"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."
Meanwhile, Nifong said, it is not uncommon for sharks and rays swim into non-saline water where alligators can't pass up a good meal.
An alligator's diet typically consists of crustaceans, snails and fish, but because alligators are opportunistic predators, Nifong said sharks may end up on the menu.
Some of the findings arose after Nifong and his colleagues pumped the stomachs of more than 500 live alligators to learn more about their diet.
"There's not a ton of people out there stomach-pumping very large alligators," he told the The Washington Post. "They're actually very difficult to stomach-pump and retrieve prey items. It's very tough to be certain that you got everything out of there."
They also equipped alligators with GPS transmitters to watch their movements and found the creatures often travel to estuaries containing both fresh and salt water.
But alligators should not feel over-confident, the researchers say — the predator-eats-predator dynamic can also go the other way.
"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 said he found news reports from the late 1800s that described battles of large masses of sharks and alligators after flooding and high tides washed the predators together.