RJ09037 43..54

Evaluation of the impacts of feral camels

G. P. EdwardsA,C, B. ZengA, W. K. SaalfeldA and P. Vaarzon-MorelB

ADepartment of Natural Resources, Environment, the Arts and Sport, PO Box 1120,Alice Springs, NT 0871, Australia.

BConsulting Anthropologist, Desert Knowledge Cooperative Research Centre, PO Box 3971,Alice Springs, NT 0871, Australia.

CCorresponding author. Email: [email protected]

Abstract. Feral camels have significant negative impacts on the environment and the social/cultural values of Aboriginalpeople. These impacts include damage to vegetation through feeding behaviour and trampling; suppression of recruitmentin some plant species; damage to wetlands through fouling, trampling, and sedimentation; competition with nativeanimals for food, water and shelter; damage to sites such as waterholes, that have cultural significance to Aboriginalpeople; destruction of bushfood resources; reduction in Aboriginal people’s enjoyment of natural areas; creation ofdangerous driving conditions; damage to people and vehicles due to collisions, and being a general nuisance in remotesettlements. Negative economic impacts of feral camels mainly include direct control and management costs, impacts onlivestock production through camels competing with stock for food and other resources and damage to production-relatedinfrastructure. The annual net impact cost of feral camels was estimated to be –$10.67million for those elements thatcould be evaluated according to market values. We established a positive density/damage relationship for camels andinfrastructure on pastoral properties, which is likely to hold true for environmental variables and cultural/social variablesas well. Therefore, irrespective of climate change, the magnitude of the negative impacts of feral camels will undoubtedlyincrease if the population is allowed to continue to increase. Furthermore, the likelihood that camels would beepidemiologically involved in the spread of exotic diseases like bluetongue and surra (were there to be outbreaks of thesediseases in Australia) is also very likely to increase with population density. On the basis of our present understanding, werecommend that feral camels be managed to a long-term target density of 0.1–0.2 camels/km2 at property to regionalscales (areas in the order of 10 000–100 000 km2) in order to mitigate broad-scale negative impacts on the environmental,social/cultural and production assets of the Australian rangelands.

Introduction

Over the last 15 or so years, there has been a paradigm shift inthe area of vertebrate pest control. The shift has been from animalcontrol to controlling animal damage (Hone 2007). This shiftrecognises the fact that pest abundance by itself is not actuallythe problem; rather, the problem is the harmful impacts of thepest (Hone 2007). Accordingly, the aim of vertebrate pest controlshould be to mitigate the damaging impacts of pests rather thancontrolling the pests themselves (AustralianPestAnimal Strategy2007; Hone 2007). Invariably there is a positive relationshipbetween pest abundance and degree of impact, so damagemitigation involves reducing pest abundance (Hone 2007). Otherfactors that can affect the extent of pest damage include theavailability of the resource that is being damaged (the more ofthe resource that is available, the greater the level of impactin absolute terms) (analogous to a functional responserelationship – see Hone 2007), variation in landscape featuresthat can lead to spatial heterogeneity in damage levels, andtime of year (Braysher 1993; Hone 2007). Often there exists athreshold pest density below which damage is non-existent,negligible, or tolerable. The presence of a threshold means that

not all pests have to be removed in order to mitigate damage(Hone 2007).

In Australia, the harmful or negative impacts of pest animalsare typically classified into three categories: economic,environmental, and social/cultural (McLeod 2004; Hart andBomford 2006; Australian Pest Animal Strategy 2007). This isconsistent with the requirement of governments and businessesto be accountable for performance in these areas and theassociated need for triple-bottom-line reporting (McLeod 2004).Typically, the economic impact of pest animals refers to theeconomic value of reduced production and research andmanagement costs associated with the pest (McLeod 2004).However, some positive impacts may flow from the value ofgoods or services produced by or from the pest (e.g. meat, hides,etc.). Harmful environmental impacts of pest animals includereduction in water quality, emissions, land degradation andreduction in biodiversity (McLeod2004).Harmful social/culturalimpacts are perhaps the most difficult to define and quantify andinclude a reduction in employment prospects within rural andregional areas, impacts on human health, traffic accidents,damage to personal and service infrastructure and to the values

� Australian Rangeland Society 2010 10.1071/RJ09037 1036-9872/10/010043

CSIRO PUBLISHING

www.publish.csiro.au/journals/trj The Rangeland Journal, 2010, 32, 43–54

of Aboriginal Australians (McLeod 2004; Hart and Bomford2006).

The monetary worth of the economic impacts caused by pestanimals can usually be estimated quite easily using marketvalues, which allows for simple economic analyses (Hone 2007).In contrast, environmental and social/cultural impacts usuallyoccur outside the market system so their monetary worth cannotbe easily quantified in monetary terms (Braysher 1993; McLeod2004). In 2004, the Pest Animal Control Cooperative ResearchCentre estimated the total cost of pest animal damage in Australiato be $720million annually for control-related costs, productionlosses, and the environmental impacts of some species (McLeod2004). This figure is considered to be at the lower end of thescale (Hart and Bomford 2006). Although the negative impactsof feral camelswere considered byMcLeod (2004), the estimatedtotal cost of the damage ($200 000 per annum for economicimpact alone) is considered an unreliable figure because therewas at that time a paucity of robust data on camel impacts.

Here we assess both the damaging (negative) impacts of feralcamels along with their realised and potential benefits (positiveimpacts).

Methods

The following non-experimental techniques were used to assessthe positive and negative impacts of feral camels:(1) Analysis of statistical information held by government

agencies,(2) Formal interviews with scientific experts, key contacts and

informants, and(3) Review of published literature and reports.

Where data on the monetary worth of impacts were available,we scaled up damage/benefit information from particular sites toassess the overall scope of the problem across the entire range offeral camels. The approaches used in particular situations aredetailed in the relevant sections below.Weconducted a simple netimpact analysis on the available impact data which were costedin monetary terms.

