Friday, 6 April 2012

Turtles and Tortoises 4: Annam Leaf Turtle

M.annamensis adult
One of the peculiar features of the fauna and flora of Europe is that many of their closest relatives live in eastern Asia, with a vast gap in between with no connecting forms. This is a signal of the geological and climate events that have effected Eurasia, including the uplifting of the Himalaya following the collision of the Indian subcontinent with Asia, and above all the glaciations of the last few million years. In Europe the main mountain chains are aligned east-west, creating roadblocks to the migration of species north and south in response to climate change, whereas in eastern Asia mountain chains tend to be aligned north-south. As a result, while glaciations caused repeated extinctions in Europe, their Asian relatives managed to survive.

M.leprosa (Spain)

Among the various animals which display this distribution pattern are the leaf or pond turtles belonging to the genus Mauremys. Today there are six species, three with a distribution centred round the Mediterranean, and another three in Eastern Asia. Recent DNA work has shown that they are closely related to the Cuora I discussed in the last post, and the Asian genera Chinemys and Ocadia are part of the same group.

The rarest of the group is the species we have at Bristol, the Annam Leaf Turtle M.annamensis. The most southerly of the Asian species, it is found only in coastal lowlands in central Vietnam. Its closest relative is believed to be the Yellow Pond Turtle, M.mutica, which is found to the north in Vietnam and southern China.

range of M.annamensis
All the Mauremys species prefer slow-moving or still waters with heavy plant growth in which they can hide, with sloping banks that enables them to climb out of the water to bask in the sun, which is very important for their health. Not only does the sunlight enable them to thermoregulate, but drying out under a hot sun kills off the leeches and other parasites that swarm in their natural habitat. So eager are they to bask they will frequently climb on top of each other to get to the best spot.

Mauremys are adapted to warm temperate and sub-tropical climates, and the western species are often exposed to very cold weather for at least part of the year. In common with other aquatic turtles, they hibernate underwater, only coming up on warm days. In the more seasonal parts of their range, where the ponds may dry up in the summer, they will also aestivate buried in the mud for part of the year.

As with most aquatic chelonians, they are omnivorous, feeding on aquatic insects, snails, worms and occasional fish, but also taking plant material. Mating takes place in the water, with the gravid females seeking out soft earth ear the water to lay a clutch of 4-8 eggs. As with most of not all chelonians, they have temperature-dependent sex determination, with egg incubation temperatures affecting whether the hatchling is male or female. In most species, the key temperature is around 30oC, but the exact temperature for M.annamensis is as far as I am aware not yet determined with certainty. Knowledge of this is however very important for conservation, as by incubating eggs at the correct temperature it is possible to maximise the number of egg-producing females and so maximise productivity in the captive population.

Captive adult M.annamensis
The threats today for the Annam leaf Turtle are the same as for all the other Asian chelonians – over-collection for food and habitat destruction. Although various species of turtle are now being farmed in China, often these animals are hybrids and therefore valueless for conservation purposes, and also belong to a fairly restricted number of species. This is not a minor operation– a paper in Oryx Vol 42/1 in January 2008 estimated the number of captive farmed turtles of various species sold in China as 300 million animals per year. The trade in captive farmed freshwater chelonians is by no means confined to Asia either, for example between 2002 and 2005 the US declared exports of over 31 million turtles, a large proportion of which were to mainland China, Hong Kong, and Taiwan. As most of these were the well-known Red-Eared Slider Trachemys scripta, there is an additional problem of disease being spread around the world and escaped farm animals becoming established in the wild and competing with native species.

To return to our own animals – we currently have 6 juveniles bred at Chester Zoo on show. They are only a few years old, so it will be at least 3 or 4 years before they are large enough to produce offspring of their own. As M.annamensis is classed as Critically Endangered, this cannot happen soon enough.

(Images from European Freshwater Turtle Breeders Association, Wikipedia, Arkive)


The freshwater turtle genus Mauremys D.Barth 2003
Declared Turtle Trade from the US – World Chelonia Trust

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