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Overview

Comprehensive Description

Biology

An uncommon primitive shark (Ref. 26346) found on outer continental and insular shelves and upper slopes, usually between 120 and 1,280 m but occasionally caught at the surface (Ref. 247). Feeds on other sharks, squid and bony fish (Ref. 26346). Ovoviviparous (Ref. 50449), litter size ranges from 2 to 10 (Ref. 37390). Not dangerous but teeth are sharp enough to inflict lacerations on the hands of the unwary scientist examining its mouth (Ref. 247). Incidental in bottom trawl catches and utilized as fishmeal and as food fish (Ref. 247).
  • Compagno, L.J.V. 1984 FAO Species Catalogue. Vol. 4. Sharks of the world. An annotated and illustrated catalogue of shark species known to date. Part 1 - Hexanchiformes to Lamniformes. FAO Fish. Synop. 125(4/1):1-249. Rome: FAO. (Ref. 247)
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Distribution

Frilled sharks are wide ranging. They have been found almost worldwide, including the eastern Atlantic coast of northern Norway, the western Indian Ocean near South Africa, the western Pacific near New Zealand, and the eastern Pacific near the coast of Chile.

Biogeographic Regions: indian ocean (Native ); atlantic ocean (Native ); pacific ocean (Native )

  • Compagno, L. 1984. Sharks of the World. FAO Species Catalogue, 4 (1): 14-15.
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Range Description

Generally rare, only a few localities where it is more common. Range almost worldwide.
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National Distribution

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

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A specimen collected by a commercial fishing vessel on the continental slope between Block and Alvin Canyons (39° 57' N, 71° 00' W)
  • North-West Atlantic Ocean species (NWARMS)
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Wide-ranging but with patchy distribution. Western Indian Ocean: off South Africa. Western Pacific: off Japan to New Zealand. Eastern Pacific: southern California, USA to northern Chile. Eastern Atlantic: northern Norway to northern Namibia, possibly the eastern Cape of Good Hope, South Africa. Three specimens have been recorded from the western Atlantic (Ref. 13608).
  • Compagno, L.J.V. 1984 FAO Species Catalogue. Vol. 4. Sharks of the world. An annotated and illustrated catalogue of shark species known to date. Part 1 - Hexanchiformes to Lamniformes. FAO Fish. Synop. 125(4/1):1-249. Rome: FAO. (Ref. 247)
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Atlantic, Pacific, but with patchy records; antitropical [not southeastern Atlantic].
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Physical Description

Morphology

Frilled sharks, or eel sharks (Taylor et al., 2002), have a long slender body with an elongate tail fin, giving them an eel-like appearance (Compagno, 1984). The body tends to be a chocolate brown color. They have a small dorsal fin located well towards the tail, above the large anal fin, and in front of the highly asymmetric caudal fin. The pectoral fins are short and rounded (Taylor et al., 2002). Chlamydoselachus africana has six gill openings (most sharks have five). The first gill is continuous across the throat, while all the gills are surrounded by frilly margins of skin-hence the name "frilled shark." The snout is short and the lower jaw is long. The teeth are alike both on the upper and lower jaws, with three elongate, sharp cusps separated by two intermediate ones (Taylor et al., 2002; Nelson, 1994). Length is usually 2 meters (Miller and Lea, 1972).

Range length: 2 (high) m.

Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry

Sexual Dimorphism: female larger

  • Miller, D., R. Lea. 1972. Guide to the Coastal Marine Fishes of California.
  • Nelson, J. 1994. Fishes of the World; 3rd Edition. New York, Chichester, Brisbane, Toronto, & Singapore: John Wiley &Sons, Inc.
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Dorsal spines (total): 0; Dorsal soft rays (total): 0; Analspines: 0; Analsoft rays: 0; Vertebrae: 146 - 171
  • Last, P.R. and J.D. Stevens 1994 Sharks and rays of Australia. CSIRO, Australia. 513 p. (Ref. 6871)
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Size

Maximum size: 2000 mm TL
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Max. size

200 cm TL (male/unsexed; (Ref. 26346))
  • Cox, G. and M. Francis 1997 Sharks and rays of New Zealand. Canterbury Univ. Press, Univ. of Canterbury. 68 p. (Ref. 26346)
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Diagnostic Description

