Pelagic stingray
Encyclopedia
The pelagic stingray is a species
of stingray
in the family
Dasyatidae, and the sole member of its genus
. It is characterized by the wedge-like shape of its pectoral fin disc, which is much wider than long, as well as by the pointed teeth in both sexes, whip-like tail with extremely long tail spine, and uniform violet to blue-green coloration. It generally reaches 59 cm (23.2 in) in width. The pelagic stingray has a worldwide distribution in waters warmer than 19 °C (66.2 °F), and migrates
seasonally to spend the summer closer to the continental shelf
and at higher latitude
s. The only stingray that almost exclusively inhabits the open ocean, this species is typically found in surface waters down to a depth of 100 m (328.1 ft). As a consequence of its midwater habits, its swimming style has evolved
to feature more of a flapping motion of the pectoral fins, as opposed to the disc margin undulations used by other, bottom-dwelling stingrays.
The diet of the pelagic stingray consists of free-swimming invertebrate
s and bony fishes. It is an active hunter, using its pectoral fins to trap and move food to its mouth, and has been known to take advantage of seasonal feeding opportunities such as spawning squid
. Like other stingrays, it is aplacental viviparous, meaning that the embryo
s are sustained initially by yolk and later by histotroph ("uterine milk"). With a short gestation period
of 2–4 months, females may bear two litters of 4–13 pups per year. Birthing generally occurs in warm water near the equator
, with the exception of the Mediterranean Sea
, with the timing varying between regions. Rarely encountered except by fishery
workers, the pelagic stingray can inflict a severe, even fatal wound with its tail spine. This species is caught as bycatch
throughout its range; it is of little economic value and usually discarded, often with high mortality. However, there is evidence that its numbers are increasing, perhaps owing to the heavy fishing of its natural predators and competitors (e.g., shark
s). Along with the pelagic stingray's global distribution and prolific life history, this has led the International Union for Conservation of Nature (IUCN) to assess it as of Least Concern
.
Charles Lucien Bonaparte
in the 1832 third volume of Iconografia della fauna italica per le quattro classi degli animali vertebrati. He named it Trygon violacea, from the Latin
viola ("purple"), and designated two specimens collected off Italy
as the species syntype
s. The genus Trygon has since been synonymized
with Dasyatis. In 1910, American zoologist Henry Weed Fowler
placed the pelagic stingray in the newly created subgenus Pteroplatytrygon, from the Greek pteron ("fin"), platus ("broad"), and trygon ("stingray"). Later authors elevated Pterplatytrygon to the rank of full genus, though some taxonomists dispute whether this species is distinct enough to warrant separation from Dasyatis.
Lisa Rosenberger's 2001 phylogenetic analysis, based on morphology
, found that the pelagic stingray is one of the more basal members of its family, being the sister taxon
to a clade
that contains Pastinachus
, Dasyatis
, and Indo-Pacific
Himantura
species. Other common name
s for the pelagic stingray include the blue stingray and the violet stingray.
pelagic
waters, between the latitude
s of 52°N and 50°S. In the western Atlantic, it has been reported from the Grand Banks of Newfoundland to North Carolina
, the northern Gulf of Mexico
, and the Lesser Antilles
, Brazil
and Uruguay
. In the eastern Atlantic, this species has been recorded from the North Sea
to Madeira
, including the Mediterranean Sea
, as well as around Cape Verde
, in the Gulf of Guinea
and off South Africa
. In the Pacific, it is known from Japan
to Australia
and New Zealand
in the west, British Columbia
to Chile
in the west, and around many oceanic islands including Hawaii
, the Galápagos
, and Easter Island
. There have been no reports of this species from much of the Indian Ocean
, but it is known to be common in the southwestern portion and around Indonesia
.
Unique amongst stingrays in inhabiting the open ocean rather than the sea floor, the pelagic stingray is generally found from the surface to a depth of 100 m (328.1 ft) over deep water. It has also been caught at a depth of 330–381 m (1,082.7–1,250 ft) over the Kyushu-Palau Ridge
, indicating that it at least occasionally approaches the bottom. This species prefers water temperatures above 19 °C (66.2 °F), and will die if the temperature drops to 15 °C (59 °F).
