A tour guide says it’s getting harder to find crocs as the weather and water heat up. (Supplied: Solar Whisper, David White)
In short:
A tour guide says warming waters in northern Queensland mean crocodiles are spending more time hiding from the heat.
University of Queensland scientists agree, and say in hot years the reptiles’ increased internal temperatures adversely impact their behaviour.
What’s next?
The long-term health impacts of the warmer waters on crocodiles will be studied in the next phase of research.
Scientists and tour guides say crocodiles in Queensland’s north are hiding from the heat as temperatures warm, potentially disrupting their ability to hunt and travel.
In Far North Queensland’s UNESCO Wet Tropics World Heritage Area, wildlife guide David White closely monitors water temperatures in the Lower Daintree River.
The water’s heat — along with his 28 years of experience on the river — will tell him which of the dozens of known crocodiles might play ball for the tourists aboard his boat that day.
The warmer water makes his job harder.
Warmer water is affecting the behaviour of crocodiles. (Supplied: Solar Whisper, David White)
“They hide for longer,” he said.
“In the past the water temperature has been up to 31 degrees [Celsius], but this year we’ve had 32 degrees,” he said.
“Warmer water makes my job very difficult because the crocodiles spend a lot of time on the bottom where it’s cooler, and they’re very hard to find in the summer months.”
Ability to hunt at risk
Scientists from the University of Queensland have been studying crocodile body temperature for fresh research published in Current Biology.
They have collected 15 year’s worth of data from sensors and trackers on 203 wild crocodiles on the Wenlock and Ducie Rivers at the northern end of Cape York, and their experiences match Mr White’s.
PhD candidate Kaitlin Barham said as the days got hotter so too did crocodiles’ internal temperature.
“During very hot years, we’re finding that their internal body temperatures are starting to reach points where we know their behaviour is impacted,” she said.
PhD candidate Kaitlin Barham (right) with Professor Craig Franklin. (Supplied: The University of Queensland)
Crocodiles are ectothermic, which means they rely on their environment to regulate body temperature.
“They’ll prioritise cooling over warming, or they’ll dive [in warm water] for a shorter period of time,” Ms Barham said.
“Because they are sit-and-wait predators, we’re concerned that shorter dive times might limit their ability to hunt, and also to hide and escape from predators, or travel.”
Wildlife Management International chief scientist Charlie Manolis said it was unlikely crocodiles would start moving south because of the current water temperatures in Far North Queensland.
Scientists say crocodiles are hiding from the hot weather and warmer water for longer, potentially disrupting their behaviour. (Supplied: Australia Zoo)
“But if they become warmer, the crocodiles will start to find those sorts of environments further south more conducive to their way of living,” he said.
“If all of a sudden, water temperatures in Far North Queensland get up to 40 degrees, crocs may struggle.
“It does highlight the need for research to be done on the crocs that live more on the southern range.”
There have been no baby saltwater crocodiles on the lower Daintree River in two years. (Supplied: Solar Whisper, David White)
Looking for hatchlings
Back on the Daintree River, Mr White said another pressing climate-related issue — extreme flooding — had been more frequent.
“The high ground is being used for agriculture, so the crocs end up nesting quite close to the water. You get a flood, and the nest goes underwater,” he said.