Speckled Guitarfish, Rhinobatos glaucostigma
The Speckled Guitarfish, Rhinobatos glaucostigma, whose common Spanish name is guitarra punteada, is a species in the Guitarfish or Rhinobatidae Family, known collectively as guitarras in Mexico. There are 39 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 Speckled 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 brown in color with symmetrically arranged slate gray spots around their eyes and on the extreme part of their upper back (pictured below). Their snout is translucent and their pectoral and pelvic fins have pale margins. Their ventral side is off-white with irregular black patches on the snout. Their snout is moderately long with a blunt point and their mouth is straight with long oblique nostrils. Their snout has two cartilaginous ridges that are parallel, fairly wide apart, and well separated throughout their length. They have a large spiracle behind each eye (pictured below), with two folds, the outer fold being larger that the inner fold. Their body is smooth to the touch, yet they have a series of small blunt spines along the middle of their back, a single group on each shoulder, and a few above each eye, and around their spiracles. Their caudal fin is asymmetrical and without a distinct lower lobe. They have two large triangular-shaped dorsal fins of equal size that originate behind their pectoral fins.
The Speckled 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 365 feet. They reach a maximum of 89 cm (35 inches) in length and 3.6 kg (8.0 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 Speckled Guitarfish are found in all waters of the Pacific with the exception that they are absent from Guerrero Negro northward along the central and northwest coasts of Baja, and from the northern 10% of the Sea of Cortez.
The Speckled Guitarfish are very similar in size and shape to several other Guitarfish but they are the only species with slate gray spots on their head and upper body making for easy identification.
The Speckled 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.
Speckled Guitarfish, Rhinobatos glaucostigna, Female. Fish provided by the commercial fishermen of the greater Los Cabos area, Baja California Sur, July 2013. Length: 88 cm (35 inches).