Roughtail Stingray

Appearance

The roughtail stingray has a diamond-shaped pectoral fin disk 1.2–1.3 times as wide as long, with straight to gently sinuous margins, rather angular outer corners, and a moderately long, obtuse snout. The eyes are proportionally smaller than other stingrays in its range and immediately followed by larger spiracles. There is a curtain of skin between the nostrils with a finely fringed posterior margin. The mouth is bow-shaped with a row of six papillae across the floor. The seven upper and 12–14 lower tooth rows at the center are functional, though the total number of tooth rows is much greater. The teeth are arranged with a quincunx pattern into flattened surfaces; each has a tetragonal base with a blunt crown in juveniles and females, and a pointed cusp in adult males.

The pelvic fins have nearly straight margins and angular tips. The tail is long and whip-like, measuring some 2.5 times the length of the disc. A long, saw-toothed spine is placed atop the tail at around half a disc length back from the tail base; sometimes one or two replacement spines are also present in front of the existing one. Behind the spine, there is a long ventral fin fold that is much lower than that of the southern stingray. Individuals under 46–48 cm across have completely smooth skin. Larger rays develop increasing numbers of distinctive tubercles or bucklers over the middle of the back from the snout to the tail base, as well as dorsal and lateral rows of thorns on the tail. The bucklers vary in size, with the largest of equal diameter to the eye, and may bear up to three thorns each. This species is a uniform dark brown or olive above, and off-white below without dark fin margins. Among the largest members of its family, the roughtail stingray can reach 2.6 m across, 4.3 m long, and 360 kg in weight. Females grow larger than males.

Distribution

The roughtail stingray is broadly but discontinuously distributed in the coastal waters of the western Atlantic Ocean. It occurs from the Georges Bank off Cape Cod southward to Florida, the Bahamas, and the northeastern Gulf of Mexico; there are also scattered reports from Venezuela to Argentina and on the Barrier reef in Belize. A single record from Kollam, India was likely a misidentification.

One of the deepest-diving stingrays, the roughtail stingray has been recorded to a depth of 274 m in the Bahamas. However, it is most common at a depth of 15–50 m. This bottom-dwelling species favors live-bottom habitat, and also frequents adjacent open areas of sand or mud. Rays in the northwestern Atlantic do not usually enter brackish water.

The favored temperature range of the roughtail stingray is 15–22 °C, which is the most important factor determining its distribution. It conducts seasonal migrations off the eastern United States: from December to May, this ray is found over the middle and outer parts of the continental shelf from Cape Hatteras in North Carolina to Florida, with larger rays occurring further south than smaller ones. In the spring, the population moves north of the Cape and towards the coast into bays, inlets, and saltier estuaries, though preserving the north-south gradient of body sizes. Pregnant females tend to be found apart from other individuals.

Behavior

The roughtail stingray is reportedly not highly active, spending much time buried in the sediment. It is a generalist predator whose diet generally reflects the most available prey in its environment. It mainly captures prey off the bottom, but also opportunistically takes free-swimming prey. A variety of invertebrates, as well as bony fishes such as sand lance and scup, are known to be consumed. Off Massachusetts, the main prey are crabs, bivalves, gastropods, squid and annelid worms. In Delaware Bay, most of its diet consists of the sand shrimp "Crangon septemspinosa" and the blood worm "Glycera dibranchiata"; the overall dietary composition there is nearly identical to that of bluntnose stingrays that share the bay. The shrimp "Upogebia affinis" is a major food source off Virginia. Off Florida, crustaceans and polychaete worms are the most important prey.

Sharks and other large fishes, in particular the great hammerhead, prey upon the roughtail stingray. The live sharksucker is sometimes found attached to its body. Known parasites of this species include the tapeworms "Acanthobothrium woodsholei", "Anthocephalum centrurum", "Lecanicephalum" sp., "Oncomegas wageneri", "Polypocephalus" sp., "Pterobothrium senegalense", and "Rhinebothrium maccallumi", the monogenean "Dendromonocotyle centrourae", and the leech "Branchellion torpedinis".

Like other stingrays, the roughtail stingray is aplacental viviparous: the developing embryo is initially sustained by yolk and later by histotroph delivered by the mother through finger-like projections of the uterine epithelium called "trophonemata". Only the left ovary and uterus are functional in adult females. Off the eastern United States, reproduction occurs on an annual cycle with mating in winter and early spring. After a gestation period of 9–11 months, females give birth to 4–6 young in fall or early winter. The newborns measure 34–37 cm across. Males and females mature at 130–150 cm and 140–160 cm across respectively,