First record of the critically endangered Black softshell turtle, Nilssonia nigricans (ANDERSON, 1875) for Nepal.

Abstract

Once Nilssonia nigricans was regarded as the rarest turtle existing, we publish a new distribution record for S-Nepal. Since soft shell turtles are difficult to identify on species level and have a cryptic life, not much is known about their biology, ecology or distribution. This new record of a critically endangered turtle species highlights the importance of the protection of the biodiversity hotspot in wetland areas of south-east Nepal.

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ARCO Veröffentlichungen – Arco-Nepal Newsletter 24, October 2022
15
First record of the critically endangered Black softshell turtle, Nilssonia nigricans
(ANDERSON, 1875) for Nepal.
Peter Praschag, Tapil Prakash Rai & Hermann Schleich
Abstract
Once Nilssonia nigricans was regarded as the rarest turtle existing, we publish a new distribution record
for S-Nepal. Since soft shell turtles are difficult to identify on species level and have a cryptic life, not
much is known about their biology, ecology or distribution. This new record of a critically endangered
turtle species highlights the importance of the protection of the biodiversity hotspot in wetland areas of
south-east Nepal.
Key words: New distribution record, Nilssonia nigricans critically endangered, SE-Nepal.
Introduction
Already GRAY (1872) pointed out, as simple as it is to identify a soft-shell turtle as such, so it is hard to
classify one by species. The distinctiveness of superficial structures and colour characteristics as well as
osteological features can change drastically during ontogeny in trionychids. In addition, the timing of final
differentiation of these characteristics is prone to intraspecific variation.
In his revision MEYLAN (1987) assigned the following four soft-shell turtles from the Indian subcontinent
to the genus Aspideretes: Indian soft-shell turtle, A. gangeticus (CUVIER, 1825); Indian peacock soft-
shell turtle, A. hurum (GRAY, 1830); Leith's soft-shell turtle, A. leithii (GRAY ,1872); and black soft-
shell turtle, A. nigricans (ANDERSON, 1875). An important osteological character shared by these
species is the presence of two neurals between the first pair of pleurals (instead of one neural as in the
remaining representatives of the tribe Trionychini sensu MEYLAN 1987). The strong morphological
similarities in coloration (of the ocelli) size, skull and shell shape among the four species also extends to
the Burmese peacock soft-shell turtle Nilssonia formosa (GRAY, 1869).
However, based on molecular and morphological evidence ENGSTROM et al. (2004) and PRASCHAG et al.
(2007) concluded that N. formosa is so closely allied to the four species of the South Asian genus
Aspideretes HAY, 1904 that all species should be placed in the same genus. Together with first records of
wild living N. nigricans in Bangladesh and N. formosa in China this molecular phylogeny of the genus
Nilssonia was confirmed by LIEBING et al. 2012. The genus name Nilssonia (GRAY 1872) has
nomenclatural priority. All five species possess a similar appearance and feature, at least in the juvenile
stage, a pattern of four to six ocelli on the carapace.
Fig. 1 a,b) Typical ocelli in juvenile and adolescent Nilssonia hurum (photo: P. Praschag)

