Scientists looking into whether reptile migration is behind big rise in number of attacks

The people of Timor-Leste have a crocodile problem.

The reptiles are revered in the island, which lies north-west of Australia in the Timor Sea. Residents refer to the animals as “grandfathers” and crocodiles are honoured with shrines around the country.

But in the last few decades, the nation has seen a more than 20-fold increase in the number of crocodile attacks. Of late, more than one person a month, in a country of 1.3 million, has been attacked by a saltwater crocodile, and more than half of the attacks have resulted in death.

The majority of the attacks (82.5%) occur while people are fishing, according to researchers, with bathing (7.5%) and water collecting (4.2%) being the next most dangerous activities. All this presents the people of Timor-Leste with an uncomfortable question: why are their ancestors turning on them?

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Some Timorese have turned to an answer more familiar in the world of politics than zoology: they are blaming migrants. Specifically, migrant crocodiles from Australia, which they say have swum the 700km journey to Timor-Leste and now fill the river systems and surround the island.

Two Australian-based researchers, Yusuke Fukuda and Sam Banks, made the journey to Timor-Leste to see if this theory might be true, collecting DNA samples from the crocodile population to see if there were any Australian crocodiles among the Timorese population.

The pair collected DNA samples from 18 crocodiles. Some were captive animals, but roughly half were sampled in the wild, using a 4-metre pole with a dart on the end.

Banks, who is a professor of animal ecology and genetics at Charles Darwin University in Darwin, said the job had its challenges.

“It’s a matter of finding ones you can sneak up on on foot … you certainly wanted to pick your targets a little more carefully,” he said. “There’s no chance of wading in the water and sneaking up on a 4-metre crocodile.”

Facebook Twitter Pinterest Sam Banks tries to collect DNA samples from a saltwater crocodile in Timor-Leste. Photograph: Yusuke Fukuda

Banks has just got back the sequencing data from the crocodiles, though he is yet to analyse it to see if there are any matches with the database of DNA from roughly 750 Australian crocodiles that he and his colleagues have collected over the last four years.

If there are Australian crocodiles among the local population, this will be the longest proven migration of the animal in history.

The existence of Australian crocodiles in Timor-Leste would also confirm that Australian efforts to conserve the animal, which was on the brink of extinction 50 years ago, are having an impact on the regional population. Since it was listed as protected in 1971, the Australian saltwater crocodile population has recovered to healthy levels. Some crocodiles can live for 80 years, and with a booming population, territory can become an issue.

“They move around, young crocodiles get kicked out by big males and are looking for new places to settle. As part of that we think that crocodiles go to remote islands like Timor,” said Fukuda, a wildlife scientist for the Northern Territory state government.

It could also mean a different approach is needed to deal with the Australian population. In Australia, there are roughly seven attacks a year, with 25% of these proving fatal.

“There’s no particular reason to think that national borders for crocodiles are the same as for humans,” Banks said. “If we find out that Australia and East Timor and Indonesia are fundamentally sharing a crocodile population, and have the same issues around human-crocodile conflict, then we need to work together to come up with a regional management plan for them.”

Though Fukuda says there is no reason to think Australian crocodiles might be more aggressive than Timorese ones, if they were to find out the crocodiles in the area were Australian ones, this may provide some solace to the people of Timor-Leste. Fukuda said residents were “quite happy” to hear that the researchers were seeking to prove what they had suspected.

“When we spoke to their government over there they seemed quite happy as well because when we bring our analysis, it will encourage people to be more careful, more croc-wise. We saw so many people in the village using the water … jumping in the river, none of them were really worried about crocodiles, though they know there are crocodiles in there, they think they are good local crocodiles.”