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Myliobatis californicaBat ray

By Katie Schmidt

Geographic Range

Bat rays are found in shallow waters and coral reefs from Oregon to the Sea of Cortez.

Habitat

Bat rays are found living close to the shores of bays, sloughs, kelp beds and coral reefs. Bat rays prefer to live in areas with sandy or muddy bottoms for it allows easier access to food. They are most commonly found in depths reaching between 3m and 12m but have occasionally been spotted as deep as 46m. (Gray, et al., 1997; Last and Stevens, 1994)

Physical Description

Bat rays are commonly distinguished from other rays because of their distinct, protruding head and large eyes ( a close look). They have a flat body with a dorsal fin at the base of the tail. The tail is whiplike and can be as long or longer than the width of the body. It is armed with a barbed stinger that is venomous. Bat rays are named for their two long pectoral fins that are shaped like the wings of a bat. The skin is smooth, dark brown or black and has no markings. Bat rays have a white underbelly. The skeleton is made of cartilage, instead of bone. Bat rays are usually born measuring 11.4 inches and can grow to reach 5.9 feet. Females are typically larger than males and have been found weighing up to 200 pounds. ( Details.) (Last and Stevens, 1994; Michael, 1993)

  • Range mass
    0 to 0 kg
    0.00 to 0.00 lb

Reproduction

Bat rays reproduce on an annual cycle, usually copulating during the spring or summer of one year and then giving birth the following spring or summer. The male chooses his mate by following close behind her and assessing her reproductive condition by smelling her chemical signals. When the male has found a suitable mate, he continues to swim close behind and moves under so that his back is touching her stomach. He rotates a clasper up and to the side of the female. After inserting it into her cloaca, they swim together with synchronous beats of the pectoral fins. Many times, males will fight over a particular female. The female may end up having more than one male clinging onto her pectoral fins at one time and will wait for one of the males to finally flip her into the correct position. Bat rays reproduce in large mating aggregations with the females clustering in one area. Females may lie on top of one another, burying females that have already mated or those that are not sexually mature yet. This allows less confusion for the males to pick a suitable mate.

The gestation period is between 8-12 months and the number of live young born depends upon the size of the mother but can be up to 10 pups at a time. The female enters a bay area to deliver in an effort to protect from larger predators in the ocean and to allow access to a more stable food source. The young pups do not require any parental care and are born with stingers ready to protect from predators. Before bat rays are actually born, the stinger is pliable and has a sheath that is sloughed. It protects the mother from the dangerous stinger during delivery but is immediately lost at the time of delivery. Bat rays reach sexual maturity around the age of 5 years, usually when they measure from wing tip to wing tip 67-68 cm. (Last and Stevens, 1994; Michael, 1993)

Lifespan/Longevity

Bat rays have been known to live up to 23 years.

  • Range lifespan
    Status: wild
    23 (high) years

Behavior

Bat Rays are usually solitary animals but have been seen swimming in groups of thousands. They also swim with other rays from the same family (eagle ray). Females stick together and usually live where large amounts of food are found. Bat Rays move around a lot, even during copulation, and are noted for their ability to "jump out of water" and skim along the surface for several seconds. This is often described as looking like "flying". (Gray, et al., 1997; Last and Stevens, 1994)

Food Habits

Bat rays are carnivorous and feed on a variety of molluscs, crustaceans, and small fishes. Diet varies with the abundance of prey locally. Juveniles eat primarily clams and shrimp. Adult bat rays eat larger prey, including larger clams, crabs, shrimp, and echiuran worms.

Bat rays use their snout to dig invertebrates from the sand, making bat rays an important benthic predator. They also capture prey by lifting the body on the pectoral fin tip, flapping the pectoral tips quickly up and down, and then using the suction created by the flapping to pull sand out from under the body, exposing hidden prey. When bat rays feed on molluscs, they eat the entire animal, crush the shell inside of the mouth, spit out the hard shell pieces, and then eat the soft part of the mollusc body. Bat rays, depending on size, may burrow with their nose deeper into the sand or mud bottoms in an effort to eat larger prey. (Gray, et al., 1997; Talent, 1982)

  • Animal Foods
  • mollusks
  • aquatic or marine worms
  • aquatic crustaceans

Predation

Predators of the bat ray are California sea lions and broadnose sevengill sharks.

  • Anti-predator Adaptations
  • cryptic

Economic Importance for Humans: Positive

Because bat rays are large predators that use their snouts to dig up food, they wind up creating extremely large pits up to 4m long and 20 cm deep. These large pits allow access to small organisms that may be the food of smaller fish. Small fish rely on this relationship with bat rays because a lot of them are unable to dig their own food out of the sand.

Economic Importance for Humans: Negative

There are no known negative impacts of bat rays on humans. They were once thought to eat large numbers of cultivated oysters in coastal California. However, research demonstrated that bat rays only rarely prey on oysters. (Gray, et al., 1997; Michael, 1993)

Conservation Status

Bat rays were once persecuted in parts of coastal California because they were thought to prey on cultivated oysters. Bat rays were routinely killed in their nursery grounds, devastating local populations. (Gray, et al., 1997)

Other Comments

Bat ray fossils have been discovered in Pliocene deposits dating back 1 million years.

The origin of the name "bat ray" was given by Gill in 1865 because of their pectoral fins which resemble bat wings.

Bat rays have been successfully bred at Sea World. (Gray, et al., 1997; Talent, 1982)

Contributors

Katie Schmidt (author), University of Michigan-Ann Arbor, Tanya Dewey (editor), Animal Diversity Web.

Glossary

Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

coastal

the nearshore aquatic habitats near a coast, or shoreline.

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

molluscivore

eats mollusks, members of Phylum Mollusca

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

reef

structure produced by the calcium carbonate skeletons of coral polyps (Class Anthozoa). Coral reefs are found in warm, shallow oceans with low nutrient availability. They form the basis for rich communities of other invertebrates, plants, fish, and protists. The polyps live only on the reef surface. Because they depend on symbiotic photosynthetic algae, zooxanthellae, they cannot live where light does not penetrate.

References

Gray, A., T. Mulligan, R. Hannah. 1997. Food habits, occurence, and population structure of the bat ray, Myliobatis Californica, in Humboldt Bay, California. Environmental Biology of Fishes, 49: 227-238.

Last, P., J. Stevens. 1994. Sharks and Rays of Australia. Australia: CSIRO.

Michael, S. 1993. Reef Sharks & Rays of the World: A guide to their identification, behavior, and ecology.. Monterey, California: Sea Challengers.

Talent, L. 1982. Food Habits of the Gray Smoothhound, Mustelus Californicus, the Brown Smoothhound, Mustelus Henlei, the Shovelnose Guitarfish, Rhinobatos Productus, and the Bat Ray, Myliobatis Californicus, in Elkhorn Slough, California. California Fish and Game, 68: 224-234.

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