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Species Name:    Rhinoptera bonasus
Common Name:         Cownose Ray

 

I.  TAXONOMY

Kingdom Phylum/Division: Class: Order: Family: Genus:
Animalia Chordata Chondrichthyes Rajiformes Myliobatidae Rhinoptera



Cownose rays, Rhinoptera bonasus. Photograph courtesy of Blue Ag.


A school of cownose rays. Photograph Zooillogix.

Species Name: 
Rhinoptera bonasus Mitchill, 1815

Common Name(s):
Cownose Ray, Cowfish, Skeete, Cara de Vaca (Spanish)

Synonymy:
Raja bonasus (Mitchell 1815)
Rhinoptera lalandi (Muller and Henle 1841)
Rhinoptera affinis (Bleecker 1863)

Species Description:
Rhinoptera bonasus is one of fifteen species of elasmobranch fishes recorded in the Indian River Lagoon (Snelson and Williams 1982). The dorsal side is brown to olive lacking spots or other markings. The ventral side of the cownose ray is white or yellowish-white with brown edges. The pectoral fins, sometimes referred to as wings, are long and pointed. The square shaped projecting snout has an indentation in the center giving the impression that it is bi-lobed. Two small fins (rostra) project from the head. The mouth is small and located on the ventral side of the ray. The tail is whip-like with a spine at the base just posterior to a small dorsal fin. A defensive venomous barb is located at the base of the spine. Species of cownose ray are sometimes only distinguishable by the morphology and number of teeth.


Potentially Misidentified Species:
Rhinoptera javanica (non Mčller and Henle 1841) is similar in appearance to Rhinoptera bonasus.


II.  HABITAT AND DISTRIBUTION 

Regional Occurrence:
The cownose rays occur worldwide in tropical and temperature oceans, bays, estuaries, and river mouths (Neer and Thompson 2005). There are five pelagic species in the genus Rhinoptera. R. bonasus is found in the western Atlantic from New England (southern Massachusetts) to Florida and further to southern Brazil (Blaylock 1993, Neer and Thompson 2005). R. bonasus also occurs in the Gulf of Mexico migrating to Trinidad, Venezuela and is suggested to be a separate population from Atlantic residents (Collins et al. 2007b). Cownose rays are usually seen on continental and insular shelves and to depths of 22 m.

IRL Distribution:
Rhinoptera bonasus was first reported in the Indian River Lagoon in 1981 by Snelson and Williams (1981). The cownose ray does not appear to be a year-round resident moving through the lagoon during August and November most likely during migratory travels.


III. LIFE HISTORY AND POPULATION BIOLOGY

Age, Size, Lifespan:
The cownose ray can have a wingspan of up to 213 cm. This species displays considerable variation in size among populations in the Gulf of Mexico and the Atlantic Ocean, including the size at which male and female individuals reach sexual maturity and longevity. Both males and females reach sexual maturity between 4 and 5 years of age. In the Gulf of Mexico, females may live as long as 18 years while males live to 16 years, whereas the oldest rays recorded in the western Atlantic Ocean were 13 years for females and 8 years for males (Neer and Thompson 2005).

Abundance:
Rhinoptera bonasus forms large schools from hundreds to thousands of individuals (Blaylock 1993). In the Chesapeake Bay, large schools of cownose rays are abundant in the summer (Blaylock 1993).

Migration:
This species migrates along the Atlantic Coast and the Gulf of Mexico (Collins et al. 2007a). In the Atlantic, Rhinoptera bonasus migrates southward in the late fall and northward in the late spring. The onset of the migrations may be influenced by changes in water temperature but this does not seem to be the case for observations made at Pine Island Sound estuary in Florida (Collins et al. 2007b). In this population, there does not appear to be a predictable seasonal/temperature related migration. Rather, cownose ray migration may be more influenced by factors such as food availability or predator avoidance in this estuary.

Reproduction:
The mode of reproduction in the cownose ray is aplacental viviparity in which the eggs hatch and babies develop inside the body of the female without a placenta to provide nourishment. As a result, the pups will eat any unfertilized eggs and each other. Usually an individual will only give birth to one pup a year measuring approximately 36 cm in width (Neer and Thompson 2005).

Embryology:
Embryos range in size from 205 to 395 mm in populations in the Gulf of Mexico. The mean gestation period reported for both Atlantic and Gulf of Mexico females is 11 to 12 months (Neer and Thompson 2005).


IV.  PHYSICAL TOLERANCES

Temperature:
Rhinoptera bonasus on the south-west coast of Florida moves off-shore to deeper, warmer waters when the water temperature in estuaries drop to 15°C (Collins et al. 2007b).

Salinity:
Rhinoptera bonasus occurs in brackish waters to hypersaline environments up to 60 ppt (Bayly 1972).


V.  COMMUNITY ECOLOGY

Trophic Mode:
The diet of Rhinoptera bonasus consists mainly of small invertebrates, in particularly crustaceans, polychaetes, and bivalve mollusks (Collins et al. 2007a). They locate food in the benthos and use their pectoral fins to stir the sand while sucking water and sediment through the gills to filter out their prey. Shells are crushed between their tooth-plates and the soft tissue is digested.

Associated Species:
The cobia, Rachycentron canadum has been observed in close association with Rhinoptera bonasus. The cobia maintains a position in close proximity to the back of the rays feeding on rejected food scraps or displaced benthos (Smith and Merriner 1982).


VI. SPECIAL STATUS

Special Status:
Interest in the cownose ray has increased because of its potential impact on commercially important shellfish stocks including the oyster, Crassostrea virginica, in Chesapeake Bay (Blaylock 1993).


VII.  REFERENCES

Bayly IAE. 1972. Salinity tolerance and osmotic behavior of animals in athalassic saline and marine hypersaline waters. Annual Review of Ecology and Systematics 3:233-268.

Blaylock RA. 1993. Distribution and abundance of the cownose ray, Rhinoptera bonasus, in lower Chesapeake Bay. Estuaries 16:255-263.

Collins AB, Heupel MR, Hueter RE and PJ Motta. 2007a. Hard prey specialists or opportunistic generalists? An examination of the diet of the cownose ray, Rhinoptera bonasus. Marine and Freshwater Research 58:135-144.

Collins AB, Heupel MR, and PJ Motta. 2007b. Residence and movement patterns of cownose rays Rhinoptera bonasus within a south-west Florida estuary. Journal of Fish Biology 71:1159-1178.

FFWCC. Undated Fish and Wildlife Research Institute. Cownose Ray information page. Available online.

FMNH. Florida Museum of Natural History Ichthyology Department. Cownose Ray information page. Available online.

Neer JA and BA Thompson. 2005. Life history of the cownose ray, Rhinoptera bonasus, in the northern Gulf of Mexico, with comments on geographic variability in life history traits. Environmental Biology of Fishes 73:321-331.

Smith JW and JV Merriner. 1982. Association of Cobia, Rachycentron canadum, with Cownose Ray, Rhinoptera bonasus. Estuaries 5:240-242.

Snelson FF and SE Williams. 1981. Notes on the occurrence, distribution, and biology of elasmobranch fishes in the Indian River Lagoon System, Florida. Estuaries 4:110-120.

Report by:  Melany P. Puglisi, Smithsonian Marine Station
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Page last updated: August 1, 2008