The pelagic stingray performs seasonal migrations
following warm water masses. In the northwestern Atlantic, it is found in or near the Gulf Stream
from December to April, and moves north of the Stream to gather near the continental shelf
from July to September. A similar migration seems to occur in the Mediterranean, though the specifics are unknown. In the Pacific, this species apparently spends the winter in oceanic waters near the equator
and move into higher latitudes and towards the coast in spring. Two Pacific populations are known: one migrates from near Central America
to California
, and the other from the central Pacific to as far as Japan and British Columbia. Off southeastern Brazil, pelagic stingrays are displaced towards the coast by upwellings of cold water in late spring and summer; in some years they may even be pushed into inshore waters less than 45 m (147.6 ft) deep.
s (paired respiratory
openings) follow immediate behind. There is a short but broad curtain of skin between the nostril
s, with a weakly fringed rear margin. The mouth is small and gently arched, with deep furrows at the corners and a tiny projection at the center of the upper jaw that fits into an indentation on the lower jaw. There are anywhere from 0 to 15 forked papillae (nipple-like structures) in a row across the floor of the mouth. There are 25–34 upper tooth rows and 25–31 lower tooth rows; the teeth of both sexes have single, pointed cusps, but those of adult males are longer and sharper than those of adult females. The margins of the pelvic fins are nearly straight in front and become rounded at the tips and in back.
The whip-like tail measures up to twice as long as the disc; it is thick at the base and tapers significantly to the extremely long, serrated spine placed approximately one-third to halfway along its length. Two spines may be present if a replacement grows in before the original drops off. Posterior to the spine origin, there is a low ventral fin fold that does not reach to the spine tip. Young rays are completely smooth-skinned; with age small prickles appear over the center of the back, as well as a row of small thorns along the midline from between the eyes to the origin of the spine. This species is a plain dark purple to blue-green above, extending onto the tail fold, and a slightly lighter shade below. When captured and handled, it exudes a thick black mucus
that covers its body. The pelagic stingray typically grows to 1.3 m (4.3 ft) long and 59 cm (23.2 in) across. The largest individuals on record are from a captive rearing experiment conducted from 1995 to 2000, in which a male reached 68 cm (26.8 in) across and 12 kg (26.5 lb), and a female 94 cm (37 in) across and 49 kg (108 lb).
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 ray
s. 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 (11.8 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 mechanoreceptor
s that detect nearby movement and ocean current
s, 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 shark
s (Carcharhinus longimanus), great white shark
s (Carcharodon carcharias), toothed whale
s, and other large, ocean-going carnivore
s. 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 monogenea
n Entobdella diadema.
s are represented in its diet: crustacean
s including amphipods, krill
, and larva
l crab
s, molluscs including squid
, octopus
, and pteropods, bony fishes including herring
, mackerel
, sea horses, and filefish
, comb jellies and medusae
, and polychaete worms. Off California, pelagic stingrays hunt large mating aggregations of squid that form from November to April. Off Brazil, this species follows groups of Atlantic cutlassfish
(Trichiurus lepturus) towards the coast in January and February, with both predators seeking small schooling fishes. Juvenile rays consume 6–7% of their body weight in food per day, which declines to just above 1% in adults.
s are at first nourished by yolk, which is later supplanted by histotroph ("uterine
milk", containing protein
s, lipid
s, and mucus
); the mother delivers the histotroph through numerous thread-like extensions of the uterine epithelium
called "trophonemata", which feed into the enlarged spiracles of the embryo. Females have only one functional ovary
and uterus, on the left, and may produce two litters per year. Mating occurs from March to June in the northwestern Atlantic, and in late spring in the southwestern Atlantic. Females are capable of storing sperm
internally for more than a year, allowing them to wait for favorable environmental conditions in which to gestate
their young. When first passed into the uterus, a batch of fertilized eggs are contained in a single membraneous capsule tapered at both ends. Shortly after, the capsule ruptures to release the eggs, and is expelled from the uterus. The gestation period
may be the shortest of any shark or ray, lasting only 2–4 months, during which time the embryos increase a hundredfold in mass
In the Pacific, females give birth in winter from November to March in a nursery area near Central America, prior to their northward migration. Similarly, in the northwestern Atlantic, birthing seems to occur in winter when the females are in warm southerly waters, possibly off the West Indies. However, records also exist of two possibly anomalous females that were pregnant much earlier in the year and would given birth in August or September, before their southward migration. In the southwestern Atlantic, birthing occurs in summer around January, again in warmer water towards the equator. As opposed to other regions, in the Mediterranean females give birth in summer before moving to warmer waters. The litter size ranges from 4 to 13 (average six), and does not increase with the size of the female. Newborns measure 15–25 cm (5.9–9.8 in) across. Rays in captivity, with ample food, grow at an average annual rate of 8.1 cm (3.2 in) (disc width), while rays in the wild grow at an average annual rate of only 1.6 cm (0.62992125984252 in). The food intake and growth rate of adults are highest in January–February and July–August, and lowest in March–April and October–November. Males reach sexual maturity
at 37–50 cm (14.6–19.7 in) across and two years of age, and females at 39–50 cm (15.4–19.7 in) and three years of age. This species may live up to 10–12 years. One of the most prolific rays, its intrinsic population growth rate is up to 31% a year.
days after being stung. This species has been kept in public aquarium
s for almost a century.
