Portuguese Dogfish Essay Information

Home » Centroscymnus coelolepis (Portuguese Dogfish)


Taxonomy [top]

KingdomPhylumClassOrderFamily
AnimaliaChordataChondrichthyesSqualiformesSomniosidae

Scientific Name:Centroscymnus coelolepis Barbosa du Bocage & de Brito Capello, 1864
Regional Assessments:
Common Name(s):
EnglishPortuguese Dogfish

Assessment Information [top]

Red List Category & Criteria: Near Threatened ver 3.1
Year Published:2003
Date Assessed:2003-04-30
Annotations:
Assessor(s):Stevens, J. & Correia, J.P.S. (SSG Australia & Oceania Regional Workshop, March 2003)
Reviewer(s):Cavanagh, R.D. (Shark Red List Authority) & Graham, K.
Justification:
Mainly a bycatch species taken by trawl and hook, although with some limited targeting, for its flesh and oil. Catches in Australia have been increasing in the last few years with relaxation of mercury laws and fishers looking for non-quota species in the South East Trawl Fishery. However, appropriate data on biomass or trends in abundance are lacking. The productivity of this species is likely to be low (although age estimates and annual fecundity are currently unknown) and further increases in catches should be viewed with concern. This species is of much lower abundance than D. calcea or C. crepidater and, although the quantitative data on populations are lacking, its lower abundance, demersal habits (not appearing to range into midwater) and suspected low productivity warrant a Near Threatened assessment.

Geographic Range [top]

Range Description:A wide but patchy distribution in the Atlantic (Iceland to South Africa, and including the western Mediterranean; Grand Banks to Delaware Bay) and western Pacific (off Japan, New Zealand and Australia (from Cape Hawke, New South Wales to Beachport (South Australia), including Tasmania).
Countries occurrence:
Angola; Australia (New South Wales, South Australia, Tasmania, Victoria); Benin; Cameroon; Canada (Newfoundland I, Nova Scotia); Congo; Côte d'Ivoire; Equatorial Guinea; France; Gabon; Gambia; Ghana; Guinea; Guinea-Bissau; Iceland; Ireland; Japan; Liberia; Mauritania; Morocco; Namibia; New Zealand; Nigeria; Portugal; Senegal; Sierra Leone; South Africa; Spain (Canary Is.); Togo; United Kingdom; United States (Delaware, Maine, Massachusetts, New Jersey, Rhode Island); Western Sahara
FAO Marine Fishing Areas:
Atlantic – eastern central; Atlantic – northeast; Atlantic – northwest; Atlantic – southeast; Indian Ocean – eastern; Mediterranean and Black Sea; Pacific – northwest; Pacific – southwest
Additional data:
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:Relatively common in the eastern North Atlantic where it is targeted off Portugal. Also relatively common off Japan, south eastern Australia and New Zealand. No data are available on population sizes or on long term trends in abundance.
Current Population Trend:Unknown
Additional data:

Habitat and Ecology [top]

Habitat and Ecology:On or near the bottom of the continental slope and abyssal plain in depths from 270 to 3,700 m. In Australia, catch rates are generally highest in depths greater than 1,000 m (Daley et al. 2002). Surveys conducted in Portugal never found this species in depths shallower than 800 m. There appears to be sex and size segregation by depth. The diet consists mainly of fish (including sharks) and cephalopods along with benthic invertebrates and cetacean species. Off southern Australia, teleost prey included relatively large demersal species such as alepocephalids and orange roughy, as well as small lantern fishes.

Population parameters in Australia are as follows (Daley et al. 2002):

Size at birth: 30 cm total length (TL)
Max size: 120 cm TL
Male maturity: 75 cm TL
Female maturity: 95 cm
Age at maturity: ?
Longevity: ?
Litter size: 12 (8-19)
Gestation:? (non-seasonal)
Breeding cycle: non-continuous

Maturity in Japan and in the north east Atlantic is reported at between 70 and 86 cm in males and at about 100 cm in females (Yano and Tanaka 1988, Girard and Du Buit 1999), with maximum size attained at 158 cm TL. There is evidence of size segregation by depth with smaller specimens at greater depths and pregnant females at shallower depths (Yano and Tanaka 1988, Girard and Du Buit 1999).
Systems:Marine

