The giant Asian river terrapin, or batagur (Batagur baska), and the closely related painted batagur (Callagur borneoensis) inhabit estuaries and tidal reaches of medium to large rivers throughout Southeast Asia. Both belong to monotypic genera and represent the largest emydid turtles, reaching a carapace length that may exceed 60 cm.
Exploitation of adults, collection of highly prized eggs, and habitat destruction have greatly reduced the numbers of these turtles (IUCN Red Data Book, 1982). Batagur baska is listed on Appendix I (Endangered) of CITES. Ernst and Barbour (1989) summarize the characteristics, taxonomy, distribution, and life histories of these taxa, and Moll (1978, 1980) provides an excellent overview of their natural history. No captive breeding schemes of significance exist for these giant batagurines, and such activities have generally been viewed as impractical. The captive-breeding successes for Batagur and Callagur reported here, however, may influence that thinking, as it appears that this practice could play a vital role in recovery programs for these turtles.
The Bronx Zoo's living turtle collection includes 9 (7 males, 2 females) B. baska and 8 (4 males, 4 females) C. borneoensis. Eight 4-year-old B. baska and 2 C. borneoensis of the same approximate age were acquired in May 1985. These juveniles were hatched from eggs collected in the wild and were received as a gift from the Department of Wildlife and National Parks, Peninsular Malaysia. An additional B. baska, a 30 kg female that has been in captivity for at least 30 years, was received from the Columbus Zoo in April 1987. Six wild-caught adult C. borneoensis subsequently joined the group. In November 1988, one male and 2 females were received from Dr. William McCord, a Hopewell Junction, New York, veterinarian, and another male and two females were rescued from a food market in Borneo by a turtle dealer and came to the zoo in July 1989.
The sexes of individuals obtained as adults were readily determined by published morphological criteria and described sexual dichromatic characters (Moll, Matson, and Krehbiel, 1981). In July 1989, the 8 B. baska and 2 C. borneoensis obtained in 1985 (retrospectively judged to be 2-4 years old at acquisition, based on observed growth rates) had reached sexual maturity based on size and color-change observations during the previous breeding season. Pre-anal tail length was not an accurate sexing technique for these young adults. Sex was confirmed by finger-probing each turtle's cloaca for absence or presence of a penis. Most males quickly responded to the initial stimulation by extruding their penis, but some males required coaxing.
Parenthetically, 9 out of 10 of the Batagur and Callagur juveniles received from Malaysia were males. The eggs from which they hatched had been incubated in captivity as part of a conservation program to return head-started animals to nature. While temperature-determined sex has not yet been reported for these taxa, the authors speculate that incubation temperatures may be too low and causing a strongly biased male-to-female hatching ratio.
Housing and Environment
Both batagur species are quartered in the multi-species Gharial River Exhibit in the Bronx Zoo's Jungle World facility. The spacious (350 m²) enclosure is shared with 8 Indian gharial (Gavialis gangeticus), a pair of Bornean pond turtles (Orlitia borneoensis), 6 Fly River turtles (Carettochelys insculpta), and several fish species.
The irregularly-shaped facility is approximately 42 m long and ranges from 6 m to 10.6 m in width. Three pools, each at a different elevation, occupy 70+ percent of the exhibit surface area. The top pool is the largest and holds about 100,000 l of water; collectively they contain 200,000 l of water. Pool 1 (top) is 1.2 m deep; pool 2, 1.5 m deep; and pool 3, 2 m deep. The top pool's elevation is about 2 m higher than the lowest pool. It receives re-circulated 28° C water at 250-400 gallons per minute. Water passes through a Stark Aquarium Systems sand filter which completely eliminates unicellular algae, which otherwise would seriously compromise water quality. Makeup water (overflow loss) at 5-10 gallons per minute and 30° C cascades over a 5 m rock face into the upper pool. Water from pool 1 empties into pool 2 over a 1 m-high, 5 m wide-falls; pool 2 empties into pool 3 over a similar structure. Temperature of pool 2 and 3 water runs 0.5 to 1.0° C lower than the pool above it, depending on time-of-year and ambient air temperature which ranges from 23 to 31° C. After filtration, water passes through a heat exchange unit where lost calories are added and returned to the top pool. Pools are gently sloped and their surfaces are smooth concrete. Each has an 8" drain so the pools can be independently and very quickly dropped for cleaning with a pressure cleaner. Beach areas are bordered by a 1.5 m artificial mud-bank barrier. Substrate is clay with a pulverized shale overburden. Heating pads are buried under the substrate of the largest beach adjacent to the upper pool to encourage nesting activity.
The exhibit is naturally lighted via a glass-paneled roof. High-energy sodium vapor floodlights provide supplemental lighting if needed. Except for occasional evening use, they are not used to extend photoperiod.
A fogging system, along with Jungle World's lush tropical vegetation, serves to keep ambient humidity levels high. The exhibit is easily accessible to reptile keepers by a hidden door behind the rock face at the head of the top pool. Both the gharials and the turtles favor this pool, presumably because it holds the warmest water, is the largest body of water, and has a large submerged log and artificial grass beds which serve as shelters. If turtles need to be handled, the exhibit waters can be easily waded and turtles captured by hand or long-handled nets. The ominous-looking 3 m gharials are easily discouraged from conditioned feeding response advances by turning snouts away with a net handle.
The batagurs are fed ad lib. several times weekly and are offered a wide variety of greens, including kale, spinach, bok choy, and dandelion. Purina Turtle Chow and earthworms are broadcast on the water for the turtles and the fish. These items are very eagerly and rapidly consumed. Gharial are fed live trout several times weekly. Both batagur species will take warm-water stunned fish without hesitation; and they consume virtually all leaves that fall into the pools from surrounding planters. No vitamin or mineral additives are offered.