The meat and cartilage
of the pelagic stingray are sometimes utilized, for example in Indonesia, but for the most part this species is considered worthless and discarded when caught. Susceptible to longlines, gillnet
s, purse seines, and bottom trawls, it is captured incidentally
in large numbers throughout its range. Rays caught on longlines suffer high mortality, as fishers are wary of being stung and remove the rays from the hooks by smashing them against the side of the boat, causing severe damage to the mouth and jaws. The extent of this bycatch has yet to be quantified. Regardless, surveys in the Pacific suggest that pelagic stingray numbers have increased since the 1950s, possibly due to commercial fisheries
depleting the dominant predators in the ecosystem, such as sharks and tuna
. The lack of population declines, coupled with its wide distribution and high reproductive rate, has led the International Union for Conservation of Nature (IUCN) to list this species under Least Concern
. Recent research has been conducted into reducing pelagic stingray bycatch on longlines by switching to larger and/or "C"-shaped hooks.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of stingray
Myliobatiformes
Myliobatiformes is one of the four orders of batoids, cartilaginous fishes related to sharks. They were formerly included in the order Rajiformes, but more recent phylogenetic studies have shown that the myliobatiforms are a monophyletic group, and that its more derived members evolved their...
in the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Dasyatidae, and the sole member of its genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
. It is characterized by the wedge-like shape of its pectoral fin disc, which is much wider than long, as well as by the pointed teeth in both sexes, whip-like tail with extremely long tail spine, and uniform violet to blue-green coloration. It generally reaches 59 cm (23.2 in) in width. The pelagic stingray has a worldwide distribution in waters warmer than 19 °C (66.2 °F), and migrates
Fish migration
Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousands of kilometres...
seasonally to spend the summer closer to the continental shelf
Continental shelf
The continental shelf is the extended perimeter of each continent and associated coastal plain. Much of the shelf was exposed during glacial periods, but is now submerged under relatively shallow seas and gulfs, and was similarly submerged during other interglacial periods. The continental margin,...
and at higher latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...
s. The only stingray that almost exclusively inhabits the open ocean, this species is typically found in surface waters down to a depth of 100 m (328.1 ft). As a consequence of its midwater habits, its swimming style has evolved
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
to feature more of a flapping motion of the pectoral fins, as opposed to the disc margin undulations used by other, bottom-dwelling stingrays.
The diet of the pelagic stingray consists of free-swimming 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 and bony fishes. It is an active hunter, using its pectoral fins to trap and move food to its mouth, and has been known to take advantage of seasonal feeding opportunities such as spawning squid
Squid
Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...
. Like other stingrays, it is aplacental viviparous, meaning that the embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
s are sustained initially by yolk and later by histotroph ("uterine milk"). With a short 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:...
of 2–4 months, females may bear two litters of 4–13 pups per year. Birthing generally occurs in warm water near the equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....
, with the exception of the Mediterranean Sea
Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...
, with the timing varying between regions. Rarely encountered except by fishery
Fishery
Generally, a fishery is an entity engaged in raising or harvesting fish which is determined by some authority to be a fishery. According to the FAO, a fishery is typically defined in terms of the "people involved, species or type of fish, area of water or seabed, method of fishing, class of boats,...
workers, the pelagic stingray can inflict a severe, even fatal wound with its tail spine. This species is caught 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...
throughout its range; it is of little economic value and usually discarded, often with high mortality. However, there is evidence that its numbers are increasing, perhaps owing to the heavy fishing of its natural predators and competitors (e.g., 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). Along with the pelagic stingray's global distribution and prolific life history, this has led the International Union for Conservation of Nature (IUCN) to assess it as of Least Concern
Least Concern
Least Concern is an IUCN category assigned to extant taxon or lower taxa which have been evaluated but do not qualify for any other category. As such they do not qualify as threatened, Near Threatened, or Conservation Dependent...
.
Taxonomy and phylogeny
The pelagic stingray was originally described by French naturalistNaturalist
Naturalist may refer to:* Practitioner of natural history* Conservationist* Advocate of naturalism * Naturalist , autobiography-See also:* The American Naturalist, periodical* Naturalism...
