Alligators aren’t just freshwater animals | Science News for Students

Alligators aren’t just freshwater animals

These reptiles have been caught in salty waters snacking on shark
Dec 6, 2017 — 7:32 am EST
alligator eating nurse shark
This alligator was spotted eating a nurse shark in a wildlife refuge on Sanibel Island, Fla., in August 2003. The sighting helped to confirm that shark is part of some gators’ diets.
COURTESY OF U.S. FISH AND WILDLIFE SERVICE J.N. "DING" DARLING NATIONAL WILDLIFE REFUGE

Hungry alligators don’t just stick to freshwater. These crafty reptiles can live quite easily in salty waters (at least for a bit) where they’ll find plenty to eat. Their diet includes crabs and sea turtles. A new study adds sharks to their menu.

“They should change the textbooks,” says James Nifong. He’s an ecologist with the Kansas Cooperative Fish and Wildlife Research Unit at Kansas State University in Manhattan. He has spent years documenting the diet of estuarine gators. (An estuary is where a river meets the ocean.)

Nifong’s most recent discovery is that the American alligator (Alligator mississippiensis) eats at least three species of shark and two species of rays. (Those last animals are essentially flattened sharks with “wings.”)

Wildlife biologist Russell Lowers works at Kennedy Space Center in Cape Canaveral, Fla. A paper he coauthored with Nifong in the September Southeastern Naturalist describes what they learned about the gator’s appetite for shark.

alligator eating bonnethead shark
This alligator was caught on film chomping on a bonnethead shark in the waters off Hilton Head, S.C.
Chris Cox

Lowers actually captured a female gator with a young Atlantic stingray in her jaws. This was near Cape Canaveral. He and Nifong gathered several other eyewitness accounts. One U.S. Fish and Wildlife Service worker, for instance, spotted a gator eating a nurse shark in a Florida mangrove swamp. That was back in 2003. Three years later, a birder photographed an alligator eating a bonnethead shark in a Florida salt marsh. A marine turtle specialist that Nifong sometimes works with saw gators consuming both bonnethead and lemon sharks in the late 1990s. And after the new paper was published, Nifong turned up yet another report of a gator eating a bonnethead shark, this time off Hilton Head, S.C.

All of these snacks required gators to venture into saltwater.

Figuring out the menu

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.

To deal with salt, Nifong explains, gators tend to just go back and forth between saltwater and freshwater. To keep salty water out, they can shut their nostrils and close off their throat with a cartilage-based shield. As they eat, alligators tip their heads up to let the saltwater drain out before gulping down their catch. And when they need a drink, gators can tip their heads up to catch rainwater or even gather freshwater from a layer floating atop saltwater after a rain shower.

Nifong has spent years catching hundreds of wild gators and pumping their stomachs to see what they had swallowed. That field work relies “on electrical tape, duct tape and zip ties,” he says. And it showed that the list of what’s on a gator’s menu is pretty long.

To snag an alligator, he uses a big blunted hook or, if the animal is small enough, he just grabs it and hauls it into the boat. Next, he puts a noose around its neck and tapes the mouth shut. At this point, it’s relatively safe to take body measurements (everything from weight to toe length) and to get blood or urine samples.

alligator intubation
To get an alligator’s stomach contents, a researcher has to reach an arm into the animal’s mouth.
J. Nifong

Once that’s out of the way, the team will strap the gator to a board with Velcro ties or rope. Now it’s time to untape the mouth. Someone quickly inserts a piece of pipe in the mouth to hold it open and tapes the mouth around the pipe. That pipe, Nifong says, is there “so they can’t bite down.” 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 reports. “They can just decide to not let it out.” In the end, the researchers carefully undo all their work to let the gator loose.

A broad and varied diet

Back in the lab, Nifong and his colleagues tease out what they can from those stomach contents. They also look for more clues about what the animals eat from samples of their blood. Gators are eating a rich marine diet, those data show. Meals may include small fish, mammals, birds, insects and crustaceans. They’ll even eat fruit and seeds.

Sharks and rays didn’t show up in these studies. Nor did sea turtles, on which gators have also been spotted munching. But Nifong and Lowers speculate that’s because the gator gut digests the tissues of those animals very quickly. So if a gator had eaten a shark more than a few days before being caught, there would be no way to know.

What alligators eat isn’t as important a finding as was the discovery that they regularly travel between saltwater and freshwater environments, Nifong says. These dual dining zones occur over “a wide variety of habitats across the U.S. Southeast,” he notes. That’s important because these gators are moving nutrients from rich marine waters into poorer, fresh waters. As such, they may be having a larger effect on estuarine food webs that anyone had imagined.

For instance, one prey item 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. The snails 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 programs.

