Animal Diversity Web

Ge­o­graphic Range

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

• Biogeographic Regions
• pacific ocean
  • native

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)

• Aquatic Biomes
• reef
• coastal

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)

• Other Physical Features
• bilateral symmetry

• 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)

• Key Behaviors
• natatorial
• motile

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)

• Primary Diet
• carnivore
  • eats non-insect arthropods
  • molluscivore

• 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

• Known Predators

  • California sea lions (Zalophus californianus)
  • broadnose sevengill sharks (Notorynchus cepedianus)

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)

• IUCN Red List

  Least Concern
  More information

• IUCN Red List

  Least Concern
  More information

• US Federal List

  No special status

• CITES

  No special status

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.

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.