Cownose ray

For other species of cownose rays, see Rhinoptera.
Cownose ray
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Elasmobranchii
Order: Myliobatiformes
Family: Myliobatidae
Genus: Rhinoptera
Species: R. bonasus
Binomial name
Rhinoptera bonasus
(Mitchill, 1815)

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, USA 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).

Gestation

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. At full term, the offspring are born live, exiting tail first.

Size and appearance

Cownose rays swimming in shallows in the Gulf of Mexico

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.

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.

A cownose ray has a stinger, called a spine, on its tail, 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.

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.

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.[1]

A touch tank can also be found in the Ripley's Aquarium of Canada, Toronto, Ontario. 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.

References

  1. ↑ "Cownose Sting Ray". Retrieved 2011-01-09.
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