Izak catshark
Encyclopedia
The Izak catshark is a species
of catshark
, family
Scyliorhinidae, common off South Africa
and southern Namibia
. It typically inhabits the outer continental shelf
at depths of 100–300 m (328.1–984.3 ft), with the males found deeper than females and juveniles. The Izak catshark has a short, wide, flattened head and a robust body tapering to a long, slender tail. It can be identified by its ornate color pattern of dark brown spots (in juveniles) or reticulations and blotches (in adults) on a light yellowish background, as well as by the enlarged dermal denticles over its pectoral fins and along its dorsal midline from the snout to the second dorsal fin
. This species reaches 69 cm (27.2 in) in length, with the males larger than females.
Bottom-dwelling and perhaps relatively active in nature, the Izak catshark feeds mainly on a diverse of bony fishes, crustacean
s, and cephalopod
s. A significant portion of its diet may be scavenged
from offal
discarded by fisheries. This species is oviparous, with females producing encapsulated eggs two at a time year-round. The Izak catshark is regularly caught incidentally
by a South African bottom trawl commercial fishery
, but is discarded rather than utilized. Despite the fishing pressure, its population has been increasing and thus the International Union for Conservation of Nature (IUCN) has assessed it as Least Concern
.
n ichthyologist John Gilchrist in a 1922 fisheries
survey report. He assigned the new species to the genus Scylliorhinus
, and gave it the specific epithet regani in honor of fellow ichthyologist Charles Tate Regan. In 1934, Henry Weed Fowler
assigned this species to his newly created Holohalaelurus
, a subgenus of Halaelurus
. Holohalaelurus has since been elevated to the rank of full genus. As there do not appear to be any existing type specimens referable to Gilchrist's account, in 2006 Brett Human designated a 63 cm (24.8 in) long male caught in Hondeklip Bay as the species neotype.
Historically, there has been much confusion in the scientific literature between H. regani, H. punctatus, and H. melanostigma, the last of which at various times had been considered a junior synonym of H. regani and was itself confounded with H. grennian. Furthermore, two forms of H. regani were once recognized: the "Cape" or "typical" form and the "Natal" or "northeastern" form. The latter "northeastern" form was described as a separate species, H. favus, in 2006.
, Namibia
in the west to Durban
, South Africa in the east. Older records further north along the East Africa
n coast (e.g. Somalia
) most likely refer to other Holohalaelurus species. This abundant, bottom-dwelling species inhabits the outer continental shelf
and upper continental slope, from 40 m (131.2 ft) to at least 1075 m (3,526.9 ft) deep. Off South Africa, it is most common in areas with a wider continental shelf, and at depths of 100–200 m (328.1–656.2 ft) off the south coast and 200–300 m (656.2–984.3 ft) off the west coast. Females and juveniles tend to be found in shallower water than males. For the most part, the number of sharks in a given area remains largely constant throughout the year. However, sharks at the southernmost point of the Agulhas Bank
may perform a small autumn migration
towards the shore.
and is followed by a spiracle
. The nostrils are preceded by triangular flaps of skin that almost reach the long, angular mouth. The mouth contains prominent papillae on both the roof and the floor, and lacks furrows at the corners. The upper and lower jaws contain on average 65 and 60 tooth rows respectively; each tooth is relatively large, with a narrow central cusp
flanked by 1–2 smaller cusplets. There are five pairs of gill slit
s.
The pectoral fins are rather long and broad. The first dorsal fin
originates over the rear of the pelvic fin bases; the second dorsal fin is slightly larger and originates over the rear of the anal fin base. The pelvic and anal fins are long and low, and larger than the dorsal fins. The free rear tips of the pelvic fins may be fused together to some degree, but never completely; males have slender, pointed claspers. The caudal peduncle is long and thin, particularly in younger sharks. The caudal fin makes up one-fourth to one-fifth of the total length and has a weak lower lobe and a ventral notch near the tip of the upper lobe. The thick skin is covered by well-calcified
dermal denticles, except around the gill slits. Enlarged, spike-like denticles are found on the upper surface of the pectoral fins and along the dorsal midline from the snout to the second dorsal fin origin. Juvenile Izak catsharks are boldly patterned with many irregularly shaped dark brown spots on a light yellow to yellowish brown background. The spots enlarge and fuse with age to form an intricate pattern of reticulations and U-shaped markings in adults. The underside is plain white, with obvious black sensory pores beneath the head, body, and paired fins. Like other Holohalaelurus species, but contrary to the pattern in most cartilaginous fishes, males attain a much greater maximum length than females: 69 cm (27.2 in) versus 52 cm (20.5 in).
