Shovelnose Guitarfish, Rhinobatos productus
The Shovelnose Guitarfish, Rhinobatos productus, whose common Spanish name is guitarra viola, is a species in the Guitarfish or Rhionobatidae Family, known collectively as guitarras in Mexico. There are twenty-nine global members of the genus Rhinobatos, two of which are found in Mexican waters of the Atlantic and four in Mexican waters of the Pacific.
The Shovelnose Guitarfish have shark-like bodies and large triangular heads that taper to a pointed blunt snout and incorporate the fused pectoral fins. Their discs are longer than they are wide. They are yellowish-brown in color with a slightly translucent snout. Their ventral side is off-white. In some fish, the snout tip is black. Most live fish have a series of paired and irregular dark blotches on their cheeks, on the rear of their head, along their upper flanks, and on their pectoral fins. Their head is relatively slender and their snout has two narrow cartilaginous ridges that are close together for the first half of their length. They have a large spiracle behind each eye (pictured below), with two skin folds, the outer fold being larger that the inner fold. Their body is covered with small denticles. They have one row of thorns along the midline of their back starting from behind their eyes to the origin of their first dorsal fin. They also have two spines on each shoulder and several around each eye and above each spiracle. Their caudal fin is asymmetrical and without a distinct lower lobe. They have two large triangular-shaped dorsal fins of equal size.
The Shovelnose Guitarfish are bottom dwellers that form large schools in shallow coastal waters over sandy and muddy bottoms in bays and estuaries at depths up to 300 feet. They reach a maximum of 1.56 meters (5 feet 1 inch) in length and 18.4 kg (47 pounds) in weight. They consume a wide variety of crustaceans and small fish. They are masters at camouflage and have the ability to rapidly change colors to match their substrate. Reproduction is via yolk sac with offspring born alive in litter sizes of four to twenty-eight.
In Mexican waters the Shovelnose Guitarfish are found in all waters of the Pacific with the exception that they are absent from of along the coast of the mainland south of Acapulco to Guatemala.
The Shovelnose Guitarfish is most likely confused with the Speckled Guitarfish, Rhinobatos glaucostigma (snout with two wide cartilaginous ridges; pectoral and pelvic fins with pale margins), the Spiny Guitarfish, Rhinobatos spinosus (body covered with spines), and the Whitesnout Guitarfish, Rhinobatos leucorhynchus (white snout).
The Shovelnose Guitarfish are caught primarily as a by-catch of benthic fisheries. They have been utilized as food by Native Americans for centuries although currently their food value is considered of very marginal quality. They are normally returned to the sea but some are retained and made into fish meal. They are considered harmless to humans.
Shovelnose Guitarfish, Rhinobatos productus. Fish caught from coastal waters off Santa Catalina Island, California, September 2016. Length: 81 cm (32 inches). Catch, photo and identification courtesy of Chris Wheaton, Loreto, Baja California Sur.
Shovelnose Guitarfish, Rhinobatos productus. Fish caught from coastal waters within the Devil’s Curve section of Magdalena Bay, Baja California Sur, January 2017. Length: 76 cm (30 inches). Catch and photo courtesy of Brad Murakami, Surrey, British Columbia, Canada.