Round stingray
Encyclopedia
The round stingray or Haller's round ray, Urobatis halleri, is a species of round ray
, family Urolophidae, found in the coastal waters of the eastern Pacific Ocean
. It is a small, common ray that feeds mostly on benthic invertebrate
s. On the beach
es of southern California
, it is responsible for numerous injuries to bathers, who are stung when they accidentally step on the fish. The wound caused by its venom
ous spine can be painful, but is non-fatal.
, until Garman (1913) moved it into his newly erected genus Urobatis. Urolophus encompasses the round rays of the western Pacific, while Urobatis encompasses the species in the eastern Pacific and western North Atlantic. The species name, halleri, is after the young son of Major G. O. Haller of the United States Army
, who was stung on the foot while wading along the shores of San Diego Bay
.
in northern California
south to Panama
. It is most common around southern California and the Baja Peninsula. They inhabit tropical to warm-temperate
waters close to shore, usually less than 15 m deep, although they have been reported to a depth of at least 91 m. This species favors soft-bottomed habitats such as mud
or sand
, often with abundant eelgrass
, which they use for camouflage
. They also occur around rocky reef
s.
Round stingrays prefer temperatures above 10 °C (50 °F); the adults are more tolerant of temperature changes than juveniles. They are most abundant in the coastal and bay waters of southern California
from spring
to fall
. In winter, they move to deeper water where the temperature is more stable. Round stingrays have been observed congregating near the warm seawater
effluent
released by coastal electric generators, which may replicate the conditions of estuary
environments.
The tail spine is periodically shed and replaced; for most of the year round stingrays have only one spine, but at the beginning of July small secondary spines begin to appear. The number of rays with secondary spines increases to a peak around September and October, then declines as the primary spines fall off and are replaced. The replacement process is complete by December.
s until they are 14 cm across. As they mature, their diet shifts towards bivalve molluscs and polychaete worms with crabs becoming less important, serving to reduce competition between adults and juveniles. Round stingrays are daytime foragers that are most active in the warm temperatures of summer and fall. Using their pectoral disc and mouths, they dig large pits to uncover buried prey. The digging of these pits plays an ecologically important role, as they also uncover prey for smaller fish.
In the northern part of its range, round stingrays are preyed upon by the northern elephant seal
and the black sea bass. Other predators include large shark
s. Numerous parasites are known for the round stingray, comprising 40 species in approximately 19 families. External parasites include copepod
s and leech
es, while 16 species of tapeworms are known from its digestive system, including Phyllobothrium hallericola n. sp. and Acanthobothrium olseni. Additional parasites that may be found in this ray's spiral valve intestine
include Eimeria chollaensis sp. nov. and Rhinebothrium spp.
As with other stingray
s, the round stingray is ovoviviparous, bearing litters of 1-6 young with an average of 2-3. The litter size increases with female size. The gestation period
is three months, with the young measuring 6-8 cm across at birth. The females able to store sperm
year-round. In southern California, the females move inshore to mate from April to June, with the young being born between June and October. Further south in the Gulf of California
, females mate and give birth earlier, from late winter to spring. A portion of the population mate and give birth in winter, allowing for a second breeding season later that same year. After giving birth, the adult females move back into deeper water while the young remain in the shallows. Female round stingrays emit a localized positive electric field
from near the spiracle
s behind each eye, which serves to attract males. The males will bite at the area, with successful contact necessary for copulation. Round stingrays grow at 3 cm per year until they reach maturity at around 31 months, at which time their growth rate slows.
Every year, hundreds of beachgoers are accidentally stung by round stingrays along the coast of southern California. The sting is not fatal, though it is quite painful. The so-called "Ray Bay" at the northern end of Seal Beach, used as a nursery ground by round stingrays, is the most notorious location for these incidents. At least 474 people were stung at that beach between April and November 1952, and over 500 people were stung over a ten-week period in 1962. During the 1990s, an average of 226 bathers were stung per year on Seal Beach, with the number of incidents rising during warmer El Niño years. Recently, local authorities and scientists have begun tagging the stingrays and clipping their spines in an effort to reduce the number of injuries. However, there is little evidence that this program has been successful, likely due to the large population of the rays, their itinerant nature around the region, and their annual spine replacement.
