The absence of robust species-specific methods to estimate the number of animals in seizures of pangolin scales is a major barrier to effective law enforcement. Therefore, studies focused on developing methods to establish accurate conversion parameters are a priority. This study proposes improved methods to estimate the number of pangolins in the illegal trade to inform law-enforcing authorities. Based on the observations of 25 specimens, Indian pangolins were on average found to possess 511 scales. Three morph-types of scales were identified: broad rhombic (n=411), elongated kite shape (n=69), and folded scales (n=31). The mean dry weight of the three-scale morph-types was 7.5 g, 4.9 g, and 6.2 g. Based on the average frequency and mean dry weight of each scale morph type, the species-specific dry weight of scales for Indian pangolins was 3.6 kg. Accordingly, we propose new and improved methods based on scale morph-type frequencies and species-specific dry weight of scales to estimate the number of Indian pangolins from quantities of scales. Their accuracy was compared with current methods, and the improved methods were found to be more accurate.

CITES, conversion parameters, illegal wildlife trade, pangolins, scale seizures, Sri Lanka

Illegal wildlife trade (IWT) has become one of the most significant contemporary global conservation issues that threatens biodiversity (Biggs et al. 2017; Harfoot et al. 2018). This multi-billion-dollar industry has rapidly escalated in recent decades and has taken center stage in the global conservation policy agenda (‘tSas-Rolfes et al. 2019). The international IWT has been largely driven by poaching African elephants and rhinoceroses, while the pressure on endangered taxa such as tigers and pangolins has increased over recent decades (Rosen and Smith 2010; Biggs et al. 2017).

Pangolins (Pholidota: Manidae) are the most trafficked wild mammals, being heavily exploited across their range in Asia and Africa (Shepherd 2009; Challender et al. 2014a; Heinrich et al. 2016; Ingram et al. 2018). IWT of pangolins is primarily driven by the demand in Asian countries, especially China and Vietnam (Pantel and Chin 2009; Challender 2011; Challender et al. 2014b; Nijman et al. 2016). Pangolin are used in traditional Chinese medicine (largely scales), and pangolin meat is considered a delicacy in many Asian and African countries (Challender et al. 2015; Shairp et al. 2016). The increased exploitation has led to a drastic decline of pangolin populations in Asia (Wu et al. 2004; Challender 2011; Challender et al. 2015). Simultaneously, a perceptible increase in the trafficking of African pangolins, almost exclusively scales, to Asian markets has occurred (Challender and Waterman 2017).

Indian pangolin has been in IWT since the early 2000s, where scales are predominantly sourced in India and Pakistan being trafficked to China along routes through Myanmar and Nepal (Challender and Waterman 2017). Indian pangolin at present is under considerable hunting pressure due to local consumption and rising demand for its scales and meat in East Asian markets (Baillie et al. 2015; Mahmood et al. 2019; Perera and Karawita 2020). The virtual extirpation of M. pentadactyla and M. javanica in East Asia is believed to be the primary driver of demand for M. crassicaudata in the present international IWT (Challender and MacMillan 2014; Mohapatra et al. 2015; Mahmood et al. 2020). The Indian pangolin populations in India and Pakistan have been over-exploited for international trade, and the growing demand and awareness of the lucrative markets for pangolin scales have expanded the source markets to Sri Lanka and Nepal (Challender and Waterman 2017; Perera et al. 2017; Mahmood et al. 2019). For instance, recent studies suggest local niche markets for pangolin meat and scales with a possibly growing international IWT of M. crassicaudata scales from Sri Lanka to South India (Perera et al. 2017; Perera and Karawita 2020).

Pangolins are usually trafficked as whole animals for their meat, possibly descaled and disemboweled (Sopyan 2008), and quantifying the number of individuals when whole is simple as they can be directly counted (Challender et al. 2015). However, estimating the number of pangolins being trafficked is more challenging when only scales are involved. Removed scales are dried and typically packed regardless of size or species and traded internationally (Sopyan 2008; Nijman et al. 2016). With a few exceptions, such as black-bellied and white-bellied pangolins, it is difficult to identify the pangolin species involved by visually inspecting scales. However, there is also a lack of capacity/knowledge among law enforcement personnel to correctly identify the species and their derivatives in illegal trade (Challender and Waterman 2017).

The current method of estimating the number of pangolins, i.e., Whole Organism Equivalents (WOEs), in the illegal trade of scales is weight-based and involves dividing the weight of a given seizure or trade volume by the weight of scales from a specific species (Challender et al. 2015; Challender and Waterman 2017). Robust estimates of the weight of scales only exist for the Chinese and Sunda pangolins (see Zhou et al. 2012). Wet weight (i.e., the weight associated with the moisture content) is more variable than the dry weight of scales. The rate of desiccation varies due to various environmental factors, including temperature and humidity. As such, dry-weight-based methods are more robust in estimating the number of animals from quantities of scales though it may not perform well in the case of Indian pangolin (Zhou et al. 2012).

