The Siamese crocodile is a medium-sized freshwater crocodile, once found across South-East Asia. It was rarely seen and thought to be extinct in the wild, until 2000 when small populations were found in the remote Cardamom Mountains in southern Cambodia. There are now thought to be less than 1000 living in the wild and it is considered Critically Endangered by the International Union for Conservation of Nature (IUCN).
The Cardamom Mountains were one of the last strongholds of the Khmer Rouge, and turmoil in the region has meant that the fauna is poorly known. It contains one of the largest and still mostly unexplored forest in South East Asia.
Cambodia is investing significant efforts in their preservation, and Dr Paul McInerney and Dr Michael Shackleton of La Trobe University’s School of Life Sciences are assisting with the efforts.
“Wild Siamese crocodiles numbers plummeted during the 20th century due to collection for crocodile farms, hunting, and habitat loss,” says Dr McInerney. “Farmed crocodiles have since been hybridised with other crocodilian species to suit market interests, representing a significant threat to the genetic viability of captive breeding programs.”
Fish constitute a large component of Siamese crocodile diets and Drs McInerney and Shackleton travelled to Cambodia to assess fish populations among release sites for captive bred Siamese crocodiles. They worked as part of a collaboration with Fauna and Flora International and The Royal University of Phnom Penh.
“There are a number of knowledge gaps in Cambodian freshwater science, and our colleagues expressed that there was a fundamental lack of expertise in fish ecology more specifically,” says Dr Shackleton. “We usually work within the Murray-Darling Basin however, our methods to assess ecosystem structure are transferable to other ecosystems, in this case tropical jungle rivers.”
Drs McInerney and Shackleton completed a pilot study at the sites to survey fish abundance and collected tissue samples to sequence DNA to gauge biodiversity. The two scientists spent three weeks sampling more than 500 fish, collecting length and weight measurements, gut contents and fin clips for DNA sequencing. All genetic information that was collected on the trip has been uploaded to an online database.
The abundance of fish among differing size classes was assessed in order to obtain an idea of the suitability of a site for the release of small crocodiles. The diets of fish were recorded so that food webs for each site could be constructed to ascertain energy pathways within the food chain.
“We came across a number of fish that didn’t match anything we could find in the database,” says Dr Shackleton. “They could be completely unknown or they just haven’t been barcoded. The places we were sampling were extremely remote with poor access, so it’s not surprising really, but it highlights some important gaps and adds knowledge of these systems.”
The Siamese crocodile is timid and largely nocturnal, making encounters in the wild rare. While collecting their samples McInerney and Shackleton only saw one Siamese crocodile in the wild.
“We spent a lot of time on the river in canoes, looking for crocodiles or signs of them, and only seeing one on the rivers of its home territory really drives home how endangered they are,” says Dr McInerney. “Although, considering I found it in the stretch of water where I was having a bath, part of me is glad I didn’t find more.”
How the crocodiles live in their potential habitat and interact with nearby humans is an important factor in choosing a suitable release site. The Cardamom Mountains is home to a number of indigenous villages, and many view crocodiles as a pest, since they often destroy the fishing nets needed to supply enough household food. Poaching has also historically been an issue in a region that is very poor.
“An important part of Fauna and Flora International's work is in the area of education.” says Dr McInerney. “They employ local crocodile wardens, to keep an eye on released crocs and talk to the local community about the importance of looking after them and keeping them alive. These crocodile wardens are well paid in comparison to other villagers, so they’re quickly learning the benefit of having crocodiles there.”
“In other areas on the Cardamom Mountains the crocs mightn’t have fared so well,” added Dr Shackleton. “A lot of indigenous animals like sun bears and gibbons are seen in terms of food or poaching. The crocodiles would struggle to stay alive.”
Drs McInerney and Shackleton are currently preparing a manuscript for submission that documents their findings. Their data will be used to inform Fauna and Flora International’s Siamese Crocodile Reintroduction program and form a basis for future collaborations. They also hope that it will form a platform for developing future work within the region.
“Our hope is that our research can help make an informed decision when choosing release sites for Siamese crocodiles,” says Dr Shackleton. “The Cambodian government have shown a great deal of dedication to the project, but the rarity of these crocodiles means that nothing can be left to chance when releasing them to the wild.”