Efficacy of field-based surveys for detecting and assessing demographics of giant snakes (Malayopython reticulatus) in Malaysia

Evaluating sustainable levels of offtake is central to regulating the commercial harvest of wildlife species, but methods developed for temperate-zone mammal and bird species may be inapplicable to tropical rainforest reptiles. For example, population viability models require information on abundance and on rates of growth, maturation, survival, and reproduction. For some intensively harvested reptiles - especially well-camouflaged ambush predators in densely vegetated habitats - such data are difficult to obtain. The feasibility of gathering this information is central to current debates about how best to evaluate the sustainability of commercial harvesting of reticulated pythons (Malayopython reticulatus) in Asia. Over a five-year period, we conducted 527 riverside surveys (with mark-recapture) for this species in a protected area in Sabah, Malaysia. Detectability of pythons was dependent on moon phase but always low (mean = 20%); and the total number of pythons captured (N = 159 total, N = 83 during standardized surveys) and recaptured (N = 25) despite that intensive long-term effort was insufficient to enable robust mathematical modelling. Our results suggest that attempts to base sustainable-harvesting targets for M. reticulatus on mathematical models are futile, and that repeated surveys of the attributes of harvested specimens provide a more reliable basis from which to evaluate sustainability.