Eel-like shark with 6 gill slits, the lower ends of the first gill slits connected t each other across throat (Ref. 247). Dark brown or grey in color, sometimes paler below (Ref. 26346). Dorsal fin small and lobe-like originating over pelvic fin bases to behind anal fin origin (Ref. 6871). Anal fin larger than dorsal fin (Ref. 6871). Pectoral fins small and paddle-shaped (Ref. 6871). Caudal fin with weak ventral lobe and without subterminal notch (Ref. 6871). Terminal mouth with tricuspid teeth in both jaws (Ref. 247).
  • Last, P.R. and J.D. Stevens 1994 Sharks and rays of Australia. CSIRO, Australia. 513 p. (Ref. 6871)
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Ecology

Habitat

Chlamydoselachus africana, is found on continental shelves and the nearshore areas of large islands, although they are occasionally reported in open waters. They are mostly benthic and occur at depths from 100 to 1,300 meters.

Range depth: 100 to 1300 m.

Habitat Regions: temperate ; tropical ; saltwater or marine

Aquatic Biomes: benthic ; coastal

  • Tricas, T., K. Deacon, P. Last, J. McCosker, T. Walker, L. Taylor. 2002. The Nature Companions Sharks and Whales. 814 Montgomery Street, San Francisco CA, 94133 USA: Fog City Press.
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Habitat and Ecology

Habitat and Ecology
Marine, demersal or benthopelagic, reported as occasionally pelagic on the upper and middle continental slope, 100 to 1,500 m, usually 500 to 1,000 m. An active predator on deepwater squid and a variety of fish (including other sharks). Large mouth with sharp inwards-pointing teeth can take large prey, but this shark is not considered dangerous to man. Born 40 to 60 cm total length (TL). Mature 97 to 117 cm TL (males), 135 to 150 cm TL (females). Maximum approximately 196 cm TL (females). Ovoviviparous with 6 to 12 pups per litter, possibly a long gestation period but life cycle basically unknown.

Systems
  • Marine
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Habitat Type: Marine

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Known from seamounts and knolls
  • Stocks, K. 2009. Seamounts Online: an online information system for seamount biology. Version 2009-1. World Wide Web electronic publication.
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benthic
  • North-West Atlantic Ocean species (NWARMS)
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Environment

bathydemersal; marine; depth range 0 - 1570 m (Ref. 10290), usually 120 - 1280 m (Ref. 247)
  • Compagno, L.J.V. 1984 FAO Species Catalogue. Vol. 4. Sharks of the world. An annotated and illustrated catalogue of shark species known to date. Part 1 - Hexanchiformes to Lamniformes. FAO Fish. Synop. 125(4/1):1-249. Rome: FAO. (Ref. 247)
  • Springer, S. 1990 Chlamydoselachidae. p. 2. In J.C. Quero, J.C. Hureau, C. Karrer, A. Post, and L. Saldanha (eds.) Check-list of the fishes of the eastern tropical Atlantic (CLOFETA). JNICT, Lisbon; SEI, Paris; and UNESCO, Paris. Vol. 1. (Ref. 10290)
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Depth range based on 58 specimens in 1 taxon.
Water temperature and chemistry ranges based on 38 samples.

Environmental ranges
  Depth range (m): 409 - 1440
  Temperature range (°C): 3.980 - 8.059
  Nitrate (umol/L): 13.189 - 35.146
  Salinity (PPS): 34.359 - 35.127
  Oxygen (ml/l): 3.111 - 6.344
  Phosphate (umol/l): 0.923 - 2.345
  Silicate (umol/l): 7.726 - 52.547

Graphical representation

Depth range (m): 409 - 1440

Temperature range (°C): 3.980 - 8.059

Nitrate (umol/L): 13.189 - 35.146

Salinity (PPS): 34.359 - 35.127

Oxygen (ml/l): 3.111 - 6.344

Phosphate (umol/l): 0.923 - 2.345

Silicate (umol/l): 7.726 - 52.547
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

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Depth: 0 - 1570m.
Recorded at 1570 meters.

Habitat: bathydemersal. Lives on the outer continental and insular shelves and upper slopes. Feeds on squid and various bottom fishes. Strange shark because of its 6 gill slits and because the first gill slit nearly encircles the head. Ovoviviparous with 8-15 pups (Ref. 6871). Size at birth 40-60 cm (Ref. 6871). Off Japan, it reproduces all year round. Teeth are sharp enough to inflict lacerations on the hands of the unwary scientist examining its mouth.
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Migration

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

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Trophic Strategy

Because of their sharp, cuspidate teeth, it is thought that their primary foods are small deep-water fishes, and squid (Taylor et al., 2002). Because frilled sharks live on the ocean floor, they may also feed on carrion floating down from the surface (Parker & Parker, 1999).

