Alligators eat sharks — and a whole lot more

Alligators don’t just stick to freshwater and the prey they find there. These crafty reptiles can live quite easily, at least for a bit, in salty waters and find plenty to eat — including crabs, sea turtles and even sharks.

“They should change the textbooks,” says James Nifong, an ecologist with the Kansas Cooperative Fish and Wildlife Research Unit at Kansas State University in Manhattan, who has spent years documenting the estuarine gator diet.

Nifong’s most recent discovery, splashed all over the news last month, is that the American alligator (Alligator mississippiensis) eats at least three species of shark and two species of rays, he and wildlife biologist Russell Lowers report in the September Southeastern Naturalist.

Lowers captured a female gator with a young Atlantic stingray in her jaws near where he works at Kennedy Space Center in Cape Canaveral, Florida. And he and Nifong gathered several other eyewitness accounts: A U.S. Fish and Wildlife employee spotted a gator consuming a nurse shark in a Florida mangrove swamp in 2003. A birder photographed an alligator eating a bonnethead shark in a Florida salt marsh in 2006. One of Nifong’s collaborators, a marine turtle researcher, saw gators consuming both bonnethead and lemon sharks in the late 1990s. And Nifong found yet another report of a gator eating a bonnethead shark in Hilton Head, S.C., after their paper was published. All of these snacks required gators to venture into salty waters.
But shark may not be the most surprising item on the alligator estuarine menu. Nifong spent years catching hundreds of wild gators and pumping their stomachs to figure out what they eat, work that relies “on electrical tape, duct tape and zip ties,” Nifong says. And he found that the menu is pretty long.

To snag an alligator, he uses a big blunted hook or, with smaller animals, just grabs the animal and hauls it into the boat. He gets a noose around its neck. Then the researchers tape the mouth shut, take body measurements (everything from weight to toe length) and get blood or urine samples.

Once that’s out of the way, the team will strap the gator to a board with Velcro ties or rope. Then, it’s time to untape the mouth, quickly insert a piece of pipe to hold it open, and tape the alligator’s mouth around the pipe. The pipe, Nifong says, is there “so they can’t bite down.” And that’s important, because next someone has to stick a tube down the gator’s throat and hold it there to keep the animal’s throat open.
Finally, “we fill [the stomach] up with water very slowly so we don’t injure the animal,” Nifong says. “Then we do basically the Heimlich maneuver.” Pressing down on the abdomen forces the gator to give up its stomach contents. Usually.
“Sometimes it goes better than other times,” he says. “They can just decide to not let it out.” Then the researchers carefully undo all their work to let the gator loose.

Back in the lab, Nifong and his colleagues teased out what they could find in those stomach contents, and looked for more clues about the animals’ diet from in the blood samples. Nifong and his colleagues found that the gators were eating a rich marine diet, including small fish, mammals, birds, insects and crustaceans. They’ll even eat fruit and seeds. The sharks and rays didn’t show up in these studies (nor did sea turtles, which gators have also been spotted munching on). But Nifong and Lowers speculate that’s because the tissue of those animals gets digested very quickly. So if a gator had eaten a shark more than a few days before being caught, there was no way to know.

Because alligators don’t have any salt glands, “they’re subject to the same pressures as me or you when being out in saltwater,” Nifong says. “You’re losing water, and you’re increasing salt in your blood system.” That can lead to stress and even death, he notes. So the gators tend to just go back and forth between saltwater and freshwater. They can also close off their throat with a cartilaginous shield and shut their nostrils to keep salty water out. And when they eat, they’ll tip their head up to let the saltwater drain out before gulping down their catch.
What alligators eat isn’t as important a finding as the discovery that they regularly travel between saltwater and freshwater environments, Nifong says. And, he notes, “it occurs across a wide variety of habitats across the U.S. southeast.” That’s important because the gators are moving nutrients from rich marine waters into poorer, fresh waters. And they may be having a larger effect on estuarine food webs that anyone had imagined.

For instance, one of the prey items on the alligator menu is blue crab. Gators “scare the bejesus out of them,” Nifong says. And when gators are around, blue crabs decrease their predation of snails, which might then eat more of the cordgrass that forms the base of the local ecosystem. “Understanding that an alligator has a role in that kind of interaction,” Nifong points out, is important when planning conservation efforts.