Monitoring Kangaroo Populations in Southeastern New South Wales

Monitoring Kangaroo Populations in Southeastern New South Wales A. R. Pople1, S. C. Cairns2 and N. Menke1 1

The Ecology Centre, University of Queensland Q 4072

2

Zoology, School of Environmental Sciences and Natural Resources Management, University of New England, Armidale NSW 2351

Prepared for the New South Wales National Parks and Wildlife Service July 2003

Pople et al.: Monitoring kangaroos in southeast NSW

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Summary 1. This study was undertaken to assess the feasibility of conducting kangaroo surveys in an area encompassed by the Braidwood, Cooma, Goulburn, Gundagai and Yass Rural Lands Protection Boards (RLPBs). National Parks and State Forests comprise almost 30% of the region and were excluded from the survey area because they preclude commercial harvesting. 2. The area was visited and discussions were held with NSW National Parks and Wildlife Service (NPWS) and RLPB staff to develop some idea of the relative density distribution of kangaroos within the area. The distribution of licences for the non-commercial cull of kangaroos provided further indication of kangaroo distribution. 3. Because of the relatively high relief of the landscape and the relatively high proportion of tree cover in the area, a helicopter rather than a fixed-wing aircraft was suggested as the most suitable survey platform. Line transect sampling conducted as double counts should minimise bias and maximise repeatability of the population estimates. 4. Using information on tree cover and the relief of the landscape, the five RLPBs were stratified into probable areas of high, medium and low kangaroo density. This enabled survey effort to be allocated to each stratum to minimise the variance of the population estimate. 5. Based upon the density stratification of the area and information drawn from helicopter surveys conducted in the northern tablelands of NSW, a survey comprising 900 km of transect line is proposed to estimates kangaroo densities in the agricultural and grazing lands of the five RLPBs. 6. A risk assessment conducted to examine to combined effects of survey precision, survey frequency and harvest rate suggested an appropriate survey strategy would be to carry out triennial helicopter line transect surveys with a precision of 20%.


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1. Introduction Currently, commercial harvesting of kangaroos in New South Wales is restricted to the inland sheep-wheat belt, the western pastoral areas and the northern tablelands (Fig. 1). No commercial harvesting of kangaroo occurs east of the Great Dividing Range, nor in the central and southern tablelands. There has, however, been an expression of interest, largely from sheep and cattle graziers, in allowing commercial harvesting in the southeast of the state. These landholders presently cull kangaroos on pest destruction (shoot-and-let-lie, SLL) licences, but recognise that this is both an inefficient means of pest control and wasteful, and could be redressed through the introduction of commercial harvesting. A further advantage of introducing commercial harvesting is that animals are likely to be killed more humanely by qualified field processors than if killed by landholders under SLL licences, and this can be policed to a far greater extent than a non-commercial cull (RSPCA 2002). If commercial harvesting is to occur in the region, then state and federal government conservation agencies require kangaroo populations to be monitored. Elsewhere in the state, harvesting of kangaroo populations is regulated by quotas that are set as proportions of population estimates determined usually by aerial survey. This is a proportional harvesting strategy employed throughout Australia for kangaroo management (Pople in press). Aerial surveys are conducted annually by fixed-wing aircraft in the western plains where most harvesting occurs. In the northern tablelands and the Barrier Ranges surveys are less frequent. This is because harvesting is less intensive in these areas and either the rugged terrain or heavy vegetation cover requires surveys to be undertaken by helicopter (Southwell and Sheppard 2000) or by ground counts (Southwell et al. 1995), which are costlier than surveys by fixed-wing aircraft. This report examines the feasibility of monitoring kangaroo populations in the southeast of New South Wales, specifically in the five Rural Lands Protection Boards (RLPBs) shown in Figure 2. This region comprises rugged terrain and heavily timbered areas, making aerial survey difficult. However, where surveys are feasible, a monitoring system is suggested. This includes survey design (i.e. transect number and placement) and survey frequency. In wildlife management, the appropriate survey frequency and precision has generally been considered with the aim of detecting trends (e.g. Caughley 1979; Gerrodette 1987; Harris 1986). In kangaroo management, harvest regulation is primarily through quotas that are set as proportions of absolute estimates of population size. Trends are of secondary importance. Imprecision in population estimates and infrequent estimates will risk applying a quota that is either too high or too low (i.e. over- or underharvest, see Pople 2003). By not harvesting at the desired rate (e.g. 15%), costs are incurred to the kangaroo industry through reduced and more variable yield, to graziers through increased competition with sheep and damage to crops and there is a social cost if kangaroos are reduced below some arbitrarily low density (i.e. quasiextinction). These costs must be balanced against the cost of more intensive and frequent surveys (i.e. there is a trade-off). Alternative harvest strategies can also be considered in order to reduce the risk of over- or


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underharvest. These include harvesting at a different, and even variable, rate, regulating effort or incorporating spatial reserves.

