Cownose ray (Rhinoptera bonasus)

Also known as: Cowfish, skeete
French: Mourine Américaine
Spanish: Cara De Vaca, Gavilan Mancha, Gavilan Manchado, Mancha, Raya Gavilán
GenusRhinoptera (1)
SizeBody width: 107 cm (1)

Classified as Near Threatened (NT) on the IUCN Red List (1).

With a conspicuous indent at the front of the head, and a specialised fin beneath the head divided into two, short rounded lobes, the cownose ray is one of the most readily identifiable ray species. Like other cownose rays, the body is disc-like, with large, broad pectoral fins forming pointed, wing-like structures along either side. A small dorsal fin is located at rear of the body, with a small, barbed poisonous spine situated directly behind it, beyond which the body tapers into a long whip-like tail (2) (3). The overall colouration of the cownose ray is light to dark brown above and white or yellowish-white below, with brownish edges on the pectoral fins. The mouth is located on the underside of the head and contains up to 11 to 13 rows of flattened, plate-like teeth, which enable the cownose ray to crush hard-shelled prey (2).

The cownose ray inhabits warm temperate and tropical waters of the western Atlantic, occurring off the coast of southern New England, north-east U.S.A., south to the Gulf of Mexico, parts of the Caribbean and southern Brazil. It has been reported as being especially abundant in Chesapeake Bay, the largest estuary in the U.S.A., during the summer months (1).

The cownose ray inhabits marine and brackish waters to depths of up to 22 metres, and can often be found in estuaries and bays (1).

A pelagic and gregarious species (1), the cownose ray forms large schools which move gracefully through the water column propelled by undulations of the wing-like pectoral fins (4). Feeding takes place on the seabed, with the cownose ray detecting its prey by sensing movement as well as weak electric signals. In order to extract buried prey, the cownose ray sucks and vents water through the gills, thereby fluidising the surrounding sand, which is further cleared by stirring motions of the pectoral fins (2) (5). The food is then manoeuvred towards the mouth with the aid of the two lobes beneath the head, and sucked inside. Inside the mouth, it is crushed by the plate like-teeth and the edible parts separated from the indigestible parts, which are expelled through the mouth (5). Prey typically includes bottom-dwelling fish, crabs, lobsters and marine molluscs, such as bivalves (2). The large scale disturbance to the seabeds caused by the feeding behaviour of schools cownose ray have led to this species being implicated in extensive damage to seagrass beds and commercial shellfish beds (1). The cownose ray is preyed upon by a number of larger species such as cobia (Rachycentron canadum), sandbar sharks (Carcharhinus plumbeus) and bull sharks (Carcharhinus leucas) (2).

The cownose ray is believed to breed between June and October. Like many sharks and rays, the mode of reproduction is via ovovivipary, in which the females produce eggs, which after fertilisation hatch internally, so that the young are “born” live. While inside the uterus, the embryos are initially nourished by the egg yolk sac, but once hatched receive additional nourishment from a nutrient-rich fluid produced by the lining of the mother’s uterus. While one female was observed to carry six young to full term, in general the cownose ray produces only a single young, which is born measuring around 36 centimetres in body width (2).

The cownose ray makes long migrations in schools which can number thousands of individuals, moving northwards in late Spring and southwards in late Autumn (1) (2). Migration is believed to be initiated by the orientation of the sun and by water temperature (2)

In U.S.A. waters, the cownose ray population is not considered to by under threat. Although it is taken as bycatch by some fisheries, it is not directly targeted, and the population appears to be healthy (1). Nevertheless, a suggestion has been made by The Virginia Sea Grant Marine Advisory Program to implement a commercial fishery for this species, in order to reduce damage to seagrass and shellfish beds. As the cownose ray takes a relatively long time to reach reproductive maturity and usually produces only a single offspring, such exploitation could have severe adverse effects on the population (1) (2). In the Central and South American parts of this species’ range, it is presently considered to be more at risk due to intense, and generally unregulated, fishery activities. While a lack of catch data means that the exact impact on the cownose ray is unknown, other related ray species in the area have shown a significant decline (1).

Owing to the cownose ray’s long distance movements, it requires coordinated national and international efforts to ensure that its population is adequately assessed. In addition, estimates of mortality through fishing throughout its entire range are urgently necessary to assess the extent to which it is being affected. Given the heavy fishing pressure in Central and South American inshore waters, management strategies and regulation are likely to be required to ensure the survival of the cownose ray and other inshore ray and shark species in this area (1).

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  1. IUCN Red List (December, 2009)