Compared to other deep-sea sharks, the Izak catshark has a large heart
suggestive of a relatively active lifestyle. It is a generalist
that feeds on a wide variety of bony fishes, crustacean
s, and cephalopod
s; larger sharks consume proportionately more crustaceans and fewer fishes. At least some part of its recorded diet probably represents scavenging
from fishery
discards, given the presence of fast-moving, pelagic species that the shark is unlikely to have captured live. Polychaete worms, hydrozoa
ns, gastropods, and hagfish
eggs may also be occasionally ingested. This species often has nematode
and flatworm
parasites in its stomach
.
The Izak catshark is oviparous and reproduction proceeds throughout the year without seasonal patterns. Mature females have a single functional ovary
and two functional oviduct
s; a single egg matures within each oviduct at a time. Each egg is contained within a purse-shaped capsule 3.6–4.3 cm (1.4–1.7 in) long and 1.2–1.5 cm (0.47244094488189–0.590551181102362 in) across. The capsule is light brown with long tendrils at the four corners that likely serve to anchor it to rocks; its surface has a velvet
-like texture and bears lengthwise striations. The rate of egg laying is unknown but thought to be high, based on this shark's resilience to fishing pressure. The preponderance of females and juveniles at shallower depths may indicate that such waters serve as nursery areas. The young hatch at under 11 cm (4.3 in) long. Males and females mature sexually
at 45–50 cm (17.7–19.7 in) and 40–45 cm (15.7–17.7 in) long respectively.
(and discarded) by a bottom trawl fishery
targeting hake south of Cape Town
. In contrast to most cartilaginous fishes, its numbers have been increasing in the presence of commercial fishing
. The reasons for this may include its high reproductive rate, its breeding in less-fished shallower waters, its hardiness allowing for high post-capture survival, and its opportunistic diet. The International Union for Conservation of Nature (IUCN) has consequently listed the Izak catshark under Least Concern
, while still noting that it merits continued population monitoring because of its highly restricted range.
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, common off 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...
and southern 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...
. It typically 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,...
at depths of 100–300 m (328.1–984.3 ft), with the males found deeper than females and juveniles. The Izak catshark has a short, wide, flattened head and a robust body tapering to a long, slender tail. It can be identified by its ornate color pattern of dark brown spots (in juveniles) or reticulations and blotches (in adults) on a light yellowish background, as well as by the enlarged dermal denticles over its pectoral fins and along its dorsal midline from the snout to the second 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...
. This species reaches 69 cm (27.2 in) in length, with the males larger than females.
Bottom-dwelling and perhaps relatively active in nature, the Izak catshark feeds mainly on a diverse of bony fishes, 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 cephalopod
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...
s. A significant portion of its diet may be scavenged
Scavenger
Scavenging is both a carnivorous and herbivorous feeding behavior in which individual scavengers search out dead animal and dead plant biomass on which to feed. The eating of carrion from the same species is referred to as cannibalism. Scavengers play an important role in the ecosystem by...
from offal
Offal
Offal , also called, especially in the United States, variety meats or organ meats, refers to the internal organs and entrails of a butchered animal. The word does not refer to a particular list of edible organs, which varies by culture and region, but includes most internal organs other than...
discarded by fisheries. This species is oviparous, with females producing encapsulated eggs two at a time year-round. The Izak catshark is regularly 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 a South African bottom trawl commercial fishery
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...
, but is discarded rather than utilized. Despite the fishing pressure, its population has been increasing and thus the International Union for Conservation of Nature (IUCN) has assessed it 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
The Izak catshark was originally described by South AfricaSouth 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...
n ichthyologist John Gilchrist in a 1922 fisheries
Fishery
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,...
survey report. He assigned the new species to the genus Scylliorhinus
Scyliorhinus
Scylorhinus is a genus of catsharks in the family Scyliorhinidae.-Species:* Scyliorhinus besnardi S. Springer & Sadowsky, 1970 * Scyliorhinus boa Goode & Bean, 1896...
