Stingrays, instantly recognizable marine animals, glide near the ocean floor with flattened bodies and elongated tails. These fish, along with skates, sharks, and sawfish, belong to the Elasmobranchii subclass of cartilaginous fish. Primarily inhabiting coastal tropical and subtropical oceanic waters globally, some species venture into the open ocean and even freshwater systems. Of the approximately 200 stingray species, scientists have observed diverse hunting strategies shaped by habitat and species.
Stingray Diversity: Habitat and Hunting Strategies
There are three primary types of stingrays: oceanic benthic, freshwater benthic, and pelagic species. They can utilize a range of hunting strategies to capture prey.
Oceanic Benthic Stingrays
The majority of stingray species are bottom-dwelling (benthic). Oceanic benthic stingrays play a huge role in the ocean’s health as they hunt near and along the ocean floor. By stirring up these sandy areas while searching primarily for small invertebrates, benthic stingrays create aerated and essential micro-habitats for phytoplankton and zooplankton. These microscopic organisms form a crucial component of the entire ocean’s food web. An example of a benthic, oceanic species is the Atlantic stingray (Dasyatis sabina), which inhabits coastal waters of the western Atlantic Ocean from the Chesapeake Bay to southern Florida and the Gulf of Mexico. This stingray features a brown/yellow disc-shaped body with a whip-like tail. They can grow up to about 14 inches wide and feature a spade-like, pointed snout. A single venomous barbed spine sits near the base of the tail and is used in defense. Atlantic stingrays hunt along the bottom of shallow waters, typically no deeper than 20 feet. Often, Atlantic stingrays use an ambush strategy called “tenting” to capture their meal. The Atlantic stingray uses a strategy called “tenting” to suction buried prey into its jaws.
Freshwater Benthic Stingrays
Currently, there are about 35-40 freshwater stingray species classified, the majority of which live in the Amazon River. They are one of the few cartilaginous fish to live in freshwater environments. Like their oceanic relatives, benthic stingrays that live in freshwater ecosystems primarily hunt crustaceans and other invertebrates. A freshwater, benthic species, the largespot river stingray (Potamotrygon falkneri) is native to the Rio Paraná and Rio Paraguay basins in Brazil, Paraguay, and Argentina. The largespot river stingray reaches a width of up to 20 inches and a total length of about 36 inches. The stirring method is commonly seen in oceanic relatives, in which benthic stingrays undulate the margins of their disc-like bodies to stir up the river bottom substrate. Charging describes the hunting strategy in which the largespot river stingray charges upon prey concentrated in the shallows of the river. Finally, researchers less commonly observed Potamotrygon falkneri plucking prey, such as aquatic insects, that were floating on the surface of the water or adhered to a substrate on the surface.
Pelagic Stingrays
There is currently one extant species of pelagic (open ocean-dwelling) stingray, Pteroplatytrygon violacea. These stingrays travel across the open ocean and utilize a distinct hunting strategy from their benthic relatives to capture free-swimming prey. The sole member of its genus in the Dasyatidae family, the pelagic stingray (Pteroplatytrygon violacea) is an ocean-going stingray. It employs a set of hunting strategies distinct from its benthic relatives. Rather than hunting primarily invertebrates along the floor of the ocean or river, the pelagic stingray preys upon free-swimming invertebrates and bony fish. Their diet includes planktonic crustaceans, jellyfish, octopus, shrimp, and small ocean-going fish such as mackerel. Typically, the pelagic stingray lives and hunts up to 330 feet deep. In contrast to the more disc-like shape of many of its benthic relatives, the pelagic stingray features triangular pectoral fins. As such, it moves more like a bird flapping its wings. Instead of hovering over the floor of the ocean to stir up prey hiding in sediment, the pelagic stingray uses swiftness against its pelagic prey. While most benthic stingrays feature notably straw jaws for crushing crustaceans, the pelagic stingray has weaker jaws with sharper teeth meant for slicing its free-swimming prey. The pelagic stingray hunts free-swimming prey, including small pelagic fish such as mackerel.
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Hunting Techniques and Sensory Adaptations
Stingrays are highly electroreceptive fish, meaning they can receive information about the world around them through electricity. Stingrays are highly electroreceptive, able to hunt prey by detecting their weak electrical fields. Most species of stingrays feature rows of sensory cells across their face, called the ampullae of Lorenzini, which allows them to detect weak electrical fields generated by potential prey. During the breeding season, males of various stingray species such as the round stingray (Urobatis halleri), may rely on their ampullae of Lorenzini to sense certain electrical signals given off by mature females before potential copulation. The flattened bodies of stingrays allow them to effectively conceal themselves in their environments. Stingrays do this by agitating the sand and hiding beneath it. Because their eyes are on top of their bodies and their mouths on the undersides, stingrays cannot see their prey after capture; instead, they use smell and electroreceptors (ampullae of Lorenzini) similar to those of sharks. Stingrays settle on the bottom while feeding, often leaving only their eyes and tails visible. Benthic stingrays (those that reside on the sea floor) are ambush hunters. They wait until prey comes near, then use a strategy called "tenting".[32] With pectoral fins pressed against the substrate, the ray will raise its head, generating a suction force that pulls the prey underneath the body. This form of whole-body suction is analogous to the buccal suction feeding performed by ray-finned fish.