Kangaroo Management Zones BOGGABILLA BOOMI HUNGERFORD GATE

BARRINGUN GOODOOGA

YETMAN

MUN GINDI

COLLARENEBRI BINNA BUNNA

Zone 1 MILPARINKA

Zone 7

WANAARING

BREWARRINA

MOREE WARIALDA

CARINDA LOUTH

QUAMBONE COOLABAH

WILCANNIA

Zone 6

BROKEN H ILL

NYNGAN

WARR EN

ARMIDALE

Zone 9

GUNNEDAH

COONAMBLE

Zone 10

HERMIDALE

TAMW ORTH

COONABARABRAN TAMBAR SPRINGS

GUYRA

BARRABA

BAAN BAA

TILPA

Zone 2

BUND ARRA

BOGGABRI

WHITE CLIFFS

GLEN INNES

BINGARA

BURREN JUNCTION WEE WAA PILLIGA NARR ABRI

PACKSADDLE

Zone 13

INVERELL

Zone 8

WALGETT

BOURKE

COBAR

TENTERFIELD

WEILMORINGLE

ENNGONIA

TIBOOBUR RA

WALCHA

Zone 14 QUIRINDI

GILGANDR A COOLAH

NEVERTIRE

NYMAGEE

NECKARBOO

DUNEDOO

NARROMINE DUBBO

TOTTENHAM MENINDEE

TOMINGLEY

TULLAMORE MOUNT H OPE

IVANHOE

PEAK H ILL CONDOBOLIN

COOMBAH WILLANDR A

BOGAN GATE PARKES FORBES

LAKE CARGELLIGO

POONC ARIE

MARSDEN

Zone 4

BOOLIGAL

RANKINS SPR INGS WEST W YALONG

Non Commercial Zone

SYDNEY

WENTWORTH GRIFF ITH

BURONGA HAY

ARDLETH AN

LEETON

BALRANALD

NARRAND ERA

MOULAMEIN

Zone 11 LOCKHART

WAKOOL

ACT DENILIQUIN

BARHAM

TOCU MW AL COROWA

N W

E S

0

50

100

150

200 Kilometers

Kangaroo Management Zones Zone 1 Tibooburra Zone 2 Broken Hill Zone 4 Lower Darling Zone 6 Cobar Zone 7 Cobar North Zone 8 Narrabri Zone 9 Armidale Zone 10 Coonabarabran Zone 11 Griffith Zone 13 Glen Innes Zone 14 Upper Hunter

Figure 1. Zones within New South Wales where commercial harvesting is allowed. Fixed-wing aerial surveys are conducted in zones 1-8, 10 and 11. Helicopter surveys are conducted in zones 9, 13 and 14 (After New South Wales National Parks and Wildlife Service 2001).


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Figure 2. The study area in southeastern NSW. The eastern third of the Braidwood Rural Lands Protection Board (RLPB) is dominated by National Parks, State Forests, areas of high relief and heavy forest cover, and so has been excluded from the study area. CR, Crookwell; GO, Goulburn; YA, Yass; CT, Cootamundra; TU, Tumut; CM, Cooma. Areas of high relief and open forest or woodland were determined from the relief coverage (Geoscience Australia 2001), which is © Commonwealth of Australia (Geoscience Australia) 2001, and landuse coverage (Bureau of Rural Sciences 2001), © Commonwealth of Australia (National Land and Water Resources Audit) 2001.


