Pelagic Stingray - Biology and Ecology

Biology and Ecology

In adopting a midwater lifestyle, the pelagic stingray exhibits several characteristics different from those of its bottom-dwelling relatives. While most stingrays propel themselves by undulating their disc margins, this species swims by oscillating (flapping) its pectoral fins in a manner approaching the "underwater flying" employed by eagle rays. Oscillatory fin motions generate lift, thus improving cruising efficiency in open water at a cost to maneuverability. The pelagic stingray is adept at swimming backwards, which may compensate for the lower fine control offered by its swimming mode.

Vision seems to be more important to the pelagic ray in finding food than in other stingrays. Compared to other members of its family, this species has less than one-third the density of electroreceptive ampullae of Lorenzini on its underside. The ampullae also cover a smaller area, though not as small as in eagle rays, and are more evenly distributed between the ventral and dorsal surfaces. This ray can detect an electric field of well under 1 nV/cm at a distance of up to 30 cm (12 in), and may be able to pick up the minute electric fields produced by moving sea water. The lateral line of the pelagic stingray, a complex system of mechanoreceptors that detect nearby movement and ocean currents, remains similar to other stingrays in covering a greater area on the ventral than the dorsal surface. However, this species is less responsive to mechanical than to visual stimuli.

Pelagic stingrays may segregate by sex, vertically in that males are found in deeper water than females, and perhaps horizontally as well. Captive individuals often act highly aggressively towards ocean sunfish (Mola mola), biting and harassing them, particularly if they are hungry. This species is preyed upon by oceanic whitetip sharks (Carcharhinus longimanus), great white sharks (Carcharodon carcharias), toothed whales, and other large, ocean-going carnivores. Its all-around dark coloration likely serves to camouflage it against its featureless habitat. The venom on its tail spine is also quite potent, causing it to be avoided by other fishes. Known parasites of this species include the tapeworms Acanthobothrium benedeni, A. crassicolle, and A. filicolle, Rhinebothrium baeri and R. palombii, and Tetragonocephalum uarnak, and the monogenean Entobdella diadema.