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Distribution
Until 2002 the Black softshell turtle (N. nigricans) was thought to be confined to the artificial pond at the
Hazrat Sultan Bayazid Bostami Shrine in Nasirabad near Chittagong, Bangladesh. From this site,
N. nigricans was described by ANDERSON (1875), and subsequent authors believed that the species either
became extinct in the wild (PRITCHARD 1979; GROOMBRIDGE 1982) or that it ‘descended from introduced
individuals of the more widespread Trionyx [now Nilssonia] gangeticus’ [gangetica] (GROOMBRIDGE
1982; KHAN 1987) or of N. hurum (RASHID 1990). For a long time, N. nigricans was thought to be one of
the world’s most endangered chelonian species, comprising not more than 150–300 individuals in the
semicaptive colony near Chittagong (GROOMBRIDGE 1982; AHSAN et al. 1991; HILTON-TAYLOR 2000).
Due to its apparent rareness and the tale that the Muslim Saint Bayazid Bostami, when founding the turtle
shrine in the year 830, turned the evil spirits of the site into turtles, N. nigricans became nationally and
internationally renowned as the ‘holy’ turtle of Bangladesh (e.g., PRITCHARD 1979; KHAN 1980;
GROOMBRIDGE 1982; OBST 1986; ERNST & BARBOUR 1989; ERNST et al. 2000). However, using mainly
skull osteology as well as colouration and pattern characters, PRASCHAG & GEMEL (2002) suggested that
N. nigricans occurs not only in the shrine pond near Chittagong, but also in the neighbouring Indian state
of Assam.
First record of Nepal
The Betana Wetland (Nepali:  ) is situated in Belbari Municipality of Morang District of
Nepal, about 15 km E of Itahari with an altitude of approx. 123 m. The lake extends of about 5.5 ha and
the forest area covers 175 ha being a part of the popular Char Kose Jhadi jungle.
The wetland is home to endangered plants and animals such as turtles, fishes, birds, mammals and
indigenous plants. About 49 species of birds have been reported from the area. The forests mainly consists
of saal and khair-sisoo trees. A small portion of the forest area homes tombstones of the Kirati people.
The pond’s depth varies from 0.5 to 1.5 m during the dry season to 1 to 2.5 m during the monsoon season
(www.landnepal.com/details/623.html). DAHAL, D.R. (2020; ppt presentation) recorded Lissemys
punctata (BONNATERRE, 1789), Nilssonia hurum (GRAY, 1831), Pangshura smithii (GRAY, 1863)
and Indotestudo elongata (BLYTH, 1854) for the Betana area.
SCHLEICH and students visited Betana wetlands several times, while last visit was in 2016. In 2002
(SCHLEICH et al.) reported Lissemys, followed by ACHARIA (2004) with N. hurum and N. gangetica (latter
only reported by shells).
To attract tourists, a mini zoo has been constructed inside the wetland area along with some other
infrastructures.
Fig. 2 a,b) View on the habitat (photo: Schleich, H. 2016)

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Fig. 3) Geographic situation of Betana wetland area ( photo: Google Earth)
Fig. 4 a - e) Nilssonia nigricans pictures taken at Betana wetland in 2016 by H. Schleich & L. Kiesl.
The specimens show the typical head pattern as well as the wider skull with more massive cheeks.
Known distribution and records from Nepal
The distribution and natural history of the Black shelled softshell turtle attended much interest as it was
for long time regarded being extinct in the wild. (IUCN, 2002). PRASCHAG & GEMEL (2002) proved the
species survival in the wild in the distributional range of the Brahmaputra river system including isolated
subpopulations (BARUAH et al. 2010) from temple ponds in Assam and Tripura NE India. In addition, the
first author could record the species from Meghna and Karnaphuli river in Bangladesh (PRASCHAG 2018,
unpublished).

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For the existence of N. nigricans in Nepal and thus the Gangetic river system and tributaries, this is the
first proven record for this critically endangered softshell turtle with the records from Betana wetlands!
The country occurrences for Nilsssonia nigricans are now Bangladesh, India and Nepal.
Characteristic features of Nilssonia nigricans
The species is difficult to differentiate from its sister taxon N. hurum, but has a more domed carapace and
heavier anterior carapace margin.
The most detailed description including ontogenetic stages as well as diagnostic differences with other S-
Asian trionychids are given by PRASCHAG & GEMEL (2002).
N. nigricans is quite similar to N. hurum also it differs in shell shape, head pattern, white labial whitish
streak and with an ossified keel in the lower mandible from subadult age onwards (BONIN et al., p.135,
PRASCHAG & GEMEL, op.cit. ). The juveniles are brightly coloured with yellowish-orange ocelles, adults
can be completely black but some showing a typical vermiculated dorsal shell pattern.
The skin above the bony disc shows longitudinal rows of elongated tubercles and irregularly scattered
tubercles occur in moderate amounts on the posterior carapace rim. On the nuchal area, a row of 15 to 20
very large, fully developed longitudinal tubercles exist. The margin of the carapace, excluding the cranial
region, is yellow to orange, and much distinct from its basic coloration. Attached to this yellow-orange
ring in its lateral and caudal regions is a zone where the dark olive-grey to brown ground colour is
interspersed with numerous yellowish dots. The paler olive -grey blotches do not penetrate inside this
zone. The plastron of neonate specimens is dark grey to black with small yellow dots which can be so tiny
and dense that the plastron receives a metallic hue.
The basic colour of the head is equally dark grey to black. A distinct grey to dirty-yellow band runs
diagonally over the base of the proboscis. A large postorbital grey to yellowish blotch and more or less
triangular shape is located immediately behind the eye.
N. hurum closely resembles N. nigricans, however, the postorbital and temporal blotches are smaller in N.
hurum. In N. nigricans, the top of the head is covered by substantially bigger blotches contributing to a
net-like, reticulated pattern.
Hatchlings of the Black soft-shell turtle are approx. 4.5 cm long (AHSAN et al. 1991) while adult females
attain a carapace length of 74 cm and adult males up to 91 cm (DAS 1995), with a mass of over 50 kg
(AHSAN & SAEED, 1989).
Fig 5. Symphyses showing typical midline crest of lower mandible in N. nigricans
(photo: Praschag, 2002)