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2. Survey feasibility Ground assessment of the study area was made in February 2003. This involved field inspection of the major environments in the region and discussions with New South Wales National Parks and Wildlife Service (NSW NPWS) staff at Bungonia, Queanbeyan, Jindabyne and Tumut, discussions with RLPB rangers at Goulburn, Cooma, Gundagai and Yass, and discussions with graziers at Yass. These discussions identified likely areas of relatively high kangaroo density within the region, and therefore those areas that should be targeted for assessment of survey feasibility. Obviously, these areas could also be used as a basis for stratification (see Section 3 below). Field inspection and discussions were also designed to identify and hopefully confirm the likely factors determining kangaroo distribution and abundance (Pople 1989; Southwell et al. 1999) within the region, thus providing a further basis for stratification. Forest cover, land use and areas of high relief within the study area are shown in Figure 2 and Appendices 1 and 2. A large proportion (28%, Table 1) of the region is in National Park, particularly Kosciuszko and Budawang National Parks, or State Forest from which commercial harvesting of kangaroos is precluded. The accuracy and repeatability of aerial surveys diminishes in areas of high relief or heavy forest cover because of low and variable visibility (Clancy et al. 1997; Pople 1999; Southwell 1989; Southwell and Sheppard 2000). Safety may also be compromised in particularly rugged terrain. Such areas occur in the region, but are largely within National Parks or State Forests (Appendices 1 and 2). In particular, there is heavy tree cover in the northwestern area of Kosciuszko National Park, the adjoining and nearby State Forests between Tumut and Wee Jasper, and the eastern slopes of the Great Dividing Range that are within the Braidwood RLPB (Appendix 1). Areas of high relief occur in the eastern slopes of the Great Dividing Range, south from the Snowy River within Kosciuszko National Park in the southwest of the Cooma RLPB (Appendix 2). The coastal area of the Braidwood RLPB stretches from Sussex Inlet to Moruya. Aside from the difficulties of surveying this area of often-heavy forest cover, the area is unlikely to be suitable for commercial harvesting because the area is heavily populated with numerous small landholdings making administration of any harvest difficult and potentially contentious. Further, the area outside National Park and State Forest is small so the absolute kangaroo population size is unlikely to support a commercial industry. The eastern third (38%) of the Braidwood RLPB, effectively east of and including Budawang National Park, was therefore excluded from the study area. The composition of the remaining area is shown in Figure 2 and quantified in Table 1. The three density strata are described in Section 3 below. A small area of relatively high relief (>500 m) occurs within the area outside National Parks and State forests. This is likely to be unsuitable for aerial survey and so was excluded from the overall survey area, effectively assuming a density of zero in areas of high relief. High relief areas are generally associated with high tree cover and the combination means kangaroo density is likely to be low in these areas and harvesting is unlikely to be feasible. The impact of this small deletion would therefore be slight.


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The survey area shown in Figure 2 ranges from low, moderately timbered ranges bordering largely open plains in the southeast (Cooma and Braidwood RLPB) and around Tumut and Wee Jasper, to rolling hills of scattered woodland in the north and west. The northern and western areas could be surveyed by fixed-wing aircraft, but correction factors would need to be developed for this and the remaining part of the region is unsuitable for this survey method. A helicopter offers a number of advantages over fixed-wing aircraft as a platform for surveying this region. It provides greater visibility and can fly lower and slower, which is particularly advantageous in rugged terrain and in areas with heavy tree cover. The greater manoeuvrability of helicopters allows surveys to be designed with shorter and more closely spaced transect lines, which is an advantage in heterogeneous landscapes. Finally, helicopters provide an appropriate platform for line transect sampling (Clancy et al. 1997), more so than fixed-wing aircraft (Pople et al. 1998), potentially allowing survey-specific correction for variations in visibility bias. Ideally, helicopter line transect surveys should be conducted as double counts (Borchers et al. 1998; Pople in press), which would allow some assessment of bias due to incomplete sighting of kangaroos on the transect line. Table 1. Areas (km2) of five Rural Lands Protection Boards (RLPBs) proposed for commercial harvesting. Harvesting is precluded from National Parks (NPs) and State Forests (SFs) and there are some areas of high relief outside NPs and SFs that are unsuitable for aerial survey. The remaining area is divided into three strata representing likely high, medium and low kangaroo density. Braidwood RLPB area

Cooma

Goulburn

Gundagai

Yass

TOTAL

8,824

11,375

6,426

9,507

6,305

42,438

261

431

35

174

146

1,047

High density Medium density Low density

135 3,848 301

0 5,981 1,291

56 4,520 1,396

3,691 1,723 959

3,067 1,451 1,097

6,949 17,524 5,044

Survey area

4,284

7,271

5,973

6,373

5,615

29,516

High relief outside NPs and SFs

3. Survey design 3.1 Objective The overall objective of a survey of kangaroos in the study area is to estimate population size from a representative sample. This initially provides an indication of whether or not harvesting is commercially viable and worth the administrative costs in the long term. If harvesting is viable, an estimate allows quotas to be set as a proportion of population size. Population size needs to be estimated efficiently, in terms of cost and time, and with a precision (i.e. confidence interval) sufficient to keep the risk of over- or underharvest to an acceptable level (see Section 4 below).


