The largest barndoor skates found have been 5-6 feet and 30-38 pounds thus deeming it the largest skate in the northwestern Atlantic. The lower surface is white, with blotchy gray spots. The dorsal surface is brown with scattered darker spots. The space between the 2 eyes is approximately 5.5 mm. Like other skates, the barndoor skate has gills. However, the tail lacks large thorns, which distinguishes it from all other skates of the genus Raja in the western north Atlantic except for 2 species. The tail does have 3 rows of smaller thorns.
The dorsal fins are far removed from the tail. There is a larger, misshaped spot on the inner part of each pectoral fin. There are also mucous pores on the ventral surface, marked by black dots and dashes. The barndoor skate has 30-40 teeth.
There are two sexes of barndoor skate. Mature males are smoother than females. Large females are rough, having small spines along a narrow margin from tip of the snout to the level of the nostrils. The young look almost exactly like the adults (Bigelow and Schroeder 1953).
Other Physical Features: bilateral symmetry
Barndoor skates seem to be found in a variety of habitats, from shoreline to nearly 235 fathoms. Most occur primarily around 5 fathoms or 70-80 fathoms. They seem to prefer sandy or gravel bottoms in shallower areas and in deeper waters, muddy bottoms. The skate appears to move closer to shore in the autumn and move further out to sea in the warmer summer months. It is believed that it does not have any north-south migratory patterns. (Bigelow and Schroeder 1953).
The barndoor skate is found in the northwestern Atlantic Ocean. It is found from the Grand Banks of Newfoundland and the southern side of the Gulf of St. Lawrence, south to North Carolina. It is also undoubtedly reported in Florida where egg cases with embryos washed ashore in the 19th century (Bigelow and Schroeder 1953).
Biogeographic Regions: nearctic (Native )
Barndoor skates do not seem to be fussy eaters. They will feed upon large crustaceans, such as lobsters, spider crabs, shrimp and crabs and even isopods. They also add to their diet bivalves like clams, and large gastropods such as worms and squid. Barndoor skates also seem to be more destructive upon fish than other local skates and have been known to bite on almost any type of bait (Bigelow and Schroeder 1953).
The barndoor skate is of no positive economic importance to humans.
There is little known and published concerning the barndoor skate. Most of the information concerns physical characteristics and conservation efforts. The world, however, is witnessing the apparent modern extinction of a marine animal that is well documented in the twentieth and twenty-first centuries. For centuries, a creature over one meter in size went unnoticed. Unfortunately, it may continue to do so until it is extinct and exits the pages of books as quickly as it had entered. (Large 1998)
The conservation of the barndoor skate is becoming an increasingly popular subject of heated discussion. Casey and Myers (1998) concluded that it is "close to extinction" due to by-catch. A once common fish in all parts of the Gulf of Maine during the 1950s, it is now rarely found by anglers. Casey and Myers said that the only way to ensure the survival of the barndoor skate is to ban all extensive areas of trawling in the northwestern Atlantic.
Estimates from St. Pierre Bank indicate that the barndoor skate population was near 600,000 during the 1950s and has since plummeted to less than 500 in the 1970s. The barndoor skate population is especially vulnerable due to its low fecundity or number of young that it produces in each hatching.
Following Casey and Myers study, there was a petition in 1999 to the National Marine Fisheries Service (NMFS) to have the barndoor skate added to the Endangered Species list. The NMFS is trying to determine if it needs to be added to the list.
