Wildlife Biologists Find American Alligators Eat Small Sharks and Stingrays

A new study published in the journal Southeastern Naturalist is the first to document that American alligators (Alligator mississippiensis) on the Atlantic and Gulf coasts occasionally eat three shark species and one species of stingray.

An American alligator (Alligator mississippiensis) caught a nurse shark in the Ding Darling National Wildlife Refuge in Sanibel, Florida. Image credit: U.S. Fish and Wildlife Service.

An American alligator (Alligator mississippiensis) caught a nurse shark in the Ding Darling National Wildlife Refuge in Sanibel, Florida. Image credit: U.S. Fish and Wildlife Service.

“Despite the freshwater and saltwater differences, it is fairly common for sharks and rays to share the water with alligators,” said study lead author Dr. James Nifong, postdoctoral researcher with the Kansas Cooperative Fish and Wildlife Research Unit at Kansas State University.

“Many sharks and rays can swim into freshwater where opportunistic alligators can’t pass up a good meal. Although alligators don’t have salt glands like true crocodiles, they are resourceful as they travel between freshwater and marine habitats.”

“Alligators seek out fresh water in high-salinity environments,” he added.

“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.”

“An alligator’s diet typically consists of crustaceans, snails and fish, but because alligators are opportunistic predators, sharks may 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.”

As part of the study, Dr. Nifong and his colleague, Russell Lowers, wildlife biologist with Integrated Mission Support Services at Kennedy Space Center, pumped the stomachs of more than 500 live and alert alligators to learn more about their diet.

The scientists also equipped the alligators with GPS transmitters to watch their movements and found that alligators travel between freshwater sources and estuaries, which are a partially enclosed coastal water body where freshwater and salt water mix and house shark nurseries.

“The frequency of one predator eating the other is really about size dynamic,” Dr. 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.”

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James C. Nifong Russell H. Lowers. 2017. Reciprocal Intraguild Predation between Alligator mississippiensis (American Alligator) and Elasmobranchii in the Southeastern United States. Southeastern Naturalist 16 (3): 383-396; doi: 10.1656/058.016.0306

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