Baska: Bewitched by Batagur
The Malay peninsula plus Sarawak on Borneo are the home to two species of Batagur: B. affinis (both subspecies: B. a. affinis and B. a. edwardmolli) and B. borneoensis (Iverson, 1992). These two species coexist in some rivers while vast differences in mating and nesting isolate the species from interbreeding. They have both been reported as existing with Sonneratia spp of Mangrove Apple trees (Guntoro, 2012a, Holloway, 2003), the fruit of which was long-thought to be a staple of the species.
The Malay names for Batagur species is "Tuntung," an onomatopoeic name that either reflects the drumming sound produced by females as they drop their plastron onto the sand to disguise their nest after depositing the eggs (Moll, 1978) or the sound of the eggs exiting the cloaca and dropping onto the other eggs (Guntoro, 2012b). Use of this as a name reflects the most visible time for the species as they historically nested communally, sometimes in huge numbers. To distinguish one from the other, B. affinis is referred to as "Tuntung sungai," (River Tuntung) and B. borneoensis as "Tuntung laut" (Sea Tuntung).
Malaysia's two species of Batagur share many of the rivers on the peninsular, being most notably segregated by the opposite appearance of dichromatic males and by their choice of nesting beach. In the Malaysian states on Borneo, it is only Sarawak, on the west of the island, that has populations of B. borneoensis, with B. affinis apparently never having made the journey across to the island.
Batagur turtles are interesting in their evolution of sexual dichromatism at breeding season. Moll and Moll (2004) offered a valuable examination of this phenomenon, explaining that species that live in large rivers must contend with high flow rate, high turbidity, and low underwater visibility. As a result, chemical scent signaling is of limited utility for males to locate females.
Somewhere along their evolutionary history, B. borneoensis began nesting on sea beaches. As they are behaviourally equipped to withstand salt water, it makes sense, when sharing the estuary with other turtle species that may engage in mass nestings, to reduce competition for nesting space. This does, however, open them up to competition with sea turtles and differences in nesting times, construction of nests, and incubation periods accommodate this.
Dispersal by Batagur terrapins appears to take place when individuals are swept out to sea in high river flow periods. At the mouth of large rivers, this causes a surface layer of fresh water out to sea that has even been documented to allow amphibia, who are highly susceptible to dessication in salt water, to colonise oceanic islands (de Queiroz, 2014, p187). Being weaker swimmers, it would appear likely that it is younger animals that are swept out thus. Barriers to this style of dispersal include large stretches of coast that don't have large rivers emptying out into them, sea currents flowing in a particular direction, or the oceanic shelf being narrow and thus causing greater mixing of any coastal water disturbing any lens of freshwater that is made.
At the southern point of the Malay peninsula, the oceanic currents in the Malacca strait (Rizal et al., 2010) and the Gulf of Thailand (Pa'suya, 2015) both circulate northward, which results in little chance in modern conditions of mixing of the subspecies of B. affinis, with B. a. affinis restricted to the west coast of Peninsular Malaysia and Sumatra and B. a. edwardmolli inhabiting those rivers draining into the Gulf of Thailand (Praschag et al., 2009).
When the last glacial maximum saw sea levels at their lowest point, Borneo was attached to Sumatra and Java but Sumatra and Borneo were connected by the Northern Sunda River (Tubagus, 2014). This leaves Java free of Batagur species although it is nearer to Sumatra than Borneo is; the modern ocean currents being inconvenient for dispersal of any presently known populations toward the populous Indonesian island.
The factors that affect the conservation of Malaysia's Batagur are quite unique throughout the genus' range and I've looked at some of them in another post.
Literature Cited
The Malay peninsula plus Sarawak on Borneo are the home to two species of Batagur: B. affinis (both subspecies: B. a. affinis and B. a. edwardmolli) and B. borneoensis (Iverson, 1992). These two species coexist in some rivers while vast differences in mating and nesting isolate the species from interbreeding. They have both been reported as existing with Sonneratia spp of Mangrove Apple trees (Guntoro, 2012a, Holloway, 2003), the fruit of which was long-thought to be a staple of the species.
The Malay names for Batagur species is "Tuntung," an onomatopoeic name that either reflects the drumming sound produced by females as they drop their plastron onto the sand to disguise their nest after depositing the eggs (Moll, 1978) or the sound of the eggs exiting the cloaca and dropping onto the other eggs (Guntoro, 2012b). Use of this as a name reflects the most visible time for the species as they historically nested communally, sometimes in huge numbers. To distinguish one from the other, B. affinis is referred to as "Tuntung sungai," (River Tuntung) and B. borneoensis as "Tuntung laut" (Sea Tuntung).Malaysia's two species of Batagur share many of the rivers on the peninsular, being most notably segregated by the opposite appearance of dichromatic males and by their choice of nesting beach. In the Malaysian states on Borneo, it is only Sarawak, on the west of the island, that has populations of B. borneoensis, with B. affinis apparently never having made the journey across to the island.
