Round Stingray – Urobatis Halleri
Geographical Distribution
The round stingray is found in the eastern Pacific Ocean from Eureka in northern California (U.S.)
south to Panama Bay, Panama. It is most abundant south of Point Conception, California.
Distinctive Features
The round stingray has a nearly circular disc-shaped body with a tail that is shorter than the
length of the disc. The snout of this ray terminates in a rounded point. The prominent pectoral fins
("wings") are rounded. Dorsal fins are absent, however the rounded caudal fin is present in contrast to
many other rays that lack this feature. A long venomous spine is located approximately halfway down
the length of the tail.
There are six species of rays that live in waters off California that possess venomous spines on
their tails. The round stingray can be identified by its true tail fin which the other species lack. These
other species instead have either a whip-like tail or a short tail with no fin. The Cortez stingray
(Urolophus maculatus) is similar to the round stingray, however the dark blotches on each side of its
disc can distinguish it. The thornback (Platyrhinoidis triseriatea) can be distinguished by the presence
of two dorsal fins and the three rows of tubercles along the back of adult individuals while the Pacific
electric ray (Torpedo californica) can be distinguished by its two dorsal fins and lack of a venomous
spine on the tail.
The round stingray is grayish brown, either plain, mottled, or spotted with dark blotches, on the
dorsal surface, fading to a pale yellow, orange, or white underside. This ray has a smooth skin, lacking
the tubercles often found on other species.
Size, Age, and Growth
The maximum size reported for the round stingray is 22.8 inches (58.0 cm) total length while the
maximum published weight is just under 3 pounds (1,360 g). The average disc width of the round
stingray is 3-10 inches (8-25 cm). Sexual maturity is reached between 2.6 and 3 years of age which
correlates to a disc width of 5.7 inches (14.6 cm). The life expectancy is believed to be about 8 years.
Food Habits
Adult round stingrays feed primarily on benthic invertebrates such as stomatopods, amphipods,
shrimp, and portunid crabs, and to a smaller extent, on polychaete worms and small fishes. They rely
on olfaction and vision in the search for prey items. This ray has been observed to scoop out large
holes in the muddy or sandy bottom by "waving" its pectoral fins and rostrum. This action serves to
expose any buried worms, crabs or small fish. Feeding occurs continuously throughout daylight
hours. Juvenile round stingrays feed on polychaetes, crustaceans, and nemerteans.
· Reproduction
Mating of round stingrays has been documented during the winter months of January through March
in the Sea of Cortez. During the mating season, solitary males search for females using visual and
electrosensory cues. An interesting scientific finding is that reproductively mature females emit
localized positive electric fields from near the spiracles behind each eye. This attracts males and
mating behavior ensues. Males often bite the posterior of the females' discs. The females often
escape, resulting in failure of copulation. However, when a male bites the anterior portion of the
female's disc, the female does not attempt to free herself. This biting behavior functions to maintain
contact between the pair during copulation.
Development of the round stingray is ovoviviparous, resulting in live birth. After a gestation period
of approximately 3 months, a litter of 3-6 young are born in shallow waters. Each newborn measures
2.5-3.1 inches (6.3-8.0 cm) disc width. The young rays will remain in shallow habitats, which provide
rich feeding grounds as well as protection from predators, until they are large enough to move out
into deeper water. One known nursery area for the round stingray is Newport Dunes in southern
California.
· Predators
Predators of the round stingray in its northern range include the northern elephant seal (Mirounga
angustirostris) and the black sea bass (Stereolepis gigas). Other potential predators of this ray include
large carnivorous fishes including sharks.
· Parasites
There are numerous parasites reported from the round stingray including approximately 19 families
and 40 species are found on or in the round stingray. The most obvious parasites are those living on
the outside of the ray's body, also known as ectoparasites. These ectoparasites include copepods and
leeches.
Sixteen species of parasitic tapeworms have been documented from the digestive system of the round
stingray. A cestode, Phyllobothrium hallericola n. sp., was documented from the spiral valve
intestine of two round stingrays from the Sea of Cortez. Another cestode that has been reported from
this stingray is Acanthobothrium olseni.
Other parasites found in the spiral valve of the intestine include Eimeria chollaensis sp. nov.
(Apicomplexa: Eimeriidae) and Rhinebothrium spp. (Tetraphyllidea: Phyllobothriidae).
Importance to Humans
Although this ray is of only minor commercial fisheries
interest, it is fished recreationally as a gamefish. It is able to
survive extended periods in captivity and is often used in
public aquarium facilities.
The round stingray is easily approached by divers, swimming
away only if disturbed.
Danger to Humans
Stingrays are aptly named for the venomous serrated spine
located on the tail, with the round stingray being no different.
Although stingrays do not attack people, the tail spines can
cause painful wounds if stepped upon or handled without
caution. The round stingray has a spine that is located halfway down the length of the tail, allowing for a
powerful stinging reflex. Due to the increased human population along the coast of California, the numbers
of stingray-related injuries is on the rise as reported from Orange County, California. People can shuffle their
feet while walking in shallow water at the beach and avoid handling live stingrays to reduce chances of
injury from stingrays. Although wounds are not life threatening, they can be very painful.