Potentially Misidentified Species:
Rhinoptera javanica (non MŸller and Henle 1841) is similar in appearance to Rhinoptera bonasus.
II. HABITAT AND DISTRIBUTION
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.
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).
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).
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
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
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
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).
Rhinoptera bonasus occurs in brackish waters to hypersaline environments up to 60 ppt (Bayly 1972).
V. COMMUNITY ECOLOGY
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
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
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).
Bayly IAE. 1972. Salinity tolerance and osmotic behavior of animals in
athalassic saline and marine hypersaline waters. Annual Review of Ecology and
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
Smith JW and JV Merriner. 1982. Association of Cobia,
Rachycentron canadum, with Cownose Ray, Rhinoptera bonasus. Estuaries
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.
Melany P. Puglisi, Smithsonian Marine Station
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Page last updated: August 1, 2008