California Butterfly Ray, Gymnura marmorata
The California Butterfly Ray, Gymnura marmorata, whose common Spanish name is raya mariposa californiana, is a species in the family Gymnuridae, the Butterfly Rays, known as raya mariposas in Mexico. Globally, there are sixteen species in the genus Gymnura, of which three are found in Mexican waters, one in the Atlantic and two in the Pacific.
The California Butterfly Ray has an extremely broad rhomboidal shaped disc that is approximately 1.5 times wider than it is long. The pectoral fins are not separated from the head giving rise to a triangularly shaped body. They are light brown covered with dense pale brown spots overlaid by scattered blackish spots. Dead fish are a uniform darker brown. The head has a bluntly pointed snout, eyes and spiracles on top, and an arched mouth equipped with numerous small teeth in bands. The front margin of the disc is slightly concave and the rear margin is rounded. A key to the identification is that the distance between the eyes is greater than the distance from the eyes to the tip of the snout. The tail is very short and approximately one-half the length of the disc with one or two large serrated venomous spines which are used for defense. They do not have a caudal fin or a dorsal fin. The skin is smooth without denticles.
The California Butterfly Ray is a bottom-dweller found in shallow coastal waters in bays and along beaches and within silty and muddy channels and estuaries at depths up to 310 feet. They feed on buried bi-valves, crabs, mollusks, and crustaceans. They reach a maximum size of 150 cm (59 inches) in width and 90 cm (35 inches) in length. The females are approximately twice the size of the males. Reproduction is via aplacental vivparity with embryos nourished by means of small yolk-sacs and young born live but the developing young are not nourished by the placenta; they do have a high fecundity level, with four to sixteen 21 – 26 cm disc width pups per litter, with a fairly rapid growth rate. In Mexican waters they are found along the entire West coast of Baja and throughout the Sea of Cortez.
The California Butterfly Ray is among the most common species taken in the Gulf of California by artisanal fishermen and a very easy identification and cannot be confused with any other species due to its wide very narrow disc and very short tail. The Longsnout Butterfly Ray, Gymnura crebipunctata (tip of snout greater than distance between the eyes), is considered by some to be the same species, and it is found from Mazatlán south along the coast of the mainland to Guatemala.
The California Butterfly Ray is one of the primary species landed by artisanal elasmobranch (sharks, rays and skates) fisheries along the coast of Baja. They show up in abundance in April and May during the breeding season and become a focus species. They are sold primarily as dried their market is only local without a significant commercial market. If you have a “fish taco” in the Baja there is a high probably you are eating this fish. They are caught on occasion by recreational fishermen in Southern California. Based on the large decline in guitarfish populations within this range attributed to intense fishing pressure it is assumed that the populations of the California Butterfly Rays are also in decline. They are also commonly taken as a bycatch of shrimp trawlers, beach seines and gillnets and are normally discarded with a high mortality rate. One positive is that heavy fishing pressure has removed the majority of the predatory sharks and upper trophic level teleosts from the environment causing a decrease both fishing pressure (fewer elasmobranch fishermen) and predatory pressure on the species. The catch of this species is basically unregulated and a limited number of seasonal bands put in place have not been enforced.