Overview

Comprehensive Description

Centrophorus granulosus (Bloch & Schneider, 1801)

Istanbul Fish Market : 1000-14 (1 spc.), 11.03.1988 .

  • Nurettin Meriç, Lütfiye Eryilmaz, Müfit Özulug (2007): A catalogue of the fishes held in the Istanbul University, Science Faculty, Hydrobiology Museum. Zootaxa 1472, 29-54: 31-31, URL:http://www.zoobank.org/urn:lsid:zoobank.org:pub:428F3980-C1B8-45FF-812E-0F4847AF6786
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Biology

A common deepwater dogfish of the outer continental shelves and upper slopes, commonest below 200 m (Ref. 247); usually benthic and epibenthic at depths from 50-1440 m with most records from 200-600 m (Compagno, pers. comm. 07/07). Solitary (Ref. 26340). Feeds mainly on bony fishes such as hake, epigonids, lanternfish, herring, smelts, cods, rattails, squid and crustaceans (Ref. 247, IUCN workshop 07/07). Ovoviviparous (Ref. 50449). Marketed smoked and dried salted for human consumption; also processed into fishmeal and a source of liver oil for squalene (Ref. 247). Number of litter recorded, one in Mediterranean females, and possibly 1 or 2 for the species. Males still immature at 45-58 cm, fully at 80-94 cm, suggesting maturity at 60-80 cm DW; females immature at 42-96 cm This species is fished in Eastern Atlantic by bottom trawls, long lines, fixed bottom nets, hook and line and pelagic trawls; caught and discarded, or utilised from by-catch fisheries (IUCN discussion 07/07).
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Description

 The gulper shark Centrophorus granulosus is a moderately large deep water member of the dogfish family reaching up to 160 cm in length. It has a uniform drab-gray dorsal colouring and a slightly paler ventral colouring. It has a moderately long and broad snout and large reflective green eyes. The gulper shark does not have an anal fin and has two dorsal fins. The first dorsal fin is quite short and the second is relatively high when compared to similar species. Both have prominent spines. Lateral tooth-like projections are present on the body.

Despite the relative abundance of Centrophorus granulosus and frequent commercial exploitation around the world, many aspects of its biology remain relatively unknown. It is known to feed on hake, lantern fish and other deepwater bony fish as well as squid (Compagno, 1984).

Unlike the leafscraper shark Centrophorus squamosus, the tooth-like projections on the of the gulper shark are flat and diamond-shaped without an elevated stalk. Furthermore the free rear tips of the pectoral fins are pointed and reach past the first dorsal fin spine.

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Distribution

Range Description

Thought to be a circumglobal species, in temperate and tropical waters, however considerable taxonomic confusion of the genus still persists (see Taxonomy). This species occurs in the following regions and countries:

Northeast Atlantic: France, Spain, Portugal, Madeira.
Mediterranean: Albania, Algeria, France, Greece, Italy, Morocco, Spain, Tunisia and Turkey. Absent from the Black Sea. (Baino et al. 2001, Boutan 1926, Maurin 1968, Jardas 1984, Fischer et al. 1987, Papakonstatinou 1988, Ungaro et al. 1994, Kabaskal 2002).
West Africa: Canary Islands, Morocco, Sahara Republic, Senegal, Liberia, Ivory Coast to Nigeria, Cameroon to Congo.
Sub Equatorial Africa: Angola, Namibia, and the west coast of South Africa (Northern Cape Province. Southern Mozambique, Madagascar, Aldabra Island.
Indian Ocean: Yemen, Somalia (the Gulf of Aden), nominal records from India, which are at least in part based on Centrophorus atromarginatus.
Australia and Oceania: Probably Australia (temperate waters off Western Australia, South Australia, Victoria, Tasmania, and New South Wales as C. uyato, but possibly including other species).
Asia and the Northwest Pacific: Taiwan Island and Japan.
Northeast Pacific: Possibly Hawaiian Islands.
Northwest Atlantic: Northern Gulf of Mexico (United States).
Central America: possibly wide ranging in the Gulf of Mexico and the Caribbean (the north coast of Cuba, Puerto Rico and the Caribbean off the Lesser Antilles (Burgess pers. comm.), possibly Colombia and Venezuela, and off French Guiana.
South America: Brazil (Northern).