We evaluated the density/damage relationship for feralcamels using the monetary value of infrastructure damagereported by Zeng and Edwards (2010, this issue) for pastorallandholders over the 2-year period (July 2005–June 2007).Although some of the pastoralists surveyed by Zeng andEdwards (2010, this issue) also provided estimates of lostproduction due to camels, we did not use these data for thisanalysis because they are largely perceived impacts – the natureand extent of resource-based competition between livestock andcamels is yet to be ascertained. In contrast, assessments ofinfrastructure damage are typically based on observed impacts(e.g. broken fences, damaged yards, etc.).

For each pastoral property that estimated the monetary valueof infrastructure damage, we assigned a camel density value onthe basis of the density distribution model in Saalfeld andEdwards (2010, this issue).Weused theSTATISTIX7.0 softwarepackage (Analytical Software, Tallahassee, FL, USA) to performANOVA and we corrected for property size in undertaking thisanalysis.

Results

Negative impacts of feral camels

Economic

Direct control and management costs. Direct control andmanagement refers to the activities and actions directed atmitigating the negative impacts of feral camels including on-ground control actions, camel control-related research, andplanning and extension activities.

From 1997 to 2008, on the basis of statistical informationheld by government agencies, the total operational investmentin direct control and management of camels by governmentagencies and research organisations was $4.37million (Fig. 1).Note that the figures in Fig. 1 do not include the resourcesinvested in camel management by pastoral or conservationlandholders or the in-kind contribution of government agencies,research organisations, camel-related industries, or individuals.

257 758

345 367

245 527

313 493

234 466244 545

230 000

336 471

598 978

890 610

668 552

0

200 000

400 000

600 000

800 000

1 000 000

1997

/199

8

1998

/199

9

1999

/200

0

2000

/200

1

2001

/200

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2002

/200

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2003

/200

4

2004

/200

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2005

/200

6

2006

/200

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2007

/200

8

Inpu

t am

ount

($)

Fig. 1. Operational input to camel management by government and research organisations overthe period 1997–2008, exclusive of in-kind support.

44 The Rangeland Journal G. P. Edwards et al.

Since 2004–05, the annual amount of money invested in camelmanagement by government agencies and research organisationshas approximately doubled.

The Northern Territory (NT) government currentlycontributes about $0.1million annually in in-kind assistance tothe management of feral camels through support of research andoperational personnel (e.g. qualified aerial shooters) involved in‘on-ground’ management (Glenn Edwards, unpubl.). Assumingthat the other two states with large camel populations [WesternAustralia (WA) and South Australia (SA), see Saalfeld andEdwards 2010, this issue] contribute the same amount of in-kindassistance, the total amount of in-kind is estimated to be$0.3million annually.

A breakdown by activity of the annual amount of moneyinvested by both government (and research organisations) andpastoral and conservation landholders in the management offeral camels over the 2-year period July 2005–June 2007(see Zeng and Edwards 2010, this issue) indicated that pastorallandholders contributed ~59%, conservation landholders ~5%and governments and research organisations ~36% of the totalamount invested (Table 1).

Damage to pastoral infrastructure. In a survey of pastorallandholders within the camel range (Zeng and Edwards 2010,this issue), 74.2% of landholders reported that camels had beenfound on their properties and 70.3% of landholders with camelsclaimed that camels caused some damage on their propertiesover the past 2 years. Figure 2 illustrates the kind of damage thatcamels can inflict on pastoral infrastructure. On the basis of theper square kilometre estimate of damage for surveyed properties,the value of infrastructure damage was estimated to be$2.40million annually across all pastoral properties within or onthe margins of the camel range (i.e. damage to fences, yards, andwater equipment) (Zeng and Edwards 2010, this issue).

The ‘dog fence’ was built to protect the sheep industry fromwild dog damage. The fence is 5614 km long, extending fromJimbour in Queensland (Qld) to the Great Australian Bight(see Saalfeld and Edwards 2008). Increasingly, feral camels aredamaging the dog fence, particularly along the southern sections.It is estimated that feral camels cause at least $43 361 damage tothe fence each year in SA alone (Michael Balharry, ExecutiveOfficer, Dog Fence Board, SA).

Lost pastoral production. About 32% of pastoral landholderssurveyed by Zeng and Edwards (2010, this issue) indicated thatcamels had a negative impact on pastoral production throughcompetition with cattle for food and water, disturbing cattle, and

damaging fences thereby allowing cattle to escape. The valueof production loss was estimated to be $3.42million annuallyacross all pastoral properties (see Zeng and Edwards 2010, thisissue).

Effects on bush food production. A small-scale commercialindustry in bush food production based on wild-harvest byAboriginal people has been in operation in central Australia forseveral decades. Between 2000 and 2005, ~30 species weretraded for food and/or landscape rehabilitation (Walsh andDouglas 2009). Harvesters sold an average of 7.5 t of seed andfruit products each year from2000 to 2004with awholesale valueof ~$90 000 per annum. The main species traded were bushtomato (Solanum centrale) fruit, mulga (Acacia aneura) anddogwood (Acacia coriacea subsp. sericophylla) seed (Walsh andDouglas 2009). In terms of the regional economy of centralAustralia, the wild-harvest bush foods industry is small and theeconomic impact of camels on the industry relatively minor.The three main commercial species are considered relativelycommon and at low risk of local extinction or damage as a resultof camel browsing (Table 2). Nevertheless, camels do affect theefficiency of seed collection by damaging seed or fruit-bearingtrees and because people collecting seed avoid areas with camelsdue to concerns over their personal safety (Walsh 2009; Vaarzon-Morel 2010, this issue). This reduces economic opportunitiesfor the development of bush produce enterprises (Fiona Walsh,CSIRO, pers. comm.).