Due to its small size and large tail spine, the round stingray is considered commercially undesirable. It is occasionally caught (and discarded) by recreational angler
s and artisanal
gillnet
fisheries. In Mexico
, the tail is usually cleaved off before the ray is discarded, likely causing high mortality. This species is also taken as bycatch
by shrimp
trawlers, who consider them a nuisance as large groups often become entangled in the nets. Due to its abundance and relatively high rate of reproduction, the round stingray is assessed as of Least Concern on the IUCN Red List
. It is docile and easily approached by divers
, and adapts readily to display in public aquaria.
Round ray
Urolophidae is a family of rays in the order Myliobatiformes, commonly known as stingarees or round stingrays; this family formerly included the genera Urobatis and Urotrygon of the Americas, which are presently recognized as forming their own family Urotrygonidae. Stingarees are found in the...
, family Urolophidae, found in the coastal waters of the eastern Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
. It is a small, common ray that feeds mostly on benthic invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
s. On the beach
Beach
A beach is a geological landform along the shoreline of an ocean, sea, lake or river. It usually consists of loose particles which are often composed of rock, such as sand, gravel, shingle, pebbles or cobblestones...
es of southern California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
, it is responsible for numerous injuries to bathers, who are stung when they accidentally step on the fish. The wound caused by its venom
Venom
Venom is the general term referring to any variety of toxins used by certain types of animals that inject it into their victims by the means of a bite or a sting...
ous spine can be painful, but is non-fatal.
Taxonomy
The round stingray was originally assigned to the genus UrolophusUrolophus
Urolophus is a genus of stingrays in the family Urolophidae.-Species:* New Ireland stingaree, Urolophus armatus Müller & Henle, 1841* Sepia stingray, Urolophus aurantiacus Müller & Henle, 1841...
, until Garman (1913) moved it into his newly erected genus Urobatis. Urolophus encompasses the round rays of the western Pacific, while Urobatis encompasses the species in the eastern Pacific and western North Atlantic. The species name, halleri, is after the young son of Major G. O. Haller of the United States Army
United States Army
The United States Army is the main branch of the United States Armed Forces responsible for land-based military operations. It is the largest and oldest established branch of the U.S. military, and is one of seven U.S. uniformed services...
, who was stung on the foot while wading along the shores of San Diego Bay
San Diego Bay
San Diego Bay is a natural harbor and deepwater port adjacent to San Diego, California. It is 12 mi/19 km long, 1 mi/1.6 km–3 mi/4.8 km wide...
.
Distribution and habitat
This species is endemic to the eastern North Pacific Ocean, from Humboldt BayHumboldt Bay
Humboldt Bay is a natural bay and a multi-basin, bar-built coastal lagoon located on the rugged North Coast of California, United States entirely within Humboldt County. The regional center and county seat of Eureka and the college town of Arcata adjoin the bay, which is the second largest enclosed...
in northern California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
south to Panama
Panama
Panama , officially the Republic of Panama , is the southernmost country of Central America. Situated on the isthmus connecting North and South America, it is bordered by Costa Rica to the northwest, Colombia to the southeast, the Caribbean Sea to the north and the Pacific Ocean to the south. The...
. It is most common around southern California and the Baja Peninsula. They inhabit tropical to warm-temperate
Temperate
In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold...
waters close to shore, usually less than 15 m deep, although they have been reported to a depth of at least 91 m. This species favors soft-bottomed habitats such as mud
Mud
Mud is a mixture of water and some combination of soil, silt, and clay. Ancient mud deposits harden over geological time to form sedimentary rock such as shale or mudstone . When geological deposits of mud are formed in estuaries the resultant layers are termed bay muds...
or sand
Sand
Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...
, often with abundant eelgrass
Zostera
Zostera is a small genus of widely distributed seagrass, commonly called marine eelgrass or simply eelgrass . The genus Zostera contains sixteen species.-Ecology:Zostera is found on sandy substrates or in estuaries submerged or partially floating...
