By nature, crocodilians (alligators, crocs and the like) and most sharks are opportunistic feeders. If they can fit in their mouths, they'll likely eat it. Tiger sharks take this attitude to the extreme, for instance, eating everything from sea turtles to rubber tires.
Because these swimming predators have such broad diets, it's not surprising that — where fresh and salt waters intermingle — they occasionally feast on each other. In September 2017 a new paper on the subject was published in the journal Southeastern Naturalist. By reviewing the scientific literature and pumping hundreds of reptile stomachs, co-authors James Nilfong and Russell Lowers were able to show that American alligators eat small sharks and rays more often than biologists previously thought.
Currently a post-doctoral researcher at Kansas State University, Nilfong's dissertation focused on the impact of American alligators on coastal ecosystems. He spent nearly ten years rounding up live specimens for study along the shorelines of Florida and Georgia. In total, Nilfong oversaw the capture of more than 500 live gators. Once caught, the reptiles received a stomach pumping treatment. Then, they were fitted with tracking devices and released.
Nilfong's teams painstakingly examined the voided stomach contents of his animals and in the process, they made a breakthrough discovery. "We documented alligators consuming three new species of sharks and one species of stingray," Nilfong said in a K-State press release. Specifically, the researchers found partly digested bits of lemon, nurse, and bonnethead sharks — along with the remains of one Atlantic stingray. Scientists had never previously documented alligators consuming any of these species.
Gator-on-shark attacks aren't exactly unheard of. Nilfong did find some reports of these predatory attacks in earlier scientific papers. However, thanks to his original research, we now know that the phenomenon is a widespread one, with alligators dining on the fish from coastal Georgia to the Florida panhandle. The revelation is bad news for loads of shark and ray conservation efforts. Nilfong noted the wild nurseries of smalltooth sawfish, an endangered ray species. "If there are alligators in the area, survival of those juveniles is going down," he says in a New Scientist article.
American gators aren't the only crocodilians who prey on sharks. In 2014, a huge Australian saltwater crocodile was photographed tearing into a bull shark. But the rivalry isn't one-sided. Great whites have been known to kill alligators in Colombia, while tiger sharks eat the occasional croc Down Under.