Environmental

Damage to vegetation. The diet of feral camels is discussed inSaalfeld and Edwards (2008). Camels have a broad diet, andalthough they are considered to be browsers, they have beenobserved to feed on most of the available plant species in areaswhere the diet has been examined, including pasture species(Dörges and Heucke 2003; Peeters et al. 2005). Camels aregenerally very flexible with food selection, particularly in timesof drought, but show distinctive preferences for certain plantspecies. During dry times camels mainly consume leaves fromtrees, whereas in wet periods they favour ground vegetation(Dörges and Heucke 2003). Camels damage trees and shrubswhen browsing and can severely defoliate preferred trees,shrubs, and vines (Copley et al. 2003; Dörges and Heucke 2003;Vaarzon-Morel 2010, this issue). They also inhibit recruitment oftheir preferred food species by suppressing flowering and fruitproduction and by browsing and killing juvenile plants (Dörgesand Heucke 2003). It is considered that camels have the ability

Table 1. Annual amount of money invested by both government (and research organisations) and pastoral and conservation landholders(excluding in-kind contributions) in the management of feral camels averaged over the period July 2005–June 2007

Survey/monitoring

($)

Research: camelmanagement

($)

Research:industry

($)

Inputs forcommercialuse ($)

Culling($)

Other actions($)

Total($)

%

Pastoral landholdersA 0 0 0 288 956 525 735 400 142 1 214 833 59.1Conservation landholdersB – – – – – – 96 729 4.7Government, research

organisations127 500 319 975 84 350 101 818 69 651 41 500 744 794 36.2

Total 127 500 319 975 84 350 390 774 595 386 441 642 2 056 356 100

ACalculated from survey data reported in Zeng and Edwards (2008a), tables 3.11, 3.16.BCalculated from survey data reported in Zeng and Edwards (2008b) tables 4.9, 4.14.

Impacts of feral camel The Rangeland Journal 45

to cause the local extinction of highly preferred specieslike the quandong (Santalum acuminatum), plumbush(S. lanceolatum), curly pod wattle (Acacia sessiliceps), nativeapricot (Pittosporum augustifolium), bean tree (Erythrinavespertilio), and Lawrencia species (Phillips et al. 2001; Dörgesand Heucke 2003). A list of the plant species eaten by camelsin central Australia with an assessment of their perceivedvulnerability to damage as a result of camel browsing isshown in Table 2. Figure 3 shows the type of impact that feralcamels have on quandong and other preferred woody vegetation.In 2008, Peter Latz (Ecological Consultant, Alice Springs,pers. comm.) noted that both quandong and native apricothad declined dramatically in the Petermann Ranges south-west of Alice Springs compared with the situation in the 1970s(see also Vintner and Collins 2008). Latz attributed thisdecline to a combination of inappropriate fire regime and camelbrowsing. Latz also noted severe damage to desert poplar(Codonocarpus cotinifolius) by camels (see also Vintner andCollins 2008).

In central Australia, serious and widespread negative impactson vegetation have been recordedwhere camels occur at densitiesof >2 animals/km2 (Dörges and Heucke 2003), and in more aridcountry near Lake Eyre, like impacts have been recorded wherecamels occur at densities of >1 animals/km2 (Phil Gee, RuralSolutions SA, pers. comm.).However damage to highly palatablespecies occurs at much lower camel densities. According to

Dörges and Heucke (2003), the long-term survival ofenvironmentally and culturally important tree species likequandong, curly pod wattle, and bean tree is compromised evenat ‘low’ densities of camels. Although Dörges and Heucke(2003) did not provide a definition for ‘low’ density of camels,they did recommend that, in order to protect the vegetationresource in managed situations, densities of camels during drytimes should not exceed 0.5 camels/km2 in woodland/shrublandhabitats and 0.3 camels/km2 in sand plain or sand dune habitats.Even in such situations, Dörges and Heucke (2003)recommended fencing off stands of highly preferred species inorder to protect them.

Damage to wetlands. There are many different types of aridwetlands: salt lakes; saline swamps; saline channels; freshwaterclay pans; open freshwater lakes; wooded swamps; shrubbyswamps; herbaceous swamps; permanent and long-lastingwaterholes and rock holes; springs; ephemeral rivers andwaterholes on large ephemeral rivers (see Duguid et al. 2005 fordefinitions). Although wetlands form a relatively smallproportion of the arid landscape, they are of high biologicalimportance (Duguid et al. 2005). Wetlands support a diverse anddistinctive range of plants and animals,manyofwhich are local orregional endemics; are important for a range of migratory birds,many of which are listed under international treaties; serve asrefugia and as source populations for aquatic animals (e.g. fish,frogs) and moisture-dependent plants (e.g. ferns), and serve asrefugia for many terrestrial animal species during drought(e.g. bats) (Duguid et al. 2005; Box et al. 2008). The largerwetlands and wetland aggregations that occur within the currentrange of the feral camel are shown in appendix 11.12 in Saalfeldet al. (2008).

The need for water coupled with the need to consume salt(Wilson 1984), which occurs naturally in vegetation fringingsaline wetlands, means that camels frequent wetland habitatsacross arid Australia (Dörges and Heucke 2003). In theseareas, the negative impacts of feral camels can be significant.Camels can drink all of the water in small waterholes, rockholes, or soaks leaving little or no water for native wildlife orpeople (Copley et al. 2003; Brim Box et al. 2010, this issue;Vaarzon-Morel 2010, this issue; Fiona Walsh 2008, CSIRO,pers. comm.). Camels also fall into rock holes and get boggedin soaks where they subsequently die causing pollution,eutrophication, and infill/siltation (Copley et al. 2003; BrimBox et al. 2010, this issue; Vaarzon-Morel 2010, this issue).Figure 4 shows some of these sorts of impacts of feral camels onwetlands.

In a survey conducted with Aboriginal landholders (Vaarzon-Morel 2010, this issue), inhabitants in 23 of the 27 settlementssurveyed raised concerns over the impacts of camels onwetlands,particularly in regards to the abundance of highly prized kuka(bush meat) species including red kangaroos (Macropus rufus),emus (Dromaius novaehollandiae), and bustards (Ardeotisaustralis). Aboriginal people saw these species as being deprivedof grass and water by camels, and being scared away, andtherefore declining in abundance (Vaarzon-Morel 2008, 2010,this issue).