Animal Foods: fish; carrion ; mollusks; aquatic crustaceans

Primary Diet: carnivore (Piscivore , Molluscivore ); detritivore

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An uncommon primitive shark (Ref. 26346) found on outer continental and insular shelves and upper slopes, usually between 120 and 1,280 m but occasionally caught at the surface (Ref. 247). Feeds on other sharks, squid and bony fish (Ref. 26346).
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Associations

Frilled sharks are bottom dwellers and may contribute to removing decomposing carcasses. This carrion floats down from the open waters of the ocean above and comes to rest on the ocean floor. Frilled sharks and other benthic decomposers play an important role in recycling nutrients.

Ecosystem Impact: biodegradation

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There are few known predators of frilled sharks. Other sharks are likely predators and humans may take these sharks incidentally as fishing bycatch. Becauses they occupy the benthos, they are sometimes caught during bottom trawling or in nets when they venture near the surface.

Known Predators:

Anti-predator Adaptations: cryptic

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Life History and Behavior

Behavior

There is very little known about the communication and perception of frilled sharks because they live in deep water and are hard to observe. Based on information from other deep water sharks, they probably use their lateral line and sense of touch to navigate along the contours of the sea bed. Deep water sharks are also sensitive to sounds or long-distance vibrations, and to electrical pulses given off by animal muscles. Also, they have the ability to detect changes in water pressure to tell up from down.

Communication Channels: acoustic ; electric

Other Communication Modes: vibrations

Perception Channels: tactile ; acoustic ; vibrations ; chemical ; electric

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Life Cycle

Ovoviviparous, embryos feed solely on yolk (Ref. 50449). Number of young 2 to 15 (Ref. 26346). Gestation period is probably very long, one to two years (Ref. 39551). Size at birth 40-60 cm (Ref. 6871). Distinct pairing with embrace (Ref. 205).
  • Breder, C.M. and D.E. Rosen 1966 Modes of reproduction in fishes. T.F.H. Publications, Neptune City, New Jersey. 941 p. (Ref. 205)
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Life Expectancy

Frilled sharks have never been kept in captivity. In the wild it is difficult to determine just how long these fish live. Because they are deep benthic creatures there is little information on lifespan. However, one source (Parker and Parker, 1999) estimates maximum lifespan at 25 years.

Range lifespan

Status: wild:
25 (high) years.

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Reproduction

Fertilization in all sharks is internal, taking place in the egg tubes or oviducts of the female. Male sharks must grab females, maneuver their bodies so that he can introduce his claspers to pass sperm into the vent. Males and females come together only to mate.

Mating System: polygynandrous (promiscuous)

Reproduction in these sharks is not well understood. Chlamydoselachus africana is an ovoviviparous shark that can bear anywhere from two to twelve live young (Dulvy & Reynolds, 1997). Young tend to be 40 cm long. Females apparently reproduce all year long and have a gestation period of about one to two years (Compagno, 1984). The size of an immature male is about 730 mm, whereas a mature male is about 970 mm long. Thus, the length of a mature male is anywhere from 730 mm to 970 mm (Nakaya & Bass). Female frilled shark length at maturity is about 1350 mm (Nakaya & Bass).

Breeding season: These sharks have the ability to breed all year.

Range number of offspring: 2 to 12.

Range gestation period: 12 to 24 months.

Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); ovoviviparous

There is little, if any, information on parental investment in frilled sharks. Sharks in general do not care for their young after their birth (Parker and Parker, 1999).

Parental Investment: no parental involvement; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female)

  • Compagno, L. 1984. Sharks of the World. FAO Species Catalogue, 4 (1): 14-15.
  • Dulvy, N., J. Reynolds. 1997.
    Evolutionary transitions among egg-laying, live-bearing and maternal inputs in sharks and rays.
    . Proc. R. Soc. Lond. B, 264: 1309-1315.. Accessed September 24, 2005 at http://www.fishbase.org/Summary/SpeciesSummary.php?id=635.
  • Parker, J., S. Parker. 1999. The Encyclopedia of Sharks. Canada & United States: Firefly Books Ltd..
  • Tricas, T., K. Deacon, P. Last, J. McCosker, T. Walker, L. Taylor. 2002. The Nature Companions Sharks and Whales. 814 Montgomery Street, San Francisco CA, 94133 USA: Fog City Press.
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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage: Chlamydoselachus anguineus

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Specimens with Barcodes: 9
Species With Barcodes: 1
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Conservation

Conservation Status

Frilled shark are classified as a near threatened species on the IUCN Red List. There are no current conservation plans for this species (Fowler & Paul).