Dietary Preferences and Feeding Behaviors
Most stingrays feed primarily on mollusks, crustaceans and, occasionally, on small fish. The Australian whipray (Himantura australis) lives in shallow coastal waters and estuaries at depths up to 135 feet. It occurs off the coast of northern Australia, western Australia, Cook Island, northern New South Wales, and Papua New Guinea. This benthic stingray forages primarily in sandy and muddy areas. Researchers engaged in a recent study comparing the feeding behaviors involving 125 individual stingrays belonging to one of two species: the Australian whipray and the cowtail stingray (Pastinachus ateri). They found that Australian whiprays created three times as many feeding pits over the study. The results demonstrated the hunting preference of the Australian whipray for stirring up sediment. By doing this, they create small pits on the muddy and sandy ocean floor to uncover hiding prey. Scientists typically refer to this behavior as foraging. Researchers discovered that the Australian whipray’s preferred method of hunting is to forage by creating feeding pits in muddy and sandy areas of the ocean floor.
Stingray Anatomy and Feeding Adaptations
The mouth of the stingray is located on the ventral side of the vertebrate. Stingrays exhibit hyostylic jaw suspension, which means that the mandibular arch is only suspended by an articulation with the hyomandibula. This type of suspensions allows for the upper jaw to have high mobility and protrude outward. In general, the teeth have a root implanted within the connective tissue and a visible portion of the tooth, is large and flat, allowing them to crush the bodies of hard shelled prey. Male stingrays display sexual dimorphism by developing cusps, or pointed ends, to some of their teeth. Some have specialized jaws that allow them to crush hard mollusk shells,[29] whereas others use external mouth structures called cephalic lobes to guide plankton into their oral cavity. Since their mouths are on the underside of their bodies, they catch their prey, then crush and eat with their powerful jaws.
Diet in Captivity
Just like people, our animals need a well-balanced diet. Our commissary team works closely with our animal care and veterinary teams to ensure that everything on the menu for our animals is healthy and enriching. Each of our eight rays - two Atlantic stingrays and six Southern stingrays - is hand-fed to make sure each is receiving their recommended diets. By feeding them individually, our Herps & Aquatics team can also do physical checks, ensuring everyone appears healthy, has a healthy appetite, and is showing normal behaviors. The rays receive 4-6% of their body weight in food per week, adjusted based on their body condition score and size of their liver. Stingrays actually store all of their body fat in their livers! Many of our stingrays have preferences for what they like to eat. Shrimp is usually a favorite for everyone, while certain fish are hit or miss. If the “wrong” species of squid is offered, they won’t touch it or anything else it touched! Our Herps & Aquatics team gets to know each ray individually and try to adjust their diet to still be balanced - but not too heavy on items they often refuse. “And their preferences can and do change over time,” Nicole said. Our rays are usually fed twice a day. They are naturally very good at regulating their appetite and don’t tend to overeat. Usually during the rays’ morning meal, they receive a vitamin called a Mazuri Shark and Ray Supplement. It’s a multivitamin with a strong focus on being an iodine, vitamin E and thiamine supplement. Iodine is essential for stingray thyroid health - similar to us, it’s actually the reason we iodize table salt!
