Little skate
Encyclopedia
The little skate, Raja erinacea, is a species of skate
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 ....

 in the family Rajidae, found from Nova Scotia
Nova Scotia
Nova Scotia is one of Canada's three Maritime provinces and is the most populous province in Atlantic Canada. The name of the province is Latin for "New Scotland," but "Nova Scotia" is the recognized, English-language name of the province. The provincial capital is Halifax. Nova Scotia is the...

 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...

 on sand or gravel habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...

s. They are one of the dominant members of the demersal 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...

 community in the northwestern Atlantic. This species is of minimal commercial importance
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...

 and is mostly utilized as bait for lobster trap
Lobster trap
Not to be confused with Lobster-tailed potA lobster trap or lobster pot is a portable trap that traps lobsters or crayfish and is used in lobster fishing. A lobster trap can hold several lobsters. Lobster traps are constructed of wire and wood. An opening permits the lobster to enter a tunnel of...

s, though its wings are also marketed for food. It is also important as a model organism
Model organism
A model organism is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the organism model will provide insight into the workings of other organisms. Model organisms are in vivo models and are widely used to...

 for biological
Biology
Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...

 and medical
Medicine
Medicine is the science and art of healing. It encompasses a variety of health care practices evolved to maintain and restore health by the prevention and treatment of illness....

 research.

Distribution and habitat

This skate is native to the western 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...

, from Nova Scotia
Nova Scotia
Nova Scotia is one of Canada's three Maritime provinces and is the most populous province in Atlantic Canada. The name of the province is Latin for "New Scotland," but "Nova Scotia" is the recognized, English-language name of the province. The provincial capital is Halifax. Nova Scotia is the...

, Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

, to Cape Hatteras
Cape Hatteras
Cape Hatteras is a cape on the coast of North Carolina. It is the point that protrudes the farthest to the southeast along the northeast-to-southwest line of the Atlantic coast of North America...

, 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...

, USA. They are most abundant in the northern Mid-Atlantic Bight
Mid-Atlantic Bight
The Mid-Atlantic Bight is a coastal region running from Massachusetts to North Carolina. It contains the New York Bight.-External links:*...

 and the Georges Bank
Georges Bank
Georges Bank is a large elevated area of the sea floor which separates the Gulf of Maine from the Atlantic Ocean and is situated between Cape Cod, Massachusetts and Cape Sable Island, Nova Scotia ....

. Little skates prefer sandy or gravelly habitats from the shore to a depth of 90 meters (300 ft), though they have been caught as deep as 329 meters (1,080 ft). They can tolerate temperatures of 1.2-21°C (34-70 °F) and salinities
Salinity
Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...

 of 27-33.8 ppt (though the optimum is 29-33 ppt). They do not undertake long 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...

, but at the inshore parts of the species' range individuals move into shallower water during the summer and deeper water during the fall and winter. At the southern extent of the range, many also move north and south with changing temperatures.

Description

The little skate has a rounded pectoral fin disk 1.2 times as wide as long, and a blunt 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...

 with a central tip. The jaw
Jaw
The jaw is any opposable articulated structure at the entrance of the mouth, typically used for grasping and manipulating food. The term jaws is also broadly applied to the whole of the structures constituting the vault of the mouth and serving to open and close it and is part of the body plan of...

s contain 38-66 series of round teeth on plates, adapted for grinding food. The pelvic fins are divided into two parts, with the forward lobe modified into a leg-like structure. 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 longer than the disk in juveniles and shorter in adults. Two small, closely spaced 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 are located near the tip of the tail. Adults have small dermal denticles and usually no midline thorns, though there are strong spines on the dorsal surfaces of the head, shoulders, and tail. Males tend to have fewer spines than females.