Charles Lucien Bonaparte
Charles Lucien Bonaparte
Charles Lucien Jules Laurent Bonaparte, 2nd Prince of Canino and Musignano was a French naturalist and ornithologist.-Biography:...
in the 1832 third volume of Iconografia della fauna italica per le quattro classi degli animali vertebrati. He named it Trygon violacea, from the Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
viola ("purple"), and designated two specimens collected off Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
as the species syntype
Syntype
In biological nomenclature, a syntype is a term used to indicate a specimen with a special status.In zoological nomenclature, a syntype is defined as "Each specimen of a type series from which neither a holotype nor a lectotype has been designated [Arts. 72.1.2, 73.2, 74]. The syntypes...
s. The genus Trygon has since been synonymized
Synonym (taxonomy)
In scientific nomenclature, a synonym is a scientific name that is or was used for a taxon of organisms that also goes by a different scientific name. For example, Linnaeus was the first to give a scientific name to the Norway spruce, which he called Pinus abies...
with Dasyatis. In 1910, American zoologist Henry Weed Fowler
Henry Weed Fowler
Henry Weed Fowler was an American zoologist born in Holmesburg, Pennsylvania.He studied at Stanford University under David Starr Jordan...
placed the pelagic stingray in the newly created subgenus Pteroplatytrygon, from the Greek pteron ("fin"), platus ("broad"), and trygon ("stingray"). Later authors elevated Pterplatytrygon to the rank of full genus, though some taxonomists dispute whether this species is distinct enough to warrant separation from Dasyatis.
Lisa Rosenberger's 2001 phylogenetic analysis, based on morphology
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
, found that the pelagic stingray is one of the more basal members of its family, being the sister taxon
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
to a clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
that contains Pastinachus
Pastinachus
Pastinachus is a genus of stingrays in the family Dasyatidae. This genus was long held to be monotypic, containing only the cowtail stingray...
, Dasyatis
Dasyatis
Dasyatis is a genus of stingray. The members of the genus Neotrygon were formerly included in Dasyatis.-Species:...
, and Indo-Pacific
Indo-Pacific
The Indo-Pacific is a biogeographic region of the Earth's seas, comprising the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the seas connecting the two in the general area of Indonesia...
Himantura
Himantura
Himantura is a genus of stingray in the family Dasyatidae, commonly known as the whiprays. They are distinguished from other stingrays by a long, slender tail without tail folds. Himantura species are very morphologically diverse and the genus may be polyphyletic...
species. Other common name
Common name
A common name of a taxon or organism is a name in general use within a community; it is often contrasted with the scientific name for the same organism...
s for the pelagic stingray include the blue stingray and the violet stingray.
Distribution and habitat
The distribution of the pelagic stingray extends nearly worldwide in tropical to warm-temperateTemperate
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...
pelagic
Pelagic zone
Any water in a sea or lake that is not close to the bottom or near to the shore can be said to be in the pelagic zone. The word pelagic comes from the Greek πέλαγος or pélagos, which means "open sea". The pelagic zone can be thought of in terms of an imaginary cylinder or water column that goes...
waters, between the latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...
s of 52°N and 50°S. In the western Atlantic, it has been reported from the Grand Banks of Newfoundland to North Carolina
North Carolina
North Carolina is a state located in the southeastern United States. The state borders South Carolina and Georgia to the south, Tennessee to the west and Virginia to the north. North Carolina contains 100 counties. Its capital is Raleigh, and its largest city is Charlotte...
, the northern Gulf of Mexico
Gulf of Mexico
The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...
, and the Lesser Antilles
Lesser Antilles
The Lesser Antilles are a long, partly volcanic island arc in the Western Hemisphere. Most of its islands form the eastern boundary of the Caribbean Sea with the Atlantic Ocean, with the remainder located in the southern Caribbean just north of South America...
, Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
and Uruguay
Uruguay
Uruguay ,officially the Oriental Republic of Uruguay,sometimes the Eastern Republic of Uruguay; ) is a country in the southeastern part of South America. It is home to some 3.5 million people, of whom 1.8 million live in the capital Montevideo and its metropolitan area...
. In the eastern Atlantic, this species has been recorded from the North Sea
North Sea
In the southwest, beyond the Straits of Dover, the North Sea becomes the English Channel connecting to the Atlantic Ocean. In the east, it connects to the Baltic Sea via the Skagerrak and Kattegat, narrow straits that separate Denmark from Norway and Sweden respectively...
to Madeira
Madeira
Madeira is a Portuguese archipelago that lies between and , just under 400 km north of Tenerife, Canary Islands, in the north Atlantic Ocean and an outermost region of the European Union...
