Spiny butterfly ray
Encyclopedia
The spiny butterfly ray or giant butterfly ray, Gymnura altavela, is a species of butterfly ray
, family Gymnuridae, native to the shallow coastal waters of the Atlantic Ocean
. A large ray that can measure over 2 meters (6 ft) across, it may be distinguished from the sympatric smooth butterfly ray
(G. micrura) by the spine at the base of its tail
and by a small tentacular
structure on the margin of each spiracle
. Slow-reproducing and valued for its meat
, in recent decades its population has experienced a decline of over 30%, and it has become Critically Endangered
in certain parts of its range.
This species has a patchy and discontinuous distribution in Atlantic tropical and warm-temperate
waters. In the western Atlantic it is found from Massachusetts
, USA to Buenos Aires Province
, Argentina
; it is rare in the Gulf of Mexico
and common in the mouths of tidal creeks along the Virginia
coast. In the eastern Atlantic, it is found from Portugal
to Ambriz
, Angola
, including the Mediterranean Sea
, the Black Sea
, and the Madeira
and Canary Islands
. It is found in shallow brackish and coastal waters over soft sandy or muddy subsubstrates, at a depth of 5–100 meters (16–330 ft). This ray is uncommon overall but can be locally abundant in suitable habitat. Individuals may segregate by sex, with females usually staying in deeper water but moving inshore to breed.
-shaped pectoral fin disk much wider than it is long, with concave front margins and abruptly rounded corners. The snout
is short and blunt. The teeth have high, conical cusp
s, numbering 98-138 rows in the upper jaw and 78-110 rows in the lower jaw. In both jaws there are 10-12 functional tooth rows with each dental band occupying 70% the width of the jaw. There is a tentacle-like structure on the inner posterior margin of each spiracle. The tail
is short and slender, measuring a quarter the disk width, with upper and lower fin folds. There are one or more serrated spines at the base of the tail.
The skin
is naked in juveniles and subadults, while adults develop a patch of denticles on the center of the disk. The coloration is dark brown above, sometimes with small lighter or darker spots and blotches in a marbled pattern, and white below. Juveniles have pale crossbars on the tail. The maximum reported size is 2.2 meters (7.2 ft) disk width in the northwest Atlantic, though there are unsubstantiated reports of rays over 4 m (13 ft) off West Africa
. The maximum published weight is 60 kg (130 lbs).
es, including Leiognathus and small shark
s, and squid
s. Off Tunisia
, they feed on crustaceans, teleosts, cephalopod
s, lamellibranchs, and gastropods, in descending order of importance. Teleost fishes apparently become more important in the ray's diet with increasing size. An active predator, the ray typically approaches a prey item slowly before rapidly spinning around over it and striking the food with the leading edge of one of their pectoral fins. This behavior likely serves to stun the prey before capture, as the pectoral fins of butterfly rays contain a high proportion of red muscle and can deliver blows of substantial force.
Potential predators of spiny butterfly rays include larger fish such as the great hammerhead
(Sphyrna mokarran), and marine mammal
s. In the northwest Atlantic, the depletion of seven large shark species by commercial fisheries has led to an increase in the population of the spiny butterfly ray and other mid-level predators. Known parasites of this species include the tapeworms Anthobothrium altavelae and Pterobothrioides petterae, and the gill parasite Heteronchocotyle gymnurae.
Spiny butterfly rays are ovoviviparous and give birth to live young. They have an annual reproductive cycle with a gestation period
of 4 to 9 months. The embryo
s initially subsist on a yolk sac
; later in development long villi develop from the uterine wall into the embryos' spiracles, which direct uterine milk into the oral cavity. Litter size is up to 8, depending on geographical location: 4 per litter in the Gulf of Mexico, 1-6 in the Mediterranean, up to 5 off Brazil, and up to 8 in the northwest Atlantic. Females have one functional ovary
(the left) and two functional uterus
es, with the embryo
s evenly distributed in each one. The newborns measure 38–44 cm (15–17 in) across; their size is inversely related to the number of young in each uterus. In the eastern Atlantic, males mature at around 78 cm (31 in) across and females at 108 cm (43 in). In the western Atlantic, males mature at around 102 cm (40 in) across and females at 155 cm (61 in). Females mature later than males and reach a larger size.
in some regions. The meat of this species is highly regarded and it is caught for human consumption, except for in the waters off the United States where it is not targeted by commercial fisheries and is rarely taken as bycatch
. Thus, there it is assessed as of Least Concern
by the World Conservation Union
.