The coloration of the little skate ranges from grayish to uniform or variable shades of brown above, becoming lighter towards the edges of the disk, and white or gray below. Most individuals have small, round, dark spots on the back. The tail has irregular dusky blotches or a dark gray ventral surface. The little skate may be confused with unspotted individuals of the winter skate (Leucoraja ocellata), which has a similar shape. This species typically measures 41–51 cm long (16–20 in) long, but may reach 54 cm (21 in) long. Little skates grow to a larger maximum size in the northern part of their range.

Biology and ecology

Little skates are more active at night and spend much of the day buried in sediment, usually near specific landscape features such as depressions excavated by other animals. They employ a curious mode of locomotion, dubbed "punting" by the first scientists to document it, to move over the sea floor. The forward lobes of the pelvic fins are modified into leg-like structures called "crura" (singular "crus"), containing three flexible joints and modified skeletal and muscular elements. The little skate pushes off the substrate with both crura and then glides a short distance on its wings while repositioning the crura for the next push. The crura are also used as pivots when the skate needs to turn. It has been speculated that using the pelvic fins in this manner assists in hunting, by reducing water turbulence that might alert the prey or distort the ray's electroreception
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...

.

The tail of the little skate contains an electric organ
Electric organ
In biology, the electric organ is an organ common to all electric fish used for the purposes of creating an electric field. The electric organ is derived from modified nerve or muscle tissue...

 that intermittently generates a weak electric field (the electric organ discharge or EOD). The EOD lasts 70 ms and has a head-negative monophasic
Phase (waves)
Phase in waves is the fraction of a wave cycle which has elapsed relative to an arbitrary point.-Formula:The phase of an oscillation or wave refers to a sinusoidal function such as the following:...

 waveform
Waveform
Waveform means the shape and form of a signal such as a wave moving in a physical medium or an abstract representation.In many cases the medium in which the wave is being propagated does not permit a direct visual image of the form. In these cases, the term 'waveform' refers to the shape of a graph...

. This electric organ is thought to function in communication, and may help potential mates locate one another.

Young and adult little skates are preyed upon by 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, other skates, teleost fishes (including cod
Cod
Cod is the common name for genus Gadus, belonging to the family Gadidae, and is also used in the common name for various other fishes. Cod is a popular food with a mild flavor, low fat content and a dense, flaky white flesh. Cod livers are processed to make cod liver oil, an important source of...

, goosefish
Goosefish
Monkfish are a family, Lophiidae, of anglerfishes. They are found in the Arctic, Atlantic, Indian and Pacific Oceans where they live on sandy and muddy bottoms of the continental shelf and continental slope, at depths in excess of ....

, sea raven
Sea raven
Sea ravens are a family, Hemitripteridae of scorpaeniform fishes. They are bottom-dwelling fishes that feed on small invertebrates, found in the northwest Atlantic and north Pacific oceans...

s, longhorn sculpins, bluefish
Bluefish
The bluefish , called tailor in Australia, is a species of popular marine gamefish found in all climates. It is the sole species of the Pomatomidae family....

, and summer flounder
Summer flounder
The Summer Flounder is a marine flatfish that is found in the Atlantic Ocean off the East coast of the United States and Canada. It is especially abundant in waters from North Carolina to Massachusetts.-Description:...

s), gray seals, and rock crabs
Cancer irroratus
Cancer irroratus, common name the Atlantic rock crab, or peekytoe crab, is a crab in the genus Cancer. Other local names are Maine crab, bay crab, sand crab and mud crab. It has nine marginal teeth on the front edge of the carapace beside each eye....

 (Cancer irroratus). Their egg cases are preyed on by the sea urchin
Sea urchin
Sea urchins or urchins are small, spiny, globular animals which, with their close kin, such as sand dollars, constitute the class Echinoidea of the echinoderm phylum. They inhabit all oceans. Their shell, or "test", is round and spiny, typically from across. Common colors include black and dull...

 Strongylocentrotus droebachiensis
Strongylocentrotus droebachiensis
Strongylocentrotus droebachiensis is commonly known as the green sea urchin because of its characteristic green color. It has the longest genus-species names in the animal kingdom...

and the whelk
Whelk
Whelk, also spelled welk or even "wilks", is a common name used to mean one or more kinds of sea snail. The species, genera and families referred to using this common name vary a great deal from one geographic area to another...

