Black softshell turtle

The black softshell turtle or Bostami turtle (Nilssonia nigricans), previously placed in genus Aspideretes, is a species of freshwater turtle found in India (Assam) and Bangladesh (Chittagong and Sylhet). It was long believed to be inbred individuals of the Indian softshell turtle (A. gangeticus or N. gangeticus) or the Indian peacock softshell turtle (A. hurum or N. hurum), but while it is a close relative of the latter, it is a distinct species.[5] In the 1800s it was believed these turtles were brought from Iran to Chittagong shrine pond by Hazrat Bayezid Bostami. His turtles he had brought to this pond were treated as sacred and respected by the public.[6] Previously declared extinct by the International Union for Conservation of Nature in 2002, these turtles were found still to exist in a temple's pond called the Hayagriva Madhava Temple located in Assam, India.[7] Through conservation methods and protection of the species, some of these turtles can be found today throughout the wild, and scientists and environmental biologists are continuing to work hard to preserve this endangered species and their natural habitat.

For the black rayed softshell turtle, see Asiatic softshell turtle.

Black softshell turtle
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Testudines
Suborder: Cryptodira
Family: Trionychidae
Genus: Nilssonia
Species:
N. nigricans
Binomial name
Nilssonia nigricans
Synonyms[3][4]
  • Trionyx nigricans
    Anderson, 1875
  • Amyda nigricans
    — Mertens, L. Müller & Rust, 1934
  • Aspideretes nigricans
    — Meylan, 1987
  • Trionix nigricans
    — Richard, 1999
  • Nilssonia nigricans
    — Praschag et al., 2007
The side profile of an adult Bostami turtle

Habitat

Originally native to the lower Brahmaputra River, the only population ever reliably known consists of a small number of the species in a man-made pond which is part of the Bayazid Bostami shrine at Chittagong, where they are dependent on humans for survival. To the locals and worshipers, the black softshell turtle is known as mazari ("Mazar inhabitant"); specimens from this shrine were used in the first scientific description.[5][8]

In a 2014 survey by Poribesh Banchao Andolon, a Bangladeshi private organization it was found that the amount of oxygen dissolved in the pond water was 2.01 mg/L, whereas the favorable level is 5 mg/L.[9] In 2012, wildlife biologists of the Center for Advanced Research in Natural Resources and Management found a small population in the wild of Sylhet.[9] Two tiny wild populations were discovered in Assam, in Kaziranga and in the Jia Bhoroli River which is a northern tributary of the Brahmaputra. Also, another temple population of these turtles was identified in the Kasopukhuri pond on Nilachal Hill, next to the Kamakhya Temple at Guwahati in Assam.[10]

Biology

Appearance

The black softshell turtle has an observably different appearance compared to that of a common turtle. This turtle, similar to all other softshell turtles, has a semi-flexible shell that is leathery, and does not obstruct movement as much as the average hardshell. The black softshell turtle also has a very distinct nose and face, with a tube like structure protruding from its nose resembling and functioning similar to a snorkel. The ligaments of this turtle are also much more distinct than those of the normal sea turtle or land tortoise, being that they have hand-like structures that are webbed, as opposed to other turtles like sea turtles who have a wider arm.[11] The softshell of the turtle does not protrude out from the body very far, and typically appears somewhat rigid with very little color and design.[7] The skin of the black softshell turtle is often black or dark brown, but can often appear with white to yellow spots that appear across the head and ligaments of the turtle.[12]

Size and weight

The average Bostani turtle adult size can range from widths of 15 inches to 31 inches, and corresponding lengths of 13 inches to 28 inches. The average area of the species can range from 195 inches squared on the low end and 868 inches squared on the larger end. However, the highest recorded size for these turtles is a length of 35 inches.[11] The weight for the average female is around 120 pounds, while the weight of the males has not yet been recorded. However, these males are visually larger indicating strong chances of a larger corresponding weight.[13]

Life span and mortality rate

The highest recorded age for the Bostani turtle has been determined by those living in the area directly, with claims that the oldest turtles present are approximately 150 years old.[14] However, this species has a high mortality rate at the beginning stages of life, with 94% of eggs without hatching capabilities. With an average clutch size of 20, this would allow for the survival of about one egg per two mating turtles.[13]

Diet

With the species existing in very limited areas with high human traffic, these turtles have become dependent upon visitors for feeding. Visitors tend to feed a mixture of grains, fruits, and various meat products.[14] These interactions with direct feeding have created a dependence for these turtles on the people, since this species no longer has a need for hunting. This had made it hard to determine the natural diet of the species. However with the ability to consume the foods provided by the people, their diet is commonly compared to that of other species within the same genus. These organisms are on the omnivore scale of the food consumption, consisting of plants and small animals like fish and worms.[11]

Reproduction
Visitors feeding the turtles in the pond.

