Giant Electric Ray, Narcine entemedor
The Giant Electric Ray, Narcine entemedor, whose common Spanish name is raya eléctrica gigante, is a species in the family Narcinidae, the Electric Rays, known as rayas eléctricas in Mexico. Globally, there are 15 species in the genus Narcine, of which three are found in Mexican waters, one in the Atlantic and two in the Pacific.
The Giant Electric Rays have elongated oval very flat discs that are slightly longer than they are wide. They are a uniform olive-brown dorsally and off-white ventrally. Juveniles have four or five dark-centered symmetrically arranged ocelli or blotches. The rear margins of their fins are white. Their head has relatively small eyes, nostrils with one opening, and a small protractile and tubular mouth with large teeth visible when closed. They have prominent well developed electric organs originating just before the eyes that are capable of delivering strong jolts to stun prey. They also have an accessory electric organ that produces low voltage discharges and may function in communications. Their skin is loose and soft and lacks denticles or thorns. They have two rounded dorsal fins, the second being slightly larger than the first. Their enlarged pectoral fins slightly overlap the front of the pelvic fins. Their caudal fin is angular and relatively tall with a straight rear margin. Their tail is shorter than the disc.
The Giant Electric Rays are a common demersal species found intertidally over sandy and rubble terrain at depths up to 330 feet. Females are larger than males and reach a maximum length of 107 cm (42 inches) compared to the maximum length of 67 cm (26 inches) for males. They are more active at night moving into shallow water environments to seek food by stirring bottom sediment with their pectoral fins and dislodging small crustaceans, mollusks, polychaetes, and teleosts on which they feed. Reproduction is via internal fertilization. Embryos develop by aplacental viviparity with a gestation period of 10 to 12 months and pups are born live. The fecundity rates are high with litter sizes ranging from four to 20 but sexual maturity is not reached by females for six years. Larger females produce the largest litters. Pups are born as miniature adults and are independent from birth. The discs of newborns vary in width from 14.0 cm (5.5 inches) to 16.0 cm (6.3 inches). Females and males have lifespans of 15 and 11 years, respectively. They are found in all Mexican waters of the Pacific with the exception of north of Guerrero Negro along the west coast of Baja. They are a rare and poorly studied species and as such very limited information is available about their behavioral patterns.
Due to its large stature and uniform brown color, the Giant Electric Ray cannot be confused with any other species.
The Giant Electric Rays are fished commercially and considered a quality food fish. From a conservation perspective populations have been decreasing in Mexico and are now considered “near threatened”. They are a major heavily overfished targeted species during the spring and early summer when females make runs to known locations for mating, spawning, and pupping. They are also caught as a by-catch of shrimp trawlers. Conservation efforts are severely hampered by poor landing rate data and the fact that this species remains essentially unregulated.