 Buccinum undatum
Buccinum undatum
Buccinum undatum, known as the common whelk, is a large edible marine gastropod in the family Buccinidae, the "true whelks".-Distribution:...

. Known parasites of the little skate include the protozoa
Protozoa
Protozoa are a diverse group of single-cells eukaryotic organisms, many of which are motile. Throughout history, protozoa have been defined as single-cell protists with animal-like behavior, e.g., movement...

ns Caliperia brevipes, Haemogregarina delagei, and Trypanosoma rajae, the myxosporea
Myxosporea
The Myxosporea are a class of microscopic parasites, belonging to the Myxozoa. They have a complex life cycle which comprises vegetative forms in two hosts, an aquatic invertebrate and an ectothermic vertebrate, usually a fish. Each host releases a different type of spore...

ns Chloromyxum leydigi and Leptotheca agilis, the nematode
Nematode
The nematodes or roundworms are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. It has been estimated that the total number of nematode...

 Pseudanisakis tricupola, and 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,...

s Eudactylina corrugata and Lernaeopodina longimana.

Feeding

The diet of the little skate consists mostly of decapod
Decapoda
The decapods or Decapoda are an order of crustaceans within the class Malacostraca, including many familiar groups, such as crayfish, crabs, lobsters, prawns and shrimp. Most decapods are scavengers. It is estimated that the order contains nearly 15,000 species in around 2,700 genera, with...

 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 and amphipods. Polychaete worms are also an important prey item, while other 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 (including isopods, bivalves, 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...

, sea squirts, and copepod
Copepod
Copepods are a group of small crustaceans found in the sea and nearly every freshwater habitat. Some species are planktonic , some are benthic , and some continental species may live in limno-terrestrial habitats and other wet terrestrial places, such as swamps, under leaf fall in wet forests,...

s) and 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 (including sand lance
Sand lance
A sand lance or sandlance is a fish belonging to the family Ammodytidae. Several species of sand lance are commonly known as "sand eels" or "sandeels", though they are not related to true eels. Another variant name is launce, and all names of the fish are references to its slender body and...

s, 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...

, cunners, and cod
Cod
Cod is the common name for genus Gadus, belonging to the family Gadidae, and is also used in the common name for various other fishes. Cod is a popular food with a mild flavor, low fat content and a dense, flaky white flesh. Cod livers are processed to make cod liver oil, an important source of...

) are rarely taken. The importance of crustaceans in the skate's diet increases with size. This species shares its benthic habitat with the similar winter skate; the little skate focuses more on epifauna (organisms living atop the substrate) while the winter skate eats more infauna (burrowing organisms). The little skate has an extremely high number of electrosensory 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...

 around its mouth, giving it a high degree of spatial precision when hunting for prey buried in the substrate.

Reproduction

Little skates are oviparous. Mating occurs frequently throughout the year and pregnant females can be found year-round. However, eggs are most common from October to December and from April to May, and least common from August to September and February to March. An average little skate spawns twice a year, in spring and fall, and produces a total of 10-35 eggs annually. Females deposit their egg capsules in pairs on sandy bottoms, in water no more than 27 meters (89 ft) deep. The egg cases are amber-colored when first laid but become greenish-brown and leathery. Each roughly rectangular case contains a single fertilized egg and measures 4.4-6.3 cm (1.7-2.5 in) long and 3-4.5 cm (1.2-1.8 in) wide. There are hollow horns at each corner with sticky tendrils to secure the egg case to the substrate; the anterior horns are half as long as the case and curved inward, while the posterior horns are as long as the case and nearly straight.

