African sawtail catshark
Encyclopedia
The African sawtail catshark (Galeus polli) is a species
of catshark
, family
Scyliorhinidae. Demersal in nature, it is found at depths of 160–720 m (524.9–2,362.2 ft) off the western Africa
n coast from Morocco
to South Africa
. This slender species has a rather long, pointed snout, a series of dark saddles along the back and tail, and a prominent crest of enlarged dermal denticles along the upper edge of the caudal fin. Its maximum known length is 46 cm (18.1 in).
The diet of the African sawtail catshark consists of small bony fishes, squid
, and crustacean
s. It is the only member of its genus known to be aplacental viviparous; reproduction proceeds year-round, with females bear litters of up to 12 pups. In relatively shallower waters, this shark is caught incidentally
and utilized for meat or fishmeal. The fisheries off Namibia
, where it is most abundant, are well-managed and do not threaten its population. Given also that sharks in deeper waters are not significantly fished, the International Union for Conservation of Nature (IUCN) has assessed this species as Least Concern
.
published a report on shark
s and chimaera
s captured during a 1948–49 Belgian oceanographic expedition off western Africa, including several seemingly ovoviviparous blackmouth catshark
s (G. melastomus). As the blackmouth catshark is known to be oviparous, Poll's account alerted French zoologist Jean Cadenat to the presence of a distinct catshark species in the region. After examining more specimens from Senegal
, Cadenat described the new species in a 1959 issue of the scientific journal
Bulletin de l'Institut Francais d'Afrique Noire (Sér A) Sciences Naturelles, naming it in Poll's honor.
to the Northern Cape Province of South Africa
. It is known to be abundant off Namibia
and rare south of the Orange River
. This species inhabits the outer continental shelf
and upper continental slope between the depths of 160 and 720 m (524.9 and 2,362.2 ft), and is most common at depths of 258–490 m (846.5–1,607.6 ft). Found on or near the bottom, this shark can tolerate water with low levels of dissolved oxygen.
s (protective third eyelids), and lack strong ridges underneath. Tiny spiracle
s are located behind the eyes. The mouth is large, wide, and arched, with well-developed furrows at the corners. The teeth have a central cusp and 1–2 pairs of smaller lateral cusplets. There are five pairs of gill slit
s.
The two dorsal fin
s are blunt-tipped and similar in size; the first is positioned over the rear of the pelvic fins and the second over the rear of the anal fin. The pectoral fins are large and broad with rounded corners, while the pelvic and anal fins are elongated and more angular. The anal fin base is close to the pelvic and caudal fins and measures 14–17% of the total length, much greater than the distance between the dorsal fins. The caudal peduncle is compressed from side to side and leads to a low caudal fin with a small lower lobe and a ventral notch near the tip of the upper lobe. The dermal denticles are small and overlapping, each with three-toothed crown that bears a median ridge. There is a crest of enlarged saw-like denticles along the dorsal edge of the caudal fin. This species is dusky above and light below. There are typically 11 or fewer dark gray or brown saddles and/or blotches outlined in white along the back and tail. The pattern tends to fade with age, and some individuals are uniformly colored. The interior of the mouth is black.
es, hakes, grenadiers, rockfish
es and lightfish
es, comprise the bulk of the African sawtail catshark's diet. Squid
and crustacean
s may also be consumed. A known predator of this species is the southern African frilled shark
(Chlamydoselachus africana). Unlike other members of its genus, the African sawtail catshark is aplacental viviparous, with females retaining eggs internally until they hatch. There is apparently no defined breeding season, and mating and birthing occur throughout the year. Adult females have two functional uterus
es and produce litters of up to 12 young; litter size increases with female size. The developing embryo
s are initially sustained an external yolk sac
, and emerge from the egg at between 2.4 and 2.8 cm (0.94488188976378 and 1.1 in) long. Pigmentation begins to develop at an embryonic length of 5 cm (2 in). At around 6 cm (2.4 in) long, the embryos have well-developed external gills
, which largely disappear by the time they are 10 cm (3.9 in) long. Near-term fetus
es weigh over twice as much as eggs, suggesting some form of secondary maternal provisioning during gestation
. The newborns measure 10–18 cm (3.9–7.1 in) long. Males and females reach sexual maturity
at 30–46 cm (11.8–18.1 in) and 30–43 cm (11.8–16.9 in) long respectively.
in bottom trawls. Landed sharks may be marketed for human consumption or processed into fishmeal. Because this species is largely protected from fishing pressure in deeper water, and the Namibian fisheries operating at its center of abundance are well-regulated, the International Union for Conservation of Nature (IUCN) has listed it under Least Concern
.