Note that the species from the SE Atlantic may not be the same as found elsewhere, or may represent two or more species. The species needs to be critically evaluated from different regions. This or a similar species has also been found in Taiwanese waters (D.A. Ebert, unpubl. data).
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Eastern Atlantic: France to South Africa, including the Mediterranean (Ref. 31367). Western Central Atlantic: northern Gulf of Mexico (Ref. 247, 6871). Indian Ocean: Mozambique, South Africa and the Aldabra Islands (Ref. 31367); Western Australia (Ref. 6871). Western Pacific: Japan, Papua New Guinea, and Australia (Ref. 31367).
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Physical Description

Morphology

Dorsal spines (total): 2; Dorsal soft rays (total): 0; Analspines: 0; Analsoft rays: 0
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Size

Maximum size: 1600 mm TL
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Max. size

160 cm TL (male/unsexed; (Ref. 6871)); 145.5 cm TL (female)
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Diagnostic Description

Description

A common deepwater dogfish of the outer continental shelves and upper slopes, commonest below 200 m. Ovoviviparous. Feeds on hake, epigonids and lanternfish. Smoked and dried salted for huma consumption; also processed for fishmeal and liver oil.
  • Anon. (1996). FishBase 96 [CD-ROM]. ICLARM: Los Baños, Philippines. 1 cd-rom pp.
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Light grayish brown dorsally, paler ventrally; eyes greenish (Ref. 6871). Adults with tips of dorsal fins dusky, not prominently marked (Ref. 31367).
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Ecology

Habitat

Habitat and Ecology

Habitat and Ecology
A large deepwater species inhabiting the upper continental slopes and outer continental shelves. Usually demersal or benthopelagic, at depths from 100 to 1,490 m (Mediterranean Sea), with most records between 300 to 800 m depth (Baino et al. 2001, Compagno 1984, Gilat and Gelman 1984, Guallart 1998).

It is thought to have schooling habits (Maurin 1962, Gilat and Gelman 1984, Compagno 1984, Compagno in prep. a) because of the abundance in some catches or by the simultaneous presence of several individuals in baited cameras set over the bottom. It may also aggregate in particular areas of the slope, particularly in the margins of submarine canyons (Guallart 1998). Some evidence suggests that individuals present in the lower half of the depth range are mainly juveniles (Guallart 1998).

Age at maturity is estimated at 12 to 16 years (females) and 7 to 8 years (males) (Guallart 1998) with earlier estimates of 4 to 5 years for both males and females (Rizzo et al. 1995). Estimates of female size at maturity are 89 to 102 cm (93 cm when half mature) (Gullart 1998) and earlier estimates range between 70 to 95 cm (Capapé 1985, Fischer et al. 1987). Mature male size estimates are 79 to 85 cm (80 cm at half maturity) (Guallart 1998) and 70 to 80 cm (Capapé 1985, Fischer et al. 1987, Rizzo et al. 1995). Maximum recorded size is about 120 cm (Fischer et al. 1987, Guallart 1998). Size at birth range from 30 to 46 cm (Guallart and Vicent 2001, Fischer et al. 1987) and C. granulosus can live for over 30 years (Guallart 1998). The average reproductive age of this species is unknown.

A lecitotrophic aplacental viviparous (ovoviviparous) species (Ranzi 1932, Guallart and Vicent 2001, C. granulosus has an extremely low reproductive rate, with only one pup/litter (Tortonese 1956, Capapé 1985, Guallart 1998), a gestation period of about two years and occasional resting periods between pregnancies (Guallart 1998). The three-generation period is estimated to be about 50 to 60 years. This probably makes it the elasmobranch species with the lowest reproductive potential.

Feeds on a variety of prey, mainly fishes but also cephalopods and other invertebrates, both benthic and mesopelagic; also probable scavenging habits (Boutan 1926, Capapé 1985, Guallart 1998).

Systems
  • Marine
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Environment

bathydemersal; marine; depth range 50 - 1440 m, usually 200 - 600 m
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Depth range based on 59 specimens in 1 taxon.
Water temperature and chemistry ranges based on 30 samples.

Environmental ranges
  Depth range (m): 47.5 - 1224
  Temperature range (°C): 5.212 - 12.939
  Nitrate (umol/L): 17.922 - 36.587
  Salinity (PPS): 34.359 - 35.621
  Oxygen (ml/l): 1.476 - 4.794
  Phosphate (umol/l): 1.331 - 2.538
  Silicate (umol/l): 13.314 - 70.747

Graphical representation

Depth range (m): 47.5 - 1224

Temperature range (°C): 5.212 - 12.939

Nitrate (umol/L): 17.922 - 36.587

Salinity (PPS): 34.359 - 35.621

Oxygen (ml/l): 1.476 - 4.794

Phosphate (umol/l): 1.331 - 2.538

Silicate (umol/l): 13.314 - 70.747
 
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 Centrophorus granulosus is a bathydemersal fully marine species which can be found offshore with a depth range of 50-1200 m.
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Depth: 100 - 1200m.
From 100 to 1200 meters.