, which they use for camouflage
Camouflage
Camouflage is a method of concealment that allows an otherwise visible animal, military vehicle, or other object to remain unnoticed, by blending with its environment. Examples include a leopard's spotted coat, the battledress of a modern soldier and a leaf-mimic butterfly...
. They also occur around rocky reef
Reef
In nautical terminology, a reef is a rock, sandbar, or other feature lying beneath the surface of the water ....
s.
Round stingrays prefer temperatures above 10 °C (50 °F); the adults are more tolerant of temperature changes than juveniles. They are most abundant in the coastal and bay waters of southern California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
from spring
Spring (season)
Spring is one of the four temperate seasons, the transition period between winter and summer. Spring and "springtime" refer to the season, and broadly to ideas of rebirth, renewal and regrowth. The specific definition of the exact timing of "spring" varies according to local climate, cultures and...
to fall
Autumn
Autumn is one of the four temperate seasons. Autumn marks the transition from summer into winter usually in September or March when the arrival of night becomes noticeably earlier....
. In winter, they move to deeper water where the temperature is more stable. Round stingrays have been observed congregating near the warm seawater
Seawater
Seawater is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% . This means that every kilogram of seawater has approximately of dissolved salts . The average density of seawater at the ocean surface is 1.025 g/ml...
effluent
Effluent
Effluent is an outflowing of water or gas from a natural body of water, or from a human-made structure.Effluent is defined by the United States Environmental Protection Agency as “wastewater - treated or untreated - that flows out of a treatment plant, sewer, or industrial outfall. Generally refers...
released by coastal electric generators, which may replicate the conditions of estuary
Estuary
An estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea....
environments.
Description
The round stingray has a nearly round pectoral fin disc usually colored brown or grayish brown above, with pale yellow spots or reticulations. Some individuals are plain or black. The underside is white to yellowish. The tail is short and stout, with a long, thick, serrated stinging spine. The teeth are small and diamond-shaped, and sexually dimorphic in that the central teeth of males are erect, sharply pointed, and curved inward. They attain a maximum pectoral fin disc width of 25 cm in males and 31 cm in females.The tail spine is periodically shed and replaced; for most of the year round stingrays have only one spine, but at the beginning of July small secondary spines begin to appear. The number of rays with secondary spines increases to a peak around September and October, then declines as the primary spines fall off and are replaced. The replacement process is complete by December.
Biology and ecology
In nature, round stingrays strongly segregate by age and sex, with the females staying in water deeper than 14 m and males and juveniles in shallower habitat. The juveniles feed on polychaete worms and small benthic crabCrab
True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...
s until they are 14 cm across. As they mature, their diet shifts towards bivalve molluscs and polychaete worms with crabs becoming less important, serving to reduce competition between adults and juveniles. Round stingrays are daytime foragers that are most active in the warm temperatures of summer and fall. Using their pectoral disc and mouths, they dig large pits to uncover buried prey. The digging of these pits plays an ecologically important role, as they also uncover prey for smaller fish.
In the northern part of its range, round stingrays are preyed upon by the northern elephant seal
Northern Elephant Seal
The northern elephant seal is one of two species of elephant seal . It is a member of the family Phocidae . Elephant seals derive their name from their great size and from the male's large proboscis, which is used in making extraordinarily loud roaring noises, especially during the mating...
and the black sea bass. Other predators include large shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....
s. Numerous parasites are known for the round stingray, comprising 40 species in approximately 19 families. External parasites include copepod
Copepod
Copepods are a group of small crustaceans found in the sea and nearly every freshwater habitat. Some species are planktonic , some are benthic , and some continental species may live in limno-terrestrial habitats and other wet terrestrial places, such as swamps, under leaf fall in wet forests,...
s and leech
Leech
Leeches are segmented worms that belong to the phylum Annelida and comprise the subclass Hirudinea. Like other oligochaetes such as earthworms, leeches share a clitellum and are hermaphrodites. Nevertheless, they differ from other oligochaetes in significant ways...
es, while 16 species of tapeworms are known from its digestive system, including Phyllobothrium hallericola n. sp. and Acanthobothrium olseni. Additional parasites that may be found in this ray's spiral valve intestine
Intestine
In human anatomy, the intestine is the segment of the alimentary canal extending from the pyloric sphincter of the stomach to the anus and, in humans and other mammals, consists of two segments, the small intestine and the large intestine...
include Eimeria chollaensis sp. nov. and Rhinebothrium spp.