US Federal List: no special status

CITES: no special status

IUCN Red List of Threatened Species: near threatened

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IUCN Red List Assessment


Red List Category
NT
Near Threatened

Red List Criteria

Version
3.1

Year Assessed
2003
  • Needs updating

Assessor/s
Paul, L. & Fowler, S. (SSG Australia & Oceania Regional Workshop, March 2003)

Reviewer/s
Shark Specialist Group Australia & Oceania Regional Group (Shark Red List Authority)

Contributor/s

Justification
A generally rare to uncommon deepwater species, with a few localities where it is taken more commonly as bycatch in several fisheries. Not an important target species, but a regular though small bycatch in many bottom trawl, midwater trawl, deep-set longline, and deep-set gillnet fisheries. As bycatch, this species is variously either used for meat, fishmeal, or discarded. Occasionally kept in aquaria (Japan). There is some concern that expansion of deepwater fisheries effort (geographically and in depth range) will increase the levels of bycatch. Although little is known of its life history, this deepwater species is likely to have very little resilience to depletion as a result of even non-targeted exploitation. It is classified as Near Threatened due to concern that it may meet the Vulnerable A2d+A3d+4d criteria.
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National NatureServe Conservation Status

United States

Rounded National Status Rank: NNR - Unranked

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NatureServe Conservation Status

Rounded Global Status Rank: GNR - Not Yet Ranked

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Population

Population
No information on population size anywhere.

Population Trend
Unknown
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Threats

Major Threats
Not a targeted fisheries species, but taken as bycatch in bottom and midwater trawls, deep-set longlines, and in deep-set gill nets. No population baseline or trends available. Some concern that increased deepwater fisheries effort (geographically and in depth range) may increase levels of bycatch. The bycatch is sometimes utilized for fishmeal and for meat. Occasionally kept in aquaria (Japan).
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Near Threatened (NT)
  • IUCN 2006 2006 IUCN red list of threatened species. www.iucnredlist.org. Downloaded July 2006.
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Management

Conservation Actions

Conservation Actions
None known for this species. A very few states are developing or have developed shark management plans within the context of the FAO IPOA-Sharks, but few if any of these include measures for the management of deepwater fisheries bycatch.
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Relevance to Humans and Ecosystems

Benefits

These are not dangerous sharks, but their teeth have lacerated the hands of the unwary scientist and or fisherman examining or holding them.

Negative Impacts: injures humans (bites or stings)

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When frilled sharks are caught as bycatch during net or long line fishing, they may be ground up for fishmeal and fish food. Frilled sharks are unique and fascinating members of oceanic ecosystems.

Positive Impacts: food ; body parts are source of valuable material

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Importance

fisheries: minor commercial; price category: unknown; price reliability:
  • Coppola, S.R., W. Fischer, L. Garibaldi, N. Scialabba and K.E. Carpenter 1994 SPECIESDAB: Global species database for fishery purposes. User's manual. FAO Computerized Information Series (Fisheries). No. 9. Rome, FAO. 103 p. (Ref. 171)
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Wikipedia

Frilled shark

The frilled shark (Chlamydoselachus anguineus) is one of two extant species of shark in the family Chlamydoselachidae, with a wide but patchy distribution in the Atlantic and Pacific Oceans. This rare species is found over the outer continental shelf and upper continental slope, generally near the bottom, though there is evidence of substantial upward movements. It has been caught as deep as 1,570 m (5,150 ft). In Suruga Bay, Japan it is most common at depths of 50–200 m (160–660 ft). Exhibiting several "primitive" features, the frilled shark has often been termed a "living fossil". It reaches a length of 2 m (6.6 ft) and has a dark brown, eel-like body with the dorsal, pelvic, and anal fins placed far back. Its common name comes from the frilly or fringed appearance of its six pairs of gill slits, with the first pair meeting across the throat.

Seldom observed, the frilled shark may capture prey by bending its body and lunging forward like a snake. The long, extremely flexible jaws enable it to swallow prey whole, while its many rows of small, needle-like teeth make it difficult for the prey to escape. It feeds mainly on cephalopods, leavened by bony fishes and other sharks. This species is aplacental viviparous: the embryos emerge from their egg capsules inside the mother's uterus where they survive primarily on yolk. The gestation period may be as long as three and a half years, the longest of any vertebrate. Litter sizes vary from two to fifteen, and there is no distinct breeding season. Frilled sharks are occasional bycatch in commercial fisheries but have little economic value. The International Union for Conservation of Nature has assessed it as Near Threatened, since even incidental catches may deplete its population given its low reproductive rate. This shark, or a supposed giant relative, is a suggested source for reports of sea serpents.

