|Dasyatis americana (Hildebrand & Schroeder, 1928)|
|Range of the southern stingray|
It has a flat, diamond-shaped disc, with a mud brown, olive, and grey dorsal surface and white underbelly (ventral surface). The barb on its tail is serrated and covered in a venomous mucous, used for self-defense.
DescriptionThe southern stingray is adapted for life on the sea bed. The flattened, diamond-shaped body has sharp corners, making it more angular than the discs of other rays. The top of the body varies between olive brown and green in adults, dark grey in juveniles, whilst the underside is predominantly 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 poisonous 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 cm, contrary to the smaller male stingrays that reach maximum size at 67 cm.
BehaviorSouthern 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 km2 in certain shallow systems thought to be nursery grounds.  Dasyatis americana exhibit wave-like locomotion using their pectoral fins. This wave-like motion is important for Dasyatis americana 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 Dasyatis americana swim along the tide, because of the greater food availability along tides. Dasyatis americana are able to do this because of their high maneuverability and efficient wave-like locomotion. Dasyatis americana either remain solitary or form groups. Groups of Dasyatis americana are usually observed when they mate, for predator protection or even when they are just resting.
ForagingIn one study, it was evident that when scientists revealed the contents of the stomach of one Dasyatis americana, they found evidence of a great variety of ingested prey (which represented a variety of phyla and families), such as small fishes, worms and crustaceans. As mentioned earlier in this article, the Dasyatis americana swim with a wave-like motion, thus making it easier for them to maneuver and help explain why they their foraging area is so vast. They can be identified as opportunistic feeders and continuous foragers, since they exhibit continuous feeding of multiple organisms throughout the day (this helps to explain the stomach contents revealed in the previously mentioned study).
PredationTo avoid predators, Dasyatis americana bury and cover themselves in substrate. In addition, they also bury themselves in the substrate to effectively hide from their prey. Their tails contain venom and are also utilized as protection from predators. Some predators of Dasyatis americana are humans and Sphyrna mokarra sharks.
Roles within their EcosystemsIn shallow waters, there is a commensal foraging relationship between Dasyatis americana fish and Phalacrocorax auritus birds in coastal areas generally like the Gulf of Mexico. When foraging, the Dasyatis americana dig through the substrate in search of food; however, this also helps to exposes certain other fish hidden in the substrate after which the Phalacrocorax auritus will follow behind the Dasyatis americana and eat.
Source: From Wikipedia, the free encyclopedia
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