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. (Schwartz, 2011)
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. (Dulcic, et al., 2008; Schwartz, 2011)
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. (Dulcic, et al., 2008; Seck, et al., 2002; Van Der Elst, 1993)
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. (Demski and Wourms, 1993; Michael, 1993)
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. (Demski and Wourms, 1993)
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. (Demski and Wourms, 1993; Michael, 1993; Militante, 2010)
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. (Michael, 1993)
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. (Last and Stevens, 2009; Lipej, et al., 2009; Moyle and Cech, 2000)
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. (Jonna and Wienheimer, 2002)
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.
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. (Jonna and Wienheimer, 2002; Moyle and Cech, 2000)
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. (Dulcic, et al., 2008; Schwartz, 2011)
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. ("Pteromylaeus bovinus", 2010; Weinheimer, 2011)
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. (Thrush, et al., 1991; Zogaris and Dussling, 2010)
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. (Seck, et al., 2002)
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. (Schwartz, 2011)
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.
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), Special Projects.
the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.
living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.
living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.
Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.
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.
areas with salty water, usually in coastal marshes and estuaries.
an animal that mainly eats meat
uses smells or other chemicals to communicate
the nearshore aquatic habitats near a coast, or shoreline.
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
uses electric signals to communicate
an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.
union of egg and spermatozoan
having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.
fertilization takes place within the female's body
the area of shoreline influenced mainly by the tides, between the highest and lowest reaches of the tide. An aquatic habitat.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
eats mollusks, members of Phylum Mollusca
having the capacity to move from one place to another.
specialized for swimming
the area in which the animal is naturally found, the region in which it is endemic.
islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.
reproduction in which eggs develop within the maternal body without additional nourishment from the parent and hatch within the parent or immediately after laying.
An aquatic biome consisting of the open ocean, far from land, does not include sea bottom (benthic zone).
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
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.
mainly lives in oceans, seas, or other bodies of salt water.
breeding is confined to a particular season
remains in the same area
reproduction that includes combining the genetic contribution of two individuals, a male and a female
associates with others of its species; forms social groups.
uses touch to communicate
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
uses sight to communicate
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