Atlantic sawtail cat shark
Encyclopedia
The Atlantic sawtail catshark (Galeus atlanticus) is a little-known species
of catshark
, family
Scyliorhinidae, found in a small area of the northeastern Atlantic Ocean
centered around the Strait of Gibraltar
and the Alborán Sea
. It is found on or close to the bottom over the continental slope, mostly at depths of 400–600 m (1,312.3–1,968.5 ft). This shark closely resembles, and was once thought to be the same species as, the blackmouth catshark
(G. melastomus); both are slender with a series of dark saddles and blotches along the back and tail, and a prominent crest of enlarged dermal denticles along the dorsal edge of the caudal fin. It differs subtly from G. melastomus in characters including snout length, caudal peduncle depth, and the color of the furrows at the corner of its mouth.
Reproduction in the Atlantic sawtail catshark is oviparous, with females carrying multiple maturing eggs at once. Mating
and spawning
occur year-round. This species is caught incidentally
by commercial deepwater fisheries
throughout its range, but the impact of fishing pressure on its population is uncertain as it is not recorded separately from G. melastomus. Given its restricted distribution, it has been assessed as Near Threatened
by the International Union for Conservation of Nature (IUCN).
Léon Louis Vaillant, in Expéditions scientifiques du "Travailleur" et du "Talisman" pendant les années 1880, 1881, 1882, 1883. Vaillant based his account on a specimen caught at a depth of 540 m (1,771.7 ft) off Cape Spartel
in northwestern Morocco. This species was long thought to be the same as the closely similar blackmouth catshark
(G. melastomus), until it was resurrected by Ramón Muñoz-Chápuli and A. Perez Ortega in 1985. Castilho and colleagues (2007) further affirmed the distinction between G. atlanticus and G. melastomus using morphometric and mitochondrial DNA
data.
in southwestern Portugal
, through the Strait of Gibraltar
into the Alborán Sea
, to as far as Cabo de Gata in southwestern Spain
. It is most abundant in the center of the Alborán Sea, and around Isla de Alborán
. This species has been recorded a few times off Morocco and once off Mauritania
; it may be extremely rare or mistaken for G. melastomus in the region. Its total range has been estimated to encompass 50000 square kilometre, about evenly divided between the northeastern Atlantic and the western Mediterranean
.
Demersal in nature, the Atlantic sawtail catshark inhabits the continental slope at a depth of 330–790 m (1,082.7–2,591.9 ft), and is most common between 400 and 600 m (1,312.3 and 1,968.5 ft). There is a lone record from shallower than 50 m (164 ft). This species does not exhibit spatial segregation by either sex or size, or conduct seasonal migrations
.
s (protective third eyelids). There is a slight ridge below each eye, and a minute spiracle
behind. The large mouth is wide and curved, with rather long furrows around the corners. The small teeth each have a narrow central cusp flanked by multiple smaller cusplets on either side. There are five pairs of gill slit
s.
The first dorsal fin
is positioned over the latter portion of the pelvic fin bases, while the second is positioned over the latter portion of the anal fin base. Both dorsal fins are angular and similar in size. The pectoral fins are large and wide, with rounded corners. The short, low pelvic fins are placed close to the anal fin, which is elongated and angular. The caudal peduncle is compressed from side to side; its height is greater than in G. melastomus, exceeding 4.5% of the total length. The caudal fin is low, with a small lower lobe and a ventral notch near the tip of the upper lobe. The skin is covered by dermal denticles, each with a leaf-shaped crown bearing a median ridge and three marginal teeth. A prominent crest of enlarged denticles runs along the front portion of the dorsal caudal fin margin. The coloration is gray above and pale below, with a series of dark gray saddles or blotches along the back and tail. The dorsal fins are dusky at the base and lighten towards the trailing margins. The trailing margin of the caudal fin is black, as is the interior of the mouth. The inside of the furrows at the corners of the mouth are dark, in contrast to G. melastomus where they are light.
