Scientists have uncovered evidence that suggests the diet of saltwater crocodiles has shifted away from marine prey towards land-based animals.

Researchers at Charles Darwin University compared bone samples from saltwater crocodiles killed around the 1960s, held at the Museum and Art Gallery of the Northern Territory, to those of contemporary saltwater crocodiles.

“We saw that crocodiles back then were primarily feeding on the estuaries, taking up fish, turtles, crabs,” Dr Mariana Campbell, who co-authored the research, said.

“Now they are primarily feeding upon the terrestrial environment, taking up feral pigs, buffalo and wallabies.

“We could see that the signature found on contemporary crocodiles, or crocodiles that we see around today, you can see that it’s more that they have been eating upon what we call the terrestrial food web.”

Dr Campbell said an increased number of feral pigs in freshwater floodplains, a reduction in estuarine prey, and more freedom to roam since the end of the crocodile-hunting era all could have contributed to why crocodile diets had changed.

The diet shift coincides with the exponential increase in the Northern Territory’s crocodile population in the past 50 years.

A ban on hunting crocodiles in the Northern Territory was introduced in 1971, when it was estimated only 3000 crocs were left in the wild.

Thanks in large part to the protection of the species, it is estimated the NT’s saltwater crocodile population is now about 100,000.

“When they were protected, no-one was really quite sure whether they could really recover,” Dr Grahame Webb, one of Australia’s most prominent crocodile scientists, said.

“But they did recover, and the whole sort of system changed, and the rest is history.”

Dr Campbell said the shift to a more land-based diet is not a behavioural change.

“It is simply to do with food availability, they are eating what they encounter,” she said.

The rapid change in the saltwater crocodile population, she said, was a success story.

“This is an incredible recovery, it’s something extremely difficult to do, and it’s something the Northern Territory can be proud of,” she said.

“We helped recover a top predator population and live alongside it.”

Dr Webb also welcomed the study.

“What I’m excited about is it just demonstrates the values of museums holding these big reference collections,” he said.

The research, he said, could lead to further studies into crocodile populations, including the prevalence of crocodile cannibalism as the population grew.

“As the crocs were recovering, crocs were eating other crocs. Cannibalism has become a really big issue, and that could be implicated in these results,” he said.

This article appeared in Cape York Weekly, 3 May 2022.

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