Cownose ray


The cownose ray is a species found throughout a large part of the western Atlantic and Caribbean, from New England to southern Brazil. These rays also belong to the order Myliobatiformes, a group that is shared by bat rays, manta rays, and eagle rays.
Cownose rays prefer to live in shallower, coastal waters or estuaries. Size, lifespan, and maturity differ between male and female rays. Rays have a distinct shape, with two lobes at the front of their head, resembling a cow nose. Cownose rays can live between 16 and 21 years, depending on sex. Rays feed upon organisms with harder shells, such as clams, crustaceans, or mollusks. They are migratory creatures, south in the winter and north in the summer. The rays are known to occupy the Chesapeake Bay in the summer.
In 2019, the species was listed as vulnerable on the IUCN Red List. The species has been subjected to overfishing due to the perceived threat of overpopulation in the Chesapeake Bay. Few conservation strategies or efforts have been undertaken for cownose rays.

Taxonomy

The generic name Rhinoptera comes from the Ancient Greek words for nose and wing. The specific name bonasus comes from the Ancient Greek for bison.

Description

A cownose ray typically has a brown back with a slightly white or yellow 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 clam and oyster shells. Male rays often reach about in width, while females typically reach about in width. The cownose ray is sometimes mistaken for a shark by beach-goers due to the tips of the rays' fins sticking out of the water, often resembling the dorsal fin of a shark.
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 spine with a toxin, 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 those of a bee sting.

Habitat and distribution

Cownose rays are migratory and social creatures and reside on the East Coast of the United States, Brazil, and the Gulf of Mexico. They prefer to live in near coastal waters and in estuarian ecosystems and are able to tolerate a wide range of salinities. The rays to have the potential to change habitats if one area gets too crowded and competition for resources is high. Cownose rays are known to be abundant in the Chesapeake Bay and migrate to the area for mating and nursery purposes, typically in the late spring and summer, typically spotted near the surface of waters.

Behavior

Diet and feeding

The cownose ray exhibits a durophagous diet, meaning it feeds upon hard-shelled organisms, such as mollusks and crustaceans; they prefer scallops or clams, which have softer shells and are bivalves. This ray tends to feed either in the early morning or in the late afternoon, when the waves are calm and visibility is higher than during the day. Feeding occurs in the benthic zone or at the bottom of the ocean.
The rays are able to capture their prey through suction by opening and closing of their jaws. Because of the type of prey cownose rays consume, their jaws needs to be able to handle the hard-shelled organisms. Their jaws are extremely robust and have teeth with a hardness comparable to that of concrete. Their cephalic lobes also assist with capturing and handling their prey by pushing it towards their mouths.

Predation

The cownose ray being high on the food chain, has few natural predators, including cobia, hammerhead sharks, and humans who fish for them.

Reproduction and lifespan

Cownose rays breed from April through October. They do not reach maturity until they are roughly 70% of their maximum size. Females reach maturity between ages 7 and 8, while males reach maturity around ages 6–7. The lifespan of the cownose ray varies by sex; the oldest female ray that has been recorded was 21, and the oldest male ray was 18, which were both observed in the Chesapeake Bay.
Cownose rays are ovoviviparous, meaning that the embryo grows within its mother until it is ready to hatch. Rays have a longer gestation period due to their K-selected species attributes. The length of gestation is believed to last between 11 and 12 months, and at full term, the offspring are born live, exiting tail first.

Migration

Rays often travel and migrate in large schools based on size and sex. Their migration pattern moves north in late spring and south in late Fall. Much of what is known about their migration has been from studies done in the Chesapeake Bay. Male and female rays enter the bay in the late spring and leave in the fall. While there, the female rays and their pups live in the estuarine waters. Males have been observed leaving the bay earlier than the females to arrive at a second feeding ground, but the reason for taking a longer migration route is not fully known. One hypothesis is that males exit the bay to reduce competition of certain resources, such as food and shelter.

Threats and conservation

The cownose ray is currently listed as vulnerable by the IUCN Red List due to extensive overfishing and commercial fishing. The overfishing is due to the perception that rays destroy oyster beds meant for the shellfish industry.
The trophic cascade in the northwest Atlantic Ocean has been cited and used to link cownose ray overpopulation to the decrease in large coastal sharks, which then causes bivalve populations valuable for commercial reasons to be depleted, but little evidence supports this hypothesis. Campaigns such as "Save the Bay, Eat a Ray" in the Chesapeake Bay used these claims to promote the fishery of these rays in hopes of preserving the bay, which can be detrimental to this species. Cownose rays reach a mature age later in their lifecycle and have long gestation periods, meaning that they are a K-selected species. This suggests that they are vulnerable and sensitive to overfishing, and their populations cannot easily bounce back after these events. Though rays have been used as a scapegoat to explain the decline in bivalves, some studies have found that cownose rays do not consume a great deal of oysters or clams. Other studies have found that much of the shellfish prey that the cownose ray consumes is influenced by the size of the shell, so oyster growers as suggested to protect their shellfish until their shells reach a certain size.
Few conservation strategies or efforts have been taken for cownose rays, except cownose ray-killing contests have been banned in Maryland.

Relationship to humans

Risk to humans

Stingrays, including the cownose ray, can pose a low to moderate risk to humans. Rays can lash their tails when threatened, posing a risk of being whipped. If threatened, cownose rays can also use their barbs as a weapon to sting the aggressor. A sting from a cownose ray can cause a very painful wound that requires medical attention. While the sting is not usually fatal, it can be so if in the abdomen. Also, a risk exists from eating meat from the sea animal that has not been prepared correctly. Shigella bacteria may be acquired from eating flesh from a cownose ray that has been contaminated with the bacteria. This bacterium causes shigellosis, and can result in dysentery. Symptoms can include diarrhea, pain, fever, and possible dehydration.

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 often had their barbs pinched or taken off, making them safe enough to touch.
These aquariums and zoos are known to have touch tanks featuring cownose rays :

US