Habitat: bathydemersal.
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Trophic Strategy

A common deepwater dogfish of the outer continental shelves and upper slopes, commonest below 200 m (Ref. 247). Solitary (Ref. 26340). Also mesopelagic (Ref. 27000). Feeds mainly on bony fishes such as hake, epigonids and lanternfish (Ref. 247).
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Life History and Behavior

Life Cycle

Ovoviviparous, embryos feed solely on yolk (Ref. 50449). Young are born from 30 to 42 cm or more (Ref. 247). Distinct pairing with embrace (Ref. 205).
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Life Expectancy

Lifespan, longevity, and ageing

Maximum longevity: 25 years (wild)
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Molecular Biology and Genetics

Molecular Biology

Barcode data: Centrophorus granulosus

The following is a representative barcode sequence, the centroid of all available sequences for this species.


There are 4 barcode sequences available from BOLD and GenBank.

Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.

See the BOLD taxonomy browser for more complete information about this specimen and other sequences.

CATAAAGATATCGGCACCCTATATTTAATCTTTGGTGCATGAGCAGGAATAGTGGGCACAGCTCTT---AGCTTACTTATTCGTACAGAATTAAGCCAACCGGGAACACTTCTGGGGGAT---GATCAAATCTACAATGTTATTGTGACTGCTCACGCTTTTGTAATAATCTTTTTTATAGTTATGCCTGTGATAATCGGCGGGTTCGGAAACTGATTAGTACCTTTAATG---ATTGGTGCACCAGATATAGCTTTCCCCCGAATAAATAATATAAGCTTTTGACTATTACCCCCCTCTCTCTTATTACTTTTAGCCTCTGCTGGTGTTGAAGCGGGCGCTGGAACCGGCTGAACGGTTTACCCTCCTCTTGCTGGTAATATAGCCCATGCTGGAGCATCCGTAGATTTA---GCCATCTTCTCACTTCATTTAGCCGGTATTTCCTCAATTTTAGCCTCTATTAATTTTATTACTACTATTATTAATATAAAACCGCCTGCCATTTCTCAATATCAAACGCCACTCTTTGTTTGATCTATCCTTGTAACCACCGTTCTTCTCCTACTTGCTCTCCCTGTCCTTGCCGCT---GCAATTACAATACTGTTAACTGACCGTAATCTAAATACAACATTTTTTGACCCTGCAGGAGGAGGAGACCCCATTCTTTACCAACATTTATTTTGATTCTTTGGCCAC
-- end --

Download FASTA File

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Statistics of barcoding coverage: Centrophorus granulosus

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 5
Specimens with Barcodes: 67
Species With Barcodes: 1
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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
VU
Vulnerable

Red List Criteria
A2abd+3d+4d

Version
3.1

Year Assessed
2006

Assessor/s
Guallart, J., Serena, F., Mancusi, C., Casper, B.M., Burgess, G.H., Ebert, D.A., Clarke, M. & Stenberg, C.

Reviewer/s
Cavanagh, R.D., Fowler, S.L. & participants of the Shark Specialist Group Northeast Atlantic Workshop (Shark Red List Authority)

Contributor/s

Justification
A rare deepwater dogfish with a widespread global distribution, inhabiting the upper continental slopes and outer continental shelf area. Believed to have the lowest reproductive potential of all elasmobranch species; its reproductive biology is characterized by a late onset of maturity (12 to 16 years in females), only one pup per litter and a two-year gestation period with occasional resting periods. This makes it extremely vulnerable to overexploitation and population depletion. Despite a lack of data for certain regions within its geographic range, this species is globally assessed as Vulnerable on the basis of its limiting life history traits and the global increase in unmanaged fishing effort to exploit deeper waters.

This species is extremely rare in the Mediterranean, which in combination with the documented localized depletion subsequent to brief targeted fishing efforts and the species? inherent vulnerability to exploitation even in moderate numbers though bycatch, leads to an assessment of Vulnerable in this region. A decline of 80 to 95% from baseline has been estimated for the Northeast Atlantic population. Due to the low level of recruitment (resulting from a low fecundity and low reproductive output), this species is assessed as Critically Endangered within the Northeast Atlantic.

