Line Transect Surveys Underdetect Terrestrial Mammals: Implications for the Sustainability of Subsistence Hunting

Abstract

Conservation of Neotropical game species must take into account the livelihood and food security needs of local human populations. Hunting management decisions should therefore rely on abundance and distribution data that are as representative as possible of true population sizes and dynamics. We simultaneously applied a commonly used encounter-based method and an infrequently used sign-based method to estimate hunted vertebrate abundance in a 48,000-km2 indigenous landscape in southern Guyana. Diurnal direct encounter data collected during three years along 216, four-kilometer -long transects consistently under-detected many diurnal and nocturnal mammal species readily detected through sign. Of 32 species analyzed, 31 were detected by both methods; however, encounters did not detect one and under-detected another 12 of the most heavily hunted species relative to sign, while sign under-detected 12 never or rarely collected species relative to encounters. The six most important game animals in the region, all ungulates, were not encountered at 11–40% of village and control sites or on 29–72% of transects where they were detected by sign. Using the sign methodology, we find that tapirs, one of the terrestrial vertebrates considered most sensitive to overexploitation, are present at many sites where they were never visually detected during distance sampling. We find that this is true for many other species as well. These high rates of under-detection suggest that behavioral changes in hunted populations may affect apparent occurrence and abundance of these populations. Accumulation curves (detection of species on transects) were much steeper for sign for 12 of 16 hunted species than for encounters, but that pattern was reversed for 12 of 16 species unhunted in our area. We conclude that collection of sign data is an efficient and effective method of monitoring hunted vertebrate populations that complements encounter and camera-trapping methods in areas impacted by hunting. Sign surveys may be the most viable method for large-scale, management-oriented studies in remote areas, particularly those focused on community-based wildlife management.

Logging and indigenous hunting impacts on persistence of large Neotropical animals

“…, Fragoso et al . ). Hunting surveys were administered to every household in the community by locally recruited indigenous technicians who were residents of the community and trained by project researchers.…”

Evaluación Del Plan De Manejo De Animales De Caza en La Reserva Nacional Pucacuro

“…El modelo de esfuerzo usa información de los cazadores, quienes conocen otras señales para encontrar a sus presas (Pérez Peña et al, 2012). A diferencia de transectos que sólo usan avistamientos y necesitan de grandes esfuerzos o recorridos para estimar las abundancias con mayor precisión (De Thoisy et al, 2008) y pueden subestimar la abundancia de algunas especies, por ejemplo los ungulados (Fragoso et al 2016). Los resultados de área de ocupación no mostraron reducción drástica como los resultados de avistamientos por transectos, porque además de avistamientos incluye registros indirectos como huellas y olores.…”

Stronger together: comparing and integrating camera trap, visual, and dung survey data in tropical forest communities

“…Overlooking methodological differences can lead to misinterpretations of the effect of human and natural disturbances on populations and communities, leading to poor management and conservation decisions (Fragoso et al. ). This is of particular concern in tropical forests as dense vegetation exaggerates differences in the detection ability of different methods (Espartosa et al.…”

“…), but tend to underestimate cryptic and small animals as they are more difficult to detect (Fragoso et al. ). Dung transects involve recording observations of dung along transects and using estimates of dung production and decay rates to quantify populations.…”

“…While comparative studies of survey methods are less common in tropical forests, several studies have compared animal counts across different methods for one species or within a group of species with shared traits (Rovero and Marshall , Fragoso et al. , Whitworth et al. , Kamgaing et al.…”