Elsewhere in the spiny butterfly ray's range, it faces heavy fishing pressure, including in its coastal nursery areas, and has experienced marked declines. It is assessed as Critically Endangered in the southwest Atlantic, where it is taken by multispecies trawls, beach-seines, and recreational fishers
. Off southern Brazil, catch rates have declined by 99% since 1982, due to fishing occurring year-round. This species is also Critically Endangered in the Mediterranean, where it is now rare or absent throughout its entire former range, especially along the southern shore such as off Sicily
. The comprehensive Mediterranean International Trawl Surveys (MITS) since 1994 have failed to recover any specimens, indicating a massive decline in numbers. In West Africa, this species is assessed as Vulnerable; it is taken intentionally or incidentally by gillnet
s, shrimp trawls, longlines, and handlines. Reports from artisan fisher
s and other observers from Mauritania
to Guinea
have reported a severe drop in abundance, as well as decreasing median size as the adults are removed.
Butterfly ray
The butterfly rays are a group of rays forming the genus Gymnura and the family Gymnuridae. They are found in warm oceans worldwide, and occasionally in estuaries....
, family Gymnuridae, native to the shallow coastal waters of the Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
. A large ray that can measure over 2 meters (6 ft) across, it may be distinguished from the sympatric smooth butterfly ray
Smooth butterfly ray
The smooth butterfly ray is a species of fish in the Gymnuridae family. It is found in Belize, Brazil, Cameroon, Colombia, the Democratic Republic of the Congo, Costa Rica, French Guiana, Gambia, Guatemala, Guyana, Honduras, Mexico, Nicaragua, Panama, Senegal, Sierra Leone, Suriname, Trinidad and...
(G. micrura) by the spine at the base of its tail
Tail
The tail is the section at the rear end of an animal's body; in general, the term refers to a distinct, flexible appendage to the torso. It is the part of the body that corresponds roughly to the sacrum and coccyx in mammals, reptiles, and birds...
and by a small tentacular
Tentacle
A tentacle or bothrium is one of usually two or more elongated flexible organs present in animals, especially invertebrates. The term may also refer to the hairs of the leaves of some insectivorous plants. Usually, tentacles are used for feeding, feeling and grasping. Anatomically, they work like...
structure on the margin of each 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...
. Slow-reproducing and valued for its meat
Meat
Meat is animal flesh that is used as food. Most often, this means the skeletal muscle and associated fat and other tissues, but it may also describe other edible tissues such as organs and offal...
, in recent decades its population has experienced a decline of over 30%, and it has become Critically Endangered
Critically Endangered
Critically Endangered is the highest risk category assigned by the IUCN Red List for wild species. Critically Endangered means that a species' numbers have decreased, or will decrease, by 80% within three generations....
in certain parts of its range.
Distribution and habitat
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. In the western Atlantic it is found from Massachusetts
Massachusetts
The Commonwealth of Massachusetts is a state in the New England region of the northeastern United States of America. It is bordered by Rhode Island and Connecticut to the south, New York to the west, and Vermont and New Hampshire to the north; at its east lies the Atlantic Ocean. As of the 2010...
, USA to Buenos Aires Province
Buenos Aires Province
The Province of Buenos Aires is the largest and most populous province of Argentina. It takes the name from the city of Buenos Aires, which used to be the provincial capital until it was federalized in 1880...
, Argentina
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...
; it is rare in the 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 common in the mouths of tidal creeks along the Virginia
Virginia
The Commonwealth of Virginia , is a U.S. state on the Atlantic Coast of the Southern United States. Virginia is nicknamed the "Old Dominion" and sometimes the "Mother of Presidents" after the eight U.S. presidents born there...
coast. In the eastern Atlantic, it is found from Portugal
Portugal
Portugal , officially the Portuguese Republic is a country situated in southwestern Europe on the Iberian Peninsula. Portugal is the westernmost country of Europe, and is bordered by the Atlantic Ocean to the West and South and by Spain to the North and East. The Atlantic archipelagos of the...
to Ambriz
Ambriz
Ambriz is a city, commune and municipality in Bengo Province, Angola.The population of Ambriz is majority Bakongo, with some Portuguese descedents.Also, the population also includes Ovimbundu and Kimbundu....