s. The tough egg case is flask-shaped and reddish, with a rounded bottom and a pair of "horns" at the top, and measuring around 3.1–3.8 cm (1.2–1.5 in) long and 1.1–1.3 cm (0.433070866141732–0.511811023622047 in) across. The egg case of G. melastomus is similar in appearance but significantly larger. Once deposited, the egg hatches within a short period of time. According to Compagno (2005), males attain sexual maturity
at about 38–42 cm (15–16.5 in) long, and females at about 40–45 cm (15.7–17.7 in) long. Rey and colleagues (2010) reported the smallest mature males and females in their study to be 33 cm (13 in) and 37 cm (14.6 in) long respectively.
data for the Atlantic sawtail catshark is inadequate as it is still recorded as G. melastomus by observers. This species is caught incidentally
on deepwater longlines and bottom trawls targeting other species, including wreckfish (Polyprion americanus), conger eel (Conger conger), Norway lobster (Nephrops norvegicus), and red shrimp (Aristeus antennatus). Most landed sharks are discarded and likely suffer high mortality due to damage sustained during capture; the larger specimens are marketed for human consumption. Given the small extent of its range and the ubiquitous heavy fishing pressure within, the International Union for Conservation of Nature (IUCN) has assessed this shark as Near Threatened
.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of catshark
Catshark
Catsharks are ground sharks of the family Scyliorhinidae, with over 150 known species. While they are generally known as catsharks, many species are commonly called dogfish....
, family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Scyliorhinidae, found in a small area of the northeastern 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...
centered around the Strait of Gibraltar
Strait of Gibraltar
The Strait of Gibraltar is a narrow strait that connects the Atlantic Ocean to the Mediterranean Sea and separates Spain in Europe from Morocco in Africa. The name comes from Gibraltar, which in turn originates from the Arabic Jebel Tariq , albeit the Arab name for the Strait is Bab el-Zakat or...
and the Alborán Sea
Alboran Sea
|300px|thumb|]]The Alboran Sea is the westernmost portion of the Mediterranean Sea, lying between Spain on the north and Morocco and Algeria on the south...
. It is found on or close to the bottom over the continental slope, mostly at depths of 400–600 m (1,312.3–1,968.5 ft). This shark closely resembles, and was once thought to be the same species as, the blackmouth catshark
Blackmouth catshark
The blackmouth catshark is a species of catshark, family Scyliorhinidae, common in the northeastern Atlantic Ocean from Iceland to Senegal, including the Mediterranean Sea. It is typically found over the continental slope at depths of , on or near muddy bottoms. The youngest sharks generally...
(G. melastomus); both are slender with a series of dark saddles and blotches along the back and tail, and a prominent crest of enlarged dermal denticles along the dorsal edge of the caudal fin. It differs subtly from G. melastomus in characters including snout length, caudal peduncle depth, and the color of the furrows at the corner of its mouth.
Reproduction in the Atlantic sawtail catshark is oviparous, with females carrying multiple maturing eggs at once. Mating
Mating
In biology, mating is the pairing of opposite-sex or hermaphroditic organisms for copulation. In social animals, it also includes the raising of their offspring. Copulation is the union of the sex organs of two sexually reproducing animals for insemination and subsequent internal fertilization...
and spawning
Spawn (biology)
Spawn refers to the eggs and sperm released or deposited, usually into water, by aquatic animals. As a verb, spawn refers to the process of releasing the eggs and sperm, also called spawning...
occur year-round. This species is caught incidentally
Bycatch
The term “bycatch” is usually used for fish caught unintentionally in a fishery while intending to catch other fish. It may however also indicate untargeted catch in other forms of animal harvesting or collecting...
by commercial deepwater 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...
throughout its range, but the impact of fishing pressure on its population is uncertain as it is not recorded separately from G. melastomus. Given its restricted distribution, it has been 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 International Union for Conservation of Nature (IUCN).
