WITH FLATTENED BODIES, RAYS HAVE TAKEN THE PECTORAL FIN/HYDRODYNAMIC LIFT CONCEPT so far as to develop their pectoral fins into broad “wings.” Eagle and manta rays’ wings let them soar through the open waters like…well, eagles…flapping and gliding. Stingrays have the same lift capabilities but spend much of their time close to or on the seafloor. They don’t swim high or far.
Rays are notable as the other cartilaginous fishes, along with sharks – that is, their skeletons are made of cartilage, lighter and more flexible than the calcium-based material of bony fishes (Hagfish and Lampreys are also cartilaginous; they’re not in my ouvre). Rays diverged from sharks some 300 million years ago.
THE USUAL SUSPECTS
On coral reefs in the Caribbean, the species you’re most likely to encounter are Southern Stingrays (Dasyatis americana), Yellow Stingrays (Urobatis jamaicensis), Spotted Eagle Rays (Aetobatus narinari) and, in the right places and with luck, Ocean Mantas (Manta birostris) and Reef Mantas (Manta alfredi). As usual, the Indo/Pacific basin counts a somewhat larger and more diverse population of Stingrays and Eagle Rays.
Each has their own approach to earning their livings. Eagle Rays and Stingrays scour the sandy bottoms to uncover the buried crustaceans, mollusks, worms, small fishes and other morsels that make up the bulk of their diets. Finding them, they use their powerful jaws to crush and grind up shells.
Stingray “wings” have developed to such an extent that they dominate the rays’ bodies, creating a fish somewhat diamond-shaped, slightly wedge-shaped at the head. Their mouths and gills are on their undersides. They use their senses of smell, vision, hearing and electroreception to detect the presence of prey. Settled on the bottom, they flap their wings – their broad pectoral fins – to stir up the sand and uncover food (They also have lots of fishy friend who follow them around hoping for easy meals from the rays’ leavings).
With Stingrays, their width across their broad pectoral fins tends to be as notable as their length. The reach of Southern Stingrays may be as much as seven feet, typically four or five feet. Typically, they may be 4 or 5 feet long, with their tails as much as two times the length of the body. Yellow Stingrays are much smaller, typically about a foot in length, not counting the tail, and 14 inches in disc width.
Famously, Stringrays’ long, whip-like tails feature a slightly venomous stinger, largely a defensive weapon. Humans are likely to experience stings by accident, say by stepping on a ray. The injury can be painful but not usually life-thratening. “Crocodile Hunter” Steve Irwin’s death in 2006 was caused by an animal’s stinger penetrating heart, not by venom.
Stingrays often hide in the sand, covering themselves as a defense from potential predators. But sandy concealment also sets them to ambush a passing prey like small fishes. In such cases, they’re notable for a technique called “tenting.” As a prey approaches, the devious ray presses its broad fins against the bottom and raises its head, creating a suction that pull the unfortunate victim underneath its body.
With its eyes and spiracles all located on its upper side, our predator ray can’t see its victims after capture. But like sharks, they utilize smell and “ampullae of Lorenzini” to detect their prey’s electrical activity.
While swimming or in the open rays breath by drawing water past their gills through their mouths. Settled on the bottom and especially covered by sand, they can draw it in through their spiracles.
Eagle Rays’ mouths and gills are also on their lower surfaces, but they have more of a snout design suitable for digging in the sediments. Swimming nearly constantly above the seabottom, they use those same senses of smell, vision, hearing and electroreception to detect prey. They dig into the sand with their shovel-shaped snouts, unearth morsels copepods, crabs and little mollusks and crush them with hardened jaws.
Manta Rays are open ocean plankton feeders. Like Whale Sharks, they charge through the waters, mouths wide open, sweeping in crustaceans, small fishes anything in their way that may serve as food. Like Whale Sharks, they cruise almost constantly.
Eagle Rays typically scale in at 4 to 6 feet across; Manta Rays at 20 feet, not counting the tails in either case.
PRINCIPAL SOURCES: Reef Fish Identification Florida, Caribbean, Bahamas, Paul Humann, Ned DeLoach; Reef Fish Identification, Tropical Pacific, Gerald Allen, Roger Steene, Paul Humann, Ned DeLoach; Marine Life, Caribbean, Bahamas, Florida, Marty Snyderman & Clay Wiseman; Reef Fish Behavior, Ned DeLoach; Peterson’s Field Guide to Atlantic Coast Fishes, C. Richard Robins, G. Carlton Ray, John Douglass; Discover Fishes, Florida Museum of Natural History; Marine Species Identification Portal; Assorted Fish Species Topics, Wikipedia, Encyclopedia Britannica.