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A survey will also indicate the distribution of kangaroos, allowing spatial allocation of quotas or effort. Precision can be greatly improved by stratifying sampling. As a rough rule of thumb, sampling effort should be allocated in proportion to the size of the population in each stratum (Thompson 1992). For this, some indication is required of the relative distribution of kangaroos amongst strata in the study area as well as strata area. Ideally, strata should be some mappable component of the environment such as vegetation cover or soil type. However, arbitrary strata can be defined so long as they can be mapped, their area is known and they are defined before a survey. Post-sampling stratification is possible, but it must obviously be based on information independent of the survey and it is likely to be well short of optimal. 3.2 Kangaroo distribution Discussions with NSW NPWS staff, RLPB rangers and graziers suggested the following distribution of eastern grey kangaroos in the study area: Goulburn. Tags issued under SLL licences (~3,000 in 2002) have been distributed throughout the district, with possible concentrations around Taralga and Lake Bathurst. There is a patchy distribution of kangaroos in the district associated with cover. Yass. Most tags issued under SLL licences (~6,000 issued in 2002 to shires administered by the Queanbeyan NPWS office) have been issued in a band running from Gunning through Crookwell to Boorowa. Graziers mapped what they considered an area of high kangaroo density in the RLPB. They considered densities were higher in Yass and Gundagai RLPBs than in Goulburn, Braidwood and Cooma RLPBs. Gundagai. The Tumut NPWS office issued ~5,000 tags under SLL licences throughout the Gundagai and Hume RLPBs in 2001. Many of these were issued in the Holbrook area (Hume RLPB) reflecting relatively high numbers. Within the Gundagai RLPB, kangaroos occur in moderate densities in valleys south of the Hume Highway where grazing properties adjoin State Forest and National Park. There are relatively high densities in hilly areas north and south of Gundagai, but much lower densities in the west towards Junee. Essentially, kangaroos were closely associated with moderate tree cover. The RLPB ranger mapped these strata. Braidwood. Relatively high kangaroo density in valleys to the south and southwest of Braidwood. Anecdotal evidence suggested an increase in grey kangaroos in the Queanbeyan district since the early 1960s. Cooma. The number of tags issued under SLL licences annually was not available, but 3,000 is a very rough guess. Kangaroos occur throughout the RLPB. One argument was that kangaroos were concentrated in the foothills and more heavily timbered areas on the margins of the RLPB, but density has become more homogeneous. Other people argued that densities of kangaroos were still higher in the higher rainfall area in the east (e.g. Kybeyan) and partly timbered


9

areas in the south and west. Overall this suggests a higher density stratum on the margins of the RLPB. Shoot-and-let-lie licences were considered to be only a rough guide to kangaroo distribution and abundance. The number of tags issued in 2002 was unusually high because of the drought. Nevertheless, it appears 20 replicate lines over the study area for adequate precision and a representative sample. Allocation of line length to strata was based on ‘rough’ estimates of the relative densities in each stratum. In the northern tablelands, surveys recorded areas of low density of ~1 kangaroo km-2, areas of medium density of 5 kangaroos km-2 and highdensity areas of ~10 kangaroos km-2 (Cairns 2003). These were used in the strata here. The required line length in each stratum in each RLPB was determined by allocating the 900 km in proportion to the estimated population size in each stratum in each RLPB (Tables 2 and 3). Transects were selected in each RLPB in turn, rather than the entire survey area at once, to ensure good coverage, at least at the RLPB scale. Only short line lengths were required in the low-density stratum, so


12

these were usually just an extension of a line in an adjoining stratum to reduce ferry time between transects. This may introduce some bias and underestimate variance because edge habitat may be oversampled. However, the problem is likely to be only slight because density should be low in this stratum and the medium density stratum includes a liberal buffer around wooded areas. The resulting survey design is shown in Figure 3. Table 2. ‘Rough’ estimates of abundance of eastern grey kangaroos in five Rural Lands Protection Boards in the southern tablelands of NSW. These are calculated from densities in three strata shown in Figure 3 and their areas (see Table 1). Densities are extrapolations from surveys in the northern tablelands of NSW (Cairns 2003). Strata density 'guess' km-2

