Fitzroy River turtle
|Fitzroy River turtle|
Legler & Cann, 1980
The Fitzroy River turtle (Rheodytes leukops) is a species of freshwater turtle in the Chelidae family. It is the only surviving member of the genus Rheodytes, the other member being the extinct form Rheodytes devisi. The species is endemic to south eastern Queensland, Australia and only found in riffle zones of the Fitzroy River.
The Fitzroy River turtle is light to dark brown in color and growing to approximately 260mm in carapace length. The shell of hatchlings is highly serrated (up to 95 mm) while adults have a rounded, smooth edged shell. The plastron is lighter in color and tapers anteriorally and posteriorally. The carapace is highly reticulated to the naked eye but this is actually a series of parallel ridges with occasional cross ridging under low magnification, however the plastron is smooth. The scutes are very thin and underlying sutures in both the carapace and plastron are visible through them in all but the darkest individuals. Pictured in the taxobox is a carapace of a subadult Rheodytes leukops (242mm length) showing the very visible sutures that can be seen through the scutes, still in place. The species, and in fact the genus, can also be identified by its very thin carapace bones a character used in diagnosing the related fossil species Rheodytes devisi. The upper surface of their necks are scattered with blunt to pointed conical skin tubercles that do not appear to have any specialized follicular centres (Legler and Winokur, 1979). The species has a single pair of barbels on the lower jaw. The Fitzroy River turtle is capable of obtaining up to 70% of necessary oxygen through its anus, in a process called cloacal respiration. Through this process, the Fitzroy River turtle can remain underwater for up to three weeks.
This turtle is an adept bottom feeder, preying on terrestrial and aquatic insects, macroinvertebrates, crustaceans, algae, aquatic snails, worms, freshwater sponges and aquatic plants such as ribbon weed (Vallisneria sp.). Stomach flushing has demonstrated that most of the diet was made up of macroinvertebrates with some freshwater sponges.
Natural history and observations in the wild
This species shows a clear preference for fast flowing water (near sand banks for egg laying) and has been found at depths as shallow as 15 cm. In most encounters, they have been found lying still, hidden by overhanging plant foliage along the shallow banks of fast flowing riffles (fast flowing streams or rapids) and under logs. In all encounters their preferred substratum was noted as coarse river sand and gravel.
There is limited sexual dimorphism with the tail of the female being marginally shorter than that of the male. The most accurate way to differentiate between sexes is to compare the distance between the anal scutes of the plastron and the cloacae. In males, the cloacae is located further away from the plastron than in females. Most other short-necked turtles in Australia show obvious differences in tail length and thickness. Multi-cluthing is demonstrated in this species in the original study by Legler and Cann (1980) as corpora lutea, current eggs and enlarged follicles were present in the females, indicating at least 3 clutches. Anecdotal records since indicate up to 5 clutches may occur.
Their habitat comprises a total area of less than 10,000 km², including the Fitzroy, Mackenzie and Dawson rivers. Its limited distribution and being the sole survivor of a once more widespread genus give it a high priority for conservation and is currently listed as Vulnerable on the IUCN checklist since 1994. The Fitzroy River turtle is known as the "bum breathing turtle" by locals. This nickname is derived from their unusual ability of being able to absorb oxygen whilst submerged, through highly vascularised bursae located in the cloaca. Rheodytes leukops is a bimodally respiring turtle that extracts oxygen from the water chiefly via two enlarged cloacal bursae that are lined with multi-branching papillae (Priest and Franklin, 2002). Therefore, the destruction of habitat which lowers the oxygen content of the water, particularly by agriculture and dams, reduces survivorship among juvenile classes. Three major impacts on the species have been identified; the reduction in invertebrate prey; conversion of fluvial to lucustrine habitat; and the increase of sedimentation impacting the cloacal breathing mode (Tucker et al. 2001) Hence it is listed as Vulnerable under both the Environment Protection and Biodiversity Conservation Act (EPBC Act 1999) and the Queensland Nature Conservation Act, 1992. The IUCN currently flags this species as in need of review
- Legler, J.M. & Cann, J. 1980. A new species of chelid turtle from Queensland, Australia. Contributions to Science (Natural History Museum of Los Angeles County) 324:1–18.
- Fritz Uwe; Peter Havaš (2007). "Checklist of Chelonians of the World" (PDF). Vertebrate Zoology. 57 (2): 343. ISSN 1864-5755. Archived from the original (PDF) on 2010-12-17. Retrieved 29 May 2012.
- Turtle Taxonomy Working Group [van Dijk PP, Iverson JB, Rhodin AGJ, Shaffer HB, Bour R]. 2014. "Turtles of the world, 7th edition: annotated checklist of taxonomy, synonymy, distribution with maps, and conservation status". PDF Chelonian Research Monographs 5 (7): 000.329–479], [doi:10.3854/ crm.5.000.checklist.v7.2014.]
- Georges A, Thomson S. 2010. Diversity of Australasian freshwater turtles, with an annotated synonymy and keys to species. Zootaxa 2496: 1–37.
- Thomson S. (2000). A Revision of the Fossil Chelid Turtles (Pleurodira) Described by C.W. De Vis, 1897. Memoires of the Queensland Museum 45(2):593–598.
- Legler, J.M. and Winokur, R.M. 1979. Unusual neck tubercles in an Australian turtle. Herpetologica. 35(4):325–329.
- "Fitzroy River Turtle (Rheodytes Leukops)" (PDF). fba.org.au. Fitzroy Basin Association and Queensland Government. Retrieved 24 May 2016.
- "New Dams May Flush Bottom-Breathers Out" (PDF). bacs.uq.edu.au. Australasian Science. June 2007. Retrieved 24 May 2016.
- IUCN Redlist Account Fitzroy River Turtle Rheodytes leukops
- Priest, T.E. & Franklin, C. E. 2002. Effect of Water Temperature and Oxygen Levels on the Diving Behavior of Two Freshwater Turtles: Rheodytes leukops and Emydura macquarii. Journal of Herpetology 36(4):555–561 [DOI: 10.2307/1565924]
- Aust Gov. SPRaT Database Rheodytes leukops
- Queensland Government Dept. of Environment and Heritage Rheodytes leukops
- Tucker, A.D., C.J. Limpus, T.E. Priest, J. Cay, C. Glen, E. Guarino., 2001, Home ranges of Fitzroy River turtles (Rheodytes leukops) overlap riffle zones: potential concerns related to river regulation., Biological Conservation, 171–181