Taxonomy
The original description of the Atlantic sawtail catshark, as Pristiurus atlanticus, was published in 1888 by French naturalistNaturalist
Naturalist may refer to:* Practitioner of natural history* Conservationist* Advocate of naturalism * Naturalist , autobiography-See also:* The American Naturalist, periodical* Naturalism...
Léon Louis Vaillant, in Expéditions scientifiques du "Travailleur" et du "Talisman" pendant les années 1880, 1881, 1882, 1883. Vaillant based his account on a specimen caught at a depth of 540 m (1,771.7 ft) off Cape Spartel
Cape Spartel
Cape Spartel is a promontory in Morocco about above sea level at the entrance to the Strait of Gibraltar, 12 km West of Tangier. It is frequently but incorrectly referred as the northernmost point of Africa, which is instead Ras ben Sakka, Tunisia....
in northwestern Morocco. This species was long thought to be the same as the closely similar blackmouth catshark
Blackmouth catshark
The blackmouth catshark is a species of catshark, family Scyliorhinidae, common in the northeastern Atlantic Ocean from Iceland to Senegal, including the Mediterranean Sea. It is typically found over the continental slope at depths of , on or near muddy bottoms. The youngest sharks generally...
(G. melastomus), until it was resurrected by Ramón Muñoz-Chápuli and A. Perez Ortega in 1985. Castilho and colleagues (2007) further affirmed the distinction between G. atlanticus and G. melastomus using morphometric and mitochondrial DNA
Mitochondrial DNA
Mitochondrial DNA is the DNA located in organelles called mitochondria, structures within eukaryotic cells that convert the chemical energy from food into a form that cells can use, adenosine triphosphate...
data.
Distribution and habitat
The Atlantic sawtail catshark is found from Cape St. VincentCape St. Vincent
Cape St. Vincent , next to the Sagres Point, on the so-called Costa Vicentina , is a headland in the municipality of Sagres, in the Algarve, southern Portugal.- Description :This cape is the southwesternmost point in Portugal...
in southwestern 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...
, through the Strait of Gibraltar
Strait of Gibraltar
The Strait of Gibraltar is a narrow strait that connects the Atlantic Ocean to the Mediterranean Sea and separates Spain in Europe from Morocco in Africa. The name comes from Gibraltar, which in turn originates from the Arabic Jebel Tariq , albeit the Arab name for the Strait is Bab el-Zakat or...
into the Alborán Sea
Alboran Sea
|300px|thumb|]]The Alboran Sea is the westernmost portion of the Mediterranean Sea, lying between Spain on the north and Morocco and Algeria on the south...
, to as far as Cabo de Gata in southwestern Spain
Spain
Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...
. It is most abundant in the center of the Alborán Sea, and around Isla de Alborán
Isla de Alborán
The Isla de Alborán is a small islet in the Alborán Sea, part of the western Mediterranean, about 50 km north of the Moroccan coast and 90 km south of the province of Almería, Spain. A Spanish possession since 1540, it was taken from the Tunisian pirate Al Borani in the Battle of Alborán. It is...
. This species has been recorded a few times off Morocco and once off 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...
; it may be extremely rare or mistaken for G. melastomus in the region. Its total range has been estimated to encompass 50000 square kilometre, about evenly divided between the northeastern Atlantic and the western Mediterranean
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...
.
Demersal in nature, the Atlantic sawtail catshark inhabits the continental slope at a depth of 330–790 m (1,082.7–2,591.9 ft), and is most common between 400 and 600 m (1,312.3 and 1,968.5 ft). There is a lone record from shallower than 50 m (164 ft). This species does not exhibit spatial segregation by either sex or size, or conduct seasonal migrations
Fish migration
Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousands of kilometres...
.
