Press release by Murdoch University
Adjunct Associate Professor Ru Somaweera tagging a saltwater crocodile. (Murdoch University).
A new study has revealed that saltwater crocodiles born or raised in captivity may not return to their breeding centres after being released into the wild, a discovery which can help inform conservation and management practices.
The ability to return home is a fundamental aspect of the natural world and is often crucial for animals’ survival and reproductive success. Most animals show homing behaviours on a small scale, such as a daily journey back to a nest or burrow after foraging for food, whereas others undertake long journeys which can take months.
“Crocodilians, the largest predators in most tropical, subtropical freshwater and brackish environments, are a unique case when it comes to homing behaviour,” said behavioural ecologist and Adjunct Associate Professor Ru Somaweera, from Murdoch University.
“Crocodiles are remarkably good at finding their way home, often returning to their original capture sites and limiting the success of relocation programs. What we still don’t fully understand, though, is how this behaviour plays out in individuals that have been bred or kept in captivity for long periods before being released back into the wild.”
Researchers Paul Beri, Sakib Ahmed, Sarowar Alam, Ru Somaweera and Zenifar Azmiri. (Murdoch University).
The research team conducted a study in the Sundarbans mangrove forest in Bangladesh, one of the last strongholds for saltwater crocodiles in the country. Intensive commercial exploitation for skins until the 1970s decimated saltwater crocodile populations in Bangladesh, and despite formal legal protection since 1973, populations have shown no measurable signs of recovery.
Today, most known populations are confined to the Sundarbans, although numbers remain low: the most recent survey estimated 140 mature individuals.
“If crocodiles who are bred and raised in captivity subsequently return to their enclosures or breeding facilities after being released, attempts to reintroduce them into the wild as part of conservation efforts will ultimately fail,” Associate Professor Somaweera said.
“The traditional approach has been to use hatchlings in reintroduction programs, but their survival rates are extremely low and they take a long time to reach reproductive maturity. Understanding whether larger, captive-bred crocodiles can be used instead represents an important knowledge gap.”
The team tagged five mature saltwater crocodiles with satellite tracking devices, including three captive‑reared females that had spent 8–22 years in captivity, one local wild crocodile caught and released in the same location, and one wild crocodile that was moved (translocated) far from where it was caught. They then monitored the crocodiles’ behaviour for months after release.
A saltwater crocodile being tagged. (Murdoch University).
Associate Professor Somaweera said the most promising finding was that the three captive-reared crocodiles showed no evidence of trying to go back to their breeding facility.
“Instead, they settled into small, well-defined areas and moved in much the same way as the local wild crocodile we tracked, which tells us they are possibly able to adapt to their new environment seamlessly,” he said.
“Unfortunately, the results weren’t as good for the wild crocodile Jongra, who was translocated about 132km from his home before being released.
“Although Jongra didn’t make it back to his original capture site during the during of the study, his movements were very clearly going in that direction. He travelled far more each day than any other crocodile we tracked, covered an exceptionally large area, and even recorded single‑day movements of more than 30 kilometres: all typical signs of homing behaviour.”
Associate Professor Somaweera said the findings could be useful for conservationists.
“These findings suggest that releasing subadult and adult captive-reared crocodiles can be a viable strategy to strengthen wild populations,” he said.
“For translocated crocodiles, it’s important there is careful release planning to manage their tendencies to return home.”
The study, What is home? Post-release movements of captive-reared and translocated mature saltwater crocodiles in Bangladesh, was published in the journal Wildlife Research, and was funded by the Deutsche Gesellschaft für Internationale Zusammenarbeit and lead by IUCN Bangladesh and the Bangladesh Forest Department.
ENDS
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