Abundance ‘guess’ Goulburn Gundagai

Braidwood

Cooma

10 (High density) (Medium density) 5 1 (Low density)

1,347 19,241 301

0 29,903 1,291

565 22,602 1,396

Survey area

20,889

31,194

24,563

Yass

TOTAL

36,911 8,616 959

30,669 7,256 1,097

69,493 87,618 5,044

46,486

39,023

162,154

Table 3. Allocation of survey line length (km) according to estimated abundance (see Table 2) in each stratum in each Rural Lands Protection Board. Strata

Braidwood

Cooma

Goulburn

Gundagai

Yass

TOTAL

High density Medium density Low density

7 107 2

0 166 7

3 125 8

205 48 5

170 40 6

386 486 28

Survey area

116

173

136

258

217

900

These very rough estimates of kangaroo numbers in each RLPB suggest that the area could be divided into two zones of similar kangaroo abundance. Yass and Gundagai could form one zone while Goulburn, Braidwood and Cooma could form the other. Survey-based estimates are obviously needed before a decision is made on this basis. Surveys could be conducted over five days, excluding weather delays. This assumes 200-250 km could be flown in a survey session.


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4. Survey precision and frequency 4.1 Methods The most appropriate harvest strategy, frequency and precision can be selected from various alternatives by comparing the risks of undesirable management outcomes from each alternative. An undesirable outcome may be couched in terms of the goals of conservation, sustained-yield harvesting or pest control, such as quasiextinction risk, reduced yield or excessive kangaroo density. Selection of the best harvest strategy and monitoring system will be constrained by feasibility, primarily cost. Risk of over- and underharvest was assessed through simulating a kangaroo population under various management scenarios of survey frequency, precision and harvest strategy. Caughley’s (1987) interactive model was used to provide conservative estimates of risk (Pople 2003) (i.e. tend to overestimate risk). Although the model was developed for an arid-zone population of red kangaroos, it can yield results relevant to eastern grey kangaroos in a more mesic environment. Firstly, predictions of such entities as harvest rates for maximised yield, average population size and harvest yield were not sought; rather the objective of the modelling was to compare management scenarios. It is the qualitative rather than the quantitative results of the modelling that are of relevance. Nevertheless, the modelled population needed to show similar dynamics and a similar response to harvesting to an eastern grey kangaroo population in southeastern NSW. The population fluctuations in Caughley’s (1987) interactive model therefore required dampening by reducing the standard deviation in seasonal rainfall by 37% so that it was equivalent to that around Yass. Modelling follows a modification of the methods described by Pople (2003). Briefly, in the interactive model, rainfall drives pasture biomass, which in turn determines the rate of increase of the kangaroo population. There are two negative feedback loops. The first is pasture biomass reducing pasture growth. The second is kangaroo density reducing kangaroo rate of increase by reducing the available biomass by eating it. Seasonal rainfall was drawn from a lognormal distribution with a mean from Menindee Post Office in western NSW (annual mean = 244 mm, s.d. = 106 mm), where Caughley’s (1987) interactive model was parameterised, but a standard deviation of 63% of the Menindee value to reflect the more stable environment (see above). The kangaroo population was harvested and the pasture grew and was grazed down in weekly time steps. Sheep competed with the kangaroo population, consuming 1.5 times the pasture eaten by the kangaroos. The initial population size for each simulation was 10 kangaroos km-2. Instantaneous harvest rates were converted to isolated rates of harvesting (Caughley 1977), appropriate to the time step, to simulate harvesting spread evenly throughout each year. Harvest offtake for each three months was determined from the most recent population estimate. Harvest offtake was therefore the same for each three months of the year, despite population size changing at each three monthly time step. Population estimates were drawn from a lognormal distribution with a standard deviation dependent upon the survey precision (standard deviation/mean). Survey precision varied from 0 to 2 (i.e. 0-200%), but was set at