According to recent studies, there is intra-specific variation in the total number of scales of Indian pangolins, ranging from 440 to 530 (Ullmann et al. 2019; Algewatta et al. 2021; Perera et al. 2021), though these disparities are likely due to different scale counting protocols adopted in various studies (Perera et al. 2020). It is further estimated that the scales account for about 30–35% of the total body weight of Indian pangolin (Mohapatra et al. 2015). Morphologically unique scale types can be observed in Indian pangolins (Perera et al. 2020; Algewatta et al. 2021). The scales differ in terms of the presence of grooves, size, and angle of the scales (Fig. 1). Such detailed morphological characteristics have been described for Indian pangolin (Manis crassicaudata) by Algewatta et al. (2021).

Figure 1.

a Broad rhombic/scapular shaped b elongated kite-shaped and c folded scales of an Indian Pangolin.

Indian pangolin is the only pangolin species recorded in Sri Lanka (Mahmood et al. 2019; Perera and Karawita 2020; Algewatta et al. 2021). There are no records to suggest that Sri Lanka is used as a transit point in the IWT of pangolin scales (Perera et al. 2017; Perera and Karawita 2020). Hence, the seizures of pangolin scales in Sri Lanka contain scales of Indian pangolins sourced from the country. In the Sri Lankan context, neither weight-based nor species-specific scale frequency methods have been used in estimating the WOEs. Hence, studies focused on developing accurate conversion parameters are essential, especially in law enforcement applications. This study establishes more accurate conversion parameters to determine the WOE for Indian pangolin scale seizures with detailed scale morphology and frequency observations.

The demand for Indian pangolins in the IWT is rising with exploitation pressure on Indian pangolin populations in new source markets such as Sri Lanka and Nepal (Challender and Waterman 2017; Mahmood et al. 2019). Indian pangolins show a wide distribution throughout Sri Lanka, occurring in a variety of habitats up to 1850 m above mean sea level with higher concentrations in the North-west, North-central, South-west lowlands, and South-eastern parts of the island (Karawita et al. 2018; Karawita et al. 2020). However, they have recently faced the threat of hunting and poaching for scales (Karawita et al. 2016; Perera and Karawita 2020). The absence of an accurate conversion parameter to determine the WOEs in confiscated scale consignments is an issue faced by law enforcement authorities. The current conversion parameters in use can lead to possible over-estimations or under-estimations WOEs in trade.

Following the descriptions and established protocols in literature (Perera et al. 2020; Algewatta et al. 2021), the species-specific dry weight of scales of an Indian pangolin was determined as 3.63 kg, based on the average frequency and mean dry weight of each scale morph type. Although this species-specific conversion parameter was indirectly approximated based on scale frequency counts of 25 specimens, and an average weight of each scale morph-type determined by weighing individual scales from scale seizures, we argue that it is the most accurate conversion parameter for the species published up to now. Nonetheless, scale frequency counts and an average weight of a scale of an Indian pangolin determined using destructive methods (remove each scale from the body of a pangolin and measure the weight) would yield the most accurate conversion parameter.

Our observations on confiscated scale consignments in Sri Lanka suggest that Indian pangolin scales in the IWT mainly comprise scales extracted from adult and sub-adult pangolins. Therefore, the scales used for dry weight measurements were predominantly from adults and sub-adults. Juvenile Indian pangolins have soft and smaller scales on their bodies, and the scales harden as they grow (Mahmood et al. 2020). Also, scales of juveniles are less differentiated into the three scale morph-types compared to sub-adults and adults. Hence, the consignments which were used to measure individual weights of scales did not include scales of juvenile pangolins.

The weight-based method utilizes the average dry scale weight of Chinese pangolin (573.47 g), as the species’ conversion parameters have been well established (Zhou et al. 2012; Ullmann et al. 2019). However, the Chinese pangolin is comparatively small, typically weighing between 3 to 8 kg, and could measure up to 89 cm (Wu et al. 2020). On the other hand, recent studies on morphometrics of Indian pangolins suggest that an Indian pangolin can outgrow the African Giant Pangolin (Smutsia gigantea), and an adult male Indian pangolin can weigh over 35 kg and measure up to 178 cm in length (Algewatta et al. 2021; Perera et al. 2021). Using the dry weight of the scales of a Chinese pangolin to determine the WOEs of Indian pangolin scale consignments could lead to severe overestimations. This was evident by the results of this study, where the highest number of WOEs were estimated with the weight-based method (Tables 4 and 6). Replacing the dry weight of the scales of a Chinese pangolin with the species-specific dry weight of scales derived for an ‘average’ Indian pangolin yielded more realistic estimates of WOEs.