, and gave it the specific epithet regani in honor of fellow ichthyologist Charles Tate Regan. In 1934, Henry Weed Fowler
Henry Weed Fowler
Henry Weed Fowler was an American zoologist born in Holmesburg, Pennsylvania.He studied at Stanford University under David Starr Jordan...
assigned this species to his newly created Holohalaelurus
Holohalaelurus
Holohalaelurus is a genus of catshark in the family Scyliorhinidae, commonly known as Izak catsharks or hallelujah sharks.-Species:* Holohalaelurus favus Human, 2006...
, a subgenus of Halaelurus
Halaelurus
Halaelurus is a genus of catshark in the family Scyliorhinidae.-Species:* Halaelurus boesemani S. Springer & D'Aubrey, 1972 * Halaelurus buergeri...
. Holohalaelurus has since been elevated to the rank of full genus. As there do not appear to be any existing type specimens referable to Gilchrist's account, in 2006 Brett Human designated a 63 cm (24.8 in) long male caught in Hondeklip Bay as the species neotype.
Historically, there has been much confusion in the scientific literature between H. regani, H. punctatus, and H. melanostigma, the last of which at various times had been considered a junior synonym of H. regani and was itself confounded with H. grennian. Furthermore, two forms of H. regani were once recognized: the "Cape" or "typical" form and the "Natal" or "northeastern" form. The latter "northeastern" form was described as a separate species, H. favus, in 2006.
Distribution and habitat
Endemic to the southern tip of Africa, the range of the Izak catshark extends from LüderitzLüderitz
Lüderitz is a harbour town in south-west Namibia, lying on one of the least hospitable coasts in Africa. It is a port developed around Robert Harbour and Shark Island.- Overview :...
, 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...
in the west to Durban
Durban
Durban is the largest city in the South African province of KwaZulu-Natal and the third largest city in South Africa. It forms part of the eThekwini metropolitan municipality. Durban is famous for being the busiest port in South Africa. It is also seen as one of the major centres of tourism...
, South Africa in the east. Older records further north along the East Africa
East Africa
East Africa or Eastern Africa is the easterly region of the African continent, variably defined by geography or geopolitics. In the UN scheme of geographic regions, 19 territories constitute Eastern Africa:...
n coast (e.g. Somalia
Somalia
Somalia , officially the Somali Republic and formerly known as the Somali Democratic Republic under Socialist rule, is a country located in the Horn of Africa. Since the outbreak of the Somali Civil War in 1991 there has been no central government control over most of the country's territory...
) most likely refer to other Holohalaelurus species. This abundant, bottom-dwelling 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, from 40 m (131.2 ft) to at least 1075 m (3,526.9 ft) deep. Off South Africa, it is most common in areas with a wider continental shelf, and at depths of 100–200 m (328.1–656.2 ft) off the south coast and 200–300 m (656.2–984.3 ft) off the west coast. Females and juveniles tend to be found in shallower water than males. For the most part, the number of sharks in a given area remains largely constant throughout the year. However, sharks at the southernmost point of the Agulhas Bank
Agulhas Bank
The Agulhas Bank is a broad, shallow part of the southern African continental shelf which extends south of Cape Agulhas before falling away steeply away to the abyssal plain....
may perform a small autumn migration
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...
towards the shore.
Description
The body of the Izak catshark is firm and stout, tapering dramatically towards the tail. The head is very short, wide, and flattened, with a blunt snout. The horizontally oval eyes are placed high on the head and have thick ridges beneath; each has a 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...
and is followed by a 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...
. The nostrils are preceded by triangular flaps of skin that almost reach the long, angular mouth. The mouth contains prominent papillae on both the roof and the floor, and lacks furrows at the corners. The upper and lower jaws contain on average 65 and 60 tooth rows respectively; each tooth is relatively large, with a narrow central cusp
Cusp (dentistry)
A cusp is an occlusal or incisal eminence on a tooth.Canine teeth, otherwise known as cuspids, each possess a single cusp, while premolars, otherwise known as bicuspids, possess two each. Molars normally possess either four or five cusps...
flanked by 1–2 smaller 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 pectoral fins are rather long and broad. 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...
originates over the rear of the pelvic fin bases; the second dorsal fin is slightly larger and originates over the rear of the anal fin base. The pelvic and anal fins are long and low, and larger than the dorsal fins. The free rear tips of the pelvic fins may be fused together to some degree, but never completely; males have slender, pointed claspers. The caudal peduncle is long and thin, particularly in younger sharks. The caudal fin makes up one-fourth to one-fifth of the total length and has a weak lower lobe and a ventral notch near the tip of the upper lobe. The thick skin is covered by well-calcified
Calcification
Calcification is the process in which calcium salts build up in soft tissue, causing it to harden. Calcifications may be classified on whether there is mineral balance or not, and the location of the calcification.-Causes:...
