Pteromylaeus bovinus

Geographic Range

The distribution of bull rays is not well-defined, but most observations report its range within tropical and subtropical waters of the Eastern Atlantic Ocean, between 44°N - 35°S, 19°W - 36°E, off the coast of Portugal down to the Saldanha Bay, South Africa. Bull rays have also been sighted in the Mediterranean Sea, the Black Sea, off the Canary Islands and Madeira, and in the Indian Ocean, off the coast of Kenya.

• Biogeographic Regions
• palearctic palearctic
  • native native
• ethiopian ethiopian
  • native native
• oceanic islands oceanic islands
  • native native
• indian ocean
  • native native
• atlantic ocean atlantic ocean
  • native native
• mediterranean sea
  • native native

Habitat

Bull rays are predominantly found in brackish coastal waters and prefer warm waters from the surf zone, which varies from one location to the next, to depths up to 150 m deep. They are commonly found in estuaries and lagoons, due to the abundance of prey in these habitats.

• Habitat Regions
• temperate temperate
• tropical tropical
• saltwater or marine saltwater or marine

• Aquatic Biomes
• pelagic pelagic
• benthic benthic
• reef reef
• coastal coastal
• brackish water brackish water

• Other Habitat Features
• estuarine estuarine
• intertidal or littoral intertidal or littoral

Physical Description

• Other Physical Features
• ectothermic ectothermic
• heterothermic heterothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• female larger
• sexes shaped differently

Development

Sexual development in bull rays begins when individuals reach approximately 100 cm in length. Disc-width at birth ranges from 250 mm to 270 mm. Total length at birth ranges from 530 mm to 560 mm, and weight ranges from 310 g to 345 g. Male and female development is divided into three stages: juvenile (I), subadult (II) and adult (III). For males, growth stage is noted by the shape and size of their tubercles. In Stage I, the anterior edge of the orbital area (the area above the eye) is smooth. In Stage II, tubercles form in the orbital area and slightly protrude above the eye. In Stage III, the tubercles are prominent and fully developed, with a cone-like shape. Juvenile and subadult males, stage I and II, respectively, have short, uncalcified and flexible claspers along with undeveloped, thread-like testes and genital ducts. During stage II, clasper grows quickly. As adults (stage III), claspers are elongated, calcified, and rigid. Adult males have fully developed and fully functional claspers, testes, and genital ducts. Female sexual development is marked by changes in appearance of their internal reproductive organs. During stage I, ovaries are white with microscopic oocytes and indistinct nidamental glands. During stage II, oocytes are translucent and the genital ducts are thread-like. During Stage III, the genital duct is fully developed.

Embryonic development in bull rays occurs through a reproductive process known as ovoviviparity. Eggs are fertilized internally, and embryos develop in egg cases while receiving nourishment from yolk sacs until they hatch out from the thin-walled membranes and continue development in the uterus. While in the uterus, embryos absorb nourishment through a combination of enriched nutrients supplied by mucus, fat, and protein from the uterine lining. This nutritional secretion is termed histotroph or “uterine milk,” and is ingested through a developing pup's mouth and spiracles. This type of nutrient supply facilitates the birth of large offspring. Gestation lasts about six months, with 3 to 7 pups produced in each litter.

Reproduction

Like most elasmobranchs , bull rays are polygynandrous and mate with different partners throughout breeding season. While little documentation exists on the mating behaviors of elasmobranchs in general, a few species of rays and skates have been observed copulating in the wild. Pre-copulatory behavior occurs in many species of rays, and is illustrated by the scars and wounds left on the dorsal surface of females. In male eagle rays , precopulatory behaviors include diving upon and biting the backs of females during courtship. The male inserts a pair of modified anal fins called claspers into the female to begin coitus. Copulation may last up to several hours. It is believed that female receptivity is dependent on hormonal status.

