Research Article |
Corresponding author: Thomas Ziegler ( ziegler@koelnerzoo.de ) Academic editor: Klaus Henle
© 2018 Truong Quang Nguyen, Hai Ngoc Ngo, Cuong The Pham, Hoang Nguyen Van, Chung Dac Ngo, Mona van Schingen, Thomas Ziegler.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Nguyen TQ, Ngo HN, Pham CT, Van HN, Ngo CD, van Schingen M, Ziegler T (2018) First population assessment of the Asian Water Dragon (Physignathus cocincinus Cuvier, 1829) in Thua Thien Hue Province, Vietnam. Nature Conservation 26: 1-14. https://doi.org/10.3897/natureconservation.26.21818
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The Asian Water Dragon, Physignathus cocincinus Cuvier, 1829, was originally described from southern Vietnam. Wild populations of this species are strongly affected by harvesting, particularly in central Vietnam, while potential negative impacts are not yet foreseeable. This study provides the first population size estimation using a capture-recapture approach and an evaluation of threats to and trade levels in P. cocincinus in Thua Thien Hue Province, central Vietnam. Field surveys were conducted at 14 sites of known occurrences of the species in Thua Thien Hue during April and June of 2016 and 2017. The estimated population size of the species amongst these sites ranged from 232 to 250 individuals. The mean abundance varied from 1.98–2.64 individuals/100 m along inhabited streams. This study revealed harvest activities for local food consumption and to supply the pet trade. Accordingly, imports of several thousand living individuals per year from Vietnam into the EU were documented. It was further demonstrated that the level of negative impacts on different sub-populations is in accordance with respective abundances and the incidence of adults. This finding indicates that rising harvest levels in concert with decreasing habitat quality, might seriously affect the wild population of P. cocincinus in the future. Thus, the authors herein emphasise the necessity for increased conservation measures and for monitoring of the species as well as its natural habitat in order to warrant a sustainable use of the species in the future.
Population size, capture-recapture method, trade, conservation, risk assessment
The Asian Water Dragon, Physignathus cocincinus, was originally described by Cuvier, 1829 from southern Vietnam, subsequently recorded from southern China, Myanmar, Thailand, Laos and Cambodia and reported as introduced in Taiwan (
Survey sites were selected based on previous reports on known occurrences of P. cocincinus in Phong Dien Nature Reserve (NR) in Phong Dien District, Sao La NR in A Luoi District and Bach Ma National Park (NP) in Nam Dong District, Thua Thien Hue Province, Vietnam (
Field surveys were conducted in April and June 2016 and 2017, respectively, during the active season of the Asian Water Dragon. During previous surveys, P. cocincinus was found to be a riparian species, being exclusively recorded in the immediate proximity to or above the water at the stream banks. Thus, the riverine vegetation of selected rocky streams was sampled from downstream to upstream by walking through the water and intensively investigating both sides of the streams equally. The surveyed streams were characterised by a width of about 1–12 m, depths of up to 200 cm and dense vegetation along and above the stream. Since P. cocincinus is a diurnal species, night excursions were conducted between 1900h and 2400h, when animals were expected to rest on branches above the water (Fig.
A Habitat of Physignathus cocincinus in Nam Dong District, Thua Thien Hue Province B Resting perch in front of waterfall C Adult male D Adult female. Photos: Hai Ngo.
In total, 14 sections of 14 different streams with lengths varying from 320 to 1400 m (see Table
Stream | District | Physignathus cocincinus | Elevation (m. asl) | Length (m) | Habitat type |
---|---|---|---|---|---|
1 | Phong Dien | Present | 44–90 | 1,160 | Primary forest |
2 | Phong Dien | Present | 43–75 | 1,300 | Primary forest |
3 | A Luoi | Present | 706–780 | 320 | Secondary forest |
4 | A Luoi | Present | 720–820 | 500 | Secondary forest |
5 | A Luoi | Present | 623–770 | 420 | Secondary forest |
6 | A Luoi | Present | 176 – 250 | 950 | Secondary forest |
7 | A Luoi | Present | 179–214 | 700 | Secondary forest |
8 | Nam Dong | Present | 129–179 | 1,400 | Primary forest |
9 | Nam Dong | Present | 173–269 | 1,300 | Primary forest |
10 | Nam Dong | Present | 111–145 | 1,000 | Secondary forest |
11 | Nam Dong | Present | 105–129 | 460 | Secondary forest |
12 | A Luoi | Absent | 550-740 | 1,000 | Secondary forest |
13 | A Luoi | Absent | 650-875 | 450 | Secondary forest |
14 | A Luoi | Absent | 690 | – | Secondary forest |
All encountered individuals were captured, individually marked with a permanent pen (Edding Eraser) and released at the same spot after taking measurements (Fig.
