Cownose ray
- For other species of cownose rays, see Rhinoptera.
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R. bonasus
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| Rhinoptera bonasus (Mitchill, 1815)
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The cownose ray (Rhinoptera bonasus) is a species of eagle ray found throughout a large part of the western Atlantic and Caribbean, from New England, United States to southern Brazil (East Atlantic populations are now generally considered a separate species, R. marginata). Cownose rays grow rapidly, and male rays often reach about 35 inches (89 cm) in width and weigh 26 pounds (12 kg). Females typically reach 28 inches (71 cm) in width and weigh 36 pounds (16 kg).
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Taxonomy
Rhinoptera bonasus, comes from the Greek dervitation of the word parts.
"rhinos"- nose
"pteron"- wing
"bonasos"- bison
Gestation and Reproductive Behavior
Cownose rays breed from June through October. A large school of cownose rays gather of varying ages and sexes in shallow waters. A female will swim with the edges of her pectoral fins sticking out of the water, with male cownose rays following her trying to grasp the fins to mate.[1]
The embryo grows within its mother with its wings folded over its body. Initially it is nourished by an egg yolk, although the uterine secretions of the mother nourish it later in its development. The length of gestation is disputed, but it is believed to last between 11 and 12 months and is variable. At full term, the offspring are born live, exiting tail first.
Life Span
Sexual maturity for both males and females is reached around 4 to 5 years of age. In the Gulf of Mexico, females may live up to 18 years, where males may only live up to 16 years.[2]
Size and appearance
The cownose ray is 11 to 18 inches (28 to 46 cm) in width at birth. A mature specimen can grow to 45 inches (1.1 m) in width, and weigh 50 pounds (23 kg) or more. There is some controversy over the size that a mature cownose ray can reach. A ray reaching a span of 84 inches has been recorded.[3]
A cownose ray is typically brown-backed with a whitish or yellowish belly. Although its coloration is not particularly distinctive, its shape is easily recognizable. It has a broad head with wide-set eyes, and a pair of distinctive lobes on its subrostral fin. It also has a set of dental plates designed for crushing clams and oyster shells. When threatened the cownose ray can use the barb at the base of its tail to defend itself from the threat.[1]
A cownose ray has a spine with a toxin, close to the ray's body. This spine has teeth lining its lateral edges, and is coated with a weak venom that causes symptoms similar to that of a bee sting.[3]
Feeding habits
The cownose ray feeds upon clams, oysters, hard clams and other invertebrates. It uses two modified fins on its front side to produce suction, which allows it to draw food into its mouth, where it crushes its food with its dental plates. Cownose rays typically swim in groups, which allows them to use their synchronized wing flaps to stir up sediment and expose buried clams and oysters.
Migration
The cownose ray often migrates from the Gulf of Mexico to Trinidad, Venezuela, and Brazil.[3] The Atlantic migration pattern consists of the cownose rays moving North in late Spring and moving South in late Fall.
MIgration may be influenced by water temperature and sun orientation, which explains the seasonal migration pattern. Southern migration may be influenced by solar orientation and Northern migration may be influenced by the change in water temperature,
Cownose rays do migrate, but as of yet, it has not been determined that their migratory behavior is due to feeding or premigratory mating activity.[1]
Habitat
Cownose rays appear naturally in the Eastern Atlantic Ocean, the Western Atlantic Ocean. Within the Eastern Atlantic Ocean, the cownose ray can often be found in Mauritania, Senegal, and Guinea. In the Western Atlantic Ocean they are located from Southern New England to Northern Florida in the United States, as well as throughout the Gulf of Mexico, Trinidad, Venezuela, and Brazil.
They live in Brackish and marine habitats and can be found at depth up to 22 meters. They are gregarious and migrate extremely long distances, often traveling in a school of cownose rays.
Aquariums
Cownose rays can be seen in many public aquaria worldwide and are often featured in special 'touch tanks' where visitors can reach into a wide but shallow pool containing the fish which have had their barbs pinched or taken off, making them safe enough to touch. One of these such tanks is located next to the right-field stands at Tropicana Field in St. Petersburg, FL.[4]
A touch tank can also be found in the Ripley's Aquarium of Canada, Toronto, Ontario.[citation needed] Also in Canada, the Vancouver Aquarium in Vancouver, British Columbia houses a touching tank which opened to the public in March 2016. The Vancouver touching tank features cownose rays as well as Southern Stingrays.[citation needed] The large shark and ray touch tank at the New England Aquarium in Boston contains a large number of cownose rays, as well as eight other species of rays and six species of sharks, that visitors can touch. The nearby Ocean Explorium in New Bedford, MA, houses these rays in their touch tank along with spotted bamboo sharks and Atlantic stingrays. They are also at the Florida Keys Aquarium Encounters on Marathon Key, FL, the Clearwater Marine Aquarium in Clearwater, FL, and Tampa's Lowry Park Zoo in Tampa, FL, as well.
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Cownose rays in the Albuquerque Aquarium
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Cownose ray at the California Academy of Sciences
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References
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- Froese, Rainer and Pauly, Daniel, eds. (2005). "Rhinoptera bonasus" in FishBase. August 2005 version.
- Florida Museum of Natural History Ichthyology Dept: Cownose Rays
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