Taxonomic issues, in combination with a paucity of data have hampered this species? assessment. Elsewhere as a result, it cannot be assessed beyond Data Deficient for the North and South west Atlantic. There is an urgent call for further research on a global level, but in particular to collect further data for these aforementioned areas, monitoring of the extent to which this species is affected by bycatch is also required. The taxonomic issues relating to this species need to be resolved and the Centrophorus spp. examined to determine the proper identification of the species involved within these regions.

History
  • 2000
    Vulnerable
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Population

Population
The determination of the range and population of this species is hindered by unresolved taxonomic issues (see taxonomy section). Within the Mediterranean, there is no evidence of the existence of different populations. No information is available on relationships between Mediterranean and Atlantic populations of Centrophorus. However, like most Mediterranean deepwater species, some degree of isolation is expected due to the barrier of the Straits of Gibraltar. Analysis of the Mediterranean International Trawl Survey (MEDITS) data from 1994 to 1999 show a low frequency of occurrence (only 2% of total hauls), for C. granulosus. Its overall biomass was estimated to be 2.9 kg/km², with a presence throughout the Mediterranean, though more abundant in the western central and in the western area (5.5 and 2.7 kg/km² respectively). The depth distribution of the biomass index show values of less than 0.1 from 50 to 100 m of depth and between 1 to >10 kg/km² between 200 to 800 m. Baino et al. give a standing stock biomass estimate of only 1,528 t (3%) for the west, north and east Mediterranean from 0?800 m depth. These data clearly indicate that this species is very rare. The MEDITS experimental trawl program surveys waters up to 800 m in depth. The depth range of this demersal deepwater shark extends from 100 to 1,490 m, however it is most commonly recorded between 300 and 800 m, therefore this data can serve as a good indicator of the abundance of this species.

Population Trend
Decreasing
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Threats

Major Threats
This is a widespread species that is reported to be heavily fished and caught as bycatch in the Northeast Atlantic, the Northwest Pacific and other regions. As the global fishing fleet tends towards deeper and deeper unexploited fishing grounds, the threat from incidental catch to this species grows.

Northeast Atlantic
In the Northeast Atlantic this species is caught with bottom trawls, long lines, fixed bottom nets, hook and line and pelagic trawls (Compagno in prep). For this region, landings data were obtained from ICES (2006) for the Portuguese coast (main distribution range). These show a strong decline in catch from about 1,000 t in 1990 to less than 100 t in 2004. As a crude index of abundance a delury depletion model was implemented, assuming constant effort over the time series. The results of this suggest that the stock has declined by between 80 and 95% of its initial size when fishing began. This is based on two assumptions of effort. This assumes that recruitment does not occur. Though this is clearly not true, the extreme low fecundity and reproductive output suggests that effect of recruitment is very low indeed.

Mediterranean:
Within the Mediterranean, one of the main threats facing this species is development of target fisheries with longlines and gillnets in areas on the continental slope, where this species tends to aggregate. However, the global trend for fisheries reaching deeper unexploited grounds may not necessarily be the case for within the Mediterranean, due to the relative low level of biomass found in the deepwaters of this sea and as the fishing fleets are composed mainly of artisanal vessels. Local factors such as the fleet characteristics, the distance from the coast to suitable substrates and the perceived appreciation of the flesh and other by products of this species may, in many countries limit the potential for a targeted fishery to develop. A number of authors have commented on the economic potential to develop a targeted fishery for Centrophorus species (e.g., Boutan 1926 in Algeria, Rancurel 1983 in France, Gilat and Gelman 1984 in Israel), however there is no information regarding potential developments at present. Given the record low reproductive potential of this species, it is highly vulnerable to overexploitation and population depletion under even moderate fishing pressure. Therefore extreme caution should be exercised before the development of any targeted fishery.

There are a few examples of fisheries targeting Centrophorus granulosus in the Balearic Sea over the last 10 years (Guallart pers. comm. 2003). One of which was an alternative fishery, which developed in periods when other target species had declined, this artisanal fleet used bottom longline gears. Abundance (catches of about 50?80 specimens or 300?400 kg/ship and journey) and price of flesh was comparable to that of the original target species. However, catches decreased dramatically within a matter of weeks. An increase in abundance within these depleted areas took place after several months, presumably by migration from other unexploited areas. In another example, a semi-industrial fishery was carried out for several years. One ship made trips of several days covering wide areas unexploited for this species. Catches reached up to 900 specimens (about 5,000 kg). Flesh, livers and tails (as lower quality shark fins) were marketed.

