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.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
IUCN Red List of Threatened Species: data deficient
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.
Known Predators:
Range mass: 5.3 to 116 kg.
Range length: 0.74 to 1.48 m.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry
Sexual Dimorphism: female larger; sexes shaped differently
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.
Range lifespan
Status: wild: 14 (high) years.
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.
Range depth: surf zone to 150 m.
Habitat Regions: temperate ; tropical ; saltwater or marine
Aquatic Biomes: pelagic ; benthic ; reef ; coastal ; brackish water
Other Habitat Features: estuarine ; intertidal or littoral
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 (Native ); ethiopian (Native ); oceanic islands (Native ); indian ocean (Native ); atlantic ocean (Native ); mediterranean sea (Native )
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.
Animal Foods: mollusks; aquatic crustaceans; other marine invertebrates
Primary Diet: carnivore (Molluscivore )
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
Commensal/Parasitic Species:
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.
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)
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.
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 ; tactile ; chemical ; electric
Perception Channels: visual ; tactile ; chemical ; electric
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)
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.
Breeding season: Mating season begins in spring and ends in fall.
Range number of offspring: 3 to 7.
Average gestation period: 6 months.
Average time to independence: 0 minutes.
Range age at sexual or reproductive maturity (female): 4 to 6 years.
Range age at sexual or reproductive maturity (male): 4 to 6 years.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); 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)
Aetomylaeus bovinus, also known as the bull ray, duckbill ray,[3] or duckbill eagle ray,[1] is a species of large stingray of the family Myliobatidae found around the coasts of Europe and Africa.[2]
The species is ovoviviparous and reach sexual maturity at 4 to 6 years old. With a low fecundity of three to four pups per litter and a long gestation of 6 to 12 months (depending on the geographical zone), this species have a very sensitive life history. Very little is known concerning the ecology and behavior of A. bovinus, however it is part of the coastal marine megafauna, with a maximum length of 222 cm (87.4 in) and 116 kg (225.7 lbs), bull rays can be considered as giants of the shallow waters. Their maximum length and very narrow depth range of 0 to 30 m exposes them to various threats. Indeed, large-body, shallow-water species are at greatest risk of threats. Bull ray appears to be extremely rare throughout the Mediterranean region and its current population trend is highly suspected to be decreasing.
This fish is named the bull ray because of the shape of its head and it is sometimes called the duckbill ray in South Africa for its long, flat, round snout.[4] Females are larger and heavier than males.
Bull rays are "bentho-pelagic" feeders, which means that they feed on the sea floor and the water column. They feed on various invertebrates including crabs, hermit crabs, squids, prawns, gastropod molluscs and bivalve molluscs. They often cause damage to clam and oyster farms.[5]
Aetomylaeus bovinus is facing various and numerous threats, from fisheries to habitat degradation. As it is a benthic and semi-pelagic feeder, it is by-catch by a large game of industrial or artisanal fishing gear, especially pelagic trawling, bottom trawling, trammel nets, gill nets and spearfishing. Little information is available concerning this species in Africa, however old literature refers to a discard of 900 tones per year of bull rays by-caught by shrimp trawlers on the West African coast in 1988 during their late juvenile and sub/adult phase.
On a global scale, Aetomylaeus bovinus is classified as Critically Endangered. The bull ray is now part of the 53% of elasmobranchs native to the Mediterranean Sea that are at risk of extinction and require urgent action to conserve their population and habitats. Bull rays appear to be extremely rare throughout the Mediterranean region and their current population trend is highly suspected to be decreasing (by 80% during the last 45 years according to IUCN). There are currently no species-specific measures in place. Much research is required on the bull ray's population, size, trend, habitat, ecology, and threats. In order to protect the bull ray, its habitat needs to be protected, its harvest monitored and managed, and implementation of education and awareness programs could be beneficial.
The full distribution of the bull ray is uncertain but it is known to be found in the Mediterranean Sea,[5] the Black Sea, the eastern Atlantic Ocean between Portugal and Guinea, the Atlantic from north of Saldanha Bay in western South Africa and round the rest of the South African coast into the Indian Ocean up to Maputo Bay in southern Mozambique, also Zanzibar and Kenya.[4][6]
It is found between the surf zone and depths of 65 m (213 ft) or more and also enters estuaries and lagoons.[4] It frequents both the bottom and the surface and sometimes leaps from the water.[4]
The population size, trend, habitat, ecology and dynamic of the species remain unknown, however, like many members of the family Myliobatidae, Aetomylaeus bovinus is a potential migratory species.
{{cite journal}}: CS1 maint: multiple names: authors list (link) {{cite web}}: CS1 maint: url-status (link) Aetomylaeus bovinus, also known as the bull ray, duckbill ray, or duckbill eagle ray, is a species of large stingray of the family Myliobatidae found around the coasts of Europe and Africa.
