Study finds crocodiles in Far North Queensland are feeling the heat

ABC NEWS (Australia)

As warmer weather sweeps across Australia it's not only human's feeling the heat. It's also impacting crocodiles in far North Queensland and their ability to hunt and survive.

Transcript

00:00Hi, Joe. So we've been tracking a population of saltwater crocodiles or estuarine crocodiles

00:08that live on the Wenlock River up in Cape York, and we've been recording their body

00:13temperature for the last 15 years to see how it's been changing. And what we found is that

00:19as the air has gotten warmer in the last 15 years, the crocs have become warmer as well.

00:26And so what's actually happening to their body temperature? Can you give us numbers?

00:30I can give you numbers, yes. It's going up by a fraction of a degree each year. So on

00:36average, we've seen that body temperature increase by about 0.1 degrees in the 15 years,

00:42which sounds like a small number, but it really does add up over time. And then the higher

00:47body temperatures that the crocs experience have been as much as half a degree higher

00:52now than they were at the beginning of this study back in 2008.

00:57And have you determined if that has more to do with the air temperature or water temperature

01:01or it's a mix of the both?

01:03So crocs are largely aquatic, and because they're cold-blooded, that means their body

01:08temperature is going to be impacted by their local environment. So by and large, this would

01:15be water temperature. But we've also seen these really interesting periods of time when

01:20the crocs become warmer or cooler than we expect, and we think that's where air temperature

01:26is coming into things. So for example, on a summer night, the air gets cooler than the

01:32water does, and we see these drops in temperature that we believe are the crocs' nocturnal basking

01:38to help them keep cool.

01:39Yeah, and that leads into my next question. What have you noticed about the effects on

01:44their behaviour from this?

01:47Yeah, so as the crocs' body temperature starts to exceed about 32 or 33 degrees, we notice

01:54that they are tending to cool rather than warm, which makes sense. But they also tend

02:01to have shorter dive length at these temperatures. The amount of time they can stay underwater

02:06becomes a bit more limited.

02:09And so when you say, when it gets to a certain temperature, that they cool rather than warm,

02:13how do they cool?

02:15Because we're tracking these body temperatures remotely, we don't have eyes on the crocs

02:20when we see this cooling happen. But there are some behaviours that we know crocodiles

02:24can use. Nocturnal basking is one of these, because water tends to hold on to the heat

02:30of the day much more than air does, and the air can become cooler at night or in the early

02:36morning. Another option is they may sit in the shade in cool runoff from springs, or

02:41if it's available, they may dive down to deep, cool pockets of water.

02:46And Caitlin, just a minor issue that I'd like to clarify with you, how do you track and

02:51monitor crocs?

02:53Sure. It's definitely easier said than done, because they do live in such a remote area

02:59and they can travel very far. So we use two technologies mainly to do this. One is satellite

03:06trackers, which are attached externally to the back of the croc's neck, and that picks

03:10up where they go and also when they're underwater. The other kind of technology is acoustic trackers,

03:17which are internally placed just below the arm, and that also picks up the body temperature

03:22of the crocs. And those tags can last up to 10 years, so we get some really incredible

03:27data from them.

03:29And Caitlin, have you been involved in attaching these satellite trackers?

03:35Yes, I've had the absolute privilege to go on a croc trip, which happens every August.

03:41I've gone on that a few times, and that's part of what we at the University of Queensland

03:47do while we're there. The main goal of it is to continue to track these crocs year-to-year.

03:52And can you tell us how you do that? Are the crocs caught in traps and then sedated and

03:57then you attach them, or how do you actually do it?

04:01Yes, so we do this work in collaboration with Australia Zoo, who are legends at croc catching.

04:08We let them do that part of the equation for us. They get the croc restrained, and then

04:15the science people come in, we attach the trackers, and we can also take measurements,

04:20see how the crocs are growing, and do some health checks.

04:23And what's it like for you to get up there in that country and be up close with these

04:28creatures that you're studying?

04:30I'm a city girl, so it is amazing to me. I really, really, it's an incredible experience

04:36being there. And because so much of my job involves looking at data, being able to actually

04:42get up close and personal with these animals that I study is such an awe-inspiring experience.

04:48Were you kind of freaked out on your first couple of experiences and then got used to

04:52it, or you were always kind of so intrigued by the science of it that you were cool, calm,

04:57and collected?

04:58I wouldn't say freaked out is the right word. There's definitely something quite incredible.

05:05The first time you see a crocodile in the wild, I had a moment of, wow, they really

05:10get that big? But over a few years, it's become something that is always incredible, but much

05:18more normal, if that makes sense.

05:21And are you concerned for their future, taking into account what you've found out about this warming?

05:28Crocs are really well adapted to the hot tropical environments where they live. And we do see

05:34that even when things get hot, they have these cooling behaviours that they can use. But

05:39even with all that, we have seen crocs approaching these thermal limits of 32, 33, 34 degrees,

05:47where we might end up seeing impacts of this into the future as the climate warms.

05:52And what's the next steps in your studies?

05:55The next step here is to see how these really hot periods are impacting the health of the

06:01crocs so that we can know what toll it might be taking, if any, on their condition.

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