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0.2 unless otherwise stated. For each scenario, the average of 1,000 simulations is reported. Population models were run in Excel with the add-in POPTOOLS (Greg Hood CSIRO 2002, http://www.dwe.csiro.au/vbc/poptools/index.htm). 4.2 Results 4.2.1 Survey frequency As expected, the risk of quasiextinction is lower than that reported for the population modelled with rainfall variability for Menindee (Pople 2003). Reducing survey frequency not surprisingly increases the probability of quasiextinction (Fig. 4). Although the increase does not appear dramatic, a five-year survey frequency returns a risk of ~10% of the population falling below 2 kangaroos km-2 and ~20% for a threshold of 5 kangaroos km-2. The equivalent risks for an annual survey frequency are 50% (Fig. 6). To make costs comparable, the potential gains and losses incurred by the kangaroo industry, graziers, conservationists and any other stakeholders from adopting various monitoring programs need to be put onto the same scale. This would require detailed exploration and so is not determined here. Instead, a simple estimate of survey cost is contrasted with quasiextinction risk for increasing survey frequency. This should provide a first approximation of the appropriate survey frequency and the nature of the trade-off. There are fixed costs associated with conducting aerial surveys that do not change if surveys are conducted less frequently. These include labour costs and can be assumed to be $50,000 per annum. The variable costs primarily comprise aircraft running costs and are assumed to be $50,000 per survey. The total five-year survey cost (fixed + variable x no. of surveys) is shown in Figure 8. This shows the everdiminishing savings from reducing survey frequency. Quasiextinction risk from Figure 4 is also shown in Figure 8, but only for a threshold density of 2 kangaroos km-2. Risk of quasiextinction increases dramatically beyond a survey frequency of every four years. The actual probability should be interpreted cautiously as it is dependent on the model structure and parameters and these have not been assessed for this population. Furthermore, the acceptable level of risk is a value judgement.


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Risk of falling below threshold in 20y

1.00 CV(N)

0.90 0.80

2.0

0.70

1.0 0.60

0.5 0.2

0.50

0.0

0.40 0.30 0.20 0.10 0.00 0

1

2

3

4

5

6

7

8

9

10

-2

Threshold density (kangaroos km )

Fig. 6. Probability of quasiextinction over 20 years from a harvest rate of 15% with a precision (SD/mean) of 0-2.

Risk of falling below threshold in 20y

1.0

Survey frequency and CV

0.9 0.8 0.7

5 and 0.5

0.6

5 and 0.2

0.5

1 and 0.5 1 and 0.2

0.4 0.3 0.2 0.1 0.0 0

1

2

3

4

5

6

7

8

9

10

-2

Threshold density (kangaroos km )

Fig. 7. Probability of quasiextinction over 20 years from a harvest rate of 15% with a precision (CV=SD/mean) of 0.2 and 0.5 and survey frequency of 1 and 5 years.


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500

0.08

450

$

P

0.06

400

0.04

350

0.02

300

0.00

250 0

1

2

3

4

5

x $1,000

Probability of D < 2km

-2

0.10

6

Survey frequency Fig. 8. Probability of the population dropping below 2 kangaroos km-2 (i.e. quasiextinction) over 20 years (solid line) from a harvest rate of 15% with a precision (SD/mean) of 0.2 and survey frequency of 1 and 5 years. Also shown is the cost of aerial surveys over five years (dotted line) given survey frequencies of 1-5 years.