Other sites of biological significance. In addition to wetlands,there are numerous other sites of biological significance withinthe range of the feral camel. These include sites with threatened

Fig. 2. Self-mustering gates on Andado station (Northern Territory) thathave been damaged by camels. Image courtesy of J. Bloomfield.


Table 2. Plant species of central Australia eaten by camels and their vulnerability to local extinction or severe impact as a result of camel browsingCultural significance of plants to Aboriginal people is shown. Species are listed by decreasing vulnerability to camel browsing

Species name Common name Significanceas contemporaryresource orcultural valueA

Contemporaryresource value

Palatabilityto camelsB

Vulnerability to localextinction/severedepletion from camelbrowsingB

Santalum acuminatum Quandong High Artefact, fruit Extremely high Extremely highErythrina vespertilio Bean tree HighC Artefacts, edible tuber,

commercial artefacts andbeads (seed, wood)

Extremely high Extremely high

Marsdenia australis andM. viridiflora

Bush banana High Fruit Very high Extremely high

Acacia oswaldii Umbrella wattle Low – Unknown Extremely highSantalum lanceolatum Bush plum Moderate

to highFruit Very high High to extremely high

Pittosporum augustifolium Native apricot Low – Very high HighEremophila longifoliaD Emu bush Moderate Ceremony Very high HighVentilago viminalis Supplejack High Ceremonial, sugarbag, gum Very high HighBrachychiton gregorii Desert kurrajong Low Seed food, shade, edible tuber High HighRhyncharrhena linearis Bush bean Moderate

to highFruit Unknown High

Acacia sessiliceps Curly-pod wattle Low – Extremely high HighSalsola tragus Buckbush Low – Very high HighCrotalaria cunninghamii Bird flower Low – Very high HighCanthium latifolium Native currant Low Fruit High HighCodonocarpus cotinifolius Desert poplar Low – Very high HighLawrencia viridigrisea andL. glomerata

– Low – High High

Ipomoea costata Bush potato High Edible tuber Very high Moderate to highCapparis mitchellii (also twonorthern species)

Bush orange,split jack

Moderateto high

Fruit, shade Very high Moderate to high

Cucumus melo subsp. agrestis Bush cucumber Moderate Fruit Unknown Moderate to highCarissa lanceolata Conkerberry Low Fruit Very high ModerateBoerhavia spp. Tar vine High Roots, caterpillars Very high ModeratePterocaulon spp. Apple bush Low medicine Very high ModerateAcacia tetragonophylla Dead finish High Seed food, medicine Very high ModerateAcacia pruinocarpaD Black gidgee High Ashes, edible gum, seed High ModerateCanthium attenuatumD Bush currant High Fruit High ModerateVigna lanceolata Pencil yam Moderate

to highEdible tuber Unknown Moderate

Owenia reticulata Desert walnut Moderate Kernel, gum, shade Unknown ModerateAtalaya hemiglauca Whitewood Low – Very high ModerateGrevillea juncifolia Desert grevillea High Honey Very high Low to moderateGrevillea eriostachya Honey grevillea High Honey High Low to moderateTecticornia verrucosa Samphire Low Seed Unknown Low to moderateAcacia victoriae Victoria wattle HighC Commercial seed Very high LowCapparis spinosa subsp.nummularia

Bush passionfruit Moderateto high

Fruit Very high Low

Acacia aneura (especially sub-species other than tenius)

Mulga HighC Firewood, shade, artefacttimber, honey, honey ant,ashes, red kangaroo habitat,commercial artefactproduction, commercialseed

High Low

Acacia kempeana Witchetty bush High Edible grub High LowAcacia coriacea Dogwood HighC Green seed food, dry seed

commercialModerate Low

Corymbia opaca Bloodwood HighC Artefacts, sugarbag, bushcoconut, commercialartefacts and beads

Moderate Low

Solanum centrale Bush tomato HighC Fruit food, commercial fruit Moderate LowSolanum ellipticum Bush tomato Moderate Fruit Moderate Low

(Continued next page)


fauna and sites of botanical significance (see Saalfeld et al.2008). The extent of the impacts of feral camels on these sitesis unquantified.

Carbon emissions. Camels produce the greenhouse gasmethane as aby-product of enteric fermentation. The contributionto carbon emission reductions that could accrue from reducingthe number of feral camels is considered in Drucker et al.(2010, this issue).

Social/cultural

Damage to infrastructure in remote settlements. Inhabitantsin 19 settlements surveyed by Vaarzon-Morel (2008, 2010, thisissue) indicated that camels caused damage to infrastructure intheir communities or on outstations near the communities.Camels were reported to have damaged buildings, fences, andwater-related infrastructure including taps, windmills, andevaporative air conditioners. The monetary cost of this damagewas not estimated in the survey.

In recent years, there have been periodic reports of largenumbers of feral camels entering some Aboriginal settlements insearch of water. The most widespread and serious of theseincursions occurred over the summer of 2006–07. At this timethere was an influx of many, perhaps tens of thousands, ofapparently starving and thirsty camels onto pastoral leases to thesouth of Alice Springs and onto Aboriginal settlements inthe Anangu Pitjantjatjara Yankunytjatjara lands in SA, theNgaanyatjarra lands in WA and in the Petermann Ranges in theNT. An account of this incident is given in Edwards et al. (2008).Key informants located in WA stated that feral camels caused$100 000 damage to infrastructure at Warakurna over thesummer of 2006/07, $5000 damage at Tjukurla in January 2008and $30 000 damage at Kalka during 2008 (see Edwards et al.2008 for details).

