Atlantic Stingray

One of the smallest stingray species, the Atlantic stingray attains a maximum length of 61 cm (24 in) and a weight of 4.9 kg (11 lb). It has a spade-shaped pectoral fin disk 1.1 times as wide as long, with rounded corners and concave anterior margins. The snout is relatively long. There are three stout papillae on the floor of the mouth; the teeth are rounded, with a flat, blunt surface. During the reproductive season, the teeth of mature males change to feature long, sharp cusps that curve towards the corners of the mouth, for gripping onto females during mating. The tail is long and whip-like, with a serrated spine measuring a quarter of the width of the disk. The spine is replaced annually between June and October. Dorsal and ventral fin folds are present on the tail. Larger Atlantic stingrays develop tubercles or thorns along the midline of the back to the origin of the tail spine. Some larger females also develop tubercles around the eyes and spiracles. The coloration is brown or yellowish brown above, becoming lighter towards the margin of the disk and sometimes with a dark stripe along the midline, and white or light gray below. The tail fin folds are yellowish. In larger individuals the tail may be flecked with gray near the base and completely dark towards the tip.

The Atlantic Stingray is found in the western Atlantic Ocean from the Chesapeake Bay southward to Florida and the Gulf of Mexico, to as far as Campeche, Mexico. Records of this species from Grenada, Suriname, and Brazil are doubtful and may represent other species. The Atlantic stingray is capable of tolerating varying salinities and can enter freshwater; it has been reported from the Mississippi River, Lake Pontchartrain, Winyah Bay, and the St. Johns River in Florida. The stingrays in the St. Johns River system represent the only permanent freshwater elasmobranch population in North America. This species inhabits shallow coastal waters over sandy or silty bottoms, estuaries, and lakes. They prefer water temperatures over 15 °C (59 °F) and can tolerate temperatures over 30 °C (86 °F). These stingrays conduct seasonal migrations to stay in warmer water: they are only present in the northerly Chesapeake Bay in the summer and fall, and elsewhere they migrate to deeper water in the winter. When inshore, they usually stay at depths of 2–6 m (6.6–19.7 ft), and after migrating offshore they may be found as deep as 25 m (82 ft).

The Atlantic stingray feeds mostly on benthic invertebrates such as bivalves, tube anemones, amphipods, crustaceans, and nereid worms, which they locate using their electroreceptive ampullae of Lorenzini. The exact composition of their diet varies by geographical location. When feeding, these rays will position themselves facing the current so that the sediment will be washed away. Numerous species of sharks, such as the tiger shark (Galeocerdo cuvier) and the bull shark (Carcharhinas leucas), are major predators of the Atlantic stingray. In freshwater habitats, they may be preyed upon by American alligators (Alligator mississippiensis). A known parasite of freshwater Atlantic stingrays is Argulus, a fish louse that feeds on skin mucus. Despite having a regular freshwater presence, the Atlantic stingray is physiologically euryhaline and no population has evolved the specialized osmoregulatory mechanisms found in the river stingrays of the family Potamotrygonidae. This may be due to the relatively recent date of freshwater colonization (under one million years), and/or possibly incomplete genetic isolation of the freshwater populations, as they remain capable of surviving in salt water. Freshwater Atlantic stingrays have only 30–50% the concentration of urea and other osmolytes in their blood compared to marine populations. …