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. Demersal in nature, it is found at depths of 160–720 m (524.9–2,362.2 ft) off the western Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
n coast from Morocco
Morocco
Morocco , officially the Kingdom of Morocco , is a country located in North Africa. It has a population of more than 32 million and an area of 710,850 km², and also primarily administers the disputed region of the Western Sahara...
to South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
. This slender species has a rather long, pointed snout, a series of dark saddles along the back and tail, and a prominent crest of enlarged dermal denticles along the upper edge of the caudal fin. Its maximum known length is 46 cm (18.1 in).
The diet of the African sawtail catshark consists of small bony fishes, 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...
, and 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. It is the only member of its genus known to be aplacental viviparous; reproduction proceeds year-round, with females bear litters of up to 12 pups. In relatively shallower waters, this shark 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...
and utilized for meat or fishmeal. The fisheries off Namibia
Namibia
Namibia, officially the Republic of Namibia , is a country in southern Africa whose western border is the Atlantic Ocean. It shares land borders with Angola and Zambia to the north, Botswana to the east and South Africa to the south and east. It gained independence from South Africa on 21 March...
, where it is most abundant, are well-managed and do not threaten its population. Given also that sharks in deeper waters are not significantly fished, the International Union for Conservation of Nature (IUCN) has assessed this species as Least Concern
Least Concern
Least Concern is an IUCN category assigned to extant taxon or lower taxa which have been evaluated but do not qualify for any other category. As such they do not qualify as threatened, Near Threatened, or Conservation Dependent...
.
Taxonomy
In 1953, Belgian ichthyologist Max PollMax Poll
Max Fernand Leon Poll was a Belgian ichthyologist who specialised in Cichlidae.In the years 1946 and 1947 he organised an expedition to Lake Tanganyika....
published a report on shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....
s and chimaera
Chimaera
Chimaeras are cartilaginous fish in the order Chimaeriformes, known informally as ghost sharks, ratfish , spookfish , or rabbitfishes...
s captured during a 1948–49 Belgian oceanographic expedition off western Africa, including several seemingly ovoviviparous 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...
s (G. melastomus). As the blackmouth catshark is known to be oviparous, Poll's account alerted French zoologist Jean Cadenat to the presence of a distinct catshark species in the region. After examining more specimens from Senegal
Senegal
Senegal , officially the Republic of Senegal , is a country in western Africa. It owes its name to the Sénégal River that borders it to the east and north...
, Cadenat described the new species in a 1959 issue of the scientific journal
Scientific journal
In academic publishing, a scientific journal is a periodical publication intended to further the progress of science, usually by reporting new research. There are thousands of scientific journals in publication, and many more have been published at various points in the past...
Bulletin de l'Institut Francais d'Afrique Noire (Sér A) Sciences Naturelles, naming it in Poll's honor.
Distribution and habitat
The African sawtail catshark is found along much of the western coast of Africa, from southern MoroccoMorocco
Morocco , officially the Kingdom of Morocco , is a country located in North Africa. It has a population of more than 32 million and an area of 710,850 km², and also primarily administers the disputed region of the Western Sahara...
to the Northern Cape Province of South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
. It is known to be abundant off Namibia
Namibia
Namibia, officially the Republic of Namibia , is a country in southern Africa whose western border is the Atlantic Ocean. It shares land borders with Angola and Zambia to the north, Botswana to the east and South Africa to the south and east. It gained independence from South Africa on 21 March...
and rare south of the Orange River
Orange River
The Orange River , Gariep River, Groote River or Senqu River is the longest river in South Africa. It rises in the Drakensberg mountains in Lesotho, flowing westwards through South Africa to the Atlantic Ocean...
. This species inhabits the outer 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,...
and upper continental slope between the depths of 160 and 720 m (524.9 and 2,362.2 ft), and is most common at depths of 258–490 m (846.5–1,607.6 ft). Found on or near the bottom, this shark can tolerate water with low levels of dissolved oxygen.