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5. Management recommendations Whether the study area should be divided into two or more zones will depend partly on whether management objectives vary within the area, partly on ease of administration and partly on the precision of population monitoring. The survey design shown in Figure 3 should provide population estimates with an acceptable precision of 20% in two zones in the study area, but this needs to be realised. Shoot-and-let-lie licences are currently issued from four NPWS offices. It would seem logical to issue commercial harvesting tags and licences and SLL licences from the same office. The problem is that NPWS administrative boundaries for the issue of SLL licences are quite different to RLPB boundaries. There are a number of options. Quotas could be issued for each RLPB and commercial tags and licences issued by all four NPWS offices. This has the advantage of tags being issued by NPWS staff most familiar with a property. There is the complication of allocating a regional quota to smaller areas, but this is done presently in the commercial zone because tags are issued to properties. The difference here is that there is an additional step in dividing the zone quotas among the four NPWS offices. This could be done fairly easily by overlaying the NPWS administrative boundaries over the map showing density strata in Figure 3. Alternatively, commercial tags and licences could be issued centrally, say from the Queanbeyan office. A survey frequency of three years with a precision of 20% appears to increase the risk of overharvest only slightly, while substantially reducing survey costs. Whether the increase in risk is acceptable is a decision for management in consultation with stakeholders. Other harvest strategies could be employed including a lower harvest rate (e.g. 10%) or perhaps limiting harvest effort by restricting the number of shooters. Given that almost 30% of the area is in National Park or State Forest, and terrain and vegetation will limit shooter access to other areas, there is a considerable safety net to guard against overharvesting. It is now well known that such spatial refuges can minimise the risk of overexploitation (Hall 1998; Lauck et al. 1998). To be effective, protected areas need to contain source populations that can repopulate areas depleted through harvesting. In the short term (i.e. 10 years. A further qualifying point is that overall kangaroo densities within these refuges are likely to be lower than the surrounding regions. The higher densities will be on the margins of refuges, where forested areas abut open grazing lands. In short, spatial refuges in the region should ensure regional persistence and will reduce the risk of overharvesting in the vicinity of a refuge, but be less effective with distance from a refuge. A further safety net would be a threshold population density below which there is no harvesting. In theory, when there is uncertainty about a population’s size and dynamics, harvest offtake can be maximised and low probability of quasiextinction achieved by imposing a threshold density and allowing higher rates of harvest above the threshold (Engen et al. 1997; Milner-Gulland et al. 2001). The problem is that the temporal variation in harvest offtake increases with the density at which the threshold is set. This has been discussed for kangaroos by Pople (2003) who


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considered that, given that the kangaroo industry is unlikely to operate at densities below 2-5 kangaroos km-2, imposing a threshold around this density would ensure that this in fact occurs. This would guard against an increase in the value of kangaroo products allowing shooters to operate at lower densities. It would also increase public confidence that the harvest is sustainable, because they would not be relying on the industry’s decision to cease harvesting being determined by market forces.

Acknowledgements Numerous people provided helpful discussion on the distribution and abundance of kangaroos in the district, including Lisa Collins, Andrew Moore, Simon Allender and Pam O’Brien from NPWS offices, Mark McGaw, Tim Sears, Col Elphick, Ian Klingham and Kevin Baker from RLPB offices, and landholders Lindsey Butt, Geoff McFarlane, Tony O’Shea, Andrew Bain and John Betts, and Bruce Hazell from Bookham Agricultural Bureau. We also thank Stephen Naven for providing coverages of RLPBs, National Parks and State Forests. References Borchers DL, Zucchini W, Fewster RM (1998) Mark-recapture models for line transect surveys. Biometrics 54, 1207-1220. Buckland ST, Anderson DR, Burnham KP, Laake JL (1993) 'Distance Sampling.' (Chapman and Hall: London) Bureau of Rural Sciences (2001) '1996/97 Land Use of Australia, Version 2.' National Land and Water Resources Audit, Canberra. Cairns SC (2003) 'A report to the New South Wales National Parks & Wildlife Service on the consultancy: Kangaroo Monitoring New England Tablelands Helicopter Survey.' Unpublished report to New South Wales National Parks and Wildlife Service, Dubbo, NSW. Cairns SC, Grigg GC (1993) Population dynamics of red kangaroos (Macropus rufus) in relation to rainfall in the South Australian pastoral zone. Journal of Applied Ecology 30, 444-458. Caughley G (1977) 'Analysis of Vertebrate Populations.' (Wiley and Sons: London) Caughley GJ (1979) Design for aerial censuses. In 'Aerial Survey of Fauna Populations' pp. 15-23. (Australian Government Publishing Service: Canberra) Clancy TF, Pople AR, Gibson LA (1997) Comparison of helicopter line transects with walked line transects for estimating densities of kangaroos. Wildlife Research 24, 397-409.


