Alligators versus Sharks

It’s the aquatic battle royale. A previously overlooked conflict between alligators and sharks has been going on for centuries at least, and it seems the alligators are winning.

James Nifong at Kansas State University has studied American alligators in marine habitats for the past decade. A keen fisherman, Nifong noticed he was catching a lot of sharks in alligator country, and wondered whether the two predators ever interacted. “Alligators are opportunistic,” he says. “They’re not going to pass up a big chunk of protein that’s swimming by.”

However, the only previous evidence of alligators eating elasmobranchs – the group to which sharks and rays belong – was an individual with stingray spines in its jaw.

Nifong searched the scientific and historical literature, and consulted experts on alligators and sharks. He found confirmed instances of alligators eating lemon, nurse and bonnethead sharks, as well as an Atlantic stingray. He says sharks and other elasmobranch fish could be a significant but underappreciated food source for alligators.

“Gators will eat almost anything that will fit in their mouths,” agrees Steven Gabrey at the Northwestern State University of Louisiana. But he has analysed the contents of many alligator stomachs and never found shark remains.

Nifong says that might be because Gabrey’s alligators lived in marshes far from salt water, so were less likely to encounter sharks. Alligators also have highly acidic stomachs, which could dissolve the cartilaginous skeletons of sharks with little trace.

Sharks bite back
The only previous accounts of sharks attacking alligators come from credulous late 19th-century newspaper articles. One described hundreds of alligators and sharks assembling in an inlet and “fight[ing] like dogs”.

Though undoubtedly exaggerated, such stories are not wholly incredible, says Nifong. Both sharks and alligators gather in large numbers to feed, and alligators were far more numerous in the 19th century than today. “That increases the probability these feeding congregations would commingle,” Nifong says.

Nifong also scoured the literature for accounts of sharks clashing with other crocodilians. He found plenty. But in many cases the crocodilians were the prey, from great white sharks preying on American crocodiles in Colombia, to tiger sharks eating estuarine crocodiles in Australia.


There are even crocodile fossils from the dinosaur era that show signs of predation by ancient sharks, suggesting this conflict is truly ancient.

Conservationists should bear the crocodilian-shark conflict in mind, says Nifong, as both groups contain endangered species. A study published in April found that many Australian sawfish – another shark relative – sported crocodile-inflicted scars. Similarly, the US nursery grounds of the endangered smalltooth sawfish are known to harbour alligators. “If there are alligators in the area, survival of those juveniles is going to go down,” says Nifong.