California Butterfly Ray (Gymnura marmorata)

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The California Butterfly Ray, Gymnura marmorata, is a member of the Butterfly Ray or Gymnuridae Family, and is known in Mexico as raya mariposa californiana. 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 Ocean.

The California Butterfly Ray has an extremely broad rhomboidal disc-shaped body that is approximately 1.5 times wider than they are long. Their pectoral fins are not separated from the head giving rise to their triangularly-shaped body. They are light brown in color and covered with dense pale brown spots overlaid by scattered blackish spots. They become a uniform darker brown upon death. Their 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 identification is the distance between the eyes which is greater than the distance from the eyes to the tip of the snout. Their tail is very short and approximately one-half the length of the disc with one or two large serrated venomous spines used for defense. They have no caudal or dorsal fins. Their skin is smooth and without denticles.

The California Butterfly Ray is a demersal species that is found in shallow coastal waters in bays and along beaches and within silty and muddy channels and estuaries at depths up to 95 m (310 feet). They reach a maximum of 1.5 m (4 feet 11 inches) in width and 90 cm (35 inches) in length. They are dimorphic with females being approximately twice the size of males. As of October 15, 2020, the International Game Fish Association world record stood at 11.11 kg (24 lbs 8 oz) with the fish caught in coastal waters off San Diego, California in August 2018. They feed on buried bivalves, crabs, crustaceans and mollusks. Reproduction is via aplacental viviparity with embryos nourished by small yolk sacs and the young born live. They have a high fecundity level, with four to sixteen pups per litter ranging in disc width from 21  cm (8.3 inches) to 26 cm (10.2 inches) and having a fairly rapid growth rate. The California Butterfly Ray The Acapulco Damselfish is poorly studied with very limited information available about their lifestyle and behavioral patterns including specific details on age, growth, longevity, movement patterns, diet, habitat use, and reproduction.

The California Butterfly Ray is a resident of Mexican waters of the Pacific but has a limited distribution being found along the entire west coast of Baja and throughout the Sea of Cortez; they are absent from along the coast of the mainland.

The California Butterfly Ray is a straight-forward identification due to its wide narrow disc and short tail. The Longsnout Butterfly Ray, Gymnura crebripunctata (tip of snout greater than distance between eyes) found from Mazatlán, Sinaloa, southward along the coast of the mainland to Guatemala is considered by some to be the same species.

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