The stingrays (and their relatives the skates) belong to the taxonomic order known as Myliobatiformes. There are about 480 species of rays and skates worldwide, divided into eight different families. Together with the sharks, they make up the class of fishes known as Chondrichthyes. This is a very primitive group of fishes–fossil sharks and rays have been found as far back as 400 million years ago. The sharks and rays were one of the first animals with jaws to appear. They are so primitive that they don’t even have any bones–their skeletons are made entirely of cartilage.
A ray is, basically, a flattened shark. The fins at the side form “wings” that can be either rounded or diamond-shaped, which the ray uses to “fly” through the water. The long trailing tail makes the ray look like a kite. The mouth is located on the underside of the head. Most rays don’t have teeth, but have flat plates instead for crushing shellfish. The eyes are on the top of the head, and behind the eyes are the spiracles–the rays breathe by drawing water in through the spiracles over the gills and then out the gill slits on the underside. Rays are bottom-feeders, sifting through the sand and mud at the ocean floor to find shrimp, shellfish and other food, which they locate using electro-sensory organisms in the front of their heads. The shells are crushed by the strong flat teeth, then the broken pieces are spit out. When resting on the bottom, rays will flap their “wings” to splash sand over top of them to hide themselves from sharks and other predators, with just their eyes and spiracles protruding from the substrate.
Unlike most fish, which lay eggs, rays give birth to live young. The males have long fingerlike claspers at the base of their tail, which they insert into the female during mating to fertilize her. The fertilized eggs are retained inside the female’s body, where they hatch and the young are nourished first by their yolk sacs, and, after those are used up, by a secretion on the inside of the female’s body called “uterine milk”. The young “pups” are then born fully developed and ready to fend for themselves. Some species have up to a dozen pups at once; others give birth to single pups.
There are about a dozen species of skate and stingray found in Florida, along both the Atlantic and Gulf coasts. These include the giant Manta Ray, the Devil Ray, the Spotted Eagle Ray, and the Lesser Electric Ray. But the most commonly encountered species are the Atlantic Ray, the Southern Ray, and the Cownose Ray.
The Atlantic Ray, Dasyatis sabina, ranges throughout the Caribbean and the Gulf of Mexico and along the coast up to the Chesapeake Bay. It is a flat diamond-shaped fish with a pointed protruding nose and a long trailing tail, greenish, brownish or yellowish on top and whiteish-grey underneath. Older individuals sometimes develop a low bumpy ridge along their back. This is one of the smaller ray species, reaching a wingspan of 2-3 feet, with the females larger than the males. Atlantic Rays are unusual in that they can tolerate a wide range of salt concentrations, and can often be found foraging in freshwater rivers like the Mississippi. In Florida’s St Johns River there is a population of Atlantic Stingrays that have taken up a completely freshwater lifestyle and never enter the ocean. These “freshwater stingrays” are sometimes found in the pet aquarium trade. They have no biological adaptations for a freshwater life, but maintain their salt balance by continuously excreting large amounts of very dilute urine, with freshwater Atlantic Rays peeing at least ten times as much as their saltwater cousins.
The Southern Stingray, Dasyatis americanus, is found in coastal waters from Brazil through the Gulf of Mexico and up the East Coast. The Southern Stingray likes water temperatures in the 80’s, but is more tolerant of cooler water than the Atlantic species, and can reach as far north as New Jersey or Massachusetts in the summertime. It prefers shallow water with a flat bottom. The Southern Ray looks a lot like the Atlantic, but its nose is blunter and it gets considerably bigger (DNA testing has shown that the Southern Stingray is likely evolved from the Atlantic Stingray, with its larger size perhaps being an adaptation for entering cooler water). The body is diamond-shaped, brownish or grayish in color, with a wingspan of 4-5 feet (the larger females can have a wingspan of 6 feet and weigh up to 200 pounds). In captivity, the males reach breeding condition at a wingspan of about 20 inches, while the females begin breeding when they reach 25 inches (about five years old). They average 4-5 pups per litter, after a gestation ranging from 5-8 months. Southern Rays are most often seen alone or in small groups. Like most rays, they are usually active at night, when they hunt along the sandy sea bottom for food by vigorously flapping their wings to stir up the sand and expose prey. When swimming, they are usually slow and placid, moving along by using wavelike ripples in their fins.
The Cownose Ray, Rhinoptera bonasus, gets its name from its unusual face, which unlike the pointy nose of other rays is squared and flattened, with two distinct round lobes that project out and down. These form a siphon that helps the fish suck prey up from the sea floor. Cownose Rays reach a width of around 4 feet, though one specimen of 7.5 feet has been recorded, with a light brown color above and a whitish-grey below. In captivity, they have lived up to 18 years, and usually bear one live pup per year. The Cownose enters open ocean far more readily than the Atlantic or Southern Stingrays, and in addition to its range in the Caribbean and northern part of South America, it can also be found along part of the west coast of Africa. It is also more gregarious than the other species and often swims together in schools of several hundred. Individual groups may make long migrations from one part of the Atlantic to another, traveling thousands of miles. It swims by flapping its large fins like wings. Because it is such an active swimmer, the Cownose does not usually rest on the bottom like many other species do.
So, what about the “sting”….? Stingrays have a hard barbed sting, shaped like a harpoon head, near the base of their tail. In large individuals, this can be a foot long. The sting is solely a defensive weapon. If the ray is disturbed while resting hidden on the bottom, it can whip its tail up and forward like a scorpion and drive the sting into its attacker. Two grooves run along the bottom of the sting, which channel venom into the wound. The venom is not very strong and human deaths from it are virtually unknown, but it causes intense pain. In Florida’s crowded summer beaches, it is unfortunately a rather common event for someone to inadvertently step on a stingray that is hidden in the sand, leading to a sting. The venom is broken down by heat, so the pain can be lessened greatly by immediately immersing the stung foot into hot water. To avoid being stung, experienced Florida beach-goers do the “Stingray Shuffle” by dragging their feet across the bottom sand as they walk, thereby kicking any hidden rays from the side so they swim away, rather than stepping on them from the top and getting zapped.
Despite their much-feared reputation, stingrays are not very dangerous and rarely cause any harm beyond a few hours of burning pain. The most famous victim of a stingray was TV personality Steve Irwin, “The Crocodile Hunter”, who was killed by an Australian Bull Ray in a freak accident while filming a segment for his show. As he was swimming along just above a Bull Ray, the cameraman in front of them apparently startled the ray and it lashed upwards with its tail, just happening to stab Irwin in the chest with the barbed sting, which punctured his ventricles and killed him almost instantly.
One thought on “Wild Florida: Stingrays”
“…using electro-sensory organisms in the front of their heads.”
Another remarkable example of symbiosis… 🙂