On the basis that (a) inhabitants in 12 of the 23 majorsettlements (population >100) surveyed by Vaarzon-Morel(2008, 2010, this issue) indicated that camels caused damage toinfrastructure (excluding fences) in their communities or onoutstations near the communities, and (b) there are 89 majorAboriginal settlements within the range of feral camels, andassuming that (c) the mean damage figure for Kalka, Tjukurla,and Warakurna ($135 000/3 = $45 000) is indicative of annualdamage figures for other remote settlements that experiencecamel damage, the total annual monetary value of cameldamage to infrastructure on remote settlements is 12/23�89�$45 000 = $2.09million. Our scaling-up process wasconservative as we did not include the four Aboriginalcommunities surveyedbyVaarzon-Morel (2008, 2010, this issue)that reported infrastructure damage only to fencing. Althoughthe estimated figure may appear high, it probably accuratelyreflects the true cost of repairing infrastructure damage of thisnature in remote settlements.

Table 2. (Continued )

Species name Common name Significanceas contemporaryresource orcultural valueA

Contemporaryresource value

Palatabilityto camelsB

Vulnerability to localextinction/severedepletion from camelbrowsingB

Solanum chippendalei Bush tomato High Fruit Unknown LowStylobasium spathulatum – LowC Commercial artefacts (seed) Unknown LowAcacia murrayana – HighC Commercial seed Unknown UnknownAcacia colei – HighC Seed food–commercial seed Unknown Unknown

AContemporary significance of species varies regionally and further consultations are required with Aboriginal people to gain a better understanding of eachspecies’ local importance.

BBased on Dörges and Heucke (2003) and information provided by Peter Latz, Theresa Nano and Fiona Walsh in 2007 and 2008.CSpecies is of commercial importance.DCamels and/or fire prevent plants from reaching maturity or full potential and may render them worthless as resource species.

Fig. 3. Quandong tree in Great Victoria Desert (Western Australia) that hasbeen damaged by camels. Image courtesy of D. Ferguson.


Damage to conservation reserves. In a survey of conservationlandholders within the camel range (Zeng and Edwards 2010,this issue), feral camels were reported as present on ~51% ofreserves. Camels were reported to cause problems on 94.4% ofthe reserves on which they were reported present. Damage towater sources was reported in 64.7% of cases, damage to fencingin 29.4% of cases, and other damage in 9% of cases. On the basisof the per square kilometre estimate of damage for surveyedreserves, the value of infrastructure damage was estimated to be$0.08million annually across all conservation lands within or onthe margins of the camel range (i.e. damage to fences, yards, andwater equipment) (see Zeng and Edwards 2010, this issue).

Damage to airstrips. There are ~1100 airstrips (airports,heliport, and landing grounds) in or on the margins of the camelrange. About one-third of these airstrips are located in areaswhere there are medium to high camel densities. These airstripsare used by local communities, the Royal Flying Doctor Service,tourism operators, mining companies and expeditions.Increasingly, feral camels pose a threat to aviation safety bydamaging the airstrip surface, damaging critical infrastructure, orby their presence on the airstrips (David Hewitt, Relief Manager,Punmu Community, Ngaanyatjarra lands WA, 2008, pers.comm.; Vaarzon-Morel 2008, 2010, this issue). We could notobtain reliable estimates of the monetary value of camel damageto airstrips but it is believed to be in the order of tens of thousandsof dollars per year.

Road crashes. As the feral camel population increases(see Saalfeld and Edwards 2010, this issue), so does the

likelihood of vehicular collisions involving camels. Suchcollisions impose a high cost on regional economies, includinglabour loss (workplace, household, and community), repair andreplacement costs for vehicles, loss of quality of life, insuranceadministration, legal fees, long-term care, travel delays, medicalfees and workplace disruption (BTE 2000).

The NT is the only jurisdiction that officially recordsinformation on whether road accidents are linked to camels.Information provided by the Department of Planning andInfrastructure of the NT shows that from 2003 to 2006 therewere 26 accidents involving horses or camels, injuring ninepeople (Table 3). Assuming that the proportion of camel-relatedcrashes is one-third (GrantWilliams 2007, Road Safety NT, pers.comm.), it is estimated that there were 2.17 camel-related crashesannually over the period, injuring 0.75 people. In June 2008 twopeople were killed when their vehicle hit a camel while travellingbetween Yuendumu and Lajamanu, north-west of Alice Springs.There were at least seven collisions between vehicles and camelson the Ngaanyatjarra Lands in WA between 2003 and mid 2008,or ~1.4 annually (Edwards et al. 2008).

In 2006, rail freight between Adelaide and Alice Springs wasdelayed by 24 h when a locomotive hit a mob of camels. Thecollision damaged the train’s air brake system and crews had torepair the train before it could continue (NT News 2006). Therewas no report of the estimated cost of this incident.

In other states, there is no specific statistical informationabout camel-related crashes, but animal-related collisions arerecorded. According to information from NRMA Insurance

Fig. 4. Camels around a dry waterhole near Docker River (Northern Territory) in February 2007.Note the dead and dying camels in the waterhole. Image courtesy of R. Bugg.

Table 3. Horse/camel-related road accidents in the Northern Territory, 2003–06

Year Totalno. of

accidents

Totalno. ofinjuries

Totalno. of

fatalities

Crash no. relatedto horses/camels

No. of injuriesin horse/camel-related crashes

No. of fatalities inhorse/camel-related

crashes

2003 2401 1114 53 8 4 02004 2142 1054 35 5 2 02005 2151 1009 55 6 2 02006 2049 911 44 7 1 0


(NRMA 2005), there were more than 17 700 vehicle collisionclaims nationally for animal-related accidents in 2003. Cameldata were pooled with data for some other species for whichthere were 81 listings in SA, 116 inWA, and 6 in the NT. TheNTfigure of 6 is 2.77 times higher than the estimated annual camel-related accident figure of 2.17 calculated above. This providesa basis for estimating the number of camel-related accidents forSA and WA (i.e. WA, 116/2.77 = 41.9; SA, 81/2.77 = 29.3).However, because the NT data on which this calculation is basedare a small sample, and camel density and the number ofsettlements varies within each jurisdiction (Lamb et al. 2010, thisissue; Saalfeld and Edwards 2010, this issue), these estimatesmay be highly inaccurate. On the basis that there have been1.4 accidents involving camels per year from 2003 to 2007 in theNgaanyatjarra Lands, which comprise ~10%of the area occupiedby camels in WA, the WA figure may be closer to 14 accidentsper year involving camels. Thus, a conservative estimate of thenumber of vehicle collisions involving camels in Australiaeach year is 27.7 (10.5 in SA, 14 in WA, 2.2 in the NT).