, including the Mediterranean Sea
Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...
, as well as around Cape Verde
Cape Verde
The Republic of Cape Verde is an island country, spanning an archipelago of 10 islands located in the central Atlantic Ocean, 570 kilometres off the coast of Western Africa...
, in the Gulf of Guinea
Gulf of Guinea
The Gulf of Guinea is the northeasternmost part of the tropical Atlantic Ocean between Cape Lopez in Gabon, north and west to Cape Palmas in Liberia. The intersection of the Equator and Prime Meridian is in the gulf....
and off South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
. In the Pacific, it is known from Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
to Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
and New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
in the west, British Columbia
British Columbia
British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...
to Chile
Chile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...
in the west, and around many oceanic islands including Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...
, the Galápagos
Galápagos Islands
The Galápagos Islands are an archipelago of volcanic islands distributed around the equator in the Pacific Ocean, west of continental Ecuador, of which they are a part.The Galápagos Islands and its surrounding waters form an Ecuadorian province, a national park, and a...
, and Easter Island
Easter Island
Easter Island is a Polynesian island in the southeastern Pacific Ocean, at the southeasternmost point of the Polynesian triangle. A special territory of Chile that was annexed in 1888, Easter Island is famous for its 887 extant monumental statues, called moai, created by the early Rapanui people...
. There have been no reports of this species from much of the Indian Ocean
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
, but it is known to be common in the southwestern portion and around Indonesia
Indonesia
Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...
.
Unique amongst stingrays in inhabiting the open ocean rather than the sea floor, the pelagic stingray is generally found from the surface to a depth of 100 m (328.1 ft) over deep water. It has also been caught at a depth of 330–381 m (1,082.7–1,250 ft) over the Kyushu-Palau Ridge
Izu-Bonin-Mariana Arc
The Izu-Bonin-Mariana arc system is an outstanding example of a plate tectonic convergent boundary. IBM extends over 2800 km south from Tokyo, Japan, to beyond Guam, and includes the Izu Islands, Bonin Islands, and Mariana Islands; much more of the IBM arc system is submerged below sealevel...
, indicating that it at least occasionally approaches the bottom. This species prefers water temperatures above 19 °C (66.2 °F), and will die if the temperature drops to 15 °C (59 °F).
The pelagic stingray performs seasonal migrations
Fish migration
Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousands of kilometres...
following warm water masses. In the northwestern Atlantic, it is found in or near the Gulf Stream
Gulf Stream
The Gulf Stream, together with its northern extension towards Europe, the North Atlantic Drift, is a powerful, warm, and swift Atlantic ocean current that originates at the tip of Florida, and follows the eastern coastlines of the United States and Newfoundland before crossing the Atlantic Ocean...
from December to April, and moves north of the Stream to gather near the continental shelf
Continental shelf
The continental shelf is the extended perimeter of each continent and associated coastal plain. Much of the shelf was exposed during glacial periods, but is now submerged under relatively shallow seas and gulfs, and was similarly submerged during other interglacial periods. The continental margin,...
from July to September. A similar migration seems to occur in the Mediterranean, though the specifics are unknown. In the Pacific, this species apparently spends the winter in oceanic waters near the equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....
and move into higher latitudes and towards the coast in spring. Two Pacific populations are known: one migrates from near Central America
Central America
Central America is the central geographic region of the Americas. It is the southernmost, isthmian portion of the North American continent, which connects with South America on the southeast. When considered part of the unified continental model, it is considered a subcontinent...
to 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...
, and the other from the central Pacific to as far as Japan and British Columbia. Off southeastern Brazil, pelagic stingrays are displaced towards the coast by upwellings of cold water in late spring and summer; in some years they may even be pushed into inshore waters less than 45 m (147.6 ft) deep.
Description
The pelagic stingray has a very thick, distinctively wedge-shaped pectoral fin disc one-third wider than long, with broadly curved leading margins, rather angular outer corners, and nearly straight trailing margins. The snout is short with a rounded tip. The eyes are minute and, unlike in other stingrays, do not protrude above the body; the spiracleSpiracle
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 (paired respiratory
Respiration (physiology)
'In physiology, respiration is defined as the transport of oxygen from the outside air to the cells within tissues, and the transport of carbon dioxide in the opposite direction...
openings) follow immediate behind. There is a short but broad curtain of skin between the nostril
Nostril
A nostril is one of the two channels of the nose, from the point where they bifurcate to the external opening. In birds and mammals, they contain branched bones or cartilages called turbinates, whose function is to warm air on inhalation and remove moisture on exhalation...
s, with a weakly fringed rear margin. The mouth is small and gently arched, with deep furrows at the corners and a tiny projection at the center of the upper jaw that fits into an indentation on the lower jaw. There are anywhere from 0 to 15 forked papillae (nipple-like structures) in a row across the floor of the mouth. There are 25–34 upper tooth rows and 25–31 lower tooth rows; the teeth of both sexes have single, pointed cusps, but those of adult males are longer and sharper than those of adult females. The margins of the pelvic fins are nearly straight in front and become rounded at the tips and in back.