, Angola
Angola
Angola, officially the Republic of Angola , is a country in south-central Africa bordered by Namibia on the south, the Democratic Republic of the Congo on the north, and Zambia on the east; its west coast is on the Atlantic Ocean with Luanda as its capital city...
, 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...
, the Black Sea
Black Sea
The Black Sea is bounded by Europe, Anatolia and the Caucasus and is ultimately connected to the Atlantic Ocean via the Mediterranean and the Aegean seas and various straits. The Bosphorus strait connects it to the Sea of Marmara, and the strait of the Dardanelles connects that sea to the Aegean...
, and the 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...
and Canary Islands
Canary Islands
The Canary Islands , also known as the Canaries , is a Spanish archipelago located just off the northwest coast of mainland Africa, 100 km west of the border between Morocco and the Western Sahara. The Canaries are a Spanish autonomous community and an outermost region of the European Union...
. It is found in shallow brackish and coastal waters over soft sandy or muddy subsubstrates, at a depth of 5–100 meters (16–330 ft). This ray is uncommon overall but can be locally abundant in suitable habitat. Individuals may segregate by sex, with females usually staying in deeper water but moving inshore to breed.
Description
The spiny butterfly ray has a very broad, lozengeLozenge
A lozenge , often referred to as a diamond, is a form of rhombus. The definition of lozenge is not strictly fixed, and it is sometimes used simply as a synonym for rhombus. Most often, though, lozenge refers to a thin rhombus—a rhombus with acute angles of 45°...
-shaped pectoral fin disk much wider than it is long, with concave front margins and abruptly rounded corners. The snout
Snout
The snout, or muzzle, is the protruding portion of an animal's face, consisting of its nose, mouth, and jaw.-Terminology:The term "muzzle", used as a noun, can be ambiguous...
is short and blunt. The teeth have high, conical cusp
Cusp (dentistry)
A cusp is an occlusal or incisal eminence on a tooth.Canine teeth, otherwise known as cuspids, each possess a single cusp, while premolars, otherwise known as bicuspids, possess two each. Molars normally possess either four or five cusps...
s, numbering 98-138 rows in the upper jaw and 78-110 rows in the lower jaw. In both jaws there are 10-12 functional tooth rows with each dental band occupying 70% the width of the jaw. There is a tentacle-like structure on the inner posterior margin of each spiracle. The tail
Tail
The tail is the section at the rear end of an animal's body; in general, the term refers to a distinct, flexible appendage to the torso. It is the part of the body that corresponds roughly to the sacrum and coccyx in mammals, reptiles, and birds...
is short and slender, measuring a quarter the disk width, with upper and lower fin folds. There are one or more serrated spines at the base of the tail.
The skin
Skin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
is naked in juveniles and subadults, while adults develop a patch of denticles on the center of the disk. The coloration is dark brown above, sometimes with small lighter or darker spots and blotches in a marbled pattern, and white below. Juveniles have pale crossbars on the tail. The maximum reported size is 2.2 meters (7.2 ft) disk width in the northwest Atlantic, though there are unsubstantiated reports of rays over 4 m (13 ft) off West Africa
West Africa
West Africa or Western Africa is the westernmost region of the African continent. Geopolitically, the UN definition of Western Africa includes the following 16 countries and an area of approximately 5 million square km:-Flags of West Africa:...
. The maximum published weight is 60 kg (130 lbs).
Biology and ecology
In the western Atlantic, the spiny butterfly ray feeds on fishFish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
es, including Leiognathus and small 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, and 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...
s. Off Tunisia
Tunisia
Tunisia , officially the Tunisian RepublicThe long name of Tunisia in other languages used in the country is: , is the northernmost country in Africa. It is a Maghreb country and is bordered by Algeria to the west, Libya to the southeast, and the Mediterranean Sea to the north and east. Its area...
, they feed on crustaceans, teleosts, cephalopod
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...
s, lamellibranchs, and gastropods, in descending order of importance. Teleost fishes apparently become more important in the ray's diet with increasing size. An active predator, the ray typically approaches a prey item slowly before rapidly spinning around over it and striking the food with the leading edge of one of their pectoral fins. This behavior likely serves to stun the prey before capture, as the pectoral fins of butterfly rays contain a high proportion of red muscle and can deliver blows of substantial force.
Potential predators of spiny butterfly rays include larger fish such as the great hammerhead
Great hammerhead
The great hammerhead is the largest species of hammerhead shark, family Sphyrnidae, attaining a maximum length of 6.1 m . It is found in tropical and warm temperate waters worldwide, inhabiting coastal areas and the continental shelf...
