User:Lrokos/Cownose ray

User:Lrokos/Cownose ray

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The cownose ray (Rhinoptera bonasus) is a species of Batoidea found throughout a large part of the Atlantic from New England, United States to Southern Brazil (the East Atlantic populations are now generally considered a separate species, the Lusitanian cownose ray (R. marginata)). 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. Female rays can have a width of 3 feet, while males only reach around 2 and 1/2 feet. Rays have a distinct shape, and it has two lobes at the front of its head, resembling a cow nose. Cownose rays can live between 16-21 years, depending on sex. Rays feed upon organisms with harder shells, such as clams, crustaceans, or mollusks. The are migratory creatures, where they migrate South in the winter and North in the summer. The rays are known to occupy the Chesapeake Bay in the summer months.

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.

Description
Male rays often reach about 2 and 1/2 feet in width, while females typically reach about 3 feet in width. However, there is some controversy over the size that a mature cownose ray can reach. A ray reaching a span of 84 inches (2.1 m) has been recorded.

A cownose ray is typically brown-backed with a whitish or yellowish 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 clams and oyster shells. When threatened, the cownose ray can use the barb at the base of its tail to defend itself from the threat. The cownose ray is often mistaken for being 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.

A cownose ray has a spine with a toxin, close to the ray's body. This spine has teeth lining its lateral edges, and it is coated with a weak venom that causes symptoms similar to that 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, as well as in the Gulf of Mexico. They prefer to live in near coastal waters and in estuarian ecosystems. Cownose rays are able to tolerate a wide ride of salinities because of the areas they occupy. This allows for the rays to have the potential to live in a wider range of 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 time. Rays are typically spotted near the surface of waters, as they are epipelagic creatures.

Diet and feeding
The cownose ray exhibits a durophagous diet, meaning it feeds upon hard-shelled organisms, such as mollusks, crustaceans, They prefer scallops or clams, which have softer shells and are categorized as bivalves. The cownose ray tends to feed either in the early morning hours or in the late afternoon hours; when the waves are calm and visibility is higher than during the day. Rays feed in the benthic zone, or at the bottom of the ocean.

The rays are able to capture their prey through suction and the opening and closing their jaw. Because of the type of prey cownose rays consume, their jaw needs to be able to handle the hard-shell organisms. Their jaws are extremely robust and have teeth with a hardness comparable to that of cement. Their cephalic lobes also assist with capturing and handling their prey by pushing them towards their mouth.

Lifespan and Reproduction
Rays will not reach a mature age until they are roughly 70% of the way to their maximum size. Females reach maturity between ages 7-8, while males reach maturity between 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. These were both observed in the Chesapeake Bay.

Cownose rays breed from April through October. A large school of cownose rays gather of varying ages and sexes in shallow waters. A female will swim with the edges of her pectoral fins sticking out of the water, with male cownose rays following her trying to grasp the fins to mate.

Cownose rays are ovoviviparous, meaning that the embryo grows within its mother until it is ready to hatch. Rays are 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 consists of the cownose rays moving north in late Spring and moving south in late Fall. Much of their migration has been from studies done in the Chesapeake Bay. Male and female rays will come to the Bay in the late spring and leave in the fall. While occupying the Chesapeake Bay, the female rays and her pups will live in the estuarine waters. Males have been observed leaving the Bay earlier than the females to arrive at a second feeding ground, and 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. It is less threatened in the Gulf of Mexico and along the Atlantic coast of North America, but the species overall has still experienced steep population declines of 30–49% in only 43 years. Rays have been subjected to commercial fishing due to their destruction of oyster beds. However, since the means to fish them are difficult, expensive to obtain, and the meat of the rays has very little demand, this solution would most likely yield too little of a profit for it to be a viable venture for any commercial fishermen. It is, however, often caught by hobby fishermen.

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 therefore cause bivalves populations valuable for commercial reasons to be depleted; however, there is little evidence that 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 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. Even 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 it has been suggested that oyster growers protect their shellfish until their shell reaches a certain size.

There are not many conservation strategies or efforts for cownose rays, besides the fact that cownose ray killing contests have been banned in the state of Maryland.