Surprisingly, there is strong opposition to the idea that the barndoor skate is on the brink of extinction. Kenchington (1999) examined Casey and Myers' findings and came to his own conclusion that "the barndoor skate is not near to biological extinction and is showing no sign that it is headed in that direction. Rather, it seems to be experiencing a slow increase in abundance in a setting where human activity poses no threat to its continued existence as a species". In rebuttal to Kenchington's comments, the barndoor skate is missing in 7 of 9 previous locations where barndoor skates were common. (Bigelow and Schroeder 1953; Close 1999; Kenchington 1999; Large 1998)
US Federal List: no special status
CITES: no special status
IUCN Red List of Threatened Species: endangered
If it were added to the Endangered Species list, then trawling in the northwestern Atlantic, which is quite common, would be more tightly restricted. This would place a further strain on the fishermen who must fish longer and harder in order to achieve past yields. Many of the animals that are used in commercial fisheries are preyed on by skates, however, there seem to be so few barndoor skates left that it does not seem to matter. (Bigelow and Schroeder 1953)
Many aspects of the reproductive cycle of the barndoor skate are still unknown but there are still aspects known. The eggs, which are quite large in size, are deposited from close to the shoreline down to the greatest depths at which the skate is found. The eggs are laid in the winter and hatch either in the late spring or in early summer. The numbers of hatchlings are quite small which gives the barndoor skate a low fecundity. The hatchlings closely resemble adults and range from 180-190 mm (Bigelow and Schroeder 1953).
Dipturus laevis és una espècie de peix de la família dels raids i de l'ordre dels raïformes.
És ovípar[4] i les femelles ponen càpsules d'ous, les quals presenten com unes banyes a la closca.[7]
Menja mol·luscs bivalves, calamars, crancs, llagostes, gambes, cucs i peixos.[4]
És un peix marí, de clima temperat i demersal que viu entre 0–750 m de fondària.[4]
Es troba a l'Oceà Atlàntic occidental: des del sud del Golf de Sant Llorenç (el Canadà) fins a Carolina del Nord (els Estats Units).[4][8][9][10][11][12][13]
És inofensiu per als humans.[4]
Dipturus laevis és una espècie de peix de la família dels raids i de l'ordre dels raïformes.
Der Scheunentorrochen (Dipturus laevis) ist der größte Rochen (Batoidea) im nordwestlichen Atlantik und für den Menschen ungefährlich. Die größten Exemplare erreichen eine Länge von 153 Zentimetern und ein Gewicht von 20 Kilogramm. Als eine von 5 Rochenarten ist er in seinem Verbreitungsgebiet kommerziell wichtig und wird von der IUCN als stark gefährdet eingestuft.[1][2][3]
Die breiten, diamantenförmigen Brustflossen des Scheunentorrochens sind an den Ecken scharf abgewinkelt, die vorderen Kanten sind konkav, die Rückenflossen sind eng beieinander. Auch die hintere Seite der Brustflossen sind abgerundet und sein Schwanz einigermaßen kurz und recht dick. Er besitzt eine rötlich-braune Färbung mit dunklen Flecken und leicht helleren Streifen. Ein besonderes Merkmal ist ein dünner und dunkler Streifen, der am Kopf beginnt und in Richtung Schwanz bis zum äußersten Rand der Brustflosse verläuft. Die Bauchseite ist weiß bis grau und bei seiner Schnauze mit dunklen Flecken gezeichnet.[3]
Er besitzt auf seinem Schwanz keine Placoidschuppen, damit kann man ihn von fast allen anderen Arten der Echten Rochen unterscheiden.[2] Der Schwanz besitzt aber drei Reihen von kleinen Dornen. Größere Exemplare besitzen solche Dornen auf dem Rücken, geschlechtsreife Weibchen auch auf dem Kopf und den Schultern. Junge Exemplare besitzen sie noch nicht.[3]
Dipturus laevis wächst langsam und wird mit einem Alter von 11 Jahren recht langlebig.[4] Als eine der größten Rochenarten im nordwestlichen Atlantik wird der Scheunentorrochen ca. 150 Zentimeter groß und maximal 18 Kilogramm schwer.[5] Unbestätigte Funde gaben sogar eine Länge von 180 Zentimetern an. Normalerweise wiegen diese Rochen bei einer Größe von 71 bis 76 Zentimetern 2 bis 3 Kilogramm.
