Throughout the Misunderstood Mesos series, we have examined numerous land-based mesocarnivores from around the world, however, the small predator niche is a vital component of marine ecosystems as well. By keeping population control over the primary consumers while providing food for larger predators, marine mesocarnivores are as equally valuable to their respective food webs as those who live on land. In some coastal systems, the level of biodiversity is almost as high as in rainforests. The cownose ray is one of the mesocarnivore species that holds such a vast trophic cascade together.
Although cownose rays have the characteristic flat body style of all rays, their unique head shape makes them easily distinguishable. The broad head has widely separated eyes and two specialized lobed subrostral fins that provide the indicative cownose appearance. However, despite their exclusive head shape, like other rays, cownose rays maintain the typical brownish coloration on their top side, while remaining white on their underside.
Most resources show cownose rays reach a maximum width of around three feet, however, sightings of up to seven feet have been reported. A typical adult weighs up to fifty pounds, but again larger specimens are believed to exist. As with most rays and their close relatives, the sharks, females tend to be larger than males on average. Both rays and sharks give birth to live young, a characteristic known as viviparity, so this size difference is thought to have evolved for promoting larger offspring.
Being one of the most populous members of the Batoidea, commonly known as the stingrays and manta rays, cownose rays are a common sight in the Atlantic Ocean. They inhabit the coastal waters of the United States, Mexico, Central, and South America. Their northernmost range is near Cape Cod, Mass, then all shallow waters spanning South along the Eastern seaboard, through the Gulf of Mexico to the Caribbean, and eventually the East Coast of South America down to their southernmost habitat in Argentina.
Their food sources all live at shallow depths, so cownose rays typically remain in less than a hundred feet of water. They commonly inhabit the sandy beaches and backwater bays of barrier islands, as well as estuaries and brackish marshes. Low visibility caused by sand or sediment disturbance from wave action assists rays in remaining camouflaged from their predators, so is preferred. Unfortunately, this sometimes puts them in contact with another animal that enjoys the surf…humans.
Cownose rays often live in relatively large schools of mixed ages and sexes, traveling along the coast in search of food. During the extended mating season of April through October, viable females will swim close to the surface with their pectoral fins breaching the surface into the air above. Once this signal is recognized, a male will swim behind the female and attempt to hold her upright fins to complete the pair bonding. After mating, gestation varies from 11-12 months long, after which the 11-18 inch wide young are live birthed.
Both male and female rays reach sexual maturity around four years old. Although the average life span for both sexes is around 14 years old, females tend to live longer than males. Some females can live up to 18 years, while males usually die before they reach 16 years. Large groupings of rays migrate South in the winter, then return north in spring. Although this mass movement is well documented, the reasoning behind the migration remains debated. A pre-courtship ritual is one of the possible motivations for this phenomenon.
Specialized to detect and prey upon mollusks, crustaceans, and other invertebrates within the turbulent surf, they scan the sandy floor for any sign of suitably sized food. A pair of adapted fins near their head creates a powerful vacuum that sucks the prey into their mouth where a series of interlocking concrete-hard plates act as teeth to crush the prey. Bivalves, such as oysters, clams, and mussels comprise most of their diet, while crabs, shrimp, and worms round out the daily menu.
Once fully grown, adult cownose rays do not have many predators, however, a few threats remain. Large adult Cobia fish (Rachycentron canadum) occasionally prey upon them, and several varieties of large sharks also dine upon the rays. Hammerhead sharks have a particular advantage in seeking out rays hidden in sand by using their extremely sensitive ampullae of Lorenzini to detect the ray’s electrical field. The exaggerated head of hammerheads acts as a radar dish to seek out hidden rays, that cannot conceal the electrical impulses they emit.
To better their foraging success, cownose rays often hunt in groups where the combined flapping of the fins helps to expose prey items buried in the sand. These schools of rays can often be seen traveling along the waves in the early morning or late afternoon when the angle of the sun allows for better visibility. When not hunting, cownose rays often swim near the surface of the water, occasionally exposing their pectoral fins. The triangular tips of these fins appear like the dorsal fin of a shark, so beachgoers can sometimes mistake them for sharks in the surf.
Cownose rays only have one defense against predators, which occasionally is used against humans when we accidentally disturb them. As the popular name ‘stingray’ implies, all rays have a serrated spike at the base of their tail they use to jab would-be predators. This spine is covered in a toxin that causes a painful sting when injected. However, the extent of the pain is often exaggerated and cownose rays will often warn intruders with a whip of their tail before utilizing their “stinger” spine.
Popular zoologist Steve Irwin was famously killed by the sting of a large ray; however, it is important to realize he was antagonizing the subject by swimming behind it with a camera when the ray suddenly became defensive and jabbed at him, striking him in the chest inadvertently. The toxin did not kill him, but rather the spine broke off into his chest, piercing his heart and leading to fatal internal bleeding. Such fatal events are extremely rare, most stings occur on the legs or feet and are comparable to the pain of a bee sting, leaving the afflicted with no permanent damage.
INTERACTIONS WITH HUMANS
Despite the low danger cownose rays pose to our safety, human persecution and overfishing are the primary threats to their continued existence. As the commercial shellfish industry began witnessing a decline in shellfish harvest in the 1990s, the industry quickly assigned blame to cownose rays. Even scientific studies at the time incorrectly implicated ray predation as the main contributor to scallop and oyster population decline. This theory began a mass effort to reduce cownose ray populations and predator control hunts began throughout the Eastern seaboard.
Cownose ray populations declined quickly until further studies in 2016 proved shellfish decline was a factor of water pollution, not ray predation. Still, by this time cownose numbers had declined 30-50% and were now designated as a Vulnerable species by the IUNC. Uncontrolled sport fishing remains a major threat to local cownose ray numbers.
Unjustified fear of cownose rays also remains an obstacle to human acceptance. Many naïve beach recreationists worry about encountering a ray while wading in the ocean surf. Realistically, rays and humans commonly share space within the surf all the time with no interaction. Cownose rays will avoid people when possible and only become defensive when stepped on. The easy method to prevent stings is to shuffle your feet when wading in murky surf. Any ray inadvertently kicked by shuffling feet will simply swim away without attempting a sting. If an unlikely sting occurs, treat the wound with hot water to neutralize the toxin quickly.
Cownose rays hold an important mesocarnivore role in North American coastal ecology, controlling bivalve and crustacean populations within one of the most productive marine ecotones. Due to the murky, turbulent water, the surf zone is a difficult waterscape for predators, yet the cownose ray is highly adapted to survive these challenging conditions. Larger ocean predators then benefit from the sustenance cownose rays provide to the higher trophic levels.
Even with the known ecological value of cownose rays, humans still have difficulty sharing the beach in harmony with them. False accusations of oyster and scallop excessive predation caused misled efforts to drastically reduce ray populations, leaving the species vulnerable to extinction. Although organized ray culling has stopped in most locations, uncontrolled sport fishing of rays remains a significant threat. Furthermore, through education, humans must learn stingrays are not a realistic threat to our safety—just shuffle your feet. Hopefully, we reverse our outlook on cownose rays before it is too late.