As with other stingray
Stingray
The stingrays are a group of rays, which are cartilaginous fishes related to sharks. They are classified in the suborder Myliobatoidei of the order Myliobatiformes, and consist of eight families: Hexatrygonidae , Plesiobatidae , Urolophidae , Urotrygonidae , Dasyatidae , Potamotrygonidae The...
s, the round stingray is ovoviviparous, bearing litters of 1-6 young with an average of 2-3. The litter size increases with female size. The gestation period
Gestation period
For mammals the gestation period is the time in which a fetus develops, beginning with fertilization and ending at birth. The duration of this period varies between species.-Duration:...
is three months, with the young measuring 6-8 cm across at birth. The females able to store sperm
Sperm
The term sperm is derived from the Greek word sperma and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell...
year-round. In southern California, the females move inshore to mate from April to June, with the young being born between June and October. Further south in the Gulf of California
Gulf of California
The Gulf of California is a body of water that separates the Baja California Peninsula from the Mexican mainland...
, females mate and give birth earlier, from late winter to spring. A portion of the population mate and give birth in winter, allowing for a second breeding season later that same year. After giving birth, the adult females move back into deeper water while the young remain in the shallows. Female round stingrays emit a localized positive electric field
Electric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...
from near the spiracle
Spiracle
Spiracles are openings on the surface of some animals that usually lead to respiratory systems.-Vertebrates:The spiracle is a small hole behind each eye that opens to the mouth in some fishes. In the primitive jawless fish the first gill opening immediately behind the mouth is essentially similar...
s behind each eye, which serves to attract males. The males will bite at the area, with successful contact necessary for copulation. Round stingrays grow at 3 cm per year until they reach maturity at around 31 months, at which time their growth rate slows.
Relationship to humans
Due to its small size and large tail spine, the round stingray is considered commercially undesirable. It is occasionally caught (and discarded) by recreational angler
Recreational fishing
Recreational fishing, also called sport fishing, is fishing for pleasure or competition. It can be contrasted with commercial fishing, which is fishing for profit, or subsistence fishing, which is fishing for survival....
s and artisanal
Artisan fishing
Artisan fishing is a term used to describe small scale low-technology commercial or subsistence fishing practices. The term particularly applies to coastal or island ethnic groups using traditional techniques such as rod and tackle, arrows and harpoons, throw nets and drag nets, and traditional...
gillnet
Gillnet
Gillnetting is a common fishing method used by commercial and artisanal fishermen of all the oceans and in some freshwater and estuary areas. The gillnet also is used by fisheries scientists to monitor fish populations. Because gillnets can be so effective their use is closely monitored and...
fisheries. In Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
, the tail is usually cleaved off before the ray is discarded, likely causing high mortality. This species is also taken as bycatch
Bycatch
The term “bycatch” is usually used for fish caught unintentionally in a fishery while intending to catch other fish. It may however also indicate untargeted catch in other forms of animal harvesting or collecting...
by shrimp
Shrimp
Shrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...
trawlers, who consider them a nuisance as large groups often become entangled in the nets. Due to its abundance and relatively high rate of reproduction, the round stingray is assessed as of Least Concern on the IUCN Red List
IUCN Red List
The IUCN Red List of Threatened Species , founded in 1963, is the world's most comprehensive inventory of the global conservation status of biological species. The International Union for Conservation of Nature is the world's main authority on the conservation status of species...
. It is docile and easily approached by divers
Diving
Diving is the sport of jumping or falling into water from a platform or springboard, sometimes while performing acrobatics. Diving is an internationally-recognized sport that is part of the Olympic Games. In addition, unstructured and non-competitive diving is a recreational pastime.Diving is one...
, and adapts readily to display in public aquaria.