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Crocodiles dive less in warmer waters

Close up of crocodile eye

The warmer it is the faster crocodiles use up their oxygen (Source: stock.xchng)


A team led by Dr Hamish Campbell, from the University of Queensland in Brisbane, report their findings today in the Proceedings of the Royal Society B.

Crocodiles spend a fair bit of their time diving under the water, foraging, resting and - when they're small - escaping predators.

But the amount of time they can spend doing this depends on how much oxygen they can take on board, and how quickly they use up that oxygen.

Since crocodiles are cold blooded animals, their body temperature and metabolic rate is affected by the temperature of the environment.

The warmer it is, the higher their metabolism and oxygen use, which could affect how much time they spend under water.

Campbell and colleagues studied the diving behaviour of freshwater crocodiles (Crocodylus johnstoni) in a national park in Queensland to see if this was the case.

Field study

Research team member Dr Matthew Gordos, a conservation manager with the NSW government, says the team attached devices to the crocodiles to measure how deep they dove and for how long.

The crocodiles were also fitted with sensors to measure the temperature of their body and of the surrounding water.

The team compared thousands of measurements taken during summer and winter.

They found that in summer the water temperature rose by a few degrees and the crocodiles' body temperature was 5°C higher than in winter.

Overall, the animals spent less time under water in summer and whenever the crocodiles dove for longer than 40 minutes they had to spend exponentially longer on the surface, says Gordos.

"In summer time they're using their oxygen up much quicker," he says.

Gordos says this is likely because the animals need time to recover from anaerobic respiration necessary for longer dives in summer.

Impacts of warming

Gordos says the findings suggest that crocodiles could be adversely affected if predicted warming of several degrees occurs.

"It exposes them to predators and if they are diving to forage they have less time because they have to spend more time at the surface," he says.

"It [a temperature rise] could put them outside a comfortable range and you might start seeing population declines or they might have to shift where they're distributed."

Gordos says the next stage would be to directly study whether changes in diving patterns due to higher temperatures affect predation, foraging and rest patterns.

The findings could also be relevant to other air-breathing ectotherms like turtles, snakes, lizards and amphibians.

Tags: climate-change, animals, animal-behaviour, reptiles