Golden Cownose Ray, Rhinoptera steindachneri
The Golden Cownose Ray, Rhinoptera steindachneri, whose common Spanish name is gavilán dorado, is a species in the Eagle Ray or Myliobatidae Family, known collectively as mantas or águilas marinas in Mexico. Globally, there are ten species in the genus Rhinoptera, three of which are found in Mexican waters, two in the Atlantic and one in the Pacific.
The Golden Cownose Rays have bodies in the form of diamond-shaped discs that are 1.7 to 1.8 times wider than they are deep. They are golden yellowish-brown dorsally and off-white ventrally with black on the tips of their wings. 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, their eye cavity. Their mouth has six to nine plate-like teeth on the top and bottom that 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 is 1.2 to 1.6 times longer than the disc length and contains one or two long venomous spines inserted 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 Golden Cownose Rays are an inshore species found in bays and coastal lagoons over sandy bottoms near rock structures and coral reefs at depths up to 215 feet. The largest Golden Cownose Rays have a maximum disc width of 1.07 meters (3 feet 6 inches), disc length of 75 cm (30 inches), and total length of 1.70 meters (5 feet 5 inches). They are highly migratory and travel in large schools with synchronous movements resembling birds in flight. They migrate to the northern portions of the Sea of Cortez in the spring and return south in the fall. They primarily consume mollusks and crustaceans. 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 one pup per year that is born live as a miniature adult having a disc width of just over 1 meter (40 inches). Gestation requires one year. Behavioral patterns including specific catch details, age, growth, longevity, movement patterns, reproduction, and range are generally poorly documented.
In Mexican waters the Golden Cownose Rays are found in all waters of the Pacific.
The Golden Cownose Ray is most likely confused with the Bat Ray, Myliobatis californica (black coloration; raised head; blunt pectoral fins with pointed tips). It is also very similar to the Cownose Ray, Rhinoptera bonasus, an Atlantic Ocean species.
The Golden Cownose Ray are frequently caught by artisanal fishermen, commercial fishermen of the greater Magdalena Bay and northern Sea of Cortez areas in gill nets and longlines, and as a by-catch of shrimp trawlers. They are sold and used primarily in fish tacos. From a conservation perspective, they are currently considered Near Threatened and their long-term viability is of concern. Although not well measured their populations are believed to be in decline, being adversely affected by a variety of factors including inshore habitat destruction to accommodate shrimp farming, schooling behavior, intense fishing pressure with large nets, long reproduction times with small litter sizes, and poorly documented and unregulated fishery. Note: Rays of the genus Rhinoptera have a venomous spine on their tail. The Golden Cownose Rays are potentially dangerous as they can inflict wounds with intense pain and slow recovery. Please refer to http://www.emedicinehealth.com/stingray_injury/article_em.htm for the treatment of stingray injuries. Approximately 1,500 stings from stingrays are reported annually.
Golden Cownose Ray, Rhinoptera steindachneri. Fish caught in coastal waters north of Puerto Los Cabos, Baja California Sur, November 2002. Disc width: 71 cm (28 inches). Weight: 6.8 kg (15 pounds). Caught out of a school of about 50 which were clearly visible and initially appeared as square stepping stones on the bottom.
Golden Cownose Ray, Rhinoptera steindachneri. Fish provided by the commercial fishermen of the greater Los Cabos area, Baja California Sur, April 2008. Disc width: 57 cm (23 inches). Disc length: 27 cm (11 inches). Tail: 39 cm (16 inches). Spines: 4.0 cm (1.6 inches) and 2.5 cm (1.0 inch).
Golden Cownose Ray, Rhinoptera steindachneri. Fish provided by the commercial fishermen of Bahía Kino, Sonora, March 2015. Disc width: 51 cm (20 inches). Disc length: 33 cm (13 inches). Tail: 37 cm (15 inches). Photo courtesy of Maria Johnson, Prescott College Kino Bay Center, Kino Bay, Sonora.