Nilssonia nigricans are oviparous organisms, in which they reproduce by laying their young as eggs to be hatched.[15] Softshell turtles are known to mature slowly with the males prepared to breed in their fourth year. The female population could take up to seven to nine years to mature.[16] A group of eggs is known as a clutch and a female black soft shelled turtle can lay anywhere between 10-38 eggs in her clutch. The baby turtles will grow in their eggs for 92–108 days before hatching.[11] Recently the hatching rate for this specific species has been decreasing due to these species being endangered.

Behavior

Hibernation

Hibernation takes place during the late autumn season until the spring for softshell turtles. They bury themselves at the bottom of a river/lake in the mud. Food is not as essential as oxygen during this period. Oxygen is needed at a reduced rate than normal and the turtles practice a technique called “pharyngeal breathing”.[16] This means that they pump water in and out of their throat (pharynx) that contain microvillus projections of small blood vessels. This structure provides them with greater surface area to absorb more oxygen.[17]

Near-extinction in the wilderness
The Bayazid Bostami shrine with its pond

As of 2002, the International Union for the Conservation of Nature classified the species as Extinct in the Wild.[2] In 2004, 408 turtles were found in the pond of the Bayazid Bastami shrine. According to the shrine committee staff, 90 more turtles were hatched in the pond in 2007, 74 in 2008, 96 in 2009, 28 in 2010, 45 in 2012 and 40 in 2014.[9]

In 2017, a singular wild turtle was found in the wetlands of Old Akuk Village in Wokha District, Nagaland. DNA from the specimen sent to Bangladesh was tested and ultimately confirmed that it was a member of the black softshell species.[18]

This extinction has been caused by human intervention, specifically the migration of people into the habitat and the contamination of water and land following this movement.[19] The land of Bangladesh that N. nigricans have been able to occupy currently had been tested for conditions of survival and mating. The survival rate of juvenile N. nigricans is relatively low due to a low mortality of egg hatching and juvenile survival following hatching.[20]

A Bostami turtle being fed by human visitors.

Human intervention has also caused a push towards extinction with intentional methods of poisoning. In 2006 there was a mass poisoning of the turtles within the Bostami Shrine pond by poachers in the area. This event occurred within the research period, as the turtles were under heavy observations and were protected from this event, while this not being the first time this method had been used. In this case many of the fish utilized by the N. nigricans for food had been poisoned, making nutrition unsustainable for the turtles. This same poisoning also changed the oxygen levels in the water, making it unsustainable for the turtles. A waiting period had passed to ensure oxygen levels were rich in the water, indicating a sustainable environment, in turn allowing the release of the species.[20]

Conservation efforts

Since 2013, TSA India has worked diligently to improve conditions at selected temple ponds in Assam where these turtles were discovered. Many of the ponds were eutrophic and overcrowded and often, turtles were fed human food as religious offerings. The turtles showed signs of poor nutrition and a lack of suitable nesting space resulted in eggs being deposited in areas where there was little chance of hatching. The goal of the project is to eventually rear and release juveniles from these captive colonies to supplement depleted wild populations. As part of that initiative, the TSA India team camped at the Nagshankar temple in April to observe nesting in the 40-45 adult females at that location. At that time, the team transferred ten nests to a hatchery and protected four nests onsite.

With TSA's efforts 44 turtles have hatched so far. The team is currently expanding a headstarting facility at Nagshankar temple to accommodate the turtle's hatchlings of 2016. Neonates and juveniles cannot be released back into the temple pond due to predation by larger turtles and exotic fish. For this reason, the team acquired an earthen pond in the nearest village to provide space for the fast-growing juveniles, improving survival prospects for this extremely rare softshell.