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Fig. 6) Head patterns of N. nigricans (PRASCHAG & GEMEL, 2002) during ontogenetic stages.
Natural history of Nilssonia nigricans
Nilssonia nigricans is known from medium-sized to very large riverine situations in the wild (PRASCHAG
& GEMEL, 2002; BARUAH et al. 2010), and several captive populations in temple ponds.
Maturity seems to be reached at about 40 cm carapace length and from 7–10 years. Females produce
clutches of 10–38 eggs (AHSAN & SAEED, 1992). The Black softshell turtle occurs in wetland areas
adjacent to river systems and directly in rivers and its larger tributaries. In the Brahmaputra N. nigricans
is sympatric with N. gangetica, N. hurum, Chitra indica (GRAY, 1831) and Lissemys p. andersoni.
Whereas N. gangetica is occupying the main river canals, N. hurum prefers the oxbows and river section
without high current. Hatchlings of N. nigricans can be found in smaller tributaries with clear and fast
flowing water together with Pangshura sylhetensis (JERSON, 1870) and Cyclemys gemeli (FRITZ,
GUICKING, AUER, SOMMER, WINK & HUNDSDÖRFER, 2008) in northeast India. Because only
hatchlings and juveniles of N. nigricans can be found in this fast flowing, smaller tributaries, it can be
assumed that gravid females migrate upstream to nest, avoiding competition for their offspring with other
soft shell turtle species. (PRASCHAG, unpublished data).
According to PRASCHAG (pers. observation) the tameness of Black soft-shell turtles is species specific.
Conservation
A latest listing for all Nepali turtle species in respect to conservation issues (IUCN/CITES/NRDB) had
been presented by SCHLEICH, H. in 2020 not including this new species record.
Nilssonia nigricans has been placed under CITES I since 01/07/1975, it is not yet listed by the Nepali
government in its National Red Data Book (NRDB) and mentioned as “Critically Endangered A4cd” by
IUCN 2021.
According to former own observations and with PANT et al (2020) statement “Due to the promotion of
the lake site as an ecotourism area, anthropic activities could further deteriorate the lentic quality and
biodiversity of the lake. Precisely, the main regulating factors of hydrochemistry in the lake include
commercial fishing, excessive use of pesticides and chemical fertilizer, irrigation, bathing, washing cloth,
waste disposed of by the tourists, and ultimately impacts the abundance and composition of the
macrophytes. Therefore, periodic evaluations of hydrochemical parameters with macrophytes are required
for the protection and long-term sustainability of the Betana wetland and its vulnerable turtle species.”

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What obviously has to be targeted and solved most urgently is to eliminate poaching and trade of local
turtle fauna through awareness and education campaigns and law enforcement. A detailed study as
suggested and offered by ARCO-Nepal since many years has to be carried out most urgently, control
artificial feeding (the fencing of the lake already showed some positive contribution against visitor
interactions) as well as chemical and physical pollutions and disturbances and to study the populations
dynamics and demography of Betana wetlands´turtle fauna since several years.
Fig. 7 a, b) (Photo: P. & Reiner Praschag) Turtles openly offered at weekend markets in the south of
Bangladesh. In the 1990ies N. hurum used to be one of the most hunted and offered species on the markets.

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Acknowledgments
The authors would like to acknowledge ARCO-Nepal, Sukhani Martyrs Memorial Foundation
(SUMMEF), Division Forest Offices of Jhapa and Morang, Betana Wetland Community Forest User
Group, and Jamunbari Community Forest User Group for their support and cooperation.
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Praschag, Peter: Turtle Island, Am Katzelbach 98, AU-8054 Graz, Austria.
Rai, Tapil Prakash: Turtle Rescue & Conservation Centre (TRCC), Arjundhara Municipality-9, 57205
Jhapa, Nepal.
Schleich, Hermann: Arco-Spain, Paraje El Cerrillo no. 1, E-04200 Tabernas, Spain.
Corresponding mail: Arco.Nepal@gmail.com