To assess the population structure of P. cocincinus, lizards were categorised into three age classes based on the snout-vent length (adult with SVL > 140 mm, sub-adult with 100 mm < SVL ≤ 140 mm and juvenile with SVL ≤ 100 mm). As sexual dimorphism is only expressed in adult P. cocincinus (e.g. presence of well-developed nuchal and dorsal crests in adult males; see Fig.
In order to assess levels of harvesting and use of the Asian Water Dragon in Thua Thien Hue Province, 21 hunting groups were interviewed between February and October 2016, including six groups from Phong Dien District, seven groups from A Luoi District and eight groups from Nam Dong District. Each group contained two or three lizard hunters. Some rapid surveys were also conducted in local markets and restaurants in district towns of Phong Dien, A Luoi, Nam Dong and in Hue City to obtain evidence of local trade and consumption of lizards. Single impacts on local sub-populations were ranked according to severity as “low” defined as being observed only once or less, “medium” defined as being observed several times or “high” defined as being recorded frequently. Furthermore, several internet platforms were screened to obtain an overview of the availability, demand, prices and evidence of trade in the species. Since the species is listed on Annex D of the Council Regulation (EC) No 338/97, which requires an import notification at EU border customs, retrospective data were obtained for the recorded imports of P. cocincinus from Vietnam into the EU from 2010 to 2016 from the UNEP-WCMC CITES trade database (
During the present study, P. cocincinus was found along 11 of 14 investigated sites within three districts of Thua Thien Hue Province. In 2016, the authors only surveyed A Luoi District and recorded a similar number of individuals of P. cocincinus in April and June along all five sites, counting 97 and 95 individuals, respectively. In 2017, a total of 167 animals (thereof 31 adults) were captured in April in Phong Dien and Nam Dong districts and 172 individuals were observed in June in all three districts, of which 28 were adults. Higher fluctuations in population sizes were observed between the two consecutive surveys in April and June 2017 in Phong Dien and Nam Dong than those in the year before in A Luoi. The estimated total population size at the survey area was about 250 animals in April 2017. Even though two additional sites in A Luoi District (viz. five sites in total) were included in the estimation, the estimated population size decreased to 233 individuals in June 2017 (Table
Summary of observed individuals as well as densities and population size estimates (N^) of Physignathus cocincinus in Thua Thien Hue Province, central Vietnam in April and June, 2016 and 2017. D: Density; ind: individuals; Asterisks indicate missing data.