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Engen S, Lande R, Saether B-E (1997) Harvesting strategies for fluctuating populations based on uncertain population estimates. Journal of Theoretical Biology 186, 201-212. Geoscience Australia (2001) ’Relief. Digital dataset.’ National Land and Water Resources Audit, Canberra. Gerrodette T (1987) A power analysis for detecting trends. Ecology 68, 1364-1372. Gilroy J (1999) Kangaroo monitoring in relation to the kangaroo management plan in New South Wales. Australian Zoologist 31, 306-308. Hall SJ (1998) Closed areas for fisheries management - the case consolidates. Trends in Ecology and Evolution 13, 297-298. Harris RB (1986) Reliability of trend lines obtained from variable counts. Journal of Wildlife Management 50, 165-171. Hill GJE (1981a) Distribution of grey kangaroos in south, inland Queensland. Australian Rangeland Journal 3, 58-66. Hill GJE (1981b) A study of the habitat preferences in the grey kangaroo. Australian Wildlife Research 8, 245-254. Lauck T, Clark CW, Mangel M, Munro GR (1998) Implementing the precautionary principle in fisheries management through marine reserves. Ecological Applications 8, s72-s78. Milner-Gulland EJ, Shea K, Possingham H, Coulson T, Wilcox C (2001) Competing harvesting strategies in a simulated population under uncertainty. Animal Conservation 4, 157-167. New South Wales National Parks and Wildlife Service (2001) ’The New South Wales Kangaroo Management Program. A management program for the utilisation of four kangaroo species in NSW.’ (New South Wales National Parks and Wildlife Service: Sydney) http://www.nationalparks.nsw.gov.au/npws.nsf/Content/Kangaroo+manageme nt+program Pople A (1989) Habitat associations of Australian Macropodoidea. In ’Kangaroos, Wallabies and Rat-kangaroos’. (Eds G Grigg, P Jarman and I Hume) pp. 755766. (Surrey Beatty and Sons: Sydney) Pople A (2003) ’Harvest management of kangaroos during drought.’ Unpublished report to New South Wales National Parks and Wildlife Service, Dubbo, NSW. Pople A (in press) Population monitoring for kangaroo management. Australian Mammalogy. Pople AR (1999) Repeatability of aerial surveys. Australian Zoologist 31, 280-286.


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Pople AR, Cairns SC, Clancy TF, Grigg GC, Beard LA, Southwell CJ (1998) Comparison of surveys of kangaroos in Queensland using helicopters and fixed-wing aircraft. The Rangeland Journal 20, 92-103. Pople AR, Grigg GC (1998) ’Commercial harvesting of kangaroos in Australia.’ Environment Australia, Canberra. http://www.ea.gov.au/biodiversity/tradeuse/wild-harvest/kangaroo/harvesting/index.html RSPCA (2002) ’Kangaroo Shooting Code Compliance: A survey of the extent of compliance with the requirements of the Code of Practice for the Humane Shooting of Kangaroos.’ Environment Australia, Canberra. Scott-Kemmis D (1979) The distribution and abundance of grey kangaroos in relation to environment in arid and semi-arid areas of New South Wales. M.Sc. thesis, University of Sydney, Sydney. Southwell C (1989) Techniques for monitoring the abundance of kangaroo and wallaby populations. In ’Kangaroos, Wallabies and Rat-kangaroos’. (Eds G Grigg, P Jarman and I Hume) pp. 659-693. (Surrey Beatty and Sons: Sydney) Southwell C, Sheppard N (2000) Assessing harvested populations of the euro (Macropus robustus erubescens) in the Barrier ranges of western NSW. Australian Mammalogy 21, 165-171. Southwell CJ, Cairns SC, Pople AR, Delaney R (1999) Gradient analysis of macropod distribution in open forest and woodland of eastern Australia. Australian Journal of Ecology 24, 132-143. Southwell CJ, Weaver KE, Cairns SC, Pople AR, Gordon AN, Sheppard NW, Broers R (1995) Abundance of macropods in north-eastern New South Wales, and the logistics of broad-scale ground surveys. Wildlife Research 22, 757-766. Thompson SK (1992) ’Sampling.’ (John Wiley and Sons: New York)


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Appendices

Appendix 1. Forest type and land use in the study area. CR, Crookwell; GO, Goulburn; YA, Yass; CT, Cootamundra; TU, Tumut; CM, Cooma. Forest type is categorised by crown cover: closed forest, 80-100%; open forest 50-80%; woodland 20-50%; open, 0-20%. The landuse coverage (Bureau of Rural Sciences 2001) is © Commonwealth of Australia (National Land and Water Resources Audit) 2001.


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Appendix 2. Landscape relief, National Parks and State Forests in the study area. Relief is calculated as the difference in elevation between the nearest ridge uphill and the nearest stream downhill in the catchment of the each stream. Calculations used the interim 9 sec DEM. CR, Crookwell; GO, Goulburn; YA, Yass; CT, Cootamundra; TU, Tumut; CM, Cooma. The relief coverage (Geoscience Australia 2001) is © Commonwealth of Australia (Geoscience Australia) 2001.