Within the Mediterranean this species is also caught as bycatch, with bottom longlines and bottom gillnets and in bottom trawls targeting red shrimp Aristeus antennatus (Fischer et al. 1987). Further information on the catch rates of this species by this trawling fleet are required before the impact that this has on the Centrophorus granulosus population can truly be assessed.

Other regions
This species is widespread throughout the Western North Atlantic at appropriate depths where it is only taken as bycatch in longline fisheries. At this time it appears that it does not constitute significant numbers in the fisheries, but data is lacking.

In southern Africa it is occasionally taken as a bycatch and possibly in the experimental Namibian deepsea fishery. However, it is uncommon relative to several other species, e.g. C. squamosus, Centroscymnus spp. and Deania spp. which are taken in far greater numbers.

Along the west African coast, this species is widespread, but scattered. It is infrequently caught along the Namibian coast, but this may represent a different species and possibly two or more species may be involved in this taxonomic confusion. Proper identification of this species in southeastern Atlantic waters is critical before this species can be reassessed.
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Vulnerable (VU) (A2abd+3d+4d)
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Management

Conservation Actions

Conservation Actions
Existing:
The General Fisheries Commission for the Mediterranean (GFCM) - the main intergovernmental decision-making body on fishery management in the Mediterranean has made the decision to refrain from expanding deep water fishing operations beyond the limit of 1,000 m. The decision was adopted at the 29th session of the GFCM held in Rome in February 2005. Unless objections from member countries arise, it will come into force in July 2005. For more information, see: Mediterranean Conservationists and Fishermen Work Together to Protect Deep Seas.

Recommended:
Further study is required for taxonomic resolution of the genus, and on reproductive cycle and general life history, validation of ageing methods, population identification, and determination of nursery areas, migrations and spatial distribution. Monitoring fishing pressure is essential. This must include recording specific fishery statistics (including bycatch), and monitoring possible plans for development of target fisheries or increasing fishing pressure in their habitat.

There are currently no conservation measures at this time in the Northwest or the Southeast Atlantic. Examination of the Centrophourus spp. which occur in the latter region is strongly recommended to determine the proper identification of the species involved.
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Relevance to Humans and Ecosystems

Benefits

Importance

fisheries: minor commercial; price category: high; price reliability: reliable: based on ex-vessel price for this species
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Wikipedia

Gulper shark

For the gulper sharks family, see Centrophoridae.

The gulper shark (Centrophorus granulosus) is a long and slender dogfish usually about three feet in length generally found in deep, murky waters all around the world. It is a light grayish brown, paler ventrally, with a long snout and large greenish eyes.[1] This deep water shark has two dorsal fins with long, grooved spines and the second dorsal fin smaller than the first. Its upper teeth are blade-like and lower have finely serrated edges.[1] This tertiary consumer feeds on mainly fishes such as bony fishes, but also cephalopods such as squid and other invertebrates like crustaceans.[1] The gulper shark is currently a vulnerable species mainly because of exploitation by humans and their abnormally long gestation period and low fecundity, preventing their population from recovering.[2]

Development and Reproduction[edit]

Gulper sharks reach maturity at around age 12 to 16 years for females, and age 7 to 8 years for males.[3] The maturity of a gulper shark can be determined by the seven-stage maturity scale for aplacental and placental viviparous sharks.[4] This scale is good for practical field use, but may not be as accurate as other maturity scales that have more than seven stages. Maturity for gulper sharks is considered when they are at stage 3 or above, which for males is when gonads are enlarged and filled with sperm, and sperm ducts are tightly coiled. For females, stage three is when ovaries are large and well rounded.[4]

A drawing of a gulper shark morphology including teeth and jaw.
Gulper Shark Morphology

On average, male gulper sharks are smaller than females.[5] The size of an average adult male is 80 to 95 cm. The size of an average adult female is from 90 to 100 cm long.[5] Differences in size between the sexes may be due to the need for space to support offspring.[5] It has been hypothesized that gulper sharks display a “depth distribution pattern associated with size” based on random human observation.[5]

Male gulper sharks tend to outnumber females 2:1, which is common for many fish species. The life expectancy, longevity, of female gulper sharks ranges between 54 and 70 years.[5] Having a long life expectancy but a low net reproduction rate suggests that the population of gulper sharks would be at a very high risk if too many of them were killed from excessive fishing.