Die Zähne der weiblichen als auch der jungen männlichen Scheunentorrochen sind sehr Nahe bei aneinander und besitzen abgerundete Kuppen. Im Gegensatz dazu besitzen geschlechtsreif männliche Rochen in Reihen angeordnete, weit auseinander stehende spitze Zähne. Der Oberkiefer besteht aus 30 bis 40 Zahnreihen. Die Zahnreihen des Unterkiefers besitzen zwischen 28 und 38 Zähnen.[3]
Der Scheunentorrochen kommt entlang der Atlantikküste Nordamerikas vor. Die nördliche Grenze seines Verbreitungsgebiets bilden die Küste Neufundlands und der südliche Teil des Sankt-Lorenz-Golfs. Nach Süden erstreckt sich sein Areal bis zu den US-Bundesstaaten North Carolina und Florida.
Im Sommer wandert der Rochen eher in tiefere Meeresgebiete, im Winter eher in seichte. Aufgrund seiner Größe sind große Haie wahrscheinlich seine einzigen Fressfeinde.
Man findet den Scheunentorrochen für gewöhnlich über weichen, schlammigen, sandigen oder steinigen Böden, in seichten als auch in tiefen Gewässern. Seine bevorzugte Meerestiefe liegt zwischen 0 und 150 Metern, maximal bis 750 Meter Tiefe. Die Wassertemperatur kann hier stark variieren: von knapp über dem Gefrierpunkt bis ca. 20 °C. Obwohl Dipturus laevis auch in Brackwasser gefunden werden kann, beträgt die optimale Salinität seines Lebensraums 31–35 ‰.[3][2][5]
Der Scheunentorrochen hält sich meist in Bodennähe auf und ernährt sich von Wirbellosen wie Muscheln, Tintenfischen, Hummern, Garnelen, Würmern und kleinen Fischen.[5] Mit seiner spitzen Schnauze gräbt er auch im Sand nach Muscheln.[3]
Diese Rochenart legt Eier; über ihren Reproduktionszyklus ist aber generell recht wenig bekannt.[2] Die Geschlechtsreife erreichen die Tiere wahrscheinlich im Alter von 8 bis 11 Jahren.[1] Bei der Paarung gibt es eine signifikante Umarmung. Nach der Paarung tragen die Weibchen ca. 6 bis 12 Monate lang die Eier aus. Diese sind ziemlich groß, ca. 7–13 Zentimeter lang, 4,5–7,5 Zentimeter breit, gelb und oder grünlich. Sie sind länglich, rechteckig und haben an den Spitzen kleine steife Hörner, mit denen sie an sandigen oder schlammigen Stellen befestigt werden. Gelegt werden sie im Winter sowohl in seichten als auch in tiefen Gewässern. Die Jungtiere schlüpfen im Frühjahr oder im Sommer. Die Zahl der Jungtiere ist recht gering. Sie sind ca. 180 bis 190 Millimeter lang und ähneln ihren Eltern. Jungtiere neigen dazu, großen Objekten wie ihrer Mutter zu folgen.[3][2][5]
Wie bei anderen Rochenarten in dieser Region wird auch Dipturus laevis von der hiesigen Fischerei bedroht, gezielt wird der Scheunentorrochen jedoch nicht gefischt. Seit 1981 sind die Fangquoten für Rochen in den USA stetig gestiegen. Diese Entwicklung ist primär aufgrund der stark gestiegenen Nachfrage nach Rochenflossen am Exportmarkt der USA zu begründen und sekundär auf die Nachfrage als Köderfisch für Hummer. Sehr oft wird der Scheunentorrochen mit Schleppnetzen als Beifang gefangen, dies stellt auch mitunter die größte Gefahr für diese Art dar. Eine Reihe von Daten zur Schleppnetzfischerei weisen einen Rückgang der Biomasse und der Verbreitung dieser Art auf. Grundsätzlich war es historisch schwer korrekte Daten zu erheben, in den 1960er und frühen 1970er Jahren sank die Population dieses Rochens rapide ab und Daten wiesen darauf hin, dass die Biomasse ca. 96 % bis 99 % abnahm. Bis zum Jahr 1990 blieb die Population niedrig und stieg ab diesem Zeitpunkt jedoch wieder an. Dieser Trend war vorerst nicht abzusehen und es wurden sogar Petitionen gestartet um diese Art als gefährdet einzustufen. Nach einer Studie die im Jahr 2002 veröffentlicht wurde, sollte dieser Rochen nicht als gefährdet eingestuft werden, da die Biomasse zunimmt. Im Jahr 2003 gelangte er aber doch auf die Rote Liste gefährdeter Arten. Gründe hierfür lassen sich auf das langsame Wachstum, die späte Geschlechtsreife, die geringe Fruchtbarkeit und auf die große Körpergröße zurückführen. Derzeit gibt es aber keine Schutzprogramme um diese Art zu schützen, die Populationen entwickeln sich stabil.[1]
Der Scheunentorrochen (Dipturus laevis) ist der größte Rochen (Batoidea) im nordwestlichen Atlantik und für den Menschen ungefährlich. Die größten Exemplare erreichen eine Länge von 153 Zentimetern und ein Gewicht von 20 Kilogramm. Als eine von 5 Rochenarten ist er in seinem Verbreitungsgebiet kommerziell wichtig und wird von der IUCN als stark gefährdet eingestuft.