The whip-like tail measures up to twice as long as the disc; it is thick at the base and tapers significantly to the extremely long, serrated spine placed approximately one-third to halfway along its length. Two spines may be present if a replacement grows in before the original drops off. Posterior to the spine origin, there is a low ventral fin fold that does not reach to the spine tip. Young rays are completely smooth-skinned; with age small prickles appear over the center of the back, as well as a row of small thorns along the midline from between the eyes to the origin of the spine. This species is a plain dark purple to blue-green above, extending onto the tail fold, and a slightly lighter shade below. When captured and handled, it exudes a thick black mucus
Mucus
In vertebrates, mucus is a slippery secretion produced by, and covering, mucous membranes. Mucous fluid is typically produced from mucous cells found in mucous glands. Mucous cells secrete products that are rich in glycoproteins and water. Mucous fluid may also originate from mixed glands, which...
that covers its body. The pelagic stingray typically grows to 1.3 m (4.3 ft) long and 59 cm (23.2 in) across. The largest individuals on record are from a captive rearing experiment conducted from 1995 to 2000, in which a male reached 68 cm (26.8 in) across and 12 kg (26.5 lb), and a female 94 cm (37 in) across and 49 kg (108 lb).
Biology and ecology
Eagle ray
The eagle rays are a group of cartilaginous fishes in the family Myliobatidae, consisting mostly of large species living in the open ocean rather than on the sea bottom....
s. 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
Electroreception
Electroreception is the biological ability to perceive natural electrical stimuli. It has been observed only in aquatic or amphibious animals, since water is a much better conductor than air. Electroreception is used in electrolocation and for electrocommunication.- Overview :Electroreception is...
ampullae of Lorenzini
Ampullae of Lorenzini
The ampullae of Lorenzini are special sensing organs called electroreceptors, forming a network of jelly-filled pores. They are mostly discussed as being found in cartilaginous fishes ; however, they are also reported to be found in Chondrostei such as Reedfish and sturgeon. Lungfish have also been...
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
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...
of well under 1 nV
Volt
The volt is the SI derived unit for electric potential, electric potential difference, and electromotive force. The volt is named in honor of the Italian physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery.- Definition :A single volt is defined as the...
/cm at a distance of up to 30 cm (11.8 in), and may be able to pick up the minute electric fields produced by moving sea water. The lateral line
Lateral line
The lateral line is a sense organ in aquatic organisms , used to detect movement and vibration in the surrounding water. Lateral lines are usually visible as faint lines running lengthwise down each side, from the vicinity of the gill covers to the base of the tail...
of the pelagic stingray, a complex system of mechanoreceptor
Mechanoreceptor
A mechanoreceptor is a sensory receptor that responds to mechanical pressure or distortion. There are four main types in the glabrous skin of humans: Pacinian corpuscles, Meissner's corpuscles, Merkel's discs, and Ruffini corpuscles...
s that detect nearby movement and ocean current
Ocean current
An ocean current is a continuous, directed movement of ocean water generated by the forces acting upon this mean flow, such as breaking waves, wind, Coriolis effect, cabbeling, temperature and salinity differences and tides caused by the gravitational pull of the Moon and the Sun...
s, 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
Ocean sunfish
The ocean sunfish, Mola mola, or common mola, is the heaviest known bony fish in the world. It has an average adult weight of . The species is native to tropical and temperate waters around the globe. It resembles a fish head with a tail, and its main body is flattened laterally...
