The saltwater crocodile population in Australia's Northern Territory has surged dramatically over recent decades, transforming the region's ecological dynamics. Once numbering fewer than 3,000 in 1971, these apex predators now exceed 100,000. This population explosion has led to significant changes in their diet and environmental impact.
Recent studies reveal a striking dietary shift in these formidable reptiles. In 1979, aquatic prey formed 65% of their diet. By 2019, this figure plummeted to 30%, with land animals like feral pigs, cattle, and Asian water buffalo now comprising the majority. The crocodiles consume approximately six feral pigs per square kilometre of wetland floodplain annually, showcasing their voracious appetite.
The increased biomass of the crocodile population is a key factor behind this dietary transition. Research published in the journal Proceedings of the Royal Society B outlines how the biomass of these reptiles now rivals that of terrestrial predators like lions on the Serengeti or wolves in Yellowstone. Remarkably, saltwater crocodiles consume about 10% of the food compared to an equal-sized lion, highlighting their unique efficiency.
“Crocodiles eat about 10% of the food of an equal-sized lion,” – Prof Hamish Campbell
The ecological influence of these reptiles extends beyond predation. The amount of nitrogen and phosphorus excreted by crocodiles into Northern Territory waterways has surged, increasing 186-fold and 56-fold respectively over the past five decades.
“They’re digesting it, and they’re excreting all those nitrates and phosphates into the water.” – Campbell
This nutrient influx has profound implications for aquatic ecosystems.
“That’s going to be having huge impacts on phytoplankton and zooplankton productivity, which are the building blocks of the food chain.” – Campbell
Utilizing fifty years of government surveys, researchers meticulously recorded crocodile size and density to model prey rates and nutrient excretion. This comprehensive analysis sheds light on the energy inputs driving the growth in crocodile numbers and biomass over this half-century period.