The barndoor skate (Dipturus laevis) is a species of marine cartilaginous fish in the skate family Rajidae of the order Rajiformes. It is native to the northwestern Atlantic Ocean, and is found from the Grand Banks of Newfoundland and the southern side of the Gulf of St. Lawrence south to North Carolina.[2] The fish is one of the largest skates found in the North Atlantic Ocean, reaching lengths up to 1.5 m (5 ft). It is carnivorous, feeding on invertebrates and other fish found near the sea floor.
After peaking in the 1950s, the population of the barndoor skate dramatically declined in the 1960s and early 1970s as a result of overfishing. In 2003, it was listed as endangered by the World Conservation Union. However, barndoor skate populations have increased substantially since 1990 and even surpassed 1960s population size by 2012. In 2019, the barndoor skate was downlisted to least concern by the IUCN based on its largely increased population, new protections within its range, and also minor expansions to its range.[1] In most cases, the barndoor skate is not intentionally harvested by the commercial fishing industry—it is usually considered bycatch in the trawling nets used to target other species of fish.
The barndoor skate is a flat-bodied fish with a large, disk-like body with sharply angled corners and a pointed snout. Its pectoral fins have evolved into broad, flat, wing-like appendages used to propel the fish through the water. These fins have a concave front edge with rounded posterior corners. Like sharks, it has a boneless skeleton made of cartilage, a tough, elastic substance composed of collagenous and/or elastic fibers, cells, and a firm, gel-like substance called the matrix. It has slot-like body openings called gill slits on the underside of the body beneath the pectoral fins that lead from the gills. The dorsal fins are close together and far removed from the tail.[3] It has two eyes on its dorsal surface, located about 5.5 centimeters (2.2 in) apart.[2]
The fish's upper surface is brown to reddish brown with many scattered darker spots, lighter streaks, and reticulations. The center of each pectoral fin is marked with an oval spot or blotch. The lower surface is light, white to grey, blotched irregularly with gray spots.[3][4] The barndoor skate is unique from other species of skate in its having a straight line that begins at the snout and ends at the anterior margin of the outer corner of the disk, but stopping short of the disk.[3]
The barndoor skate is one of the largest skates found in the North Atlantic Ocean.[2] It can reach lengths of up to 1.5 m (5 ft) and can weigh up to 18 kg (40 lb).[5] There have been unconfirmed reports of individuals reaching lengths of 1.8 meters (6 ft).[3] A 71–76 cm (28–30 in) barndoor skate typically weighs 2–3 kg (4–7 lb).[3]
The tail is moderately short and does not have large, thorn-like structures called dermal denticles that are normally found on skates. This lack of denticles distinguishes it from all but two species of skates found in the western Atlantic.[2] Larger individuals do have three rows of smaller denticles on the tail, and mature females also possess denticles on the head and shoulders, and along the dorsal midbelt of the disk and tail. Denticles are completely absent on small individuals.[3]
The barndoor skate occurs in a range extending from the banks of Newfoundland, the southern Gulf of St. Lawrence, and along the northeastern coast and offshore banks of Nova Scotia south to North Carolina.[6] Reports in the 19th century said the range of the fish extended as far south as northeastern Florida, but more recent research suggests that the Florida discoveries may have actually been a misidentification of R. floridana.[7] It is found on various types of ocean bottoms, including soft muddy, sandy, and rocky bottoms. It can be found from the shoreline to depths to 750 m (2,460 ft), although it is most commonly found at depths less than 150 m (500 ft). It inhabits waters in a broad range of temperatures, from just above freezing to 20 °C (68 °F).[6] It appears to move closer to shore in the autumn and further out to sea in the warmer months. It tolerates brackish water where the salinity is as low as 21 to 24 parts per thousand, but it prefers salinity between 31 and 35 parts per thousand.[5] It is believed to not exhibit any north-south migratory patterns.