Taxonomy and phylogeny[edit]

Line drawing of a frilled shark curled on its side, with insets depicting dorsal and ventral views of the head, and of two teeth
Garman's illustration of the frilled shark, accompanying his 1884 species description

The frilled shark was first scientifically recognized by German ichthyologist Ludwig Döderlein, who visited Japan between 1879 and 1881 and brought two specimens to Vienna. However, his manuscript describing the species was lost, so the first description of the frilled shark was authored by American zoologist Samuel Garman, working from a 1.5-m-long female caught from Sagami Bay in Japan. His account, entitled "An Extraordinary Shark", was published in an 1884 volume of Proceedings of the Essex Institute.[2][3] Garman placed the new species in its own genus and family, and gave it the name Chlamydoselachus anguineus from the Greek chlamy ("frill") and selachus ("shark"), and the Latin anguineus for "snake-like".[4] Other common names for this species include frill shark, lizard shark, scaffold shark, and silk shark.[1][5]

Several early authors believed the frilled shark to be a living representative of otherwise long-extinct groups of elasmobranchs (sharks, rays, and their ancestors), based on its multiple-pointed teeth, the articulation of its upper jaw directly to the cranium behind the eyes (called "amphistyly"), and its "notochord-like" spinal column with indistinct vertebrae.[6] Garman proposed that it was allied with the "cladodonts", a now-obsolete taxonomic grouping containing forms that thrived during the Palaeozoic era, such as Cladoselache from the Devonian period (416–359 Mya). His contemporaries Theodore Gill and Edward Drinker Cope suggested it was instead related to the hybodonts, which were the dominant sharks during the Mesozoic era. Cope went as far as to assign this species to the fossil genus Didymodus.[7][8]

More recent investigations have found the similarities between the frilled shark and extinct groups may have been overstated or misinterpreted, and this shark exhibits a number of skeletal and muscular traits that firmly place it with the neoselachians (modern sharks and rays), and more specifically with the cow sharks in the order Hexanchiformes (though systematist Shigeru Shirai has proposed that it be placed in its own order, Chlamydoselachiformes).[6][8] Nevertheless, the frilled shark belongs to one of the oldest still-extant shark lineages, dating back to at least the Late Cretaceous (about 95 Mya) and possibly to the Late Jurassic (150 Mya).[9] Because of their ancient ancestry and "primitive" characteristics, the frilled shark and other members of this lineage have been described as a "living fossil".[3] However, the frilled shark itself is a relatively recent species, with the earliest known fossil teeth belonging to this species dating to the early Pleistocene epoch.[10]

Distribution and habitat[edit]

A shark swimming in dark water over sand; the labels indicate that it was taken on August 26, 2004 at a depth of 2866 ft, a temperature of 4.3°C, and a salinity of 35
The first footage of a frilled shark in its natural habitat, taken east of Georgia, USA on the Blake Plateau

Rather uncommon, the frilled shark has been recorded from a number of widely scattered locations in the Atlantic and Pacific Oceans. In the eastern Atlantic, it occurs off northern Norway, northern Scotland, and western Ireland, from France to Morocco including Madeira, and off Mauritania.[11] In the central Atlantic, it has been caught at several locations along the Mid-Atlantic Ridge, from north of the Azores to the Rio Grande Rise off southern Brazil, as well as over the Vavilov Ridge off West Africa. In the western Atlantic, it has been reported from off New England, Georgia, and Suriname.[12][13][14] In the western Pacific, it is known from southeastern Honshu, Japan, to Taiwan, off New South Wales and Tasmania in Australia, and around New Zealand. In the central and eastern Pacific, it has been found off Hawaii, California, and northern Chile.[1][11] The frilled sharks off southern Africa were described as a different species, C. africana, in 2009.[14]

The frilled shark inhabits the outer continental shelf and upper to middle continental slope, seeming to favor upwellings and other biologically productive areas.[4] Though it has been caught from a depth of 1,570 m (5,150 ft), it usually does not occur deeper than 1,000 m (3,300 ft).[1][5] In Suruga Bay, it is most common at a depth of 50–200 m (160–660 ft), except from August to November when the temperature at the 100 m (330 ft) water layer exceeds 15 °C (59 °F) and the sharks shift into deeper water.[15][16] On rare occasions, this species has been seen at the surface.[11] The frilled shark is usually found close to the bottom, with one individual observed swimming over an area of small sand dunes.[1][12] However, its diet suggests that it does make substantial forays upward into open water.[17] This species may make vertical migrations, approaching the surface at night to feed.[4] There is spatial segregation by size and reproductive condition.[16]

Description[edit]

The head of a preserved shark, with the large mouth open
The frilled shark has long, terminally positioned jaws.
The head of a preserved shark lying on its side, showing large, flared gill slits
The frilled shark's first pair of gill slits are continuous across its throat.