(Sphyrna mokarran), and marine mammal
Marine mammal
Marine mammals, which include seals, whales, dolphins, and walruses, form a diverse group of 128 species that rely on the ocean for their existence. They do not represent a distinct biological grouping, but rather are unified by their reliance on the marine environment for feeding. The level of...
s. In the northwest Atlantic, the depletion of seven large shark species by commercial fisheries has led to an increase in the population of the spiny butterfly ray and other mid-level predators. Known parasites of this species include the tapeworms Anthobothrium altavelae and Pterobothrioides petterae, and the gill parasite Heteronchocotyle gymnurae.
Spiny butterfly rays are ovoviviparous and give birth to live young. They have an annual reproductive cycle with a 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 4 to 9 months. 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 initially subsist on a yolk sac
Yolk sac
The yolk sac is a membranous sac attached to an embryo, providing early nourishment in the form of yolk in bony fishes, sharks, reptiles, birds, and primitive mammals...
; later in development long villi develop from the uterine wall into the embryos' spiracles, which direct uterine milk into the oral cavity. Litter size is up to 8, depending on geographical location: 4 per litter in the Gulf of Mexico, 1-6 in the Mediterranean, up to 5 off Brazil, and up to 8 in the northwest Atlantic. Females have 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...
(the left) and two functional uterus
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...
es, with 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 evenly distributed in each one. The newborns measure 38–44 cm (15–17 in) across; their size is inversely related to the number of young in each uterus. In the eastern Atlantic, males mature at around 78 cm (31 in) across and females at 108 cm (43 in). In the western Atlantic, males mature at around 102 cm (40 in) across and females at 155 cm (61 in). Females mature later than males and reach a larger size.
Relationship to humans
Spiny butterfly rays are harmless to humans, though if stepped on its tail spine can cause a painful wound. It is listed as a game fishGame fish
Game fish are fish pursued for sport by recreational anglers. They can be freshwater or marine fish. Game fish can be eaten after being caught, though increasingly anglers practise catch and release to improve fish populations. Some game fish are also targeted commercially, particularly...
in some regions. The meat of this species is highly regarded and it is caught for human consumption, except for in the waters off the United States where it is not targeted by commercial fisheries and is rarely 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...
. Thus, there it is assessed 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...
by the World Conservation Union
World Conservation Union
The International Union for Conservation of Nature and Natural Resources is an international organization dedicated to finding "pragmatic solutions to our most pressing environment and development challenges." The organization publishes the IUCN Red List, compiling information from a network of...
.
Elsewhere in the spiny butterfly ray's range, it faces heavy fishing pressure, including in its coastal nursery areas, and has experienced marked declines. It is assessed as Critically Endangered in the southwest Atlantic, where it is taken by multispecies trawls, beach-seines, and recreational fishers
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....
. Off southern Brazil, catch rates have declined by 99% since 1982, due to fishing occurring year-round. This species is also Critically Endangered in the Mediterranean, where it is now rare or absent throughout its entire former range, especially along the southern shore such as off Sicily
Sicily
Sicily is a region of Italy, and is the largest island in the Mediterranean Sea. Along with the surrounding minor islands, it constitutes an autonomous region of Italy, the Regione Autonoma Siciliana Sicily has a rich and unique culture, especially with regard to the arts, music, literature,...
. The comprehensive Mediterranean International Trawl Surveys (MITS) since 1994 have failed to recover any specimens, indicating a massive decline in numbers. In West Africa, this species is assessed as Vulnerable; it is taken intentionally or incidentally by 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, shrimp trawls, longlines, and handlines. Reports from artisan fisher
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...
s and other observers from Mauritania
Mauritania
Mauritania is a country in the Maghreb and West Africa. It is bordered by the Atlantic Ocean in the west, by Western Sahara in the north, by Algeria in the northeast, by Mali in the east and southeast, and by Senegal in the southwest...
to Guinea
Guinea
Guinea , officially the Republic of Guinea , is a country in West Africa. Formerly known as French Guinea , it is today sometimes called Guinea-Conakry to distinguish it from its neighbour Guinea-Bissau. Guinea is divided into eight administrative regions and subdivided into thirty-three prefectures...
have reported a severe drop in abundance, as well as decreasing median size as the adults are removed.