The average cost of a road crash in SA is $29 303 (in 2004AUD) (Baldock and McLean 2005). Using this figure, theestimated minimummonetary cost of camel-related road crashesin WA, SA, and NT is currently about $900 000 (in 2008 AUD)annually, assuming an annual inflation rate of 2.5%.

Damage to Aboriginal culturally significant sites. Aboriginalculturally significant sites include sacred sites, burial sites,ceremonial grounds, water places, places of birth, places(including trees) where spirits of deceased people are said todwell, and resource points (areas with concentrations of food orareas where ochres, flints, particular food types, or otherimportant resources can be obtained) (P. Vaarzon-Morel 2008,unpubl.). In particular, water places (waterholes, rock holes,soaks, springs, etc.) are special places for desert Aboriginalpeople and many, but not all, are sacred sites (Yu 2002).Prehistorically, wetlands were drought refugia for Aboriginalpeople, providing not only water but also good hunting, even indry times. Today, wetlands still provide reliable drinking waterfor Aboriginal people when they are out on country and are usedfor recreational and ceremonial purposes. Thus, the negativeimpacts of camels on wetland areas (which are described above)also have a very important social/cultural dimension (Vaarzon-Morel 2010, this issue). Recall that inhabitants in 23 Aboriginalsettlements surveyed by Vaarzon-Morel (2010, this issue) raisedconcerns over the impacts of camels on wetlands. Inhabitants in19 settlements also indicated that camels caused damage toculturally significant sites other thanwater-related sites (Vaarzon-Morel 2010, this issue). The negative impacts of camels on sitesthat are culturally important because of plant/food resources aredescribed in the next section.

Damage to plant species of cultural value to Aboriginalpeople. Many plant species are of cultural and/or economicvalue to desert Aboriginal people. At least 35 of the plant speciesthat occur in central Australia and are known to have acontemporary resource value to Aboriginal people are eitherhighly palatable or preferred camel food species and, as such, arevulnerable to damage and decline by camel browsing(Table 2). These plants are used by Aboriginal people formedicinal and ceremonial purposes, artefact production, and as afood resource (Latz 1995).Many species are of great significance

due to their dreaming associations, though it was not within thescope of this research to consider the impact of camels on thisaspect in any exhaustive manner. Inhabitants in 20 Aboriginalsettlements surveyed by Vaarzon-Morel (2010, this issue)indicated that camels caused damage to plants of cultural oreconomic value.

It is important to realise that the collection of bush foods,whether for commercial sale or personal use, is extremelyimportant to Aboriginal people in the cultural/social sense (FionaWalsh 2008, CSIRO, pers. comm.). There are multiple culturalvalues inherent in bush foods and bush food collection activities.Bush food collecting trips provide an opportunity to engage inother cultural activities such as burning and the maintenance ofculturally important sites. They also provide for the transfer ofknowledge and skills from older to younger people and for socialcommunication between individual harvesters (NPYWC 2003).Just as importantly, collecting bush foods (and associatedactivities) provides enjoyment and an opportunity to escape themany pressures associated with living on remote settlements(Walsh and Douglas 2009). Currently, the impact of camels onbush foods is much more important from a cultural/socialperspective than an economic one.

Safety concerns. Inhabitants in 17 Aboriginal settlementssurveyed by Vaarzon-Morel (2010, this issue) expressedconcerns over the dangers that camels posed both on and off theroad. This is affecting the way that people use country, forexample, many people claimed that they no longer camped out inareas with lots of camels andwould not leave children unattendedin such areas (Vaarzon-Morel 2010, this issue). This may restrictthe transmission of cultural knowledge and practices concerningcountry to future generations (Vaarzon-Morel 2008, 2010, thisissue).

Disease risk. In general, camels in Australia suffer littledisease. This is fortuitous because it was at least 40 years afterthe first importation of camels into Australia (in 1840) thatquarantine regulationswere developed and enforced for importedcamels (McKnight 1969). Skin disease, including sarcopticmange, is the most prevalent cause of camel morbidity inAustralia (Brown 2004). Camel pox, another skin disease thatcauses considerable morbidity and fatalities in camelsinternationally (Koenig2007), is not present inAustralia. In1999,a review of Australia’s preparedness for exotic diseaseoutbreaks focusing on feral herbivores concluded that camelswere unlikely to be involved in exotic disease outbreaks(Henzell et al. 1999). This conclusion was underpinned by acamel population estimate of 170 000 (based on that of Shortet al. 1988 with an estimated correction factor of 4) (RobertHenzell 2008,SAAnimal andPlantControlGroup, pers. comm.).This centred on the assumptions that camels were sparselydistributed in the arid zone, mainly inhabited remote areas, hadlittle contact with other species (especially stock), and onlyinfrequently visited water points (Henzell et al. 1999). Thesituation is now quite different: the current camel population isestimated to be at least 7 times higher than the estimate used forthe Henzell et al. (1999) review (Saalfeld and Edwards 2010,this issue); camels are increasingly moving out of remote areasand coming into regular contact with cattle and other feralanimals (Zeng and Edwards 2010, this issue); and camels nowregularly visit water points across their range, including stock


waters on pastoral leases (Zeng and Edwards 2010, this issue).While it is arguably still the case that the likelihood of an exoticdisease being introduced into an area occupied by camels is stilllower than for many other parts of Australia, there is now anincreased likelihood that camels would be epidemiologicallyinvolved in the spread of diseases like bluetongue, Rinderpest,Rift valley fever, surra (trypanosomosis), andbovine tuberculosiswere there to be outbreaks of these diseases in Australia (Brown2004; Robert Henzell 2008, SA Animal and Plant ControlGroup, pers. comm.). An additional factor is that camelsbridge the tropics and the Mediterranean climates over a largeportion of the continent. Whether camels would beepidemiologically involved in the spread of foot-and-mouthdisease is still open to debate (Manefield and Tinson 1996;Wernery and Kaaden 2004).