With its elongated, eel-like body and strange appearance, the frilled shark has long been likened to the mythical sea serpent. The head is broad and flattened with a short, rounded snout. The nostrils are vertical slits, separated into incurrent and excurrent openings by a leading flap of skin. The moderately large eyes are horizontally oval and lack nictitating membranes (protective third eyelids). The very long jaws are positioned terminally (at the end of the snout), as opposed to the underslung jaws of most sharks. The corners of the mouth are devoid of furrows or folds. The tooth rows are rather widely spaced, numbering 19–28 in the upper jaw and 21–29 in the lower jaw.[2][14] The teeth number around 300 in all; each tooth is small, with three slender, needle-like cusps alternating with two cusplets.[4][17] There are six pairs of long gill slits with a "frilly" appearance created by the extended tips of the gill filaments, giving this shark its name. The first pair of gill slits meet across the throat, forming a "collar".[2]

The pectoral fins are short and rounded. The single, small dorsal fin is positioned far back on the body, about opposite the anal fin, and has a rounded margin. The pelvic and anal fins are large, broad, and rounded, and also positioned well back on the body. The caudal fin is very long and roughly triangular, without a lower lobe or a ventral notch on the upper lobe. There are a pair of thick skin folds of unknown function running along the belly, separated by a groove.[2] The midsection is relatively longer in females than in males, with the pelvic fins pushed closer to the anal fin.[17][18] The dermal denticles are small and shaped like the tip of a chisel, becoming enlarged and sharp on the dorsal margin of the caudal fin.[2] This species is a uniform dark brown or gray.[4] The frilled shark differs from its southern African relative, C. africana, in having more vertebrae (160–171 vs 147) and more turns in the spiral valve intestine (35–49 versus 26–28), as well as in various proportional measurements such as a longer head and shorter gill slits.[14] The maximum known length is 1.7 m (5.6 ft) for males and 2.0 m (6.6 ft) for females.[4]

Biology and ecology[edit]

Highly specialized for life in the deep sea, the frilled shark has a reduced, poorly calcified skeleton and an enormous liver filled with low-density lipids, allowing it to maintain its position in the water column with little effort.[17] It is one of the few sharks with an "open" lateral line, in which the mechanoreceptive hair cells are positioned in grooves that are directly exposed to the surrounding seawater. This configuration is thought to be basal in sharks and may enhance its sensitivity to the minute movements of its prey.[17][19] Many frilled sharks are found with the tips of their tails missing, probably from predatory attacks by other shark species.[16] Parasites identified from this shark include a tapeworm in the genus Monorygma, the fluke Otodistomum veliporum,[20] and the nematode Mooleptus rabuka.[21]

Feeding[edit]

Close up of the lower jaw of a preserved shark, showing many small, sharp teeth
The numerous needle-like teeth of the frilled shark are suited for snagging soft-bodied squid.

The long jaws of the frilled shark are highly distensible with an extremely wide gape, allowing it to swallow whole prey over one-half its size.[4] However, the length and articulation of its jaws means it cannot deliver as strong a bite as more conventionally built sharks.[22] Most captured individuals are found with no or barely identifiable stomach contents, suggesting a fast digestion rate and/or long intervals between feedings.[15] This species preys upon cephalopods, bony fishes, and smaller sharks.[4] One 1.6 m (5.2 ft) long individual, caught off Chōshi, was found to have swallowed a 590 g (1.30 lb) Japanese catshark (Apristurus japonicus).[17] Squid comprise some 60% of the diet of sharks in Suruga Bay; this includes not only slow-moving, deep-dwelling types such as Chiroteuthis and Histioteuthis, but also relatively large, powerful swimmers of the open ocean such as Onychoteuthis, Sthenoteuthis, and Todarodes.[15]

