On Exhibit: Monterey Bay Habitats
molluscs, crustaceans, small fishes
female wingspan of six feet (1.8 m) and weigh 200 pounds (91 kg); males are smaller
manta rays, pelagic stingrays; Subclass: Elasmobranchii (skates, rays and sharks); Family: Myliobatidae (eagle rays)
eastern Pacific from Oregon to the Sea of Cortez and near the Galapagos Islands
Bat rays swim gracefully by flapping their batlike wings (pectoral fins) bird style—a feature that gives these rays their common name and their family name, "eagle rays." They are found in muddy and sandy bottom bays, kelp forests and close to coral reefs.
Those batlike wings also serve in the hunt for food. Bat rays flap their pectoral fins in the sand to expose buried prey, like clams. Rays also use their lobelike snouts to dig prey from sandy bottoms. The resulting pit can be up to 13 feet (4 m) long and eight inches (20 cm) deep—an important source of "leftover" small prey for fishes that can't dig. Bat rays have one to three venomous barbed spines at the base of their long tails, but these docile animals sting only to defend themselves.
Bat ray teeth are fused into plates that can crush the strongest clam shells. The rays crush the entire clam, or other molluscs, inside their mouths, spit out the shells, and then eat the soft, fleshy parts. If a tooth breaks or wears out, a new one replaces it. Rays grow new teeth continuously, like their shark kin.
Because they struggle actively when caught, bat rays are popular with and even sought after by sport fishermen. There are no commercial fisheries along the California coast, but commercial fishing exists in Mexican waters, where bat rays are a food fish.
For many years, oyster growers trapped bat rays because they thought bat rays ate large numbers of oysters. But recently researchers have discovered that bay rays rarely eat oysters, and that crabs were destroying the oyster beds. The oyster growers were actually causing the destruction of their own oyster beds by trapping bat rays, which eat crabs.
Several bays and wetland areas along the California and Pacific Coast of Baja, including nearby Elkhorn Slough, are important nursery and feeding grounds for bat rays.
Sea lions, white sharks and broadnose sevengill sharks prey on bat rays. Divers have seen a "pack" of juvenile broadnose sevengill sharks attack a large bat ray.
Bat rays reproduce on an annual cycle, mating during spring or summer. After a gestation period of nine to 12 months, females give live birth to two to 10 pups—the number depends on the size of the mother. Pups emerge tail first, with their wings wrapped around their bodies. To protect the mothers, the pups' stinging spines are pliable and covered with a sheath that sloughs off after birth. The spine soon hardens, ready for defense within a few days.
Bat rays usually lead a solitary life, but may be found in groups of thousands. If disturbed while resting on the seafloor, bat rays raise themselves up on the tips of their pectoral fins with their backs arched, ready to swim away if a diver approaches too closely. Rays are known for their ability to jump out of the water and skim along the surface. In aquariums, observers have seen bat rays swim upside down on the water's surface.