Positive impacts of feral camels

Economic

Benefits to landholders. Zeng and Edwards (2010, this issue)found that 4.8% of pastoral landholders who responded to theirsurvey derived some income from selling camels, 15.3% reportedeating camels, and 1.0% reported deriving some other economicbenefit from camels (e.g. weed control). The value of the benefitrealised from feral camelswas estimated to be about $0.59millionannually across all pastoral properties (Zeng and Edwards 2010,this issue).

Three out of 70 conservation reserves surveyed by Zeng andEdwards (2010, this issue) derived some income from sellingcamels, while three reported eating camels. The value of thebenefit realised from feral camels was estimated to be about$0.03million annually across all conservation reserves (Zengand Edwards 2010, this issue).

Although camels are not widely used as a livestock animalin Australia, there may be advantages in this approach incertain situations. Co-grazing camelswith cattle can substantiallyincrease the mass of livestock carried per square kilometrewithout causing deleterious environmental impacts (Phillipset al. 2001). This may represent one of the few opportunities forenterprise diversification available to beef producers in desertAustralia in shrubby country considered marginal for cattleproduction (Phillips et al. 2001).

Inhabitants in nine Aboriginal settlements surveyed byVaarzon-Morel (2008, 2010, this issue) indicated that they had atsome stage derived economic benefit from mustering and sellingcamels, inhabitants in nine settlements indicated that they killedand ate camels, whereas inhabitants in 13 settlements indicatedthat theyderivedother benefits fromcamels,mainly fromkeepingyoung camels as pets. People in most settlements expressedthe view that feral camels should be used to provide benefits tolocal people including income and jobs (Vaarzon-Morel 2008,2010, this issue). In some instances, camels are harvested forcommercial purposes fromAboriginal landsbyexternal operatorswho pay a small stipend to local people for access to the resource.A good example of this is the pet meat operation at Warakurnain WA (Zeng and McGregor 2008), which has removed nearly7000 camels over the period March 2007–April 2009 (AlexKnight, Manager Land and Culture, Ngaanyatjarra Council,pers. comm.).

Benefits to those involved in the meat and pet meat industries.The economic benefits of commercially utilised feral camelsaccrue along the supply chain. In 2007 it was estimated that3600–4600 feral camels were harvested for pet meat in Australia,fewer than 400 for live export and ~1000 for mainly domesticconsumption, and the gross worth of camel products sold wasestimated to be $1.9–2.5million in current terms (Zeng andMcGregor 2008).

Tourism. The tourism industry uses a small number of camels,mainly in trekking-type businesses and in novel racing events.Currently, there are around 28 camel tourism businesses (camelfarms) established primarily for camel rides and camel deserttrekking. Some of these enterprises are Aboriginal owned. Towhat extent these tourism-based enterprises rely on feral asopposed to domesticated camels is unclear (Zeng and McGregor2008). What is clear is that only a relatively small number ofcamels are involved.

There are two relatively well known camel races in Australia:the Alice Springs Camel Cup and the Boulia Desert Sands camelraces. These races are held annually and are primarily tourismevents that use domesticated camels; there is no camel racingindustry in Australia.

Environmental

There are currently ~5000 camels in captivity in Qld andsome are being used for controlling woody weeds like PricklyAcacia (Acacia nilotica), Mesquite (Prosopis spp.), andParkinsonia (Parkinsonia aculeata) on pastoral lands (NickSwadling 2007, Industry Development Officer, Department ofPrimary Industries and Fisheries, Qld, pers. comm.). This isthe only acknowledged environmental benefit attributable tocamels.

Relationship between negative impacts on pastoralinfrastructure and camel density

There was a positive association between camel density and thelevel of infrastructure damage reported by pastoral landholders(Fig. 5). ANOVA with damage as the dependent variable

0

5

10

15

20

25

0–0.1 0.1–0.2 0.2–0.3 0.3–0.4 >0.4

Density category (camels/km2)

Dam

age

cost

($/

km2 )

74 14

11

98

Fig. 5. The relationship between the mean value of infrastructure damagereported by pastoral landholders over the period July 2005–June 2007 and theestimated mean density of feral camels on the property. Note: the figures aresample sizes. Range is standard error.


indicated that there were significant differences in the level ofdamage at different densities (F4,111 = 9.4, P < 0.001). TheBonferroni multiple-range test indicated the following groupingsby density category for the damage means (groups withinmatching brackets were not significantly different):

ð0� 0:10:1� 0:2½0:2� 0:3Þ0:3� 0:4� > 0:4Damage at camel densities <0.2 camels/km2 was significantly

lower than at densities >0.3 camels/km2 and damage at densities>0.4 camels/km2 was significantly greater than that incurred atdensities <0.3 camels/km2.

Net impact of feral camels

Table 4 provides a summary of themonetary value of the impactsof feral camels described in this study. We have considered onlythose benefits that accrue to landholders who live within thecamel’s range.On the basis of this approach, the negative impactsoutweigh the positive impacts by a factor of ~18. The net cost ofimpact is –$10.67million annually.

Discussion

The total annual cost of the negative impacts of feral camels(–$11.3million) estimated here is ~56 times higher than thatgiven by McLeod (2004) for camels and is significantly higherthan the equivalent measure derived for feral goats in Australia(–$7.7million; McLeod 2004), even allowing for an annualinflation rate of 3%. Thus, feral camels are the large feralherbivore with the leading economic impact in Australia, evenallowing for the conservative nature of the figures used inMcLeod (2004).