The WOE estimation method based on scale frequency and weight proposed by Ullmann et al. (2019) assumes that an Indian pangolin has 495 scales on average. Based on a larger sample of Indian pangolin specimens (n=25), we determined that an Indian pangolin has 447 ‘tradable’ scales as smaller scales on the head region are difficult to remove, thus seldom found in scale seizures. We argue that this is a more prudent estimate of the scale frequency of pangolin in IWT. Nonetheless, the final estimates of the WOEs in seizures derived from Ullmann et al. (2019) method and, when scale frequency is replaced by this study’s estimate (447 scales), did not differ substantially.

This study further proposed and tested a method based on the frequency of scale morph-type to estimate the WOEs in Indian pangolin seizures. We argue that the maximum number WOEs in a given consignment of Indian pangolin scales can be most accurately determined by obtaining the maximum ratio between fractions of “number of scales of a specific morph-type in the seizure” (numerator) and the “average number of scales if the same morph-type in a pangolin” (denominator). Folded scales are the least frequent scale morph-type (31 scales) in an Indian pangolin (Algewatta et al. 2021); thus, for the seizure of Indian pangolin scales examined in this study, this is the most accurate estimate of the number of WOEs. Using other scale types in the calculations leads to underestimates, as evident by the results (Table 6). Similarly, all other estimation methods tested in this study yielded underestimations of the WOEs.

Both Ullmann et al. (2019)’s method and the proposed scale morph-type frequency-based method are based on samples drawn from the seizure. The sample size has a significant effect on the accuracy of WOE estimates. For instance, our observations revealed that about 4 to 5 samples of 200 g had to be drawn from a scale consignment weighing 5.8 kg to arrive at consistent estimates of WOEs from these two methods (i.e., cumulative sample of about 15% of the weight of the consignment was required). Furthermore, smaller scales in containers are likely to settle at the bottom; hence thorough mixing is required before drawing samples (Ullmann et al. 2019). Thus, using Ullmann’s et al. (2019) method and the proposed scale morph-type frequency-based method for large seizures of Indian pangolin scales may be cumbersome procedures for law enforcement entities to follow, especially in occasions where quick estimation of WOEs is desired. However, the proposed scale morph-type frequency-based method can yield more accurate estimates of WOEs for smaller consignments often confiscated at airports by customs officers.

The weight-based method with a species-specific average dry weight of scales derived for an Indian pangolin can be recommended as a more practical approach in estimating WOEs. This simple and straightforward approach only requires the weight of the seizure. In the Sri Lankan context, there have been about five confiscations of Indian pangolin scales by the law enforcement authorities between 2012 and 2019, where WOEs have been estimated on only one occasion (Perera et al. 2017; Perera and Karawita 2020). The four seizures made by the Sri Lanka Customs at Bandaranayake International Airport weighed between 1.7 and 11 kgs, and the WOEs have not been estimated in determining the fines (Perera and Karawita 2020). The largest stock of 130 kgs of Indian pangolin scales was discovered from Kalpitiya in the North-western part of the country by the Police in November 2017. It was estimated that the seizure represents approximately 150 WOEs with no conversion parameters cited (Perera and Karawita 2020). On weight-based conversions, it appears that 0.87 kg has been used as the conversion factor. According to our study findings, these are serious overestimations of the WOEs, where the seizure would represent only 37 WOEs according to species-specific dry weight of scales established in this study. As such, the findings of this study will be beneficial in the future for the reliable estimation of WOEs in Indian pangolin scale seizures. The scale morph-type frequency-based method proposed in this study can be further developed as a validation tool.

An Indian pangolin, on average, has 411 broad rhombic scales, 69 elongated kite-shape scales, and 31 folded shape scales. The mean dry weight of the three-scale morph-types is 7.5 g, 4.9 g, and 6.2 g, respectively. Accordingly, the average dry weight of scales of an Indian pangolin in IWT is 3.6 kg. Using the species-specific dry weight of scales for Indian pangolin (3.6 kgs) as the conversion parameter in weight-based conversions yields more realistic estimates of WOEs involved in IWT, and the method is particularly suited for large seizures of scales. The proposed scale morph-type frequency-based method provides the most accurate estimates of the WOEs but has limitations in the applicability at ground level. Nonetheless, the method can be used to determine the WOEs for smaller seizures typically confiscated at airports.

The authors would like to acknowledge the Department of Wildlife Conservation, Sri Lanka, Pinnawala Zoological Garden of the Department of National Zoological Gardens, National Museum Colombo Sri Lanka and Sri Lanka Customs for granting permission to access their specimens, and the University of Sri Jayewardenepura, Sri Lanka for facilitating the research.

This research was funded by the University of Sri Jayewardenepura (Research grant No: ASP/01/RE/SCI/2017/14) and the Center for Sustainability of the Department of Forestry and Environmental Science, University of Sri Jayewardenepura.