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Vol. 54, 2015
Guanaco abundance and monitoring in Southern Patagonia:
distance sampling reveals substantially greater numbers than previously
reported
Alejandro Travaini1,
Sonia C Zapata2, Javier Bustamante3, Julieta
Pedrana1,4, Juan I Zanón2,5 and Alejandro
Rodríguez6*
1Centro
de Investigación de Puerto Deseado, Universidad Nacional de la
Patagonia Austral, CONICET, Avenida Prefectura Naval s/n, 9050 Puerto
Deseado, Santa Cruz, Argentina
2Centro de Investigación de Puerto Deseado,
Universidad Nacional de la Patagonia Austral, Avenida Prefectura Naval
s/n, 9050 Puerto Deseado, Santa Cruz, Argentina
3Department of Wetland Ecology, Remote Sensing and GIS
Lab (LAST-EBD), Estación Biológica de Doñana, CSIC, Américo Vespucio
s/n, 41092 Sevilla, Spain
4Recursos Naturales y Gestión Ambiental, Instituto
Nacional de Tecnología Agropecuaria, EEA Balcarce, CC 276, 7620
Balcarce, Buenos Aires, Argentina
5Centro para el Estudio y Conservación de las Aves
Rapaces en Argentina, UNLPam, INCITAP, CONICET, Avda. Uruguay 151, 6300
Santa Rosa, La Pampa, Argentina
6Department of Conservation Biology, Estación
Biológica de Doñana, CSIC, Américo Vespucio s/n, 41092 Sevilla, Spain
Abstract
Background: Guanacos (Lama guanicoe) are thought to have
declined in Patagonia mainly as a result of hunting and sheep ranching.
Currently accepted estimates of total population size are extrapolated
from densities obtained through strip transects in local studies. We
used road surveys (8,141 km) and distance sampling to estimate guanaco
density and population size over major environmental gradients of Santa
Cruz, a large region in southern Patagonia. We also calculated the
survey effort required to detect population trends in Santa Cruz.
Results: We found considerable spatial variation
in density (1.1 to 7.4 ind/km2), with a mean value of 4.8
ind/km2, which is more than twice the mean value
guessed for central and northern Patagonia. Consequently, guanaco
numbers in Santa Cruz were estimated at 1.1 million individuals (95% CI
0.7 to 1.6), which almost doubles current estimates of guanaco
population size in South America. High guanaco abundance was found in
arid lands, overgrazed and unable to support profitable sheep stocks.
Detecting a 50% change in guanaco population size over a 10-year period
requires substantial monitoring effort: the annual survey of between 40
and 80 30-km transects, which becomes up to 120 transects if trends are
to be detected over 5 years.
Conclusions: Regional patterns in
guanaco density can only be detected through large-scale surveys.
Coupling these surveys with distance sampling techniques produce robust
estimates of density and its variation. Figures so obtained improve
currently available estimates of guanaco population size across its
geographic range, which seem to be extrapolated from strip counts over
small areas. In arid lands degraded by sheep overgrazing, sustainable
use of guanaco populations would help harmonize guanaco conservation,
socio-economic progress of rural areas, and eventually the restoration
of shrub-steppes.
Key words: Distance sampling; Guanaco;
Livestock; Monitoring; Patagonian shrub-steppe; Sustainable uses.
*Correspondence: E-mail: alrodri@ebd.csic.es
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