Female gulper sharks typically have between 2 to 10 pups in their lifetime, with generally one pup per pregnancy, this is considered to be a low fecundity.[5] Once fertilized, females can hold up to 6 mature egg cells, or oocytes, in their body at a time. The length of time these egg cells are kept inside the female’s body is called the gestation period. Gulper sharks have a long gestation period, around two years.[2] Gulper sharks can have long resting periods between pregnancies.[1]

They are ovoviviparous, meaning the only parental care they give their young is during the incubation period.[4] Since not all oocytes form into pups, when a pup or two is formed inside the female, they eat the remaining fertilized eggs, known as oophagy.[1] After they are born, they are on their own. Having a low fecundity, a long gestation period, breaks between pregnancies, and a late age of maturity all contribute to the gulper shark having a very low net reproduction rate.[1] It is believed that the gulper shark has the lowest reproduction rate of any elasmobranch species.[1]

Geographic Range[edit]

The gulper shark is a deepwater oceanic species, living in waters ranging between 100 to 1490 meters in depth,[2] with the juveniles being the main occupant of the lower half of the depths.[6] Acceptable habitats for gulper populations are found globally, wherever temperate and tropical waters are found. The gulper shark is most commonly found in the 300 to 800 meter depth range, inhabiting the upper continental slopes and outer continental shelves,[2] the gulper is highly migratory species and has schooling habits based on multiple sharks being present around baited cameras.[7]

Due to the frequency and patterns of migration the gulper shark population estimates may be inaccurate with some sharks being counted twice, which are exacerbated by inappropriate tagging techniques. There are multiple species of gulper sharks, which has contributed to misidentification in the past. For example, populations of the gulper shark in the Southeast Atlantic Ocean may represent a separate species.[2] Therefore, taxonomic confusion may influence current geographical range.

Human Interaction[edit]

Fishing and Bycatch[edit]

Human interaction with the gulper shark exists mainly in the form of fishing. Longline fishing is a typical method for fishing at the depth required to catch gulper sharks, and the broad distribution of gulper habitat leads to this method being used to catch gulpers around the world. However, gulper sharks are not always caught intentionally. The deep waters in which the gulper and similar shark species live is difficult to harvest, and longlines are an unspecific form of fishing. Longlines intended for other species can easily catch gulper sharks.[8]

A photo of a gulper shark that has been caught.
Gulper shark that has been caught by a fishing boat

When a fish species other than the intended catch is caught, it is called bycatch. Although bycatch is not always a significant cause of loss to population size, it highlights the unpredictable nature of deepwater fish exploitation 19.[9] Rules and regulations regarding bycatch treatment are difficult to enforce by the nature of the bycatch being unintentional. Bycatch is often not treated as a serious issue until a species has declined to a point where small bycatch has a large effect, so data on the effect of bycatch on gulper populations is not abundant. Gulper shark populations have dropped as much as 80% in some areas, so bycatch is only recently becoming a big issue for them.[2]

Consumables[edit]

The reasons why the gulper shark would be harvested are just as important as how it is harvested. Gulper sharks do not constitute any particular resource that is not common to most deepwater sharks. Fins and meat are two components generally taken from them, but are also those harvested from any other shark. It is the liver oil at which the gulper shark presents a harvesting advantage. Compared to similar species such as the dogfish shark, the gulper has a larger liver with more oil. Traditionally, shark oil is a folk remedy for a variety of ailments, but also has been shown to contain compounds of contemporary medicinal value, most notable squalene, although the compound can also be extracted from plants.[10] This compound makes the liver of the gulper shark very valuable and is a large part of gulper-specific fishing.

Ecology[edit]

Life History[edit]

The life history of an organism describes the timing of important events for the typical individual of a species. The life history of the gulper shark shows that vulnerability to harvesting is inherent in its biology. The slow rate of gulper growth and development leads to a life strategy that is more centered on competition with one another than escaping predation, especially from humans. This is demonstrated from even the earliest part of an individual gulper's life history where it consumes other fertilized eggs inside its parent's body.[1]

A long gestation period, later maturity, and long lifespan all contribute to a K-selected tendency that favors intraspecific competition, or competition with similar species, over survival defenses having to do with predation. Harvesting is a form of predation that slow, invested reproduction does not easily alleviate. The long gestation, low fecundity, and breaks in individual reproduction lead to slow repopulation ability.[1] Slow reproduction is a part of the species biology, and cannot be changed in one generation based on sudden predation pressure. A group of gulper sharks that undergoes predation by humans may take fifteen years or longer to recover, if at all, based on their maturation time of twelve to sixteen years.[3] Large populations of gulper sharks must be built over long periods of time.