District | Phong Dien | A Luoi | Nam Dong | Total | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Stream | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | |
April-2016 | ||||||||||||
Total (observed) | * | * | 4 | 4 | 6 | 25 | 21 | * | * | * | * | 60 |
Mature (obs.) | * | * | 1 | 4 | 0 | 7 | 2 | * | * | * | * | 14 |
D[ind/100 m of stream] | * | * | 1.25 | 0.8 | 1.43 | 2.63 | 3.0 | * | * | * | * | 1.98 |
N^ | * | * | 6 | 6 | 12 | 35 | 38 | * | * | * | * | 97 |
June-2016 | ||||||||||||
Total (observed) | * | * | 4 | 5 | 5 | 22 | 22 | * | * | * | * | 58 |
Mature (obs.) | * | * | 3 | 2 | 1 | 5 | 0 | * | * | * | * | 11 |
D[ind/100 m of stream] | * | * | 1.25 | 1.0 | 1.19 | 2.32 | 3.14 | * | * | * | * | 1.98 |
N^ | * | * | 5 | 9 | 6 | 42 | 33 | * | * | * | * | 95 |
April-2017 | ||||||||||||
Total (observed) | 13 | 86 | * | * | * | * | * | 26 | 25 | 17 | * | 167 |
Mature (obs.) | 0 | 18 | * | * | * | * | * | 5 | 6 | 0 | * | 29 |
D[ind/100 m of stream] | 1.12 | 6.62 | * | * | * | * | * | 1.86 | 1.92 | 1.7 | * | 2.64 |
N^ | * | 124 | * | * | * | * | * | 74 | 52 | * | * | 250 |
June-2017 | ||||||||||||
Total (observed) | 33 | 67 | * | * | * | 25 | 22 | * | 2 | 20 | 3 | 172 |
Mature (obs.) | 8 | 17 | * | * | * | 2 | 1 | * | 0 | 0 | 0 | 28 |
D[ind/100 m of stream] | 3.84 | 5.15 | * | * | * | 2.63 | 3.14 | * | 0.15 | 2.0 | 0.65 | 2.51 |
N^ | 56 | 87 | * | * | * | 35 | 24 | * | * | 30 | * | 232 |
In total, most individuals were encountered in Phong Dien District, where the highest incidence of adult individuals was also recorded compared to the other two sub-populations. The mean density of P. cocincinus along suitable stream transects was estimated to be around 25–26 individuals per km of transect. By comparing different habitat sites, the highest abundance of P. cocincinus was found in April 2017 at site 2 in Phong Dien District (about 6.6 individuals per 100 m stream length). In A Luoi District, being situated at elevations of 623–820 m, densities ranged from 0.8 to 1.4 individuals per 100 m stream length along sites 3, 4 and 5. The authors failed to observe any lizards along the other three sites, namely 12, 13 and 14, in April and June 2017. In comparison, densities along transects of lower elevations (from 49–269 m), even though in a slightly disturbed habitat, were about or higher than two individuals per 100 m stream length during at least two surveys (sites 6 and 7).
Comparing the data achieved in the different months, the investigated population of P. cocincinus in Thua Thien Hue Province consisted mainly of juveniles (139 individuals) in April, followed by sub-adults, adult males and adult females (60 %, 19 %, 11 %, 10%, respectively; Fig.
According to interviews with local hunters and the authors’ own observations, wild P. cocincinus populations are affected by negative anthropogenic impacts in all investigated districts (Table
Impacts on Physignathus cocincinus at study sites based on interview data and own observations.
District | Trapping/ hand collection | Use for traditional medicine | Consumption in restaurants | Incidence on local markets | Habitat degradation | Total impact |
---|---|---|---|---|---|---|
Phong Dien | High | Low | Medium | High | Low | Medium |
A Luoi | High | – | Medium | High | High | High |
Nam Dong | High | Low | High | High | High | High |
Threats to Physignathus cocincinus in Thua Thien Hue Province: A A trapped individual in Nam Dong District B Specimens collected for food in Hue City C The Asian Water Dragon served as food in a restaurant in Hue City D Eggs of P. cocincinus preserved in alcohol in Nam Dong District.
With respect to the international trade in the species, a total of 43,100 specimens have been officially exported by Vietnam into the EU between 2010 and 2016 according to the UNEP-WCMC trade database. Thereof, most specimens had an unknown origin and some were stated to be “wild caught”, while the purpose was “for commercial use” in any case. Germany was the country with by far the most imports. It can be assumed that the majority of exported specimens with unknown origin are actually wild individuals, since there is no knowledge about breeding facilities. According to interviews with locals, there have been some people keeping and rearing P. cocincinus to supply local restaurants for a short period. However, these facilities were recently closed, because it is allegedly more convenient to collect wild animals than to spend time and efforts in breeding them, as long as animals can be found in the wild.
It was found that habitat loss and habitat alterations, such as road building and illegal timber logging (Figs
In order to manage the wild populations of the Asian Water Dragon properly and to implement conservation measures accordingly, the assessment of its population status, abundance and distribution is important. In total, the estimated population size probably does not encompass all occurrences of P. cocincinus in Thua Thien Hue Province, however due to the strong association of the species with small freshwater streams, which only represent small areas of the Province, it can be assumed that the total population is not disproportionately higher. A detailed further assessment on the availability of suitable habitats would be helpful.