• Mating System
• polygynandrous (promiscuous) polygynandrous (promiscuous)

Rays in the family Myliobatidae , which includes bull rays, reproduce on a yearly cycle that ranges begins in spring and ends in fall. Gestation in bull rays lasts approximately 6 months and results in 3 to 7 pups per litter. Most individuals become sexually mature by 4 to 6 years after birth.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
  • internal internal
• ovoviviparous ovoviviparous

Females carry developing pups and nourish them with histotroph until they are born. There is no documentation of post-birth parental care in the family Myliobatidae . Bull ray pups are born fully developed and independent, able to fend for themselves.

• Parental Investment
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female

Lifespan/Longevity

There is little information available regarding the average lifespan of bull rays. Commonly, rays grow and mature slowly, and bull rays have been known to live up to 14 years in the wild.

Behavior

While there is little information the general behavior of bull rays, other members of the family Myliobatidae tend to be active swimmers, generally swimming in open water, near reefs, or near the surface. Myliobatid rays may exhibit social behavior, and have been observed swimming in pairs and in schools of a hundred or more. Members of this family have also been known to leap high out of water, an activity that some researchers believe may help rid them of parasites. Like other Mylobatidae , bull rays swim by undulating or flapping their enlarged wing-like pectoral fins to propel themselves forward through the water, resulting in a characteristic “flying” motion. Bull rays use their snout to plow through the sand while searching for prey.

• Key Behaviors
• natatorial natatorial
• motile motile
• sedentary sedentary
• solitary solitary
• social social

Home Range

Although no information is available regarding the average home range size of bull rays, members of their parent family, Mylobatidae , are not known to maintain home ranges.

Communication and Perception

Like most members of Chondrichthyes , bull rays have a lateral line, which they use to perceive their immediate environment. They also have nares for olfactory perception and eyes. Like other elasmobranchs , bull rays possess small electrical sensing organs, known as ampullae of Lorenzini, which form a subcutaneous electrosensory detection system. Located on the underside of the snout, the ampullae of Lorenzini detect weak electrical currents generated by the muscular contractions of their prey. Using this organ system, bull rays can detect prey buried several centimeters below the seafloor.

• Communication Channels
• visual visual
• tactile tactile
• chemical chemical
• electric electric

• Perception Channels
• visual visual
• tactile tactile
• chemical chemical
• electric electric

Food Habits

Bull rays are carnivores that feed on benthic invertebrates. Important food items include brachyuran crabs , hermit crabs , prawns , and other bottom-dwelling crustaceans . They also feed on gastropod molluscs , bivalves , and small squids . A predominant prey item for the bull ray in South Africa is the sand-burrowing surf clam .

• Primary Diet
• carnivore carnivore
  • molluscivore molluscivore

• Animal Foods
• mollusks
• aquatic crustaceans
• other marine invertebrates

Predation

Humans are a significant predator of bull rays. In addition, they are often caught in trawl nets as bycatch by shrimp fishermen, and in shark exclusion nets deployed at coastal beaches along South Africa. Natural predators include great hammerhead sharks and various pinniped species, such as South African fur seals .

Ecosystem Roles

Bull rays are shallow water predators in soft-bottomed environments of the neritic zone. They forage and feed upon benthic fish and small invertebrates, and in doing so, are important secondary and tertiary consumers within their environment. Rays excavate the soft bottoms of the sea floor while foraging for invertebrate prey. Disturbed sediments are rapidly recolonized by macrofauna and their larvae. Thus, foraging and predatory activities create habitat diversity and environmental heterogeneity.

Bull rays are host to numerous endoparasites, including trematode flatworms , monogenean flatworm , and ascarid worm .

• Ecosystem Impact
• creates habitat

Economic Importance for Humans: Positive

Although they are occasionally pursued by humans , bull rays are very rare and not commonly caught by fisherman. Otherwise, there are no known positive effects of bull rays on humans.

Economic Importance for Humans: Negative

Bull rays have sharp barbs on their tails, which can be troublesome for humans. Bull rays may rest on sandy bottoms within the intertidal zone, where humans may accidentally encounter them. Otherwise, there are no known adverse effects of bull rays on humans.

• Negative Impacts
• injures humans
  • bites or stings

Conservation Status

Bull ray population size and trends are unknown, making it difficult to determine the potential conservation needs of this species. Bull rays are classified as “data deficient” on the IUCN's Red List of Threatened Species, indicating there is insufficient data to adequately evaluate its conservation status.