Eggs raised in captivity hatch in 5–6 months, while those in the wild may take up to 12 months to hatch, depending on temperature. While inside the case, 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 have a whip-like extension on the tail believed to be used for circulating water. The newborns measure 9.3-10.2 cm (3.7–4 in) long and are perfectly formed miniatures of the adults. After hatching, the empty egg capsules often wash ashore and are known as "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". Growth is about 10 cm (4 in) per year for the first three years, then slows down to 5 cm (2 in) per year between the third and fourth years. At adolescence, males become larger than the females, and this difference persists through adulthood. Males mature at 32–43 cm (13–17 in) long and females at 36–45 cm (14–18 in) long. Very few little skates over 5 years old have been found, suggesting a high mortality rate
Mortality rate
Mortality rate is a measure of the number of deaths in a population, scaled to the size of that population, per unit time...

 at that age.

An unusual little skate specimen found off Fisher's Island, New York
New York
New York is a state in the Northeastern region of the United States. It is the nation's third most populous state. New York is bordered by New Jersey and Pennsylvania to the south, and by Connecticut, Massachusetts and Vermont to the east...

 contained a developed testis, vas deferens
Vas deferens
The vas deferens , also called ductus deferens, , is part of the male anatomy of many vertebrates; they transport sperm from the epididymis in anticipation of ejaculation....

, and functional clasper on its left side and an adolescent 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...

, shell gland, oviduct
Oviduct
In non-mammalian vertebrates, the passageway from the ovaries to the outside of the body is known as the oviduct. The eggs travel along the oviduct. These eggs will either be fertilized by sperm to become a zygote, or will degenerate in the body...

, and abortive clasper on its right. This example of hermaphroditism is one of very few known for elasmobranch fishes.

Human interactions

Euell Gibbons
Euell Gibbons
Euell Theophilus Gibbons was an outdoorsman and proponent of natural diets during the 1960s.He was born in Clarksville, Texas, on September 14, 1911, and spent much of his youth in the hilly terrain of New Mexico during the dust bowl era. His mother taught him about foods available in the wild...

 promoted the consumption of the little skate in his cookbook
Cookbook
A cookbook is a kitchen reference that typically contains a collection of recipes. Modern versions may also include colorful illustrations and advice on purchasing quality ingredients or making substitutions...

 Stalking the Blue-eyed Scallop (1964), noting that its wings, properly cut, could be treated like scallop
Scallop
A scallop is a marine bivalve mollusk of the family Pectinidae. Scallops are a cosmopolitan family, found in all of the world's oceans. Many scallops are highly prized as a food source...

s. Round cuts from the little skate's wings are marketed as "scallops", though due to their small size their commercial importance is limited. Little skates are also often used to bait traps, especially for lobster
Lobster
Clawed lobsters comprise a family of large marine crustaceans. Highly prized as seafood, lobsters are economically important, and are often one of the most profitable commodities in coastal areas they populate.Though several groups of crustaceans are known as lobsters, the clawed lobsters are most...

s and eel
Eel
Eels are an order of fish, which consists of four suborders, 20 families, 111 genera and approximately 800 species. Most eels are predators...

s. Skates are typically 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...

 in otter trawls; the little skate is not currently considered to be overfished
Overfishing
Overfishing occurs when fishing activities reduce fish stocks below an acceptable level. This can occur in any body of water from a pond to the oceans....

. Along with the spiny dogfish
Spiny dogfish
The spiny dogfish, spurdog, mud shark, or piked dogfish, Squalus acanthias, is one of the best known of the dogfish which are members of the family Squalidae in the order Squaliformes. While these common names may apply to several species, Squalus acanthias is distinguished by having two spines ...

 (Squalus acanthias), the little skate is often used as a model organism
Model organism
A model organism is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the organism model will provide insight into the workings of other organisms. Model organisms are in vivo models and are widely used to...

 in biomedical research. A BAC genomic library
Gene library
A genomic library is a population of host bacteria, each of which carries a DNA molecule that was inserted into a cloning vector, such that the collection of cloned DNA molecules represents the entire genome of the source organism...

for the little skate was completed in January 2005.
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