Round Stingray

Urobatis halleri

These smaller stingrays have an almost circular pectoral disc, with a slightly rounded point at the snout, and a short tail that lacks dorsal fins but does have a small caudal (tail) fin, which is unusual for rays. It also has a venomous spine halfway down its tail, so caution should be used handling these rays, or when in its habitat.

They are gray on top, sometimes with darker blotches or spots, and pale yellow-orange to white underneath. While they can grow to over 22 inches long, they average only 8 to 10 inches long generally.

Order: Rajiformes
Family: Urolophidae
Genus: Urobatis
Species: halleri

Common Names

Common names in the English language include round stingray, little round stingray, and Haller’s round ray. Other common names are ignelivatoz (Turkish), pastinaca (Italian), peitschenrochen (German), pigrokke (Danish), pilrokke (Norwegian), raie ronde de Haller ( French), raya (Spanish), raya de espina (Spanish), raya redonda de Haller (Spanish), ronde doornog (Dutch), sálahi trygéna (Greek), siba zutulja (Serbian), stechrochen (German), stingrocka (Swedish), trigono (Italian), trygon kolisty (Polish), and volina (Serbian).

Importance to Humans

Although this ray is of only minor commercial fisheries interest, it is fished recreationally as a game fish. 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.

Conservation Status

The round stingray is currently listed as a species of “Least Concern” with the World Conservation Union (IUCN). The IUCN is a global union of states, governmental agencies, and non-governmental organizations in a partnership that assesses the conservation status of species.

> Check the status of the round stingray at the IUCN website.

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.

Habitat

Similar to other species of rays, the round stingray lives in sandy and muddy bottoms in relatively shallow waters off beaches as well as in bays, channels, and inlets. It has also been observed swimming around rocky reef structures. This ray occurs to depths from the surface to 300 feet (91 m), however it is primarily found in waters less than 50 feet (15 m) in depth. It often lies motionless in the sand, exposing only its eyes. Observations indicate that round stingrays segregate by age and sex, with females residing in deeper water while males and juveniles occupy shallower habitats.

Biology

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.

Coloration
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.

Denticles
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 isAcanthobothrium olseni.

Other parasites found in the spiral valve of the intestine include Eimeria chollaensis sp. nov. (Apicomplexa: Eimeriidae) and Rhinebothrium spp. (Tetraphyllidea: Phyllobothriidae).

Taxonomy

Cooper originally described the round stingray in 1863 as Urolophus halleri. This name was changed that same year to the currently valid Urobatis halleri (Cooper, 1863). The genus name Urobatis is derived from the Greek “oura” meaning tail and “batis” meaning a ray. Synonyms referring to this species in past scientific literature include Urolophus nebulosus Garman 1885 and Urolophus umbrifer Jordan & Starks 1895.

Prepared by: Cathleen Bester