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| I was lucky enough to meet this wild male B. borneoensis in breeding colouration |
Somewhere along their evolutionary history, B. borneoensis began nesting on sea beaches. As they are behaviourally equipped to withstand salt water, it makes sense, when sharing the estuary with other turtle species that may engage in mass nestings, to reduce competition for nesting space. This does, however, open them up to competition with sea turtles and differences in nesting times, construction of nests, and incubation periods accommodate this.
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| A hatchling B. affinis in Terengganu |
Dispersal by Batagur terrapins appears to take place when individuals are swept out to sea in high river flow periods. At the mouth of large rivers, this causes a surface layer of fresh water out to sea that has even been documented to allow amphibia, who are highly susceptible to dessication in salt water, to colonise oceanic islands (de Queiroz, 2014, p187). Being weaker swimmers, it would appear likely that it is younger animals that are swept out thus. Barriers to this style of dispersal include large stretches of coast that don't have large rivers emptying out into them, sea currents flowing in a particular direction, or the oceanic shelf being narrow and thus causing greater mixing of any coastal water disturbing any lens of freshwater that is made.
At the southern point of the Malay peninsula, the oceanic currents in the Malacca strait (Rizal et al., 2010) and the Gulf of Thailand (Pa'suya, 2015) both circulate northward, which results in little chance in modern conditions of mixing of the subspecies of B. affinis, with B. a. affinis restricted to the west coast of Peninsular Malaysia and Sumatra and B. a. edwardmolli inhabiting those rivers draining into the Gulf of Thailand (Praschag et al., 2009).
When the last glacial maximum saw sea levels at their lowest point, Borneo was attached to Sumatra and Java but Sumatra and Borneo were connected by the Northern Sunda River (Tubagus, 2014). This leaves Java free of Batagur species although it is nearer to Sumatra than Borneo is; the modern ocean currents being inconvenient for dispersal of any presently known populations toward the populous Indonesian island.
The factors that affect the conservation of Malaysia's Batagur are quite unique throughout the genus' range and I've looked at some of them in another post.
Literature Cited
- de Queiroz, A. 2014. The Monkey's Voyage, How Improbable Journeys Shaped the History of Life. Basic Books, New York. 359pp.
- Guntoro, J. 2012a. The Body Size and Some Field Notes of Painted Terrapin (Batagur borneoensis) in District of Aceh Tamiang, Indonesia. Asian Journal of Conservation Biology, 1(2): 74 -77
- Guntoro, J. 2012b. Tracing the footsteps of Painted Terrapin (Batagur borneoensis) in Aceh Indonesia. Preliminary Observation. Radiata 21(1): 60-67.
- Holloway, R.H.P. 2003. Natural History Notes on the River Terrapin, Batagur baska (Gray, 1831) in Cambodia. WCS Research Fellowship Program Report. 15pp.
- Iverson, J. 1992. A Revised Checklist with Distribution Maps of the Turtles of the World. Privately Printed, 382pp.
- Moll, D. and E. O. Moll 2004. The Ecology, Exploitation, and Conservation of River Turtles. Oxford University Press, 383pp.
- Pa'suya M. F. B., B. N. Peter, A. Hassan, A. H. M. Din, and K. M. Omar. 2015. Sea Surface Current in the Gulf of Thailand Based on Nineteen Years Altimetric Data and GPS Tracked Drifting Buoy. Conference paper for The 36th Asian Conference on Remote Sensing.
- Praschag, P., R. Holloway, A. Georges, M. Packert, A. K. Hundsdorfer, and U. Fritz. 2009. A new subspecies of Batagur affinis (Cantor, 1847), one of the world's most critically endangered chelonians (Testudines: Geoemydidae). Zootaxa 2233: 57-68.
- Rizal, S., I. Setiawan, Y. Ilhamsya, M. A. Wahid, and M. Musman. 2010. Currents Simulation in the Malacca Straits by Using Three-Dimensional. Sains Malaysiana 39(4): 519–524
- Tubagus Solihuddin. 2014. A Drowning Sunda Shelf Model during Last Glacial Maximum (LGM)
- and Holocene: A Review. Indonesian Journal on Geoscience 1(2) August 2014: 99-107
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