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Hot Crocs Can’t Hide Long

When frightened, young crocodiles will dive and remain submerged until the threat has passed. However, the length of time they can stay submerged is limited by their metabolic rate, which is expected to rise as water temperatures increase due to climate change.

Prof Craig Franklin of The University of Queensland measured how long scared juvenile crocodiles could remain submerged at both current river water temperatures and the temperatures that crocodiles are predicted to encounter in 2100 to find out how these reptiles may fare in the future.

After adapting the young crocodiles to current (28°C water) or future (34°C) climate scenarios for 2 months, co-worker Dr Essie Rodgers startled the animals with a gentle tap on the back and timed how long they remained submerged. The crocodiles that were adapted to current climate conditions were content to remain submerged for 18.5 minutes, extending to more than an hour if they felt particularly harassed after performing four consecutive dives.

However, the hot-water crocodiles could only remain under water for 9 minutes after a single tap on the back, and the more threatened animals only stayed down for 28 minutes.

Rodgers also measured the animals’ heart rates and oxygen consumption to try to understand why the hot-water animals’ refuge tactics were so impaired, and found that the crocodiles that had adapted to water at 34°C were unable to lower their metabolism as much as the cooler crocodiles. They were burning through oxygen at a faster rate, forcing them to return to the surface sooner than their cooler cousins.

“This finding suggests predator avoidance dives may be shortened if water temperatures continue to increase in marine and freshwater habitats,” warn Rodgers and Franklin, who are concerned that crocodile youngsters will become more vulnerable to predators as they are likely to have to surface more frequently if the temperature continues rising.

The research has been published in the Journal of Experimental Biology.