Last fall, a tour company in Australia stumbled upon a rare find: a dead whale. But what they had spotted turned out to be even rarer than that, as the video footage captured both sharks and a large saltwater crocodile tearing at the carcass—something no one had ever seen before.
It was an exciting enough observation to catch the attention of Austin Gallagher, chief scientist and CEO of Beneath the Waves. “I saw the post online on Facebook,” he told me, where it had already gone somewhat viral.
Gallagher, a shark expert, admitted to having a ‘closet interest’ in scavenging ecology in particular, so when he saw the video, he got really excited. He quickly reached out to the charter company and the drone pilot to learn more, and worked with them and a couple of his scientific colleagues to write up the observation, which was recently published in Journal of Ethology.
Obviously saltwater crocodiles are known to venture into the seas for their meals—it’s right there in the name—but whales aren’t usually a part of their diet, said Gallagher.
“The crocodile was incredible here,” he said with awe. When the whale washed up later, a dozen or so of the animals all came together to feast, but only one went into the ocean. Gallagher thinks the croc likely saw the whale in the distance from shore, as they’re highly visual predators, and took a chance. “There was just one brave crocodile that who went for it, and swam out 1,000 meters to find this food source.”
— Dr. Austin Gallagher (@DrAustinG) March 12, 2018
While both sharks and crocodiles are known to scavenge carcasses when they’re available, this is the first time the two have been recorded feeding together—though, perhaps it’s not that surprising the two would seize the same opportunity. “This is no different than when you have a dead zebra on the Serengeti, and everybody is competing for a piece of the prize,” Gallagher explained.
The video captured the croc feeding in two different ways, ripping at the carcass in normal crocodilian fashion and doing a more vertical tearing action, using its tail as a lever of sorts. But what really stood out was its complete lack of concern about the other diners. As Gallagher noted, crocodiles and their relatives will feed on sharks, and vice versa, so it’s entirely possible that saltwater crocodiles and sharks have an antagonistic relationship most of the time.
Yet “the crocodile seemed largely undeterred or unaffected by the presence of the sharks,” noted Gallagher. The sharks, on the other hand, were far less happy about sharing. One of the tiger sharks actually tried to scare the crocodile away, according to Gallagher, even though they usually don’t show aggression towards one another when feeding on dead whales.
The crocodile couldn’t have cared less. “After the tiger shark did that, the crocodile actually went deeper into the underbelly of the whale to try to get a better piece, and then actually rested on the fluke with its front legs, taking a breather.”
To Gallagher, the event is also pretty incredible because it reveals just how much technology has changed how we interact with our world. “Drones have made the discovery of natural history phenomena so much more prevalent for the everyday person.”
But while anyone can now capture an incredible sight like this, “these kind of events fascinate scientists just as much, if not more, than they do the general public,” Gallagher said, “because these are the types of patterns we’re always looking to try to understand and detect in nature through our research.” Even a one-off observation like this tells scientists a lot they didn’t know about animal behavior.
The way the sharks treated the crocodile differently than they do other sharks, for example, is really interesting, and gives scientists a window into the way they evaluate potential competitors. And the fact that this one crocodile dared to swim a kilometer into the depths after some big, floating thing it saw from shore that might be edible reveals a lot about how they make food-related decisions and what kinds of lengths they’re willing to go to to secure a meal.
And while a lot of the take aways from this event are somewhat nebulous, one-off observations like this are still incredibly valuable to scientists. “These natural history notes don’t necessarily change the world—in fact they don’t change the world—but they inspire people,” said Gallagher. “And I think that is so important for creating a narrative of respect and appreciation for the natural world.”
— Dr Caitlin Syme (@taphovenatrix) September 29, 2017
Citation: Gallagher et al. 2018. Apex predatory sharks and crocodiles simultaneously scavenge a whale carcass. Journal of Ethology, Online First. doi:10.1007/s10164-018-0543-2