Description
The African sawtail catshark attains a maximum known length of 46 cm (18.1 in); females tend to be larger than males. It has a slender, firm body and a slightly flattened head with a long, pointed snout. The anterior rim of each nostril bears a triangular flap of skin. The eyes are horizontally oval, 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), and lack strong ridges underneath. Tiny 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 are located behind the eyes. The mouth is large, wide, and arched, with well-developed furrows at the corners. The teeth have a central cusp and 1–2 pairs of smaller lateral cusplets. 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 two 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 blunt-tipped and similar in size; the first is positioned over the rear of the pelvic fins and the second over the rear of the anal fin. The pectoral fins are large and broad with rounded corners, while the pelvic and anal fins are elongated and more angular. The anal fin base is close to the pelvic and caudal fins and measures 14–17% of the total length, much greater than the distance between the dorsal fins. The caudal peduncle is compressed from side to side and leads to a low caudal fin with a small lower lobe and a ventral notch near the tip of the upper lobe. The dermal denticles are small and overlapping, each with three-toothed crown that bears a median ridge. There is a crest of enlarged saw-like denticles along the dorsal edge of the caudal fin. This species is dusky above and light below. There are typically 11 or fewer dark gray or brown saddles and/or blotches outlined in white along the back and tail. The pattern tends to fade with age, and some individuals are uniformly colored. The interior of the mouth is black.
Biology and ecology
Small bony fishes, including lanternfishLanternfish
Cooper Lanternfishes are small mesopelagic fish of the large family Myctophidae. One of two families in the order Myctophiformes, the Myctophidae are represented by 246 species in 33 genera, and are found in oceans worldwide. They are aptly named after their conspicuous use of bioluminescence...
es, hakes, grenadiers, rockfish
Sebastidae
Sebastidae is a family of marine fish in the order Scorpaeniformes. Their common names include rockfishes, thornyheads and rockcods. Despite the latter name, they are not closely related to the cods in the genus Gadus, nor the rock cod, Lotella rhacina.Not all authorities recognise this family as...
es and lightfish
Phosichthyidae
Lightfishes are small stomiiform fishes in the family PhosichthyidaeThey are very small fishes found in oceans throughout the world: most species grow no longer than 10 cm, while those in the genus Vinciguerria only reach 4 cm or so....
es, comprise the bulk of the African sawtail catshark's diet. 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...
and 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 may also be consumed. A known predator of this species is the southern African frilled shark
Southern African frilled shark
The southern African frilled shark is a species of shark in the family Chlamydoselachidae, described in 2009. It is found in deep water from off southern Angola to southern Namibia. This species is difficult to distinguish from the better-known frilled shark The southern African frilled shark...
(Chlamydoselachus africana). Unlike other members of its genus, the African sawtail catshark is aplacental viviparous, with females retaining eggs internally until they hatch. There is apparently no defined breeding season, and mating and birthing occur throughout the year. Adult females have two functional uterus
Uterus
The uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...
es and produce litters of up to 12 young; litter size increases with female size. The developing 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 are initially sustained an external yolk sac
Yolk sac
The yolk sac is a membranous sac attached to an embryo, providing early nourishment in the form of yolk in bony fishes, sharks, reptiles, birds, and primitive mammals...
, and emerge from the egg at between 2.4 and 2.8 cm (0.94488188976378 and 1.1 in) long. Pigmentation begins to develop at an embryonic length of 5 cm (2 in). At around 6 cm (2.4 in) long, the embryos have well-developed external gills
External gills
External gills are the gills of an animal, most typically an amphibian, that are exposed to the environment, rather than set inside the pharynx and covered by gill slits, as they are in most fishes. Instead, the respiratory organs are set on a frill of stalks protruding from the sides of an animals...
, which largely disappear by the time they are 10 cm (3.9 in) long. Near-term fetus
Fetus
A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...
es weigh over twice as much as eggs, suggesting some form of secondary maternal provisioning during gestation
Gestation
Gestation is the carrying of an embryo or fetus inside a female viviparous animal. Mammals during pregnancy can have one or more gestations at the same time ....
. The newborns measure 10–18 cm (3.9–7.1 in) long. Males and females reach 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 30–46 cm (11.8–18.1 in) and 30–43 cm (11.8–16.9 in) long respectively.
Human interactions
There is intensive fishing activity in the shallower portions of the African sawtail catshark's distribution, where it is caught incidentallyBycatch
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. Landed sharks may be marketed for human consumption or processed into fishmeal. Because this species is largely protected from fishing pressure in deeper water, and the Namibian fisheries operating at its center of abundance are well-regulated, the International Union for Conservation of Nature (IUCN) has listed it under Least Concern
Least Concern
Least Concern is an IUCN category assigned to extant taxon or lower taxa which have been evaluated but do not qualify for any other category. As such they do not qualify as threatened, Near Threatened, or Conservation Dependent...
.