(Mola mola), biting and harassing them, particularly if they are hungry. This species is preyed upon by oceanic whitetip shark
Oceanic whitetip shark
The oceanic whitetip shark, Carcharhinus longimanus, is a large pelagic shark inhabiting tropical and warm temperate seas. Its stocky body is most notable for its long, white-tipped, rounded fins....
s (Carcharhinus longimanus), great white shark
Great white shark
The great white shark, scientific name Carcharodon carcharias, also known as the great white, white pointer, white shark, or white death, is a large lamniform shark found in coastal surface waters in all major oceans. It is known for its size, with the largest individuals known to have approached...
s (Carcharodon carcharias), toothed whale
Toothed whale
The toothed whales form a suborder of the cetaceans, including sperm whales, beaked whales, dolphins, and others. As the name suggests, the suborder is characterized by the presence of teeth rather than the baleen of other whales.-Anatomy:Toothed whales have a single blowhole on the top of the head...
s, and other large, ocean-going carnivore
Carnivore
A carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of animal tissue, whether through predation or scavenging...
s. Its all-around dark coloration likely serves to camouflage
Crypsis
In ecology, crypsis is the ability of an organism to avoid observation or detection by other organisms. It may be either a predation strategy or an antipredator adaptation, and methods include camouflage, nocturnality, subterranean lifestyle, transparency, and mimicry...
it against its featureless habitat. The 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...
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 monogenea
Monogenea
Monogenea are a group of largely ectoparasitic members of the flatworm phylum Platyhelminthes, class Monogenea.-Characteristics:Monogenea are very small parasitic flatworms mainly found on skin or gills of fish....
n Entobdella diadema.
Feeding
The pelagic stingray is an active predator that captures prey by wrapping its pectoral fins around it, before manipulating it to the mouth. It is the only stingray in which both sexes have pointed teeth, for grasping and cutting into slippery prey. A wide variety of organismOrganism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
s are represented in its diet: crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s including amphipods, krill
Krill
Krill is the common name given to the order Euphausiacea of shrimp-like marine crustaceans. Also known as euphausiids, these small invertebrates are found in all oceans of the world...
, and larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
l crab
Crab
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, molluscs including squid
Squid
Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...
, octopus
Octopus
The octopus is a cephalopod mollusc of the order Octopoda. Octopuses have two eyes and four pairs of arms, and like other cephalopods they are bilaterally symmetric. An octopus has a hard beak, with its mouth at the center point of the arms...
, and pteropods, bony fishes including herring
Herring
Herring is an oily fish of the genus Clupea, found in the shallow, temperate waters of the North Pacific and the North Atlantic oceans, including the Baltic Sea. Three species of Clupea are recognized. The main taxa, the Atlantic herring and the Pacific herring may each be divided into subspecies...
, mackerel
Mackerel
Mackerel is a common name applied to a number of different species of fish, mostly, but not exclusively, from the family Scombridae. They may be found in all tropical and temperate seas. Most live offshore in the oceanic environment but a few, like the Spanish mackerel , enter bays and can be...
, sea horses, and filefish
Filefish
Filefish are tropical to subtropical tetraodontiform marine fish of the diverse family Monacanthidae. Found in the Atlantic, Pacific and Indian Oceans, the filefish family contains approximately 107 species in 26 genera...
, comb jellies and medusae
Jellyfish
Jellyfish are free-swimming members of the phylum Cnidaria. Medusa is another word for jellyfish, and refers to any free-swimming jellyfish stages in the phylum Cnidaria...
, and polychaete worms. Off California, pelagic stingrays hunt large mating aggregations of squid that form from November to April. Off Brazil, this species follows groups of Atlantic cutlassfish
Largehead hairtail
The largehead hairtail , Trichiurus lepturus, is a member of the cutlassfish family, Trichiuridae. It is a long, slender fish found throughout the tropical and temperate waters of the world...
(Trichiurus lepturus) towards the coast in January and February, with both predators seeking small schooling fishes. Juvenile rays consume 6–7% of their body weight in food per day, which declines to just above 1% in adults.
Life history
Like other stingrays, the pelagic stingray is aplacental viviparous: the developing embryoEmbryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
s are at first nourished by yolk, which is later supplanted by histotroph ("uterine
Uterus
The uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...
milk", containing protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
s, lipid
Lipid
Lipids constitute a broad group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins , monoglycerides, diglycerides, triglycerides, phospholipids, and others...
s, and mucus
Mucus
In vertebrates, mucus is a slippery secretion produced by, and covering, mucous membranes. Mucous fluid is typically produced from mucous cells found in mucous glands. Mucous cells secrete products that are rich in glycoproteins and water. Mucous fluid may also originate from mixed glands, which...
