Big skate
Encyclopedia
The big skate is the largest species of skate
, family Rajidae, in the waters off North America
. They are found along the Pacific coast from Alaska
to Baja California
, typically from the intertidal zone
to a depth of 120 m (393.7 ft), and feed on benthic invertebrate
s and small fish
es. They are unusual among skates in that their egg cases may contain up to seven eggs each. This species is one of the most commercially important skates off California and is sold for food.
This species was described by Charles Frédéric Girard
in 1855; its specific epithet binoculata is derived from the Latin
bi meaning "two", and oculatus meaning "eyed", referring to the two prominent eyespots on its wings. Girard also described what would later be determined to be a junior synonym of R. binoculata, R. cooperi, based on notes made by James G. Cooper on a decaying big skate found ashore near the entrance of Shoalwater Bay
, Washington. In some older literature this species is placed in the genus Dipturus
.
, from the eastern Bering Sea
and the Aleutian Islands, as far south as Cedros Island
off central Baja California
. It is rare south of Point Conception
, California
. It occurs in coast
al bay
s, estuaries, and over the continental shelf
, usually on sandy or muddy bottoms but occasionally on low strands of kelp
. Though reported to a depth of 800 m (2,624.7 ft), it is usually found no deeper than 120 m (393.7 ft). It frequents progressively shallower water in the northern parts of its range. This species is abundant off British Columbia
, where it prefers a depth of 26–33 meters (85–108 ft) and a temperature of 7.6–9.4 °C (45.7–48.9 F).
. The eyes are small and placed just ahead of the large spiracle
s. The teeth are small with raised cusp
s, numbering 24-48 rows in the upper jaw and 22-45 in the lower. There are two small dorsal fin
s on the tail, the anal fin is absent, and the caudal fin is reduced to a simple fold. There is a weak notch in each pelvic fin.
Juveniles have smooth skin
, while adults have small prickles on the dorsal surface and the underside on the snout, between the gill slit
s, and on the abdominal region
. There are 2-3 thorns on the middle of the back, a row of 12-55 (usually 13-17) thorns along the midline of the tail, and an interdorsal thorn. Some older individuals have a thorn above each eye. The back is colored a mottled brown to reddish brown, olive-brown, or gray, with rosettes of small white spots or scattered dark blotches. There are two large dark spots with pale borders, one on each wing. The ventral side is white, sometimes with dark spots or blotches.
Big skates are usually seen buried in sediment with only their eyes showing. They feed on polychaete worms, molluscs, crustacean
s, and small benthic fish
es. Polychaetes and molluscs comprise a slightly greater percentage of the diet of younger individuals. A known predator of big skates is the broadnose sevengill shark
(Notorhynchus cepedianus); the eyespots on the skates' wings are believed to serve as decoys to confuse predators. Juvenile northern elephant seal
s (Mirounga angustirostris) are known to consume the egg cases of the big skate. Known parasites of the big skate include the copepod
Lepeophtheirus cuneifer.
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This species is oviparous, and is one of the few skate species that typically have more than one embryo
within each egg capsule, commonly called "mermaid's purse
s" when they are found washed up on beaches. The egg capsule of a big skate is the largest of any skate, measuring 23–31 cm (9.1–12.2 in) long and 11–19 cm (4.3–7.5 in) wide. Each capsule is oblong in shape and has a highly arched dorsal surface, nearly flat ventral surface, and parallel lateral edges that become somewhat concave towards the center of the case. At the corners of the case, there are four blunt, broad horns with the posterior pair being slightly longer. A single egg capsule may contain 1-7 (usually 3-4) eggs.
The female deposits her eggs in pairs on sandy or muddy flats; there is no discrete breeding season
and egg-laying occurs year-round. Females may utilize discrete spawning beds, as large numbers of egg cases have been found in certain localized areas. The young emerge after 9 months and measure 18–23 cm (7.1–9.1 in). Female big skates mature at 1.3 metre long and 12–13 years old, while males mature at 0.9 metre long and 7–8 years old. The growth rate of big skates in the Gulf of Alaska
are comparable to those off California, but differ from those off British Columbia. The lifespans
of big skates off Alaska are up to 15 years, while those off British Columbia are up to 26 years.
, who usually release or discard them. It adapts well to captivity and is often displayed in public aquaria. This species is one of the three most important skates fished off the coast of California
, though compared to other commercial fisheries
it is of only minor importance. This species is usually taken as bycatch
in bottom trawls; the pectoral fins are sold as "skate wings" and are eaten baked or fried. In the 1990s, the market value of skate wings rose to $0.40-$1.00 USD per pound, and catches of the big skate off California increased tenfold as the trawl fishery began marketing its skate and ray bycatch. In 2003, a targeted fishery for the big skate and the longnose skate (Raja rhina) commenced in the Gulf of Alaska
. Population data following this increased exploitation is lacking, but the big skate's slow reproductive rate has led it to be assessed as Near Threatened
by the World Conservation Union
.