How the ostensibly weak-swimming frilled shark captures active, fast-moving squid is a matter of speculation. One possibility is that it takes advantage of injured squid, or those that are exhausted and dying after spawning.[15] Alternatively, it may surprise its prey by curving its body and, bracing itself with its posteriorly positioned fins, launching a quick strike forward in the manner of a snake. It may also be able to close its gill slits and create negative pressure to suck prey into its mouth.[17] The many small, sharp, recurved teeth of the frilled shark are functionally similar to squid jigs and could easily snag the body or tentacles of a squid, particularly as they are rotated outwards when the jaws are protruded. Observations of captive frilled sharks swimming with their mouths open suggest that the small teeth, light against the dark mouth, may even fool squid into attacking and entangling themselves.[14]

Life history[edit]

The frilled shark is aplacental viviparous; the developing embryos are mainly nourished by yolk, though the difference in weight between the egg and the newborn indicates that the mother also provides additional nutrition via unknown means. Adult females have two functional ovaries and one functional uterus, on the right. Unsurprisingly, there is no defined breeding season for either sex, as this shark inhabits depths at which there is little to no seasonal influence.[16] A possible mating aggregation of 15 male and 19 female sharks has been recorded over a seamount on the Mid-Atlantic Ridge.[13] The litter size ranges from two to fifteen, with an average of six.[4] Females ovulate eggs into the uterus about once every two weeks; vitellogenesis (yolk formation) and the growth of new ovarian eggs halt during pregnancy, apparently due to insufficient space inside the body cavity.[16]

Newly ovulated eggs and early-stage embryos are enclosed in a thin, ellipsoid, golden-brown capsule. When the embryo is 3 cm (1.2 in) long, the head is pointed when seen from above or below, the jaws are barely developed, the external gills have begun to appear, and all the fins are present. The egg capsule is shed when the embryo grows to 6–8 cm (2.4–3.1 in) long, and is expelled from the female's body; at this time the embryo's external gills are fully developed.[16][23] The size of the yolk sac remains mostly constant until around an embryonic length of 40 cm (16 in), whereupon it begins to shrink, mostly or completely disappearing by an embryonic length of 50 cm (20 in). The embryonic growth rate averages 1.4 cm (0.55 in) per month, and therefore the entire gestation period may last three and a half years, far longer than any other vertebrate.[16][17] Newborn sharks measure 40–60 cm (16–24 in) long; males attain sexual maturity at 1.0–1.2 m (3.3–3.9 ft) long, and females at 1.3–1.5 m (4.3–4.9 ft) long.[1]

Human interactions[edit]

The frilled shark has seldom been encountered alive, and thus poses no danger to humans (though scientists have accidentally cut themselves examining its teeth).[11] On August 27, 2004, the first observation of this species in its natural habitat was made by the ROV Johnson Sea Link II, on the Blake Plateau off the southeastern United States.[12] On January 21, 2007, a Japanese fisherman discovered a 1.6 m (5.2 ft) long female alive at the surface, perhaps there because of illness or weakness from the warm water. It was brought to Awashima Marine Park in Shizuoka, where it died after a few hours.[24] Garman, and numerous authors since, have advanced the frilled shark as an explanation for sea serpent sightings. Because of the shark's modest size, some cryptozoologists have posited the existence of a giant relative, particularly as larger Chlamydoselachus species are known from the fossil record.[2][3]

Small numbers of frill sharks are caught incidentally by various deepwater commercial fisheries around the world, using trawls, gillnets, and longlines.[1] In particular, it is regularly taken in Suruga Bay in bottom gillnets meant for sea breams and gnomefishes, and in midwater trawls meant for the shrimp Sergia lucens. Japanese fishers regard it as a nuisance, as it damages the nets.[16] This shark is sometimes sold for meat or processed into fishmeal, but is not economically significant. Because of its very low reproductive rate and the continuing expansion of commercial fisheries into its habitat, the International Union for Conservation of Nature (IUCN) has listed it as Near Threatened.[1]

References[edit]