Additional Information
Spiracles are small openings that allow some fish and amphibians to breathe. Stingray spiracles are openings just behind its eyes. The respiratory system of stingrays is complicated by having two separate ways to take in water to use the oxygen. Most of the time stingrays take in water using their mouth and then send the water through the gills for gas exchange. This is efficient, but the mouth cannot be used when hunting because the stingrays bury themselves in the ocean sediment and wait for prey to swim by. So the stingray switches to using its spiracles. With the spiracles, they can draw water free from sediment directly into their gills for gas exchange. These alternate ventilation organs are less efficient than the mouth, since spiracles are unable to pull the same volume of water. Stingrays exhibit a wide range of colors and patterns on their dorsal surface to help them camouflage with the sandy bottom. Some stingrays can even change color over the course of several days to adjust to new habitats. Like its shark relatives, the stingray is outfitted with electrical sensors called ampullae of Lorenzini. Located around the stingray's mouth, these organs sense the natural electrical charges of potential prey. The stinger of a stingray is known also as the spinal blade. It is located in the mid-area of the tail and can secrete venom. Stingrays are not usually aggressive and ordinarily attack humans only when provoked, such as when they are accidentally stepped on. Stingrays can have one, two or three blades. Contact with the spinal blade or blades causes local trauma (from the cut itself), pain, swelling, muscle cramps from the venom and, later, may result in infection from bacteria or fungi. The injury is very painful, but rarely life-threatening unless the stinger pierces a vital area. The blade is often deeply barbed and usually breaks off in the wound. The venom of the stingray has been relatively unstudied due to the mixture of venomous tissue secretions cells and mucous membrane cell products that occurs upon secretion from the spinal blade. The spine is covered with the epidermal skin layer. During secretion, the venom penetrates the epidermis and mixes with the mucus to release the venom on its victim. Typically, other venomous organisms create and store their venom in a gland. The stingray is notable in that it stores its venom within tissue cells. The toxins that have been confirmed to be within the venom are cystatins, peroxiredoxin and galectin. Galectin induces cell death in its victims and cystatins inhibit defense enzymes. The venom is produced and stored in the secretory cells of the vertebral column at the mid-distal region. These secretory cells are housed within the ventrolateral grooves of the spine. The cells of both marine and freshwater stingrays are round and contain a great amount of granule-filled cytoplasm. The stinging cells of marine stingrays are located only within these lateral grooves of the stinger. The stinging cells of freshwater stingray branch out beyond the lateral grooves to cover a larger surface area along the entire blade. Rays are edible, and may be caught as food using fishing lines or spears. Stingray recipes can be found in many coastal areas worldwide. For example, in Malaysia and Singapore, stingray is commonly grilled over charcoal, then served with spicy sambal sauce. In Goa, and other Indian states, it is sometimes used as part of spicy curries. Generally, the most prized parts of the stingray are the wings, the "cheek" (the area surrounding the eyes), and the liver. Stingrays are usually very docile and curious, their usual reaction being to flee any disturbance, but they sometimes brush their fins past any new object they encounter. Several ethnological sections in museums,[48] such as the British Museum, display arrowheads and spearheads made of stingray stingers, used in Micronesia and elsewhere.[49] Henry de Monfreid stated in his books that before World War II, in the Horn of Africa, whips were made from the tails of big stingrays and these devices inflicted cruel cuts, so in Aden, the British forbade their use on women and slaves.
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Conservation Status
Stingray species are progressively becoming threatened or vulnerable to extinction, particularly as a consequence of unregulated fishing.[5] As of 2013, 45 species have been listed as vulnerable or endangered by the IUCN.
Evolutionary History
Stingrays diverged from their closest relatives, the panrays, during the Late Jurassic period, and diversified over the course of the Cretaceous into the different extant families today. Permineralized stingray teeth have been found in sedimentary deposits around the world as far back as the Early Cretaceous. The oldest known stingray taxon is "Dasyatis" speetonensis from the Hauterivian of England, whose teeth most closely resemble that of the extant sixgill stingray (Hexatrygon). Full-body stingray fossils are very rare but are known from certain lagerstätten that preserve soft-bodied animals.
Reproduction and Development
When a male is courting a female, he follows her closely, biting at her pectoral disc. Reproductive ray behaviors are associated with their behavioral endocrinology, for example, in species such as the atlantic stingray (Hypanus sabinus), social groups are formed first, then the sexes display complex courtship behaviors that end in pair copulation which is similar to the species Urobatis halleri. Furthermore, their mating period is one of the longest recorded in elasmobranch fish. Individuals are known to mate for seven months before the females ovulate in March. During this time, the male stingrays experience increased levels of androgen hormones which has been linked to its prolonged mating periods. The behavior expressed among males and females during specific parts of this period involves aggressive social interactions. Frequently, the males trail females with their snout near the female vent then proceed to bite the female on her fins and her body. Although this mating behavior is similar to the species Urobatis halleri, differences can be seen in the particular actions of Hypanus sabinus. Seasonal elevated levels of serum androgens coincide with the expressed aggressive behavior, which led to the proposal that androgen steroids start, indorse and maintain aggressive sexual behaviors in the male rays for this species which drives the prolonged mating season. Similarly, concise elevations of serum androgens in females has been connected to increased aggression and improvement in mate choice. When their androgen steroid levels are elevated, they are able to improve their mate choice by quickly fleeing from tenacious males when undergoing ovulation succeeding impregnation. Stingrays are ovoviviparous, bearing live young in "litters" of five to thirteen. During this period, the female's behavior transitions to support of her future offspring. Females hold the embryos in the womb without a placenta. Instead, the embryos absorb nutrients from a yolk sac and after the sac is depleted, the mother provides uterine "milk".[23] After birth, the offspring generally disassociate from the mother and swim away, having been born with the instinctual abilities to protect and feed themselves. At the Sea Life London Aquarium, two female stingrays delivered seven baby stingrays, although the mothers have not been near a male for two years. The stingray uses its paired pectoral fins for moving around.
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