Southern stingray

Appearance

The southern stingray is adapted for life on the sea bed. Its flattened, diamond-shaped body is more angular than other rays. The top of the body varies between olive brown and green in adults, dark grey in juveniles, whilst the underside is white. The wing-like pectoral fins are used to propel the stingray across the ocean bottom, whilst the slender tail possesses a long, serrated and venomous spine at the base, used for defence. These spines are not fatal to humans, but are incredibly painful if stepped on. The eyes are situated on top of the head of the southern stingray, along with small openings called spiracles. The location of the spiracles enables the stingray to take in water whilst lying on the seabed, or when partially buried in sediment. Water enters the spiracles and leaves through the gill openings, bypassing the mouth which is on the underside. Female stingrays can grow to a disc width of 150 centimetres, while the smaller male stingrays reach a maximum size of 67 centimetres.

Behavior

Southern stingrays are nocturnal predators, who spray water from their mouths or flap their fins vigorously to disturb the substrate and expose hidden prey. This bottom-dwelling species is often found singly or in pairs, and can reach population densities estimated up to 245 per square kilometre in certain shallow systems thought to be nursery grounds. "Hypanus americanus" exhibit wave-like locomotion using their pectoral fins. This wave-like motion is important for "Hypanus americanus" because it allows them to escape predators, forage efficiently, and generally maneuver quickly. Typically, they travel large distances and their foraging area is very expansive. One study provided observations that "Hypanus americanus" swim along the tide, because of the greater food availability along tides. "Hypanus americanus" are able to do this because of their high maneuverability and efficient wave-like locomotion. "Hypanus americanus" either remain solitary or form groups. Groups of "Hypanus americanus" are usually observed when they mate, for predator protection or even when they are just resting.Studies of "Hypanus americanus" have shown that they communicate through pheromone signaling. Males communicate with females before copulating by touching and biting the females. Also, after the female gives birth, she releases pheromones that are most likely believed to be produced in her cloaca; one study reported that the birth of offspring attracted males. As previously mentioned in the article, since a female has the ability to mate soon after giving birth, it is plausible that these are sex pheromones. The role of pheromones in communication also make sense since "Hypanus americanus" have strong senses of smell. They have many Ampullae of Lorenzini, usually heavily concentrated around the head. In addition, this gives them the ability to sense certain electric fields which are emitted from hidden prey. In addition, they have special mechanisms for senses vibrations in the water as well as for hearing.

Reproduction

"Hypanus americanus" are ovoviviparous. Fertilized eggs develop inside the mother's body. The embryos receive nutrients from the yolk sack early in development. After the yolk sac is absorbed, the embryos obtain nutrients from the histotroph. Females reproduce annually. This species gives live birth after a pregnancy which usually lasts between seven and eight months. Parental care ceases once the young are born. In captivity, gestation lasted 135 to 226 days, after which a litter of two to ten young were born.

There is little knowledge or published evidence about the mating systems of "Hypanus americanus". Mating stingrays are rarely encountered in the wild. One study, however, does provide detailed observations of" Hypanus americanus "mating. This study involves observations of one female mating with two males. The study mentions that the female was chased by the two males, with one of the male's biting the female's fin and releasing her after copulation. Females have the ability to mate again soon after giving birth.