Skate
Skates are cartilaginous fish belonging to the family Rajidae in the superorder Batoidea of rays. There are more than 200 described species in 27 genera. There are two subfamilies, Rajinae and Arhynchobatinae ....
, family Rajidae, in the waters off North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
. They are found along the Pacific coast from Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
to Baja California
Baja California
Baja California officially Estado Libre y Soberano de Baja California is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is both the northernmost and westernmost state of Mexico. Before becoming a state in 1953, the area was known as the North...
, typically from the intertidal zone
Intertidal zone
The intertidal zone is the area that is above water at low tide and under water at high tide . This area can include many different types of habitats, with many types of animals like starfish, sea urchins, and some species of coral...
to a depth of 120 m (393.7 ft), and feed 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 and small fish
Fish
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. They are unusual among skates in that their egg cases may contain up to seven eggs each. This species is one of the most commercially important skates off California and is sold for food.
This species was described by Charles Frédéric Girard
Charles Frédéric Girard
Charles Frédéric Girard was a French biologist specializing in ichthyology and herpetology.Born in Mulhouse, France, he studied at the College of Neuchâtel, Switzerland as a student of Louis Agassiz. In 1847, he accompanied Agassiz as his assistant to Harvard...
in 1855; its specific epithet binoculata is derived 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...
bi meaning "two", and oculatus meaning "eyed", referring to the two prominent eyespots on its wings. Girard also described what would later be determined to be a junior synonym of R. binoculata, R. cooperi, based on notes made by James G. Cooper on a decaying big skate found ashore near the entrance of Shoalwater Bay
Shoalwater Bay
Shoalwater Bay is a large bay on the central coast of Queensland, Australia, located 100 km north of the coastal town of Yeppoon and 628 km north-north-west of the state capital, Brisbane. Since 1966, the land surrounding Shoalwater Bay has been under the ownership of the Australian Defence Force,...
, Washington. In some older literature this species is placed in the genus Dipturus
Dipturus
Dipturus is a large genus of skates in the family Rajidae. It currently has 49 described species.-Species:* Dipturus acrobelus Last, W. T. White & Pogonoski, 2008 * Dipturus apricus Last, W. T...
.
Distribution and habitat
The big skate is found in the northeastern Pacific OceanPacific 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...
, from the eastern Bering Sea
Bering Sea
The Bering Sea is a marginal sea of the Pacific Ocean. It comprises a deep water basin, which then rises through a narrow slope into the shallower water above the continental shelves....
and the Aleutian Islands, as far south as Cedros Island
Cedros Island
Cedros Island is a Mexican island in the Pacific Ocean....
off central Baja California
Baja California
Baja California officially Estado Libre y Soberano de Baja California is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is both the northernmost and westernmost state of Mexico. Before becoming a state in 1953, the area was known as the North...
. It is rare south of Point Conception
Point Conception
Point Conception is a headland along the Pacific coast of U.S. state of California, located in southwestern Santa Barbara County. It is the point where the Santa Barbara Channel meets the Pacific Ocean, and as the corner between the mostly north-south trending portion of coast to the north and the...
, 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 occurs in coast
Coast
A coastline or seashore is the area where land meets the sea or ocean. A precise line that can be called a coastline cannot be determined due to the dynamic nature of tides. The term "coastal zone" can be used instead, which is a spatial zone where interaction of the sea and land processes occurs...
al bay
Bay
A bay is an area of water mostly surrounded by land. Bays generally have calmer waters than the surrounding sea, due to the surrounding land blocking some waves and often reducing winds. Bays also exist as an inlet in a lake or pond. A large bay may be called a gulf, a sea, a sound, or a bight...
s, estuaries, and over 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,...
, usually on sandy or muddy bottoms but occasionally on low strands of kelp
Kelp
Kelps are large seaweeds belonging to the brown algae in the order Laminariales. There are about 30 different genera....
. Though reported to a depth of 800 m (2,624.7 ft), it is usually found no deeper than 120 m (393.7 ft). It frequents progressively shallower water in the northern parts of its range. This species is abundant off 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...
, where it prefers a depth of 26–33 meters (85–108 ft) and a temperature of 7.6–9.4 °C (45.7–48.9 F).
Description
The maximum known length of a big skate is 2.4 m (7.9 ft), though this species usually does not exceed 1.8 m (5.9 ft) and 91 kg (200.6 lb). This species has a flattened, diamond-shaped pectoral fin disk slightly wider than it is long, with a long, moderately pointed snoutSnout
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...
. The eyes are small and placed just ahead of the large 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. The teeth are small with raised 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 24-48 rows in the upper jaw and 22-45 in the lower. There are two small dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
s on the tail, the anal fin is absent, and the caudal fin is reduced to a simple fold. There is a weak notch in each pelvic fin.
Juveniles have smooth 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...