Photo of shark liver oil capsules consumed
Shark liver oil capsule

Gulper life strategy is also consistent with their trophic level and place in the deepwater community. They are tertiary consumers with no apparent predators, so their biological gear toward competition is an ecologically sound strategy.[11] The introduction of human interaction with gulper sharks is the introduction of a higher trophic level, and presents a relationship that current gulper biology is not equipped to handle while maintaining steady or growing population size.

While the fishing of gulper sharks and utilization of squalene from their livers is not inherently an activity that drives them toward extinction, overexploitation of the species can be a problem. The status of gulper sharks on the ICUN red list is currently only vulnerable rather than endangered.[2] The squalene taken from the gulper liver is in high demand as a possible cancer therapy component among other uses, leading to unchecked harvesting of the species. When the populations are declining due to overexploitation, each viable individual is important. As much as 80% of the gulper population has been depleted in some areas, so any harvesting can have a large effect on the decline of the species or possible recovery.[2]

The key to overexploitation in gulper sharks is that they require nearly as much time as humans to mature and reproduce. Their life strategy indicates that the frame of view for gulper fishing plans needs to be based on longer amounts of time, to allow for the consideration of the next generation of individuals. Gulper shark do not mature much faster than humans, so they need to be exploited based on a schedule that reflects this. However, being harvested by a species with similar growth patterns means that the gulper shark is unlikely to be considered in this way. It is highly susceptible to overexploitation leading to widespread population decline and its status and a species vulnerable to endangerment.

Conservation Efforts / Legislation[edit]

The gulper shark has been classified as vulnerable status by the IUCN since 2000 due to heavy overfishing and exacerbated through bycatch and low reproductive rates. The General Fisheries Commission for the Mediterranean (GFCM), which is in charge of almost all intergovernmental fishery management decisions, mandated in 2005 to stop expanding deep water fishing beyond 1,000 meters.[12] This mandate however, does not support the main population of gulper sharks, which generally live 300–800 meters below the surface. This decision also does not stop any current deepwater fishing; it simply stops any further expansion.[2] This is an insufficient conservation attempt, as it does not help gulper populations under stress, it simply stops more stress from accumulating. The current level of fishing may already be enough to render that population critically endangered in that region, especially considering the low reproductive rate of gulpers.

Small tied bales of flat gray objects, messily stacked underneath a translucent tentlike roof between white walls.
Shark fins confiscated from the King Diamond II

Other areas of gulper shark populations have no current regulations. The Northwest Atlantic Ocean currently has no rules in regard to the harvesting of gulper sharks, and has already seen a decrease in gulper population of 80-95% since 1990.[13]

While not many specific laws apply to gulpers specifically, some blanket laws, which cover many different species, are being created. Although they are for sharks in general, many people do not realize that the gulper is not, in fact, a shark. The United States Government passed the Shark Conservation Act in 2010, which prohibited removing fins from sharks that were usually caught as bycatch and then sold to Chinese markets for shark fin soup. This law seals many of loopholes by requiring that any fins or tails brought to land must be “naturally attached to the corresponding carcass” and that no U.S. ship in foreign waters is allowed to possess shark fins.[11] This act protects all species of sharks within 50 nautical miles of the U.S. coast.[11] This is a much more effective law than that by the GFCM, because it addresses shark finning directly and cuts down on the amount of gulpers killed for their fins. Since this law point-blank cuts down on bycatching, it should be an effective effort at the conservation of shark species off U.S. coasts.

Issues for Effective Conservation[edit]

While conservation attempts are being made, certain issues like fishery guidelines and catch verification pose problems for furthering conservation attempts.

A comprehensive list of similarities in Centrophorus.
Morphological Similarities in Centrophorus

The fisheries concept is a closely regulated way to harvest gulpers, while monitoring the species population to ensure it does not crash. They generally use body mass as an indicator of when to harvest the sharks to allow growth of the population. When these ratios are incorrect, the fishery can easily crash because sharks are harvested before they can reproduce. This is especially true with the gulper shark, which has a two year long gestational period and a twelve to sixteen year maturity for females. Biery and D. Pauly from The University of British Columbia Fisheries Centre in Vancouver, Canada executed a review on species-specific fin to body-mass ratios in 2012. Their paper concludes that current regulated ratios are not appropriate for all species and that regulations based off a general ratio for all species is inadequate and may be harming fisheries. The ratios used by many fisheries were originally compiled by a politically affiliated group called The Regional Fishery Management Organizations, RFMO. Biery and Pauly collected fin to body-mass ratios for 50 different species and eight different countries and observed that actual fin to body-mass ratios varied by species and location. Species specific mean ratios ranged from 1.1% to 10.9% and estimated mean ratios by country ranged from 1.5% to 6.1% indicating that current regulations will crash fisheries and not promote population growth [14]

