“Rhinoptera bonasus”
Why do Golden Stingrays migrate? They are oceanodromous, which means “truly migratory fishes that live and migrate wholly in the sea”. Twice a year, up to 10,000 Golden Stingrays gather near Yucatan Peninsula and migrate about 800 miles across the Gulf of Mexico. They swim to western Florida in the spring and back to the Yucatan Peninsula in fall. In the Atlantic Ocean, Golden Stingray populations also migrate northward as far as New England in late spring and southward as far as southern Brazil in late fall. No one yet knows why they migrate or what initiates the sociable gathering of so many thousands to make the swim together. Some guesses are that changes in water temperature coupled with a certain orientation of the sun tells them “time to head out”. The migration hasn’t yet been linked to feeding or mating activity. One oddity is that the southbound groups seem to be larger than the northbound but again, we don’t know what’s behind that. Golden Stingrays are pelagic meaning they live in the open ocean, although they are sometimes found in inshore, brackish waters. They are extremely gregarious and live in groups known as a fever as opposed to a school. Their mass biannual migration must be quite a show, as they are excellent swimmers as fast as 56 mph and natural acrobats. They use their pectoral fins like wings to swim, glide, twist & turn, measuring up to 7 feet wide (2.1 meters) from tip to tip makes for some pretty impressive acrobatic tricks. They seem to like flipping over and curling their 2 fin tips above the surface of the water, especially the females. Since they are brownish with a pale under-body, some people mistake them for sharks especially with the 2 pectoral fins gliding along jaws-style. They look much like the dorsal fins of a pair of sharks (especially to swimmers, who may react with impressive gymnastic feats of their own). Unlike other stingrays, Golden Stingrays rarely rest on the seabed where unsuspecting humans can step on them and prefer to be on the move, in water from the surface to about 70 feet down (22 meters). They can settle on the bottom to sleep during the day but in deep water, they have to sleep by swimming slowly along or “hang-gliding” in a rising current (rays have no swim bladder, so they sink if they stop swimming). The Golden Stingray is related to sharks, like all 70 species of stingrays. The genus name is derived from the Greek “rhinos” meaning nose and “pteron” meaning wing. The species name bonasus is from the Greek “bonasos” meaning bison. Golden Stingrays are also known as the Cownose Stingray because of their anatomy featuring their long, pointed pectoral fins separate into two lobes on their distinctive, broad head. The lobes and their wide-set eyes give them a cow-like look. Their skeletons are cartilaginous as they have no bones in their bodies therefore no bone marrow, so red-blood cells are produced in the spleen. They are jawed fish with paired fins, paired nares (nostrils), scales and two-chambered hearts. They have no ribs, so if placed on the ground, the larger specie’s own body weight would crush their internal organs long before they would suffocate. They detect prey by sensing movement as well as weak electric signals. They also use their supple, synchronized pectoral fins to forage for food. It’s a nightly group activity. They swim along the bottom, flapping their fins over the sand to expose buried crabs, shellfish and oysters. In front of their mouths, 2 modified fins produce suction so they can whisk the food in and vent water out through their gills.
Golden Stingrays are ovoviviparous: the females produce eggs, which after fertilization hatch internally, so that the young are “born” live. They mate every winter and females produce usually only one young ray, but can have five or six. The embryo grows within its mother with its wings folded over its body. The gestation period is believed to be 11-12 months, although some evidence suggests that Golden Stingrays might have two gestation periods lasting 5-6 months. At full term, the pup is born live exiting tail first. The Golden Stingray is a foot to a foot & a half wide (28-46 centimeters) at birth and grows to about 45 inches (1.1 meters) wide at maturity, although some have been seen that are about twice that size. It can weigh 50 pounds (23 kilograms) or more. The mother will protect her young until they mature, but they feed themselves. Often called the “pussycats of the sea”, Golden Stingrays are generally docile creatures. Even when isolated, they will attack only when cornered or threatened and they do come armed. Their stinger is a spine (barb) like a fingernail, but actually a scale with serrated, razor-sharp edges. On the Golden Stingray, it is located near the base of its tail not at the tip. This whip-like tail is 2 to 3 times as long as the body and can actually smack you to make the barb especially effective. The blow can sever arteries or even the Achilles tendon in a human leg. The spine carries venom, a protein-based toxin that can produce a drastic decrease in blood pressure, altered respiration, increased pulse, dizziness and shock. If the stingray loses one of its barbs while defending itself, it immediately begins to grow a new one. Stingrays shed and re-grow their spines on a regular basis regardless of whether they use them.
Sandbar Sharks, Tiger Sharks, Great Hammerhead Sharks and Bull Sharks are the Golden Stingray’s main predators. Another predator is man. Big fisheries don’t yet harvest them for food or their population would already be in danger most likely. Golden Stingrays are being fished commercially in a small way on the U.S. east coast. Golden Stingrays are an important part of the ecosystem. If their numbers have increased as fishermen report, it is because their predator’s numbers have dropped. Scientists report that intense fishing for these top predators has caused their numbers to drop by more than 97% along the East Coast over the last several decades. As for those shellfish they’re blamed for over-eating, their numbers may have dropped because they are over-harvested by humans and their habitats like grass beds destroyed by construction, dredging, propellers and pollution. Golden Stingrays are also at risk as an accidental catch during intense, mostly unregulated, fishing in Central & South America. Related ray species have shown a significant decline there. More statistics are needed for the Golden Stingray populations in the Gulf of Mexico, in the western Atlantic and in the population in the eastern Atlantic off Mauritania, Senegal and Guinea. The Golden Stingray is vulnerable as a species because they mature relatively late (females at 8 or 9 years old), have low levels of reproduction and if females are killed before giving birth, the population will get depleted at a greater percentage.