Generally, P. cocincinus was found in monthly densities of 2.6 and 2.5 individuals per 100 m in April and June, 2017, respectively. However, three stream transects (3, 4 and 5) in A Luoi District, located at higher elevations (623–820 m), revealed a constantly lower density of P. cocincinus than found in other streams, although the habitat was not disturbed. It seems that not only hunting activities, but also elevation and habitat quality of each stream, might influence the abundance of the species. Recently,
Regarding the sex ratio of the species, investigations in 2016 and 2017 showed that the number of adult males was slightly higher than that of adult females in April. However, adult females were observed more frequently in June, which might be an indication for targeted harvest. Most of the local hunters, who have been interviewed, preferred collecting adult males of P. cocincinus, because of their bigger size compared to adult females, an important aspect in terms of food consumption. There was a significant difference in age structure in P. cocincinus between April and June, with juveniles accounting for the dominant percentage in April and sub-adults being predominant in June. This trend can be explained by the fact that juveniles of P. cocincinus reach the sub-adult stage relatively fast (after only two months), indicating that the survival rate is relatively high in the species. Overall estimates of the population size of P. cocincinus in the survey areas within Thua Thien Hue Province, central Vietnam, revealed that the population remained relatively stable between April and June with 250 to 232 individuals respectively in 2017. This trend was constantly observable at each survey site, except for the sub-population in Nam Dong District with a distinct decline in encountered individuals from April to June. This might be explained by the fact that the population in Nam Dong District is heavily affected by hunting activities.
In total, several critical threats to the population and habitat of P. cocincinus were recorded in Thua Thien Hue Province, namely harvesting for food consumptions and to supply trade, as well as habitat fragmentation through road construction and timber logging. It is assumed that similar impacts are certainly to be observed in other areas in Vietnam. Besides local use of the species, the recorded imports of more than 43,000 animals from Vietnam into the EU for commercial use during recent years indicate an increasing international interest in the species. Most of those specimens had an “unknown” origin. According to interviews with local people involved in the trade in P. cocincinus, there are no attempts at breeding of the species in captivity, since harvesting from the wild is currently the most economic way. Thus, it is expected that most of the reported imports will represent wild individuals. In addition, this data represents only the tip of the iceberg of actual international trade levels in the species, since only imports into the EU are recorded. In addition to the international trade, the species is also harvested in large amounts for national use. According to these high levels of exploitation, it is recommended that continuous monitoring of wild populations be undertaken in order to warrant the sustainable use of the species. It is also recommended to extend monitoring activities on further populations in the North and South of Vietnam. Moreover, captive breeding could be an alternative, as currently undertaken at the Me Linh Station for Biodiversity in northern Vietnam and in Phong Dien District as well as in Hue City in Central Vietnam. Such breeding programmes could later be transferred to local communities to reduce the pressure on wild populations and supply the high demand for the species. The listing of the species in CITES Appendix III and the establishment of a sustainable export quota could support a shift from the use of wild harvested specimens to captive bred ones. Furthermore, it is herewith recommended to improve conservation measures in the natural habitats in collaboration with the local authorities to enable the long-term persistence and sustainable use of the species.
We are grateful to the directorates and staff of the Bach Ma National Park, Phong Dien and Sao La Nature Reserves (Thua Thien Hue) for support of our field work and issuing relevant permits. We thank S. V. Nguyen (IEBR), T. Pagel and C. Landsberg (Cologne Zoo) for support of our research. We thank T. V. Nguyen, T. Q. Le, T. V. Nguyen (Hanoi), B. V. Ngo and L. C. Nguyen (Thua Thien Hue) for their assistance in the field. We thank G. Benyr (Vienna) and U. Schepp (Bonn), as well as the subject editor K. Henle (Leipzig) for their constructive comments to improve an earlier version of the manuscript. This research was funded by the Vietnam Academy of Science and Technology and the People’s Committee of Thua Thien Hue Province (grant number: VAST.NĐP.01/17-18) as well as Cologne Zoo.