Although we were unable to estimate the monetary value ofthe negative environmental and many social/cultural impactsof feral camels, it is likely that these costs far outweigh the

economic ones given the sizeable contribution that biodiversity(Environment Australia 2003) and culture make to the nationaleconomy.

Many of the impacts of feral camels listed in this paper mayhave multiplier or flow-on effects. On the positive side, theconsumption of camel meat by Aboriginal people in remotecommunities can lead to better health outcomes, particularly if itinvolves hunting (Morse 2005) and if there is a correspondingdecline in the consumption of processed foods. Income derivedfrom feral camels can improve the viability of pastoral enterprises(Phillips et al. 2001), enhance the viability of regionalcommunities and can lessen the degree of welfare dependency inremote communities (Morse 2005). On the negative side, camelscontribute to global warming through the production of methane(Drucker et al. 2010, this issue).

The negative environmental impacts of camels couldultimately lead to the regional or even total extinction of nativefauna and flora. Species immediately at risk are plants which arehighly preferred food for camels and animals and plantswhich aredependent on wetland habitats. Quandong is now listed asvulnerable in the NT in part due to camel damage (Woinarskiet al. 2007). Through reducing opportunities for the transfer ofcultural knowledge, the presence and actions of camels alsoundermines Aboriginal culture.

The positive density/damage relationship established forcamels and infrastructure on pastoral properties is likely tohold true for environmental variables and cultural/social variablesas well. Therefore, the magnitude of the negative impacts offeral camels will undoubtedly increase if the population isallowed to continue to increase. Furthermore, the likelihoodthat camels would be epidemiologically involved in the spread ofexotic diseases (were there to be outbreaks of these diseasesin Australia) is also very likely to increase with populationdensity.

Table 4. The annualised monetary value of the impacts of feral camelsInformation is limited to those impacts that could be costed using market values. The positive economic impacts

are those for landholders, not those that accrue along the commercial supply chain

Cost/benefit component Cost ($ million)

Benefit($ million)

Net cost/benefit($ million)

(1) Direct control and management costsGovt in-kind management cost –0.30 – –0.30Govt management/research costA –0.75 – –0.75Pastoralist management cost –1.21 – –1.21Conservation land management cost –0.10 – –0.10

(2) Damage to infrastructure/property/peoplePastoral stations –2.40 – –2.40Aboriginal settlements –2.09 – –2.09Conservation reserves –0.08 – –0.08Dog fence –0.04 – –0.04Road crashes –0.90 – –0.90

(3) Production lossPastoral stations –3.42 – –3.42

(3) Landholder benefitSelling, eating, other uses (pastoral) – 0.59 0.59Selling, eating, other uses (conservation) – 0.03 0.03

Total –11.29 0.62 –10.67

AIncludes non-government conservation lands.


Another factor which is likely to influence the magnitude ofthe impacts of feral camels in future years is climate change. Theclimate change forecast for arid Australia out to 2030 is for atemperature increase of 1–1.28C, higher frequency of hot days,a decline in rainfall of between 2 and 5%, higher evaporationrates, and higher frequency of droughts (CSIRO 2007). Underthis scenario, even if camel populations remain static, thenegativeimpacts of camels are likely to be exacerbated. Water will be ascarcer resource and camels will put more pressure on waterresources on pastoral leases, in remote settlements, and inwetlands. As droughts increase in frequency so too will thefrequency of camels moving en-masse onto pastoral leases andinto remote settlements in search of water.Wetlands will becomeincreasingly important as refugia in arid Australia as thefrequency of droughts increases, and this will magnify the effectsof feral camels on the environment. The exotic disease riskassociated with feral camels is also likely to increase if camels arebrought into closer contact with stock as they seek out scarcerwater resources.

On the basis of our current understanding, we recommendthat feral camels be managed to a long-term target density of0.1–0.2 camels/km2 at property to regional scales (areas inthe order of 10 000–100 000 km2) in order to mitigate broadscale negative impacts on infrastructure on pastoral stations andin remote settlements, and plant species which are highlysusceptible to camel browsing. At these densities, the degreeof damage to pastoral infrastructure is in the order of$2000–3000/km2 over 2 years. For most pastoralists, this maybe a tolerable level of damage. Given that camels alreadyoccur at localised densities >1 animals/km2 over a largeexpanse of their current range (Saalfeld and Edwards 2010,this issue), there is an urgent need to act now to safeguard theenvironmental, social/cultural and production assets of theAustralian rangelands.

Note that the level of control suggested in this paper is notnecessarily the optimal level of control, i.e. the point wherethe marginal costs of control equate with the marginal benefitsof implementing a particular control method (see Choquenotet al. 1996; Hone 2007). For pest animals, the optimal level ofcontrol can be determined in specific situations for particularcontrol methods using marginal economic analysis providedthat the costs of impacts can be estimated usingmarket values andthe costs of implementing the controlmethodare knownat a rangeof pest animal densities. Because of the quality of the datacurrently available, such an analysis has not been done in thisresearch.

Acknowledgments

The work reported in this publication was supported by funding fromthe Australian Government Natural Heritage Trust through the DesertKnowledge CRC; the views expressed herein do not necessarily represent theviews of the Australian Government or the Desert Knowledge CRC or itsparticipants. We thank Petronella Vaarzon-Morel, Fiona Walsh, DavidAlexander,DavidHewitt,AndrewDrenen,MichaelBalharry,NickSwadling,Grant Williams, Peter Latz, Theresa Nano, Bob Henzell, Brian Watts, ChrisMoon, Phil Gee, Tony Pople and Mark Williams for their advice and inputwith respect to various aspects of the research.BoRaphael, LyndeeMatthews,James Wright, and Jenine Baker provided useful comments on drafts of theoriginal chapter.

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Manuscript received 26 June 2009; accepted 18 December 2009


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