Mongolian gazelle population assessment 761
Railway bisects the gazelle range in Mongolia along a north- west/south-east axis (Fig. 1). In Russia, there are c. 115 vil- lages within the gazelle’s range, primarily located along rail- roads, and the town of Borzya with a population of .30,000 people. There are c. 0.4 million livestock (mostly cattle) in the Russian range of the gazelle, and ,3% of the steppe is converted to croplands. Existing linear infrastruc- ture in Russia, apart from 125 km of border sections with strong fences, is relatively permeable, enabling the gazelles to move across the landscape within the country and across its borders (Kirilyuk, 2021).
Methods
Population surveys in Mongolia Gazelle population surveys were conducted during May– June in 2019 and 2020, prior to the calving season, across three regions: central and eastern Mongolia (steppe and mountain steppe ecosystems), southern Gobi, and Khomiin Tal National Park (Fig. 1). The total extent of the three survey regions is 535,575 km2 (81% central and eastern Mongolia, 18% southern Gobi and 1% Khomiin Tal National Park), which represents 79% of the gazelle range in Mongolia. The remaining 146,288 km2 (21%) of known gazelle range in south-western Mongolia were not surveyed as the region is generally unsuitable for driving line transects and gazelles are only documented occasion- ally and in small numbers. However, by utilizing distance sampling data from the neighbouring regions, we gener- ated an approximate estimate of the gazelle population in this region. Gazelle numbers were recorded by driving line trans-
ects and using distance sampling protocols in the central, eastern and southern regions of Mongolia (Buckland et al., 2001, 2015;Young et al., 2010; Olson et al., 2011; Buuveibaatar et al., 2017). This method accurately estimates the mean density of ungulate groups as it ac- counts for detectability and considers the proportion of groups not seen by observers in the area sampled by
fitting a detection function to the distances measured to the centre of the observed groups. Estimated group dens- ity (groups per unit area) together with the expected group size allows for the estimation of individual density (individuals per unit area), which in turn provides the population size when combined with the area of the sur- vey region.We designed the survey and analysed the data using the programme Distance (Strindberg et al., 2004; Thomas et al., 2010). Weconducted the distance sampling surveys in May and
June in 2019 and 2020 across 98,216 km2 and in the southern Gobi and 433,245 km2 in the central and eastern steppe re- gions (Fig. 1). In 2019,we drove 64 transects of 4–205 km in length (total effort of 3,464 km; Table 1) in three teams (each consisting of four observers). In 2020,we drove an addition- al 40 transects of 33–587 km in length (total effort of 13,895 km) in six teams simultaneously. Each team received train- ing in distance sampling survey protocols prior to the field surveys. The spacing between the survey transects was 20 km for the southern Gobi and 30 km for central and eastern Mongolia (Fig. 1). We orientated the transects for both sur- veys in a north–south direction, to systematically cover the different habitats within the heterogeneous landscape (e.g. mountain forest, steppe and Gobi Desert). Whilst driving at 20–40 km/h, following the transect lines as closely as pos- sible, observers searched for gazelle groups.Werecorded ra- dial distance from the transect line to the centre of the group, the compass bearing to the centre of the group and group size using a handheld laser range finder (maximum range c. 2,500 m), compass, binoculars and GPS units. We estimated the gazelle population in Khomiin Tal
National Park from total counts because the Park is rela- tively small (4,114 km2) compared to the other two survey regions and gazellemovement outside the area is restricted by lakes, sand dunes and mountains. We conducted this survey inMay 2020,with 11 rangers simultaneously driving along c. 656 km of survey routes covering the entire National Park. The rangers counted gazelle groups en- countered along the routes using binoculars and spotting scopes.
TABLE 1 Survey details and observation statistics from line transect surveys for the Mongolian gazelle Procapra gutturosa in the southern Gobi in 2019 and central and eastern Mongolia in 2020 (Fig. 1). The table shows, for the different strata and overall, the survey year, area and effort, numbers of observed groups and individuals, and the mean, median and range of the number of individuals per group.
Stratum Southern Gobi
Central & eastern Mongolia West
Central
North Kherlen South-west Menen
Overall (central & eastern Mongolia)
2019 98,216 2020 138,912
2020 76,516 2020 83,194 2020 108,941 2020 25,682 2020 433,245
Year Area (km2) Effort (km) Groups Individuals Mean Median Range 1–600
3,462 4,220
2,345 3,310 3,297 723
13,895 58
226 303 179 208 131
1,047
1,719 5,081
34,921 79,277 9,136
23,276 151,691
29.6 22.5
6.0 7.0
115.3 25.0 442.9 63.0 43.9 12.5 177.7 12.0 160.4 16.0
Oryx, 2024, 58(6), 759–768 © The Author(s), 2024. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605323001515 1–221
1–2,850 1–16,200 1–950
1–8,400 1–16,200
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