  1. ^ a b c d e f g h Paul, L. and Fowler, S. (2003). "Chlamydoselachus anguineus". IUCN Red List of Threatened Species. Version 2010.1. International Union for Conservation of Nature. Retrieved April 25, 2010. 
  2. ^ a b c d e f Garman, S. (January 17, 1884). "An Extraordinary Shark". Bulletin of the Essex Institute 16: 47–55. 
  3. ^ a b c Bright, M. (2000). The Private Life of Sharks: The Truth Behind the Myth. Stackpole Books. pp. 210–213. ISBN 0-8117-2875-7. 
  4. ^ a b c d e f g h i Ebert, D.A. (2003). Sharks, Rays, and Chimaeras of California. University of California Press. pp. 50–52. ISBN 0-520-23484-7. 
  5. ^ a b Froese, Rainer and Pauly, Daniel, eds. (2010). "Chlamydoselachus anguineus" in FishBase. April 2010 version.
  6. ^ a b Compagno, L.J.V. (1977). "Phyletic Relationships of Living Sharks and Rays". American Zoologist 17 (2): 303–322. doi:10.1093/icb/17.2.303. 
  7. ^ Garman, S. and Gill, T. (March 21, 1884). "'The Oldest Living Type of Vertebrata,' Chlamydoselachus". Science 3 (59): 345–346. doi:10.1126/science.ns-3.59.345-a. PMID 17838181. 
  8. ^ a b Martin, R.A. Chlamydoselachiformes: Frilled Sharks. ReefQuest Centre for Shark Research. Retrieved on April 25, 2010.
  9. ^ Martin, R.A. The Rise of Modern Sharks. ReefQuest Centre for Shark Research. Retrieved on April 25, 2010.
  10. ^ Marsili, S. (2007). Analisi sistematica, paleoecologica e paleobiogeografica della selaciofauna plio-pleistocenica del Mediterraneo.
  11. ^ a b c d Compagno, L.J.V. (1984). Sharks of the World: An Annotated and Illustrated Catalogue of Shark Species Known to Date. Food and Agricultural Organization of the United Nations. pp. 14–15. ISBN 92-5-101384-5. 
  12. ^ a b c Jenner, J. (2004). Estuary to the Abyss: Excitement, Realities, and "Bubba". NOAA Ocean Explorer. Retrieved on April 25, 2010.
  13. ^ a b Kukuev, E.I. and Pavlov, V.P. (2008). "The First Case of Mass Catch of a Rare Frill Shark Chlamydoselachus anguineus over a Seamount of the Mid-Atlantic Ridge". Journal of Ichthyology 48 (8): 676–678. doi:10.1134/S0032945208080158. 
  14. ^ a b c d e Ebert, D.A. and Compagno, L.J.V. (2009). "Chlamydoselachus africana, a new species of frilled shark from southern Africa (Chondrichthyes, Hexanchiformes, Chlamydoselachidae)". Zootaxa 2173: 1–18. 
  15. ^ a b c d Kubota, T., Shiobara, Y. and Kubodera, T. (January 1991). "Food habits of the frilled shark Chlamydoselachus anguineus collected from Suruga bay, central Japan". Nippon Suisan Gakkaishi 57 (1): 15–20. doi:10.2331/suisan.57.15. 
  16. ^ a b c d e f g h Tanaka, S., Shiobara, Y., Hioki, S., Abe, H., Nishi, G., Yano, K. and Suzuki, K. (1990). "The reproductive biology of the frilled shark, Chlamydoselachus anguineus, from Suruga Bay, Japan". Japanese Journal of Ichthyology 37 (3): 273–291. 
  17. ^ a b c d e f g h Martin, R.A. Deep Sea: Frilled Shark. ReefQuest Centre for Shark Research. Retrieved on April 25, 2010.
  18. ^ Last, P.R. and J.D. Stevens (2009). Sharks and Rays of Australia (second ed.). Harvard University Press. pp. 34–35. ISBN 0-674-03411-2. 
  19. ^ Martin, R.A. Hearing and Vibration Detection. ReefQuest Centre for Shark Research. Retrieved on April 25, 2010.
  20. ^ Collett, R. (1897). "On Chlamydoselacnus anguineus Garman. A remarkable shark found in Norway 1896". Christiania 11: 1–17. 
  21. ^ Machida, M., Ogawa, K. and Okiyama, M. (1982). "A new nematode (Spirurida, Physalopteridae) from frill shark of Japan". Bulletin of the National Science Museum Series A (Zoology) 8 (1): 1–5. 
  22. ^ Moss, S. (1977). "Feeding Mechanisms in Sharks". American Zoologist 17 (2): 355–364. doi:10.1093/icb/17.2.355. 
  23. ^ Nishikawa, T. (1898). "Notes on some embryos of Chlamydoselachus anguineus, Garm.". Annotationes Zoologicae Japonenses 2: 95–102. 
  24. ^ Japanese Marine Park Captures Rare 'Living Fossil' Frilled Shark; Pictures of a Live Specimen 'Extremely Rare'. Underwatertimes.com. January 24, 2007. Retrieved on April 25, 2010.
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