Power Words

(for more about Power Words, click here)

Atlantic     One of the world’s five oceans, it is second in size only to the Pacific. It separates Europe and Africa to the east from North and South America to the west.

biology     The study of living things. The scientists who study them are known as biologists.

cartilage    A type of strong connective tissue often found in joints, the nose and ear. In certain primitive fishes, such as sharks and rays, cartilage provides an internal structure — or skeleton — for their bodies.

colleague     Someone who works with another; a co-worker or team member.

conservation     The act of preserving or protecting something. The focus of this work can range from art objects to endangered species and other aspects of the natural environment.

crustaceans     Hard-shelled water-dwelling animals including lobsters, crabs and shrimp.

diet     The foods and liquids ingested by an animal to provide the nutrition it needs to grow and maintain health. (verb) To adopt a specific food-intake plan for the purpose of controlling body weight.

ecology      A branch of biology that deals with the relations of organisms to one another and to their physical surroundings. A scientist who works in this field is called an ecologist.

ecosystem     A group of interacting living organisms — including microorganisms, plants and animals — and their physical environment within a particular climate. Examples include tropical reefs, rainforests, alpine meadows and polar tundra.

environment     The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of components in some electronics system or product).

estuary     (adj. estuarine) The mouth of a large river, where it empties into the ocean and freshwater and saltwater mix. Such regions are often nurseries for young fish.

food web     (also known as a food chain) The network of relationships among organisms sharing an ecosystem. Member organisms depend on others within this network as a source of food.

force     Some outside influence that can change the motion of a body, hold bodies close to one another, or produce motion or stress in a stationary body.

freshwater     A noun or adjective that describes bodies of water with very low concentrations of salt. It’s the type of water used for drinking and making up most inland lakes, ponds, rivers and streams, as well as groundwater.

gland     A cell, a group of cells or an organ that produces and discharges a substance (or “secretion”) for use elsewhere in the body or in a body cavity, or for elimination from the body.

habitat     The area or natural environment in which an animal or plant normally lives, such as a desert, coral reef or freshwater lake. A habitat can be home to thousands of different species.

marine     Having to do with the ocean world or environment.

marsh     A low-lying wetland usually covered with grasses and shrubs, not trees. It’s a prime feeding and nesting ground for waterfowl.

nutrient     A vitamin, mineral, fat, carbohydrate or protein that a plant, animal or other organism requires as part of its food in order to survive.

predation     A term used in biology and ecology to describe a biological interaction where one organism (the predator) hunts and kills another (the prey) for food.

pressure     Force applied uniformly over a surface, measured as force per unit of area.

prey     (n.) Animal species eaten by others. (v.) To attack and eat another species.

rays     (in biology) Members of the shark family, these kite-shaped fish species resemble a flattened shark with wide fins that resemble wings.

reptile     Cold-blooded vertebrate animals, whose skin is covered with scales or horny plates. Snakes, turtles, lizards and alligators are all reptiles.

salt     A compound made by combining an acid with a base (in a reaction that also creates water). The ocean contains many different salts — collectively called “sea salt.” Common table salt is a made of sodium and chlorine.

sea     An ocean (or region that is part of an ocean). Unlike lakes and streams, seawater — or ocean water — is salty.

sharks     A family of primitive fishes that rely on skeletons formed of cartilage, not bone. Like skates and rays, they belong to a group known as elasmobranchs. Then tend to grow and mature slowly and have few young. Some lay eggs, others give birth to live young.

species     A group of similar organisms capable of producing offspring that can survive and reproduce.

stress     (in biology) A factor — such as unusual temperatures, movements, moisture or pollution — that affects the health of a species or ecosystem.

tissue     Made of cells, any of the distinct types of materials that make up animals, plants or fungi. Cells within a tissue work as a unit to perform a particular function in living organisms. Different organs of the human body, for instance, often are made from many different types of tissues.

Velcro     The commercial name for a widely hook-and-loop type adhesive.

Citation

Journal:​ ​​J.C. Nifong and R.H. Lowers. Reciprocal intraguild predation between Alligator mississippiensis (American Alligator) and Elasmobranchii in the Southeastern United States. Southeastern Naturalist. Vol. 16, September 2017, p. 383-396. doi: 10.1656/058.016.0306.

Journal: J.C. Nifong. Living on the edge: Tropic ecology of Alligator mississippiensis (American Alligator) with access to a shallow estuarine impoundment. Bulletin of the Florida Museum of Natural History. Published online December 7, 2016.

Journal: J.C. Nifong et al. Putative predation and scavenging of two sea turtle species by the American Alligator, Alligator mississippiensis, in Coastal Southeastern United States. Herpetological Review. Vol. 42, 2011, p. 511-513.