American alligators on the Atlantic and Gulf coasts are eating small sharks and stingrays, according to a new study published in the journal Southeastern Naturalist, in what is the first documented evidence of widespread interaction between the freshwater and marine animals.
"In the article, we documented alligators consuming four new species of sharks and one species of stingray," said James Nifong, an author of the study and postdoctoral researcher with the Kansas Cooperative Fish and Wildlife Research Unit at Kansas State University.
"Before this, there have only been a few observations from an island off the Georgia coast, but the new findings document the occurrence of these interactions from the Atlantic coast of Georgia around the Florida peninsula to the Gulf Coast and Florida panhandle."
Though there has been anecdotal evidence of alligators eating sharks previously, this is the first scientific study of its kind.
Even though alligators live in freshwater, and sharks and stingrays reside in the ocean, it is fairly common for them to share the same water, according to Nifong. Many sharks and rays can occasionally swim into freshwater, while opportunistic alligators can also travel between freshwater and marine habitats, despite not having salt glands like crocodiles.
"Alligators seek out fresh water in high-salinity environments," Nifong said. "When it rains really hard, they can actually sip fresh water off the surface of the salt water. That can prolong the time they can stay in a saltwater environment."
Normally, alligators eat crustaceans, snails and fish, but they are not ones to pass up the chance of a larger meal, which explains why rays and small sharks end up on the menu.
"The findings bring into question how important sharks and rays are to the alligator diet as well as the fatality of some the juvenile sharks when we think about population management of endangered species," Nifong said.
During the research, Nifong pumped the stomachs of more than 500 live alligators to learn more about their diet. The reptiles were also equipped with GPS transmitters to monitor their movements.
The researchers found that the alligators travelled between freshwater sources and estuaries – partially enclosed coastal bodies of water where freshwater meets the sea. These estuaries often house nurseries of young sharks.
"The frequency of one predator eating the other is really about size dynamic," Nifong said. "If a small shark swims by an alligator and the alligator feels like it can take the shark down, it will. But we also reviewed some old stories about larger sharks eating smaller alligators."
Nifong found news reports from the 1800s which described large battles between sharks and alligators after flooding and high tides washed the two predators together.