); the mother delivers the histotroph through numerous thread-like extensions of the uterine epithelium
Epithelium
Epithelium is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. Epithelial tissues line the cavities and surfaces of structures throughout the body, and also form many glands. Functions of epithelial cells include secretion, selective...
called "trophonemata", which feed into the enlarged spiracles of the embryo. Females have only one functional ovary
Ovary
The ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in anatomically female individuals are analogous to testes in anatomically male individuals, in that they are both gonads and endocrine glands.-Human anatomy:Ovaries...
and uterus, on the left, and may produce two litters per year. Mating occurs from March to June in the northwestern Atlantic, and in late spring in the southwestern Atlantic. Females are capable of storing 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...
internally for more than a year, allowing them to wait for favorable environmental conditions in which to gestate
Gestation
Gestation is the carrying of an embryo or fetus inside a female viviparous animal. Mammals during pregnancy can have one or more gestations at the same time ....
their young. When first passed into the uterus, a batch of fertilized eggs are contained in a single membraneous capsule tapered at both ends. Shortly after, the capsule ruptures to release the eggs, and is expelled from the uterus. 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:...
may be the shortest of any shark or ray, lasting only 2–4 months, during which time the embryos increase a hundredfold in mass
In the Pacific, females give birth in winter from November to March in a nursery area near Central America, prior to their northward migration. Similarly, in the northwestern Atlantic, birthing seems to occur in winter when the females are in warm southerly waters, possibly off the West Indies. However, records also exist of two possibly anomalous females that were pregnant much earlier in the year and would given birth in August or September, before their southward migration. In the southwestern Atlantic, birthing occurs in summer around January, again in warmer water towards the equator. As opposed to other regions, in the Mediterranean females give birth in summer before moving to warmer waters. The litter size ranges from 4 to 13 (average six), and does not increase with the size of the female. Newborns measure 15–25 cm (5.9–9.8 in) across. Rays in captivity, with ample food, grow at an average annual rate of 8.1 cm (3.2 in) (disc width), while rays in the wild grow at an average annual rate of only 1.6 cm (0.62992125984252 in). The food intake and growth rate of adults are highest in January–February and July–August, and lowest in March–April and October–November. Males reach sexual maturity
Sexual maturity
Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...
at 37–50 cm (14.6–19.7 in) across and two years of age, and females at 39–50 cm (15.4–19.7 in) and three years of age. This species may live up to 10–12 years. One of the most prolific rays, its intrinsic population growth rate is up to 31% a year.
Human interactions
The pelagic stingray is not aggressive and rarely encountered because of its habitat preferences, but its very long tail spine demands extreme caution be exercised in handling it. It has been responsible for two known fatalities: a worker on a tuna longliner who was impaled by a captured ray, and another fishery worker who succumbed to tetanusTetanus
Tetanus is a medical condition characterized by a prolonged contraction of skeletal muscle fibers. The primary symptoms are caused by tetanospasmin, a neurotoxin produced by the Gram-positive, rod-shaped, obligate anaerobic bacterium Clostridium tetani...
days after being stung. This species has been kept in public aquarium
Public aquarium
A public aquarium is the aquatic counterpart of a zoo, housing living aquatic species for viewing. Most public aquariums feature tanks larger than those kept by home aquarists, as well as smaller tanks. Since the first public aquariums were built in the mid-19th century, they have become popular...
s for almost a century.
The meat and cartilage
Cartilage
Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...
of the pelagic stingray are sometimes utilized, for example in Indonesia, but for the most part this species is considered worthless and discarded when caught. Susceptible to longlines, 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...
s, purse seines, and bottom trawls, it is captured incidentally
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...
in large numbers throughout its range. Rays caught on longlines suffer high mortality, as fishers are wary of being stung and remove the rays from the hooks by smashing them against the side of the boat, causing severe damage to the mouth and jaws. The extent of this bycatch has yet to be quantified. Regardless, surveys in the Pacific suggest that pelagic stingray numbers have increased since the 1950s, possibly due to commercial fisheries
Commercial fishing
Commercial fishing is the activity of catching fish and other seafood for commercial profit, mostly from wild fisheries. It provides a large quantity of food to many countries around the world, but those who practice it as an industry must often pursue fish far into the ocean under adverse conditions...
depleting the dominant predators in the ecosystem, such as sharks and tuna
Tuna
Tuna is a salt water fish from the family Scombridae, mostly in the genus Thunnus. Tuna are fast swimmers, and some species are capable of speeds of . Unlike most fish, which have white flesh, the muscle tissue of tuna ranges from pink to dark red. The red coloration derives from myoglobin, an...
. The lack of population declines, coupled with its wide distribution and high reproductive rate, has led the International Union for Conservation of Nature (IUCN) to list this species under Least Concern
Least Concern
Least Concern is an IUCN category assigned to extant taxon or lower taxa which have been evaluated but do not qualify for any other category. As such they do not qualify as threatened, Near Threatened, or Conservation Dependent...
. Recent research has been conducted into reducing pelagic stingray bycatch on longlines by switching to larger and/or "C"-shaped hooks.