the smaller parks, anti-poaching in Kruger National Park and biological management across South African national parks? Nonetheless, curbing rhino poaching in Kruger National Park remains the highest priority for SANParks’ contribution to South Africa’s rhino initiatives.

The status of rhinos in South African national parks at the end of 2015 provides guidelines for requirements to achieve the 2020 targets. That in itself is challenging. Contemporary trends in south-western black rhinos suggest the 2020 contribution will easily be met by SANParks if conditions prevail. Sustaining the contemporary trends is unlikely as annual growth rates recorded are higher than what optimal survival and fecundity schedules predicts for closed populations (Rachlow & Berger 1998). SANParks can enhance population performances through conservation husbandry in Addo Elephant, Mountain Zebra, Karoo and Mokala National Parks that seeks to skew sex ratios in favour of adult cows and introducing more young adult cows. Removals of existing rhinos to skew sex ratios should focus on sub-adult males.

Even so, biological management interventions require more land – removed sub-adult males need localities to contribute to creating new populations; however, south-western black rhinos notoriously have density-dependent social constraints that impose on interventions such as translocations (SANParks Unpublished data⁵). Several other South African national parks, such as Tankwa Karoo, Namaqua, Richtersveld, Kalahari, Augrabies and Cambedoo National Parks that may have suitable habitat within the historical distribution of south-western black rhinos (Skead 1980) provide additional options, but currently do not have security measures in place or do not have adequate fencing. A further challenge is to source young adult cows. By 2014, Namibia was the stronghold for south-western black rhinos (AfRSG Unpublished data⁶). The rise in poaching incidents in Namibia (AfRSG Unpublished data⁷) reduces the likelihood of sourcing south-western black rhinos from there. An encouraging prospect is that SANParks’ conservation husbandry approach from 2011 to 2015 resulted in an inflated increase in south-western black rhino numbers within South African national parks.

South-central black rhinos require a 9% increase in numbers per annum to reach the SANParks contribution to South Africa’s 2020 target. This exceeds the maximum growth predicted by best survival, the ages at which cows have their first calves (Hitchins & Anderson 1983) and how often thereafter (Ferreira et al. 2011; Hitchins & Anderson 1983). In addition, SANParks only have two parks where south-central black rhinos occur within their natural distribution. Conservation husbandry and expanding Marakele National Park (Ferreira & Greaver 2016) should continue, but these practices were not enough to compensate for the losses experienced in Kruger National Park from 2011 to 2015. The poaching onslaught in Kruger National Park is the most significant threat to SANParks’ ability to achieve its south-central black rhino target by 2020.

The 5% annual increase required for southern white rhino populations is biologically realistic. In fact, the age at which a cow has her first calf, along with birth intervals and survival rates (Owen-Smith 1988) predict >5% potential annual growth rates. For instance, southern white rhinos realised 9% annual growth in Kruger National Park prior to the poaching onslaught that began in 2008 (Ferreira & Okita-Ouma 2012).

SANParks should continue to implement rhino protection in small parks, anti-poaching in Kruger National Park and biological management across all of its national parks. Implementation has borne some results – in the 18 months before the end of 2015, only one rhino was confirmed poached in the small parks (SANParks Unpublished data⁸). The number of confirmed rhinos poached in Kruger National Park was one less during 2015 (826) compared to 2014 (827) (SANParks Unpublished data¹¹). This contrasts the pattern from 2008 to 2014 when there was a 32% annual increase in the number of rhinos poached (SANParks Unpublished data¹¹). SANParks anticipate that the full implementation of zone-, technology- and intelligence-driven anti-poaching in Kruger National Park will provide improved control of poaching within the park. If complimented with game-changing interventions, including disrupting organised crime (Haas & Ferreira 2015) and empowering people (Lunstrum 2013) outside the park, authorities can curb rhino poaching. Several ongoing national and international collaborations, as well as new initiatives could aid in ensuring the long-term persistence of rhinos in Kruger National Park.

The results of our analysis suggest three key directives for conserving south-central black rhinos: (1) the existing conservation targets require revision of the 5% annual increase requirements in the Black Rhino Biodiversity Management Plan (Knight et al. 2013). Given the effect of poaching (Ferreira et al. 2015), the targeted numbers of SANParks’ contribution will require higher annual growth rates, (2) taking control and curbing the effect of poaching on south-central black rhinos in Kruger National Park requires urgent interventions including a prioritised security response using interdiction patrol and hot pursuit tactics (Haas & Ferreira 2017; Park et al. 2016) informed by predictions of spatial distribution of rhinos (Rachlow, Kie & Berger 1999) extracted from intensive biological monitoring programmes and (3) we recommend that land for use by south-central black rhinos be increased. The northern part of Kruger National Park provides an ideal opportunity for expansion. Although south-central black rhinos mostly occur in southern Kruger at present, rangers noted several cases of south-central black rhinos previously using landscapes in northern Kruger (Ferreira et al. 2011). Expansion into the area can only be considered if authorities adequately address the internal and external factors driving rhino poaching in the park.

Conclusion

The trends of two of the three sub-species of rhinos in national parks are of key concern. Poaching, specifically in Kruger National Park, has disrupted the ability of SANParks to achieve its contribution to South Africa’s rhino conservation targets for 2020. Achieving targets is feasible for south-western black rhinos, less so for southern white rhinos, and most challenging for south-central black rhinos. This requires SANParks to continue to implement compulsory anti-poaching and innovative biological management interventions in Kruger National Park. For monitoring, it is critical that SANParks undertakes annual assessments of rhino population status in order to detect trends in population growth. For south-western black rhinos, registration studies that make use of a variety of individual recognition techniques including ear notching and genetic markers obtained through direct, indirect and technology-based observations provide for SANParks needs. South-central black rhinos require mark-recapture and aerial sample-based approaches, while southern white rhinos need aerial total counts and sample-based approaches. Ensuring funding to undertake the surveys, as well as capacity to perform the analysis, needs emphasis. The lessons learnt from this study are similarly applicable to surveys of large mammalian herbivores, particularly those undergoing either rapid increases or declines.

Acknowledgements

We are grateful for the assistance provided during the Kruger National Park surveys. We would like to thank observers Ben Wigley, Scott Ronaldson, Steven Khosa, Marius Renke, Etienne le Roux, Adolf Manganyi, Corli Wigley, Pauli Viljoen, Isaac Sibiya, Izak Smit and Elana Mol. We also thank pilots John Bassi, Grant Knight, Charles Thompson, Jaco Mol and Brad Grafton. We appreciate the support from SANParks senior management for census requirements during resource restricted times.

The authors declare that they have no financial or personal relationships that may have inappropriately influenced them in writing this article.

S.M.F. was responsible for study conceptualisation, analyses, report writing and editing. C.B., A.G. and C.G. were responsible for data collection and contributed to study design, report writing and editing. C.R.C., J.H., M.H., L.M-v.d.V. and D.Z. contributed to report writing and editing.

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Original Research

The status of rhinoceroses in South African National Parks

Sam M. Ferreira, Charlene Bissett, Carly R. Cowell, Angela Gaylard, Cathy Greaver, Jessica Hayes, Markus Hofmeyr, Lizette Moolman-van der Vyver, David Zimmermann

Abstract

Introduction

Material and methods

Study populations, data collection and collation

Analysis of trends in population estimates and growth rates

Determining optimal survey requirements

Results

Contribution of various subpopulations to rhino population size targets

Contemporary trends and requirements to meet conservation targets

Optimal survey intervals and requirements

Discussion

Conclusion

Acknowledgements

Competing interests

Authors’ contributions

References

Appendix 1

Footnotes