Young saltwater crocodiles take shorter dives and put their safety at risk when faced with long-term exposure to rising water temperatures, according to new research.

The finding, published today in Conservation Physiology, indicated increasing temperatures could have a profound effect on the iconic reptile's daily life in Australia's north.

"Crocodiles are ectotherms, meaning their body temperature is closely tied to environmental temperatures," explained PhD student Essie Rodgers, who led the study.

"We have known for a while now that diving capacity in many ectotherms, such as marine and freshwater turtles, sea snakes and iguanas is generally compromised at high water temperatures.

"What we didn't know is whether crocodiles can adjust to the long-term elevations in water temperatures that are predicted to come with climate change."

Saltwater crocodiles (Crocodylus porosus) spend up to 11 hours a day submerged. Their ability to dive is important to avoid predators, forage for underwater prey, rest and socialise.

To assess the reptile's capacity to withstand heat, Ms Rodgers and her colleagues assessed the temperature sensitivity and 'fright dive' response of 11 juvenile salties that had been exposed to one of three temperature regimes: current summer, 28 degrees C; moderate climate warming, 31.5 degrees C; and high climate warming, up to 35 degrees C.

They found while all study animals dived to the same depth and at the same frequency, those diving in 28-degree water spent an average of 36.8 minutes underwater, while crocs diving in 31.5 and 35-degree waters spent an average of only 23.5 and 21.3 minutes submerged respectively.

When the crocs were exposed to a frightening noise — a plastic lid being banged on the back of the dive tank — submergence times halved with every 3.5-degree water temperature increase.

Those in the 28-degree tanks stayed down for eight minutes, while the high-temperature crocs surfaced after only 2.3 minutes.

Options limited if waters warm

The researchers said the difference in dive capacity was due to the fact oxygen stores are consumed more rapidly at warm temperatures, forcing the animals to surface more frequently to breathe or spend longer at the surface recovering between dives.

"Juvenile estuarine crocodiles were unable to adjust to long-term (30 days) elevations in water temperatures, which suggested their diving performance would likely be compromised under future climate warming," Ms Rodgers said.

With little capacity to compensate for water temperature changes, crocodiles were left with few options, she added.

"This [finding], together with the 70 - 80-year lifespan of estuarine crocodiles, suggests that they may have to rely on behavioural strategies to buffer extreme temperatures," she said.

"They may be able to seek refuge in deep, cool water pockets or shift their geographical range to cooler, southerly waters."