dermal denticles, except around the gill slits. Enlarged, spike-like denticles are found on the upper surface of the pectoral fins and along the dorsal midline from the snout to the second dorsal fin origin. Juvenile Izak catsharks are boldly patterned with many irregularly shaped dark brown spots on a light yellow to yellowish brown background. The spots enlarge and fuse with age to form an intricate pattern of reticulations and U-shaped markings in adults. The underside is plain white, with obvious black sensory pores beneath the head, body, and paired fins. Like other Holohalaelurus species, but contrary to the pattern in most cartilaginous fishes, males attain a much greater maximum length than females: 69 cm (27.2 in) versus 52 cm (20.5 in).
Biology and ecology
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
suggestive of a relatively active lifestyle. It is a generalist
Generalist and specialist species
A generalist species is able to thrive in a wide variety of environmental conditions and can make use of a variety of different resources . A specialist species can only thrive in a narrow range of environmental conditions or has a limited diet. Most organisms do not all fit neatly into either...
that feeds on a wide variety of bony fishes, 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 cephalopod
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...
s; larger sharks consume proportionately more crustaceans and fewer fishes. At least some part of its recorded diet probably represents scavenging
Scavenger
Scavenging is both a carnivorous and herbivorous feeding behavior in which individual scavengers search out dead animal and dead plant biomass on which to feed. The eating of carrion from the same species is referred to as cannibalism. Scavengers play an important role in the ecosystem by...
from fishery
Fishery
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,...
discards, given the presence of fast-moving, pelagic species that the shark is unlikely to have captured live. Polychaete worms, hydrozoa
Hydrozoa
Hydrozoa are a taxonomic class of very small, predatory animals which can be solitary or colonial and which mostly live in saltwater. A few genera within this class live in freshwater...
ns, gastropods, and hagfish
Hagfish
Hagfish, the clade Myxini , are eel-shaped slime-producing marine animals . They are the only living animals that have a skull but not a vertebral column. Along with lampreys, hagfish are jawless and are living fossils whose next nearest relatives include all vertebrates...
eggs may also be occasionally ingested. This species often has 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...
and flatworm
Flatworm
The flatworms, known in scientific literature as Platyhelminthes or Plathelminthes are a phylum of relatively simple bilaterian, unsegmented, soft-bodied invertebrate animals...
parasites in its stomach
Stomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
.
The Izak catshark is oviparous and reproduction proceeds throughout the year without seasonal patterns. Mature females have a single functional 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...
and two functional 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...
s; a single egg matures within each oviduct at a time. Each egg is contained within a purse-shaped capsule 3.6–4.3 cm (1.4–1.7 in) long and 1.2–1.5 cm (0.47244094488189–0.590551181102362 in) across. The capsule is light brown with long tendrils at the four corners that likely serve to anchor it to rocks; its surface has a velvet
Velvet
Velvet is a type of woven tufted fabric in which the cut threads are evenly distributed,with a short dense pile, giving it a distinctive feel.The word 'velvety' is used as an adjective to mean -"smooth like velvet".-Composition:...
-like texture and bears lengthwise striations. The rate of egg laying is unknown but thought to be high, based on this shark's resilience to fishing pressure. The preponderance of females and juveniles at shallower depths may indicate that such waters serve as nursery areas. The young hatch at under 11 cm (4.3 in) long. Males and females mature sexually
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 45–50 cm (17.7–19.7 in) and 40–45 cm (15.7–17.7 in) long respectively.
Human interactions
The Izak catshark is harmless and of no commercial value. It is regularly 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...
(and discarded) by a bottom trawl fishery
Fishery
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,...
targeting hake south of Cape Town
Cape Town
Cape Town is the second-most populous city in South Africa, and the provincial capital and primate city of the Western Cape. As the seat of the National Parliament, it is also the legislative capital of the country. It forms part of the City of Cape Town metropolitan municipality...
. In contrast to most cartilaginous fishes, its numbers have been increasing in the presence of commercial fishing
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...
. The reasons for this may include its high reproductive rate, its breeding in less-fished shallower waters, its hardiness allowing for high post-capture survival, and its opportunistic diet. The International Union for Conservation of Nature (IUCN) has consequently listed the Izak catshark 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...
, while still noting that it merits continued population monitoring because of its highly restricted range.