Cownose Ray, Rhinoptera bonasus
Cownose Ray, Rhinoptera bonasus. Fish caught off a coastal waters off Tampa, Florida, December 2013. Length: 46 cm (18 inches). Catch, photograph, and identification courtesy of Ben Cantrell, Peoria, Illinois.
The Cownose Ray, Rhinoptera bonasus, is a member of the Cownose Ray or Rhinopteridae Family, and is known in Mexico as gavilán cubanito. Globally, there are ten species in the genus Rhinoptera, of which three are found in Mexican waters, two in the Atlantic and one in the Pacific Ocean.
The Cownose Ray body forms a diamond-shaped disc that are 1.7 to 1.8 times wider than they are deep. They are uniform golden-brown dorsally and white to yellowish-white ventrally with brown on the ventral edges of their disk. Their head is distinctly protruding with an overhanging snout that is deeply notched in the front. They have “wings” attached to the front and sides of their head. They have large spiracles directly behind, and approximately equal in size to, the eye cavity on their sides. They have a small mouth located on their underside that is equipped with 7 plate-like teeth set in 11 to 13 rows on the top and bottom and are specialized for crushing and grinding hard-bodied prey. They have a small single dorsal fin at the base of their slender whip-like tail. Their tail can be up to 2 times longer than the disc length and contains 1 or 2 long venomous spines close to the tail base with injecting barbs used for self-defense. Their pectoral fins are long and pointed with curved tips and concave rear margins. They have no caudal fin. Their skin is smooth and lacks denticles and thorns.
The Cownose Ray is an inshore pelagic species found in bays and coastal lagoons (including brackish waters) over sandy bottoms near rock structures and coral reefs close to the continental shelf at depths up to 20 m (65 feet). They are fast-growing with a maximum disc width of 2.13 m (7 feet 0 inches). They are dimorphic with females being larger than males; 23 kg (50 lbs) versus 12 kg (26 lbs). They are highly migratory and travel in large schools that can number several hundred to thousands of individuals with synchronous movements resembling birds in flight. They migrate long distances along the Atlantic coast and within the Gulf of Mexico moving northward in late spring and southward in late fall. They will also migrate to avoid water temperatures that drop below 15oC (59oF). They primarily consume small invertebrates including crustaceans, polychaete worms, and bivalve mollusks. In turn they are preyed upon by various sharks. They have a strange relation with the Cobia, Rachycentron canadum, as small Cobias are prey for Cownose Rays but also benefit from their leftover food. Reproduction occurs via aplacental viviparity with internal fertilization. Embryos are initially fed on yolk then receive additional nourishment from the mother by indirect adsorption of uterine fluid enriched with mucus, fat, and protein. Each female produces just 1 pup annually that is born live as a miniature adult having a disc width of just over 1 meter (3 feet 4 inches). Gestation period are between six and twelve months. Females have lifespans of up to eighteen years; males lifespans are sixteen years. The Cownose Ray is poorly studied with very limited information available about their lifestyle and behavioral patterns including specific details on age, growth, longevity, movement patterns, diet, habitat use, and reproduction.
The Cownose Ray is a resident of all Mexican waters of the Atlantic Ocean including the Gulf of Mexico and the east coast of the Yucatán Peninsula in the Caribbean.
The Cownose Ray is most likely confused with the Brazilian Cownose Ray, Rhinoptera brasiliensis (nine sets of tooth plates on each jaw). It is very similar to the Golden Cownose Ray, Rhinoptera steindachneri, a Pacific Ocean species.
From a conservation perspective the Cownose Ray is currently considered to be Near Threatened, due to heavy, unregulated, and poorly documented fishing pressure in most of their range, therefore their long-term viability is of concern. Although populations are not accessed they are believed to be in decline, being adversely affected by a variety of factors including inshore habitat destruction to accommodate shrimp farming, inshore schooling behavior, intense fishing pressure with large nets, and long reproduction cycles with small litter sizes. They can be pests in some areas as they can quickly destroy oyster beds and various sea grasses. They are caught frequently by artisanal fishermen and on a limited basis by commercial fishermen utilizing gill nets and longlines. They are also a by-catch of shrimp trawlers. They are difficult to harvest and process, which drives up costs, and are known to contain Shiga toxin. They are sold and used primarily in fish tacos. They are common inhabitants of many large public aquariums and often found in “touch tanks” after the fish have had their barbs surgically removed. Their migratory patterns in very large schools near the surface have drawn the attention of divers and photographers alike.