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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 MŸller 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).