, while adults have small prickles on the dorsal surface and the underside on the snout, between the gill slit
Gill slit
Gill slits are individual openings to gills, i.e., multiple gill arches, which lack a single outer cover. Such gills are characteristic of Cartilaginous fish such as sharks, rays, sawfish, and guitarfish. Most of these have five pairs, but a few species have 6 or 7 pairs...
s, and on the abdominal region
Abdomen
In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...
. There are 2-3 thorns on the middle of the back, a row of 12-55 (usually 13-17) thorns along the midline of the tail, and an interdorsal thorn. Some older individuals have a thorn above each eye. The back is colored a mottled brown to reddish brown, olive-brown, or gray, with rosettes of small white spots or scattered dark blotches. There are two large dark spots with pale borders, one on each wing. The ventral side is white, sometimes with dark spots or blotches.
Biology and ecology
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, and small benthic fish
Fish
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. Polychaetes and molluscs comprise a slightly greater percentage of the diet of younger individuals. A known predator of big skates is the broadnose sevengill shark
Broadnose sevengill shark
The broadnose sevengill shark is the only extant member of the genus Notorynchus, in the family Hexanchidae. It is recognizable because of its seven gill slits, while most shark species have five gill slits, with the exception of the members of the order Hexanchiformes and the sixgill sawshark.The...
(Notorhynchus cepedianus); the eyespots on the skates' wings are believed to serve as decoys to confuse predators. Juvenile 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...
s (Mirounga angustirostris) are known to consume the egg cases of the big skate. Known parasites of the big skate include the 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,...
Lepeophtheirus cuneifer.
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...
within each egg capsule, commonly called "mermaid's purse
Mermaid's purse
An egg case or egg capsule, colloquially known as a mermaid's purse or devil's purse, is a casing that surrounds the fertilized eggs of some sharks, skates, and chimaeras. They are among the common objects which are washed up by the sea. They are made of collagen protein strands...
s" when they are found washed up on beaches. The egg capsule of a big skate is the largest of any skate, measuring 23–31 cm (9.1–12.2 in) long and 11–19 cm (4.3–7.5 in) wide. Each capsule is oblong in shape and has a highly arched dorsal surface, nearly flat ventral surface, and parallel lateral edges that become somewhat concave towards the center of the case. At the corners of the case, there are four blunt, broad horns with the posterior pair being slightly longer. A single egg capsule may contain 1-7 (usually 3-4) eggs.
The female deposits her eggs in pairs on sandy or muddy flats; there is no discrete breeding season
Breeding season
The breeding season is the most suitable season, usually with favourable conditions and abundant food and water, for breeding among some wild animals and birds . Species with a breeding season have naturally evolved to have sexual intercourse during a certain time of year in order to achieve the...
and egg-laying occurs year-round. Females may utilize discrete spawning beds, as large numbers of egg cases have been found in certain localized areas. The young emerge after 9 months and measure 18–23 cm (7.1–9.1 in). Female big skates mature at 1.3 metre long and 12–13 years old, while males mature at 0.9 metre long and 7–8 years old. The growth rate of big skates in the Gulf of Alaska
Gulf of Alaska
The Gulf of Alaska is an arm of the Pacific Ocean defined by the curve of the southern coast of Alaska, stretching from the Alaska Peninsula and Kodiak Island in the west to the Alexander Archipelago in the east, where Glacier Bay and the Inside Passage are found.The entire shoreline of the Gulf is...
are comparable to those off California, but differ from those off British Columbia. The lifespans
Maximum life span
Maximum life span is a measure of the maximum amount of time one or more members of a population has been observed to survive between birth and death.Most living species have at least one upper limit on the number of times cells can divide...
of big skates off Alaska are up to 15 years, while those off British Columbia are up to 26 years.
Relationship to humans
The big skate is frequently caught by recreational anglersRecreational 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....
, who usually release or discard them. It adapts well to captivity and is often displayed in public aquaria. This species is one of the three most important skates fished off the coast of 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...
, though compared to other 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...
it is of only minor importance. This species is usually 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...
in bottom trawls; the pectoral fins are sold as "skate wings" and are eaten baked or fried. In the 1990s, the market value of skate wings rose to $0.40-$1.00 USD per pound, and catches of the big skate off California increased tenfold as the trawl fishery began marketing its skate and ray bycatch. In 2003, a targeted fishery for the big skate and the longnose skate (Raja rhina) commenced in the Gulf of Alaska
Gulf of Alaska
The Gulf of Alaska is an arm of the Pacific Ocean defined by the curve of the southern coast of Alaska, stretching from the Alaska Peninsula and Kodiak Island in the west to the Alexander Archipelago in the east, where Glacier Bay and the Inside Passage are found.The entire shoreline of the Gulf is...
. Population data following this increased exploitation is lacking, but the big skate's slow reproductive rate has led it to be assessed as Near Threatened
Near Threatened
Near Threatened is a conservation status assigned to species or lower taxa that may be considered threatened with extinction in the near future, although it does not currently qualify for the threatened status...
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...
.