The fish is carnivorous, with its prey consisting mainly of benthic invertebrates and fishes. Such food items include polychaetes, gastropods, bivalve mollusks, rock crabs, cancer crabs, spider crabs, lobsters, shrimps, squids, and fishes including spiny dogfish, alewife, Atlantic herring, menhaden, hakes, sculpins, cunner, tautog, sand lance, butterfish, and various flounders. Juveniles primarily subsist on benthic invertebrates such as polychaetes, copepods, amphipods, isopods, crangon shrimp, and euphausiids.[8] Individuals have been found with the denticles on the snout worn smooth, indicating that the snout is used to dig in the mud or sand to obtain bivalve mollusks.[3]
The barndoor skate is one of five skates in the Gulf of Maine that has commercial value, but of those, the species that are most frequently targeted are the winter skate (Leucoraja ocellata) and the thorny skate (Amblyraja radiata).[8] The barndoor skate is most commonly considered bycatch by commercial trawlers operating in the northwestern Atlantic that target other commercially valuable species of fish using bottom trawling.[5] When harvested, the flesh of the barndoor skate is used as bait, fish meal, and pet food, and the meat from its wings is sold for human consumption.[3] Since 1981, landings of skates have increased substantially, partly in response to increased demand for lobster bait, and more significantly, to the increased export market for skate wings.[9] The commercial retention and sale of barndoor skates was prohibited in the United States from 2003 until 2018.[1]
Abundances of barndoor skate dropped precipitously in the 1960s and early 1970s, coinciding with the period of intense fishing by foreign factory trawlers. The abundance remained very low through around 1990, but increased nearly exponentially from 1990–2005, and have been approaching the levels observed in the 1960s.[10] In 2012, they surpassed 1960s population levels.[1] In 1998, Casey and Myers[11] published a controversial study claiming that the barndoor skate was nearly extinct; however, they only presented data through 1993, so the recovery that had started in the early 1990s was not yet clearly evident. In 1999, two conservation groups, GreenWorld, based in Cambridge, Massachusetts, and the Center for Marine Conservation, based in Washington, DC, petitioned the National Marine Fisheries Service (NMFS) to have the barndoor skate listed under the Endangered Species Act. After a 12-month study, the NMFS announced in 2002 that listing the species as endangered or threatened was not warranted. It cited increases in abundance and biomass of barndoor skate observed during surveys since 1993, which had become quite rapid by that time.[12] In 1994, the World Conservation Union had listed the barndoor skate as "vulnerable" under the 1994 Categories and Criteria, but in 2003, it reassessed the species as endangered on the IUCN Red List.[1] In 2019, the species was downgraded to least concern because of its greatly increased population size.[1]
Each year, the National Oceanic and Atmospheric Administration (NOAA) estimates current population levels for a variety of aquatic species of special interest, and releases an annual report showing the progress being made to reduce harvesting of overfished species. When a species has been determined to be either overfished or subject to overfishing, the regional fishery management councils are required to develop a plan to correct the problem. In 2006, NOAA published a press release stating that as a result of conservation efforts, between 2004 and 2005, monitored stocks of the barndoor skate had grown to a level that the NOAA no longer considers "overfished".[13]
The fish was originally described as Raja laevis by Samuel Latham Mitchill in 1818. The scientific name was later changed to the currently valid name Dipturus laevis. It has also been misidentified as Raia granulata by Theodore Gill, an American ichthyologist, in 1879.[14] The genus name, Dipturus, is derived from the Greek words di, meaning two, and pteryx, meaning wing. Raja, the original genus which was coined by Carl Linnaeus in 1758, is still recognized as a valid subgenus.[3]
{{cite journal}}: Cite journal requires |journal= (help) {{cite journal}}: Cite journal requires |journal= (help) "Dipturus laevis". Integrated Taxonomic Information System. Retrieved 14 November 2006.