In 2018, Das et al. had collected population sizes of N. nigricans from 2006 to 2012. The population size had shown a gradual increase over time, indicating that the calculated area per turtle had decreased in accordance. He indicated that without an increase in habitat size, the carrying capacity of the species will be reached quicker. This can decrease the overall growth of the species and not allow it to grow past the current conservation status.[20]

In 2011, Dr. Jayaditya from the Help Earth NGO found a grouping of black softshell turtles in a temple pond in Hajo, Assam. He revitalized contributions aimed towards saving and replenishing the species once again. He and his team embanked the sides of the temple pond and made adjustments to simulate a natural river system and create an ecosystem more conducive to the turtle's natural habitat. Thereafter, they observed a positive egg ratio produced around the temple premises. The State Zoo of Assam is playing an important role in this conservation project, serving as the location where baby turtles are reared for six months. When deemed fit and healthy, and capable of surviving, the young turtles are released into the wild. As of 2016, the State Zoo of Assam has released 300 turtles. Now 16 temples in Assam are helping in this important project.

References
  1. Rhodin 2011, p. 000.207
  2. IUCN Status report
  3. Fritz Uwe; Peter Havaš (2007). "Checklist of Chelonians of the World" (PDF). Vertebrate Zoology. 57 (2): 311. ISSN 1864-5755. Archived from the original (PDF) on 2011-05-01. Retrieved 29 May 2012.
  4. "Nilssonia nigricans". The Reptile Database. www.reptile-database.org.
  5. Praschag et al. (2007)
  6. "'Bostami turtle' found in wild". The Daily Star. 13 July 2020.
  7. Weston, Phoebe (11 June 2019). "Indian temple helps nurture 'extinct' turtle back to life". Independent.
  8. Anderson (1875), Praschag et al. (2007)
  9. Uddin, Minhaj. "Rare Bostami Turtles of Ctg city in peril". The Daily Star. Retrieved 2015-08-17.
  10. Asmat (2002), Praschag & Gemel (2002), Praschag et al. (2007)
  11. Brock (2020). "Black Softshell Turtle (Bostami Turtle)". All Turtles.
  12. Glenn, C (2006). "Black Softshell Turtle". Earth's Endangered Creatures.
  13. "Bostami Turtle - Banglapedia". en.banglapedia.org. Retrieved 2020-04-17.
  14. Abu Saeed, M (2009). "Bostami Turtle (Aspideretes nigricans) No Longer Endemic Only to Bangladesh". Tiger Paper. 36: 29–32.
  15. "Species | The Reptile Database". reptile-database.reptarium.cz. Retrieved 2020-04-17.
  16. "How Do Softshell Turtles Survive?". animals.mom.me. Retrieved 2020-04-17.
  17. "Pharyngeal Breathing in Softshell Turtles | Center for Environmental Communication | Loyola University New Orleans". www.loyno.edu. Retrieved 2020-04-17.
  18. Longchar, Imiti. "Turtle species thought extinct in the wild discovered in Nagaland". Morung Express. Retrieved 2017-03-24.
  19. "IUCN Red List of Threatened Species: Black Softshell Turtle". IUCN Red List of Threatened Species. 2002-01-01. Retrieved 2020-04-17.
  20. Das, Subhasish Das (June 2018). "Conservation Status of Black Soft Shell Turtle (Nilssonia nigricans) in Bangladesh". ResearchGate. 6: 12–16.

Bibliography

Further reading
  • Anderson J (1875). "Description of some new Asiatic Mammals and Chelonia". Annals and Magazine of Natural History, Fourth Series 16: 282–285. (Trionyx nigricans, new species, pp. 284–285).
  • Praschag P, Gemel R (2002). "Identity of the black softshell turtle Aspideretes nigricans (Anderson 1875) with remarks on related species". Faunistische Abhandlungen 23: 87–116.
  • Praschag P, Hundsdörfer AK, Reza AHMA. Fritz, U (2007). "Genetic evidence for wild-living Aspideretes nigricans and a molecular phylogeny of South Asian softshell turtles (Reptilia: Trionychidae: Aspideretes, Nilssonia)". Zoologica Scripta 36 (4): 301–310. (Nilssonia nigricans, new combination). doi:10.1111/j.1463-6409.2007.00282.x (HTML abstract).
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