Detailed biological data are informative, but robust trends are needed for informing sustainability of wildlife harvesting: a case study of reptile offtake in Southeast Asia

Conservation biologists often use sophisticated models of population functioning to predict the levels at which harvesting of wild populations will be sustainable. We argue that this approach is not useful for species that, although abundant, are near impossible to survey cost-effectively with enough precision to gather key data to input as model parameters. Our examination of >7000 Reticulated Pythons (Malayopython reticulatus), collected for the commercial skin industry, provides extensive information on life-history traits, population size structure, sex ratio and diets across sites in Kalimantan, Sumatra and Peninsular Malaysia. Our data reveal many interesting divergences between populations from north vs south of the equator (e.g., in body sizes, reproductive frequencies, seasonal timing of reproduction), and a trend for snakes to be smaller from more intensively harvested sites. In combination with earlier analyses, >10,000 individuals of M. reticulatus have been dissected for information on ecological attributes (more than for any other snake species worldwide). Nonetheless, in the absence of demographic data (e.g., on underlying abundances and rates of survival and growth of free-ranging snakes), the most robust estimate of sustainability of the harvest comes from long-term trends in mean body sizes, life history traits, and offtake rates. Because mathematical models depend upon accurate estimation of abundance and demography, parameters unobtainable for these secretive, well-camouflaged reptiles, managers should prioritise gathering long term data on harvest trends instead.