Bat Ray, Myliobatis californica
The Bat Ray, Myliobatis californica, whose common Spanish name is tecolote, is a species in the family Myliobatidae, the Eagle Rays, known as águilas marinas in Mexico. The Bat Ray received its common name from its pectoral fins which resemble bat wings. Globally, there are eleven species in the genus Myliobatis, of which five are found in Mexican waters, one in the Atlantic, three in the Pacific, and one in both oceans.
The Bat Rays have flat triangularly-shaped bodies with a distinctive face. They are uniformly olive, dark brown or black dorsally and off-white ventrally with the exception of the undersides of their pectoral fins, which are dark (pictured below) and have no distinguishing marks. Their head is large, bulbous, and protruding with a blunt rounded snout that projects well before the disc. They have large eyes and spiracles on their sides, a mouth on the underside equipped with seven series of flat, pavement-like plates of strong teeth utilized for crushing and grinding prey. They have a single dorsal fin at the base of a slender and whip-like tail that can be as long as or up to three times longer than the body. Their tail has a spine located just behind the body that can have up to three venomous barbed spines used for self-defense. Their pectoral fins are bluntly pointed with concave rear margins. They have smooth skin without denticles.
The Bat Rays are bottom dwellers found in muddy and sandy bottomed bays, rocky bottoms, and kelp forests; they are found in both shallow waters and at depths up to 575 feet. They reach a maximum disc width of 1.8 meters (5 feet 11 inches) and weight of 108 kg (240 pounds). Females can be up to three times larger than males. The largest fish caught by a recreational angler in California weighed 82 kg (181 pounds). They are the most abundant and best studied of the Eagle Rays and therefore a significant amount of information is available about their lifestyle and behavioral patterns. They are more active at night traveling as solitary individuals or in large schools of up to 1,000 individuals with other Bat Rays or with species of other Eagle Rays. They are known to migrate to warmer inshore waters in the spring and early summer for breeding and pupping and then to cooler deeper waters during the summer. They generate speed by flapping their pectoral fins like birds. They are known to breach and also to skim along the surface for extended periods of time. They are opportunistic benthic feeders that stir the bottom with their pectoral fins in order to dislodge small crustaceans, small fish, mussels, and worms on which they feed. They crush clams and other mollusks with their teeth, spit out the shells, and consume the fleshy parts. In turn they are preyed upon by large sharks and sea lions, however, man is probably their most important predator. Reproduction occurs annually via aplacental viviparity with internal fertilization followed by an eight to twelve month gestation period with litter sizes of two to twelve pups born live. The pups are born tail first with their pectoral fins folded over their body and their tail spine enclosed in a protective sheath; their disc width averages 30 cm (12 inches) and their weight averages 1 kg (2 pounds). Larger fish have bigger litter sizes than smaller fish. They are fast growing and reach maturity fairly quickly. They are found in all Mexican waters of the Pacific with the exception of Mazatlán south along the west coast of the mainland. They are more common in the northern portions and exceedingly rare in the southern parts of these ranges. They have a lifespan of up to 24 years.
The Bat Ray is usually confused with the Manta Ray but lacks the arm-like cephalic fins present on either side of the Manta Ray’s head. It can be confused with the Golden Cownose Ray, Rhinoptera steindachneri (red-brown color; large square head) and the Longnose Eagle Ray, Myliobatis longirostris (red-brown color; narrow pointed head with shovel-like snout; black aft edges of disc).
The Bat Rays are used extensively in the aquarium trade with the majority being found in large public aquariums. Due to their strength and stamina, they are also targeted by sports fishermen who use heavy tackle with shrimp, clams, or crabs as bait. They are a bycatch of demersal shrimp trawls, longlines, and gill nets and are normally discarded with a high mortality rate. There is a small commercial fishery for the Bat Ray in the northern parts of Baja where they are consumed for food and also sold commercially on a limited basis. They were believed to be a pest to oyster growers in Northern California in the mid-1950’s when 43,000 Bat Rays were caught by various methods and removed from the environment. It was later discovered that the Bat Rays visited the oyster beds to consume the Red Rock Crabs that were preying on the oysters, thus they were actually not guilty of oyster predation. At present there are no conservation measures in place for the Bat Ray. They are considered harmless to humans. Fossils of Bat Rays have been dated in excess of 1 million years old. This species was believed to be an important food source for the Native Americans of California. Note: Rays of the genus Myliobatis have tails with a venomous spine. Although the Bat Rays are classified as “harmless to humans”, they are potentially dangerous as they can inflict wounds with intense pain and slow recovery. Please refer to http://www.clubcruceros.org/StingrayInjuries.html for the treatment of stingray injuries. Approximately 1,500 stings from stingrays are reported annually.