Population densities of crocodiles plummeted as
much as 77 per cent in some areas following toad
invasion.

The first evidence has been found for the destructive effect of the cane toad invasion on one of northern Australia's top predators, the freshwater crocodile.

A University of Sydney team led by Dr Mike Letnic from the School of Biological Science found up to a 75 per cent reduction in the numbers of freshwater crocs in the Victoria River District of the Northern Territory following the toads' recent arrival in the river system.

"During surveys of the Victoria River in the semi-arid tropical region of the Northern Territory, we documented massive mortality of freshwater crocodiles at the toad invasion front," said Dr Letnic.

The Sydney team found that population densities of crocodiles plummeted as much as 77 per cent in some areas following toad invasion, with some of the dead crocs found to have undigested toads in their stomachs.

"The impact of invasive species is particularly important as their removal can generate a substantial cascade of secondary effects in the local environment," said Dr Letnic.

Dr Letnic will present his research at the 14th Australasian Vertebrate Pest Conference in Darwin in June.