# Crocodiles dive less in warmer waters



## slim6y (Jul 13, 2010)

*Published On:* -
*Source:* ABC Science

Warmer temperatures may make it harder for crocodiles to dive for food, say researchers.

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.



---- Note ----

Currently we're expected to pass through a La Nina event - typically water temperatures will be lower, therefore the above (global warming prediction) hasn't taken this into account at all.

Never-the-less it's a common sense newspaper article which does share the concerns for a warmer planet and our reptilian friends.

*Go to Original Article*


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## syeph8 (Jul 13, 2010)

interesting read. makes perfect sense. ive heard a lot about this el nina, when is this supposed to happen? wasnt it like 2 years ago? what evidence suggests it will happen? im not refuting it, merely asking a number of questions


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## slim6y (Jul 14, 2010)

syeph8 said:


> interesting read. makes perfect sense. ive heard a lot about this el nina, when is this supposed to happen? wasnt it like 2 years ago? what evidence suggests it will happen? im not refuting it, merely asking a number of questions


 
Go to the BOM site and look up El Nino and La Nina (loosely translates to little boy and little girl respectively). 

The Southern Oscillation Index is a predictor of sorts - this is the pressure difference between Tahiti and Darwin measured - when it's negative there's an El Nino phase current, when positive La Nina... Obviously there's a little more to it than that.... But that's basics in less than a paragraph!

During La Nina the water temperatures can be significantly lower (even as much as several degrees Celsius), conditions in the north and east of Australia are generally wetter - although slightly warmer over night, generally speaking the average temperature during the day is lowered.

There is strong correlation to the end of an El Nino to the beginning of a La Nina phase....

But my background knowledge was mostly from New Zealand - as when I studied these things I was living there in the South Island hoping for strong El Nino and big snows!!!

Crocs on the other hand - they'll be wetter, and cooler and need to eat more and therefore will be able to dive more. But as less will be killed by predators (because of the diving ability) then maybe in the years to come there'll be an influx of crocs on our northern rivers?


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## syeph8 (Jul 15, 2010)

true true.. but how will these conditions affect other animals in the area, like egg eaters, and how will these conditions affect croc egg hatching? not saying that it wont lead to increased numbers though, as crocs are well renowned for being almost perfect survival machines. and im not also sure of how much a cooling we are talking about.


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