Away from the commercial side of conservation, there are tagging efforts to monitor gulper populations. Tagging is a common ecological tool to study the species characteristics. A large problem with monitoring the populations of Australian and Indonesian dogfish is that discriminating between the seven local species by morphological attributesalone is unreliable. In 2012 a study conducted by Ross Daley, Sharon Appleyard, and Matthew Koopman from the CSIRO Marine and Atmospheric Research Center in Hobart, Australia aims to help monitored recovery plans by implementing a new catch data verification plan. Their study focuses on using the 16s mitochondrial gene region to differentiate these species and when sequenced, all but C. harrissoni and C. isodon were distinguishable.[15] They concluded that 16s gene is a strong marker suitable for fishery catch verification and that using this technique is a reliable and efficient system for routine testing. However, specialized primers needed for trials are sensitive to decay. Therefore, preservation problems need to be researched to further the prospective use of a 16s mitochondrial classification. This system for routine testing is only available to scientists and would require substantial training for fishermen to be able to use this technique.[15]

Uncertainties and Inconsistency in Data[edit]

While information concerning gulper sharks exists, there is no place to centrally compile the information so that other researchers may easily obtain it. This leads to repetition in basic data and less depth into the subject matter. Information presented may also be inaccurate as many genus of Centrophorus are morphologically similar. While attempts are being made to make it easier to identify different genus, such as Daley’s use of 16s mitochondrial DNA listed above,[15] older data listed for gulper sharks could be for ones other than the granulosus, such as the dumb gulper shark. This also means that current populations numbers could account for other dogfish than just the gulper sharks. Lastly, due to the frequency and patterns of migration, the recorded gulper shark populations may be inaccurate.

References[edit]

  1. ^ a b c d e f g h i ARKive, “Gulper Shark Fact File”, “[www.arkive.org/gulper-shark/centrophorus-granulosus]”, 3/21/2013
  2. ^ a b c d e f g h i Guallart, Serena, Mancusi, Casper, Burgess, Ebert, Clarke, Stenberg, “IUCN Red List of Threatened Species”, 2006, “[www.iucnredlist.org]”, 1 March 2013
  3. ^ a b Clarke, Connolly, Bracken, “Journal of Fish Biology”, 4 Apr 2015, “[1]”, 3/20/2013
  4. ^ a b c MedSudMed, “FAO Sicily”, Dec 2008, “[2]”, 3/21/2013
  5. ^ a b c d e f Severino, Afonso-Dias, Delgado, “Life and Marine Sciences 26: 57-61”, 2009, “[www.horta.uac.pt/intradop/images/stories/arquipelago/26/57-61_Severino_etal_09_ARQ26.pdf]”, 3/20/2013
  6. ^ Guallart, “Tesis doctoral, Universitat de Valencia”, 1998, “[3]”, 4/17/13
  7. ^ Gilat, Gelman, “Fisheries Research Amsterdam 2(4): 257-271”, 1984, “[4]”, 4/17/13
  8. ^ “Seafood Watch”, Fishing Methods Fact Card, “[5]”, 4/18/13 April
  9. ^ Hogan, Michael, 2010, “Overfishing”, [“http://www.eoearth.org/article/Overfishing?topic=49521”], eds. Sidney Draggan and C.Cleveland. Washington DC.
  10. ^ National Geographic [“http://news.nationalgeographic.com/news/2009/12/091229-sharks-liver-oil-swine-flu-vaccine/]
  11. ^ a b c ”US Shark Conservation Act of 2010”, 2010, “[6]”, 3/26/2013
  12. ^ “ICES WGFE”, 2006, “[www.artsdatabanken.no/ICES_WGFE_08_rapport_cU3hd.pdf.file]”, 4/10/2013
  13. ^ “GFCM”, 2005, “[7]”, 4/10/2013
  14. ^ Pauly: Biery, “Journal of Fish Biology 80 (5), 2012, “[ doi:10.1111/j.1095-8649.2011.03215.x.]”, 3/14/2013
  15. ^ a b c Daley:Appleyard:Koopman, “Marine and Freshwater Research CSIRO Publishing. 63, 708-714”, 2012, “[8]”, 3/14/2013
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