Cownose ray

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The cownose ray (Rhinoptera bonasus) is a species found throughout a large part of the western Atlantic and Caribbean, from New England to southern Brazil (the East Atlantic ones are now generally considered a separate species, the Lusitanian cownose ray (R. marginata)).<ref name=":02">Template:Cite journal</ref> These rays also belong to the order Myliobatiformes, a group that is shared by bat rays, manta rays, and eagle rays.<ref name=":2">Template:Cite web</ref>

Cownose rays prefer to live in shallower, coastal waters or estuaries.<ref name=":02" /> 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.<ref name=":32">Template:Cite book</ref> Rays feed upon organisms with harder shells, such as clams, crustaceans, or mollusks.<ref name=":02" /> They are migratory creatures, south in the winter and north in the summer.<ref name=":32" /> 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.<ref name="iucn status 18 November 2021"/> The species has been subjected to overfishing due to the perceived threat of overpopulation in the Chesapeake Bay.<ref name=":22">Template:Cite journal</ref> Few conservation strategies or efforts have been undertaken for cownose rays.

Taxonomy

The generic name Rhinoptera comes from the Ancient Greek words for nose (Template:Transliteration) and wing (Template:Transliteration). The specific name bonasus comes from the Ancient Greek for bison (Template:Transliteration).

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 Template:Convert in width, while females typically reach about Template:Convert in width.<ref name=":32" /> 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.<ref name=":0">Template:Cite web</ref>

When threatened, the cownose ray can use the barb at the base of its tail to defend itself from the threat.<ref name=":0"/> 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.<ref name=":1">Template:Cite web</ref>

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.<ref name=":02" /> They prefer to live in near coastal waters and in estuarian ecosystems<ref name=":02" /> and are able to tolerate a wide range of salinities.<ref name=":7">Template:Cite journal</ref> The rays to have the potential to change habitats if one area gets too crowded and competition for resources is high.<ref name=":7" /> 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,<ref name=":02" /> typically spotted near the surface of waters.<ref name=":02" />

Behavior

Diet and feeding

Cownose ray teeth and mouthparts: Stingray teeth consist of interlocking bars (dental plates) that crush food.

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.<ref name=":02" /> 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.<ref name=":12">Template:Cite journal</ref> Feeding occurs in the benthic zone or at the bottom of the ocean.<ref name=":02" />

The rays are able to capture their prey through suction by opening and closing of their jaws.<ref name=":12" /> 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.<ref name=":12" /> Their cephalic lobes also assist with capturing and handling their prey by pushing it towards their mouths.<ref name=":12" />

Predation

The cownose ray being high on the food chain, has few natural predators, including cobia, hammerhead sharks, and humans who fish for them.<ref>Template:Cite web</ref><ref>Template:Cite web</ref>

Cownose rays swimming in shallows in the Gulf of Mexico

Reproduction and lifespan

Cownose rays breed from April through October.<ref name=":02" /> They do not reach maturity until they are roughly 70% of their maximum size.<ref name=":02" /> Females reach maturity between ages 7 and 8, while males reach maturity around ages 6–7.<ref name=":02" /> 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.<ref name=":32" />

Cownose rays are ovoviviparous, meaning that the embryo grows within its mother until it is ready to hatch.<ref name=":32" /> 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.<ref name=":32" />

Migration

Rays often travel and migrate in large schools based on size and sex.<ref>Template:Cite journal</ref> Their migration pattern moves north in late spring and south in late Fall.<ref name=":02" /> 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.<ref name=":02" /> While there, the female rays and their pups live in the estuarine waters.<ref name=":02" /> 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.<ref name=":02" /> One hypothesis is that males exit the bay to reduce competition of certain resources, such as food and shelter.<ref name=":02" />

Threats and conservation

The cownose ray is currently listed as vulnerable by the IUCN Red List<ref name="iucn status 18 November 2021"/> due to extensive overfishing and commercial fishing.<ref name="iucn status 18 November 2021"/> The overfishing is due to the perception that rays destroy oyster beds meant for the shellfish industry.<ref name=":22" />

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.<ref name=":22" /> 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.<ref name=":22" /> Cownose rays reach a mature age later in their lifecycle and have long gestation periods, meaning that they are a K-selected species.<ref name=":22" /> 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.<ref name=":22" /> 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.<ref>Template:Cite journal</ref>

Few conservation strategies or efforts have been taken for cownose rays, except cownose ray-killing contests have been banned in Maryland.<ref name="iucn status 18 November 2021"/>

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.<ref>Template:Cite web</ref> 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.<ref name=":3">Template:Cite web</ref>

Aquariums

The underside of a cownose ray

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 (they eventually regrow, similar to human nails), making them safe enough to touch.

These aquariums and zoos are known to have touch tanks featuring cownose rays (alone or with other fish):

US


Canada

References

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