Description
The Atlantic sawtail catshark reaches a maximum known length of 45 cm (17.7 in). Slender and firm-bodied, it has a slightly flattened head with a moderately long, flattened snout. The head is proportionately shorter and narrower, and the nostrils relatively farther from the snout tip, than in G. melastomus. The nostrils are partially covered by triangular flaps of skin on their anterior rims. The eyes are horizontally oval and equipped with rudimentary nictitating membraneNictitating membrane
The nictitating membrane is a transparent or translucent third eyelid present in some animals that can be drawn across the eye for protection and to moisten it while maintaining visibility. Some reptiles, birds, and sharks have a full nictitating membrane; in many mammals, there is a small...
s (protective third eyelids). There is a slight ridge below each eye, and a minute 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...
behind. The large mouth is wide and curved, with rather long furrows around the corners. The small teeth each have a narrow central cusp flanked by multiple smaller cusplets on either side. There are five pairs of 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.
The first 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...
is positioned over the latter portion of the pelvic fin bases, while the second is positioned over the latter portion of the anal fin base. Both dorsal fins are angular and similar in size. The pectoral fins are large and wide, with rounded corners. The short, low pelvic fins are placed close to the anal fin, which is elongated and angular. The caudal peduncle is compressed from side to side; its height is greater than in G. melastomus, exceeding 4.5% of the total length. The caudal fin is low, with a small lower lobe and a ventral notch near the tip of the upper lobe. The skin is covered by dermal denticles, each with a leaf-shaped crown bearing a median ridge and three marginal teeth. A prominent crest of enlarged denticles runs along the front portion of the dorsal caudal fin margin. The coloration is gray above and pale below, with a series of dark gray saddles or blotches along the back and tail. The dorsal fins are dusky at the base and lighten towards the trailing margins. The trailing margin of the caudal fin is black, as is the interior of the mouth. The inside of the furrows at the corners of the mouth are dark, in contrast to G. melastomus where they are light.
Biology and ecology
The Atlantic sawtail catshark is rarer than the blackmouth catshark, which shares its range. Its natural history is poorly understood. Reproduction is oviparous, with mating and spawning proceeding throughout the year. Females can contain up to nine maturing eggs at a time, divided between the two functional oviductOviduct
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...
s. The tough egg case is flask-shaped and reddish, with a rounded bottom and a pair of "horns" at the top, and measuring around 3.1–3.8 cm (1.2–1.5 in) long and 1.1–1.3 cm (0.433070866141732–0.511811023622047 in) across. The egg case of G. melastomus is similar in appearance but significantly larger. Once deposited, the egg hatches within a short period of time. According to Compagno (2005), males attain sexual maturity
Sexual maturity
Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...
at about 38–42 cm (15–16.5 in) long, and females at about 40–45 cm (15.7–17.7 in) long. Rey and colleagues (2010) reported the smallest mature males and females in their study to be 33 cm (13 in) and 37 cm (14.6 in) long respectively.
Human interactions
FisheryFishery
Generally, a fishery is an entity engaged in raising or harvesting fish which is determined by some authority to be a fishery. According to the FAO, a fishery is typically defined in terms of the "people involved, species or type of fish, area of water or seabed, method of fishing, class of boats,...
data for the Atlantic sawtail catshark is inadequate as it is still recorded as G. melastomus by observers. This species is caught incidentally
Bycatch
The term “bycatch” is usually used for fish caught unintentionally in a fishery while intending to catch other fish. It may however also indicate untargeted catch in other forms of animal harvesting or collecting...
on deepwater longlines and bottom trawls targeting other species, including wreckfish (Polyprion americanus), conger eel (Conger conger), Norway lobster (Nephrops norvegicus), and red shrimp (Aristeus antennatus). Most landed sharks are discarded and likely suffer high mortality due to damage sustained during capture; the larger specimens are marketed for human consumption. Given the small extent of its range and the ubiquitous heavy fishing pressure within, the International Union for Conservation of Nature (IUCN) has assessed this shark 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...
.