Lighting the Ivory Track: Are Near-Infrared and Chemometrics Up to the Job? A Proof of Concept

Abstract

A rapid tool to discriminate rhino horn and ivory samples from different mammalian species based on the combination of near-infrared reflection (NIR) spectroscopy and chemometrics was evaluated. In this study, samples from the Australian Museum mammalogy collection were scanned between 950 nm and 1650 nm using a handheld spectrophotometer and analyzed using principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA). An overall correct classification rate of 73.5% was obtained for the classification of all samples. This study demonstrates the potential of NIR spectroscopy coupled with chemometrics as a means of a rapid, nondestructive classification technique of horn and ivory samples sourced from a museum. Near-infrared spectroscopy can be used as an alternative or complementary method in the detection of horn and ivory assisting in the combat of illegal trade and aiding the preservation of at-risk species.

Light at the museum – A near impossible result

“…We found that the PCA loadings associated with the first PC were observed around 1075 nm, 1200 nm and 1400 nm corresponding with N–H and O–H overtones were the most important. 2 The PLS-DA model developed correctly classified more than 74% of the samples in the entire data set. While Rhino samples were classified correctly (95%) elephant, walrus and hippo samples yield low to intermediate classification rates (between 60 and 75%).…”

“…Similar results were reported by other authors where ivory samples were analysed using short wavelengths in the NIR region. 2,13–15…”

“…The spectra were collected using a MicroNIR spectrophotometer device (Viavi, Santa Rosa, CA, USA) working in the wavelength range between 950 and 1650 nm. 2 The averaged spectra were analysed by a combination of principal component analysis (PCA) and partial least square discriminant analysis regression (PLS-DA) using The Unscrambler X software (version 10.5, CAMO Software AS, Oslo, Norway). Information and details about the instrument setup, operational protocols (e.g.…”

“…As highlighted by the original podcast that captured the attention of my colleagues and I, illegal trade is a major contributor to the destruction of wildlife species due to the high commercial value attributed to their animal products. 2,8–12 Quantifying the illegal harvest of protected animal products is essential for the conservation and protection of endangered species, however it is also recognised as being incredibly time consuming and labour intensive requiring significant analyst expertise. 2,8–12 Moreover, the expansion of the application of the descriptor ivory with it no longer being restricted to the tusks of elephants but now describing any mammalian tooth or tusk has inflated the responsibilities and scope of these experts role.…”

“…Rhino horn is another animal product that due to its illegal trade, predominately driven by its use in traditional Asian medicine, poses a significant threat to the global survival of the rhinoceros. 2,8–12 Unlike ivory, rhino horn is composed of keratinous materials which can be classified as either α- or β- types with its structure often described as an epidermal derivative, consisting of keratinised tubules within a melanin and calcium matrix. 2,8–12…”