Saturday, 5 May 2012

Turtles 8: It swam with Dinosaurs

Young C.inscuplta
The last of Bristol Zoo’s chelonians (for now) is perhaps the strangest freshwater turtle in the world, the Fly River or Pig-nosed Turtle, Carettochelys insculpta. Now known only from Papua New Guinea and parts of northern Australia, it is the last survivor of an ancient turtle lineage related to the more familiar soft-shell turtles Trionyx, and which was once found all over the world. The family dates back to the early Cretaceous, but became progressively restricted in distribution after the end of the age of dinosaurs and it has probably been restricted to its current range since the start of the Pliocene.

Carettochelys is perhaps the most highly aquatic of all freshwater turtles, and has its limbs modified into flippers similar to those seen in marine turtles. Males spend their entire lives in the water, and females only emerge to lay eggs on sand banks at the start of the dry season. Although they spend the majority of their time in fresh water, they have been known to enter brackish water or fully marine environments in search of food. As with many turtles, Carettochelys is mainly herbivorous, feeding ona variety of aquatic plants, plus fruit and foliage that falls into the water. It will also feed on carrion however, and will also catch larger aquatic invertebrates. It needs a lot of food, as it can grow to a considerable size (over 60cm has been recorded), although females mature at around 30cm. To obtain this, they range over large areas, with a single individual being recorded has having a home range of 10km of river.
C.insculpta in habitat
Females seem to produce eggs every other year, probably using the non-breeding years to build up resources. They usually lay 2 clutches in breeding years, with a typical clutch size of 10-12 eggs. Eggs are laid in sandy beaches, usually used by most of the females in the area, at the start of the dry season, and the fully formed unhatched young wait in a state of aestivation in their shells until rising water floods the nests, when they hatch explosively and quickly make their way into the water. Thee young feed mainly on Vallisneria, a familiar aquarium plant, and take many years to reach maturity – 16 years or so for females. With that long a developmental period, the lifespan is probably just as long as other turtles, probably at least 50 years.
Newly hatched C.insculpta
Carettochelys and its eggs have been eaten by people since earliest times, but today a major threat comes from feral water buffalo, which crush and trample eggs on the nesting beaches. These pressures, combined with natural enemies like crocodiles (which eat adults), and monitor lizards (which eat eggs), has placed the species in the Vulnerable category on the IUCN red list.

With its aquatic lifestyle, captive care of Carretochelys is somewhat different to other turtles. At Bristol we have three which live in one of the large tanks in the Aquarium, which they share with various large Asian fish. At present ours are only around 20cm shell length, so they have some time before they are large enough to breed. At that size, we will have to take steps to provide them with a nesting beach, assuming we have a pair (males and females are identical when young). For an account of how are animals were bred at Rotterdam zoo, see the link below.

(Images from Wikipedia, Arkive)

Further reading: The Ecology and sex determination of the Pig-Nosed Turtle, Carettochelys insculpta, in the wet-dry tropics of Australia.J.Sean Doody

Breeding Caretochelys at Rotterdam Zoo:

No comments:

Post a Comment