The barndoor skate (Dipturus laevis) is a species of marine cartilaginous fish in the skate family Rajidae of the order Rajiformes. It is native to the northwestern Atlantic Ocean, and is found from the Grand Banks of Newfoundland and the southern side of the Gulf of St. Lawrence south to North Carolina. The fish is one of the largest skates found in the North Atlantic Ocean, reaching lengths up to 1.5 m (5 ft). It is carnivorous, feeding on invertebrates and other fish found near the sea floor.
After peaking in the 1950s, the population of the barndoor skate dramatically declined in the 1960s and early 1970s as a result of overfishing. In 2003, it was listed as endangered by the World Conservation Union. However, barndoor skate populations have increased substantially since 1990 and even surpassed 1960s population size by 2012. In 2019, the barndoor skate was downlisted to least concern by the IUCN based on its largely increased population, new protections within its range, and also minor expansions to its range. In most cases, the barndoor skate is not intentionally harvested by the commercial fishing industry—it is usually considered bycatch in the trawling nets used to target other species of fish.
'Raja laevis''' es una especie de peces de la familia de los Rajidae en el orden de los Rajiformes.
Los machos pueden llegar alcanzar los cm de longitud total y 18 kg de peso.
Come moluscos bivalvos, calamars, cangrejos, langostas, gambas, gusanos y peces hueso.
Es ovíparo y las hembras ponen huevos envueltos en una cápsula córnea.[1]
Es un pez de mar y Clima templado y demersal que vive entre 0–750 m de profundidad.
Se encuentra en el Océano Atlántico occidental: desde el sur del Golfo de San Lorenzo (el Canadá) hasta Carolina del Norte (los Estados Unidos ).
Es inofensivo para los humanos.
Actualmente está en peligro de extinción, y es una especie vulnerable para la IUCN. No es una especie comercial, pero el uso de arrastreros la puso en peligro.
La Grande raie (Dipturus laevis) se retrouve du sud du golfe du Saint-Laurent à la Caroline du Nord.
Synonyme : Raja laevis
Cette grande raie de 160 cm de long a frôlé l'extinction dans les années 90 à cause des prises accidentelles dans les filets des chalutiers et de la forte demande internationale en ailes de raie. L'interdiction de sa pêche entre 2003 et 2018 aux États-Unis et la mise en place de quotas au Canada ont stoppé l'hécatombe et probablement, au moins provisoirement, sauvé cette espèce[1].
La Grande raie (Dipturus laevis) se retrouve du sud du golfe du Saint-Laurent à la Caroline du Nord.
Synonyme : Raja laevis
Cette grande raie de 160 cm de long a frôlé l'extinction dans les années 90 à cause des prises accidentelles dans les filets des chalutiers et de la forte demande internationale en ailes de raie. L'interdiction de sa pêche entre 2003 et 2018 aux États-Unis et la mise en place de quotas au Canada ont stoppé l'hécatombe et probablement, au moins provisoirement, sauvé cette espèce.
Dipturus laevis is een vissensoort uit de familie van de Rajidae.[1] De wetenschappelijke naam van de soort is voor het eerst geldig gepubliceerd in 1818 door Mitchill.
Bronnen, noten en/of referenties
Эти скаты не являются объектом целевого промысла, однако попадаются в качестве прилова. В водах США за период с 1960 по 1990 года численность этого вида в уловах на глубине до 400 м сократилась на 96—99 %. Международный союз охраны природы присвоих виду охранный статус «Уязвимый».