Additional Links

Encyclopedia of Life

Contributors

Dylan Barrera (author), San Diego Mesa College, Caleb Dickerson (author), San Diego Mesa College, Bleu Grano (author), San Diego Mesa College, John Lambert (author), San Diego Mesa College, Paul Detwiler (editor), San Diego Mesa College, John Berini (editor), Animal Diversity Web Staff.

References

Demski, L., J. Wourms. 1993. The Reproduction and Development of Sharks, Skates, Rays, and Ratfishes: Introduction, History, Overview, and Future Prospects . Dordrecht, The Netherlands: Kluwer Academic Publishers.

Dulcic, J., L. Lovrenc, M. Bonaca, R. Jenko, B. Grbec, O. Guélorget, C. Capapé. 2008. The Bull ray in the Adriatic Sea. Cybium , 32/2: 119-123.

Jonna, R., M. Wienheimer. 2002. "Myliobatidae" (On-line). Encyclopedia of Life. Accessed May 04, 2011 at http://www.eol.org/pages/8882?expertise=middle .

Last, P., J. Stevens. 2009. Sharks and Rays of Australia . Collingwood, Australia: CSIRO.

Lipej, L., B. Mavric, J. Dulcic. 2009. Size of the Bull ray, Pteromylaeus bovinus (Geoffroy Saint-Hilaire, 1817), from the northern Adriatic. Journal of Applied Ichthyology , 25/Supplement 1: 103-105.

Michael, S. 1993. Reef Sharks and Rays of the World: A Guide to their Identification, Behavior, and Ecology . Annapolis, MD: Lighthouse Press.

Militante, C. 2010. " Pteromylaeus bovinus " (On-line). FishBase. Accessed March 18, 2011 at http://www.fishbase.org/Summary/SpeciesSummary.php?ID=5011&AT=bull+ray .

Moyle, P., J. Cech. 2000. Fishes: An Introduction to Ichthyology . Upper Saddle River, NJ: Prentice-Hall.

Schwartz, J. 2011. Tail spine characteristics of stingrays (Order Myliobatiformes) found in the northeast Atlantic, Mediterranean, and Black seas. Electronic Journal of Ichthyology , 1/1: 1-9.

Seck, A., Y. Diatta, A. Gueye-Ndiaye, C. Capapé. 2002. Observations on the reproductive biology of the Bull ray, Pteromylaeus bovinus (E. Geoffrey Saint-Hilare, 1879) (Chondrichthyes: Myliobatidae) from the coast of Senegal (eastern tropical Atlantic). Acta Adriatica , 43/1: 87-96.

Thrush, F., R. Pridmore, J. Hewitt, V. Cummings. 1991. Impact of ray feeding disturbances on sandflat macrobenthos: Do communities dominated by polychaetes or shellfish respond differently?. Marine Ecology Progress Series , 69: 245-252. Accessed May 15, 2010 at http://www.int-res.com/articles/meps/69/m069p245.pdf .

Van Der Elst, R. 1993. A Guide to the Common Sea Fishes of Southern Africa . Cape Town: Struik.

Vassiliades, G. 1982. Helminthes parasites des Poissons de mer des cotes du Senegal. Bulletin de P.I.F.A.N. , 44: 78-99. Accessed May 15, 2010 at http://www.sist.sn/gsdl/collect/publi/index/assoc/HASHafde/6284353f.dir/doc.pdf .

Weinheimer, M. 2011. "Animal Diversity Web" (On-line). Myliobatidae. Accessed January 02, 2011 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Myliobatidae.html .

Zogaris, S., U. Dussling. 2010. On the occurrence of the Bull ray Pteromylaeus bovinus (Chondrichthyes: Myliobatidae) in the Amvrakikos Gulf, Greece. Mediterranean Marine Science , 11/1: 177-184.

International Union for Conservation of Nature and Natural Resources. 2010. " Pteromylaeus bovinus " (On-line). Accessed April 14, 2011 at http://www.iucnredlist.org/apps/redlist/details/60127/0 .