Threats [top]

Major Threat(s): This shark has been exploited commercially for a long time. In Japan exploitation peaked during World War II, (because the livers are rich in squalene: 22 to 49% by weight), but quickly declined due to decreasing numbers caught. Taken by trawl, hook and gillnet both as a target and bycatch species for its liver oil and flesh. Important fisheries for this species exist in Suruga Bay, Japan and Portugal where it is targeted by a deepwater longline fishery. Between 1986 and 1999 catches in Portugal varied between about 300-900 tonnes with an increasing trend. The price of landed wet weight in Portugal has also been increasing since 1986 (US$1.5/kg in 1986 to US$3.5/kg in 1999), which suggests that demand is driving the fishing industry to continue exploitation. However, CPUE data were lacking and it is not currently possible to assess changes in abundance and biomass from any areas.

Conservation Actions [top]

Conservation Actions: 2002 regulations in the South East Trawl fishery in Australia prohibits the landings of livers unless the accompanying carcass is also landed.

The Portuguese dogfish (Centroscymnus coelolepis) is your quintessential “deep-water fish”, being one of the deepest dwelling shark species. It likes to stay way down in the ocean depths, most commonly around 1000 m (3300 ft). However it has been recorded down to 3.7 km (2.3 mi) beneath the surface!

This common and heavily exploited species is also referred to as the Portuguese shark. While the original species description was based on a specimen caught off of Portugal, this is a widespread shark that occurs around the globe.

The stocky body is dark brown, and has a shape that is more like a typical bony fish than a shark. It has large dermal denticles, no anal (bottom) fin, and the body reaches a maximum length of 1.58 m (5.2 ft).

Portuguese Dogfish Facts

This is a slow growing shark that is thought to live up to 70 years of age.

It belongs to the family known as “Sleeper Sharks” (Somniosidae), so named because they were originally thought to be sluggish bottom-dwellers. Sleepers? Well as it turns out, not so much. These sharks are in fact active, stealth predators.

Habitat and Range

This shark has a wide but patchy global distribution, encompassing the western North Atlantic Ocean, the eastern Atlantic, the western Mediterranean Sea, and the western Pacific Ocean.

While much information is available about this species because it has been the target of fisheries for so long, little data are available on its general biology, population sizes, or changes over time.

A recent genetic study looked at population structure of this species in the eastern Atlantic, off the coasts of Ireland, Portugal, Madeira, Mauritania, South Africa, and the Azores (Mid-Atlantic Ridge). The researchers found high levels of genetic diversity in the fish examined, however this was spread evenly across sampling locations. They found no evidence of distinct populations, indicating that there is a large amount of dispersal happening throughout the eastern Atlantic.

The preferred habitat of the Portuguese dogfish is the bottom of continental slopes and deep ocean plains. However, the depth at which individuals tend to reside depends on their sex and size. Younger sharks are generally found at greater depths than adults, and pregnant females in particular stay in shallower waters. The reason for this difference has not been demonstrated.

Feeding Behavior

The upper teeth of this dogfish are spearlike: each has a long narrow cusp, or point. The lower teeth are blade-like and slightly larger than the uppers, each with a cusp that is slanted to the side.

Like all dogfish, this species is a successful predator. It seems to have a low diet diversity and feeds mainly on cephalopods, although fish (including some other sharks) and benthic invertebrates may also be consumed. Occasionally it acts as an opportunistic scavenger, meaning that when it’s really hungry it will take whatever it can get!

It is thought that this shark’s preference for deep waters may be explained by avoidance of competition with other shark species that have a similar trophic position (i.e. feeding habits), such as the Velvet belly lanternshark (Etmopterus spinax).

Breeding

This is a species with late reproductive maturity, a long gestation period of possibly more than a year, and a relatively low rate of reproduction. Body size varies with geographic location, but in general males mature at about 85 cm (2.8 ft), and females at about 1m (3.3 ft) in length.

The breeding system is ovoviviparous, with females bearing anywhere from 5 to 29 young per litter. Pups are about 30 cm (11.8″) at birth. The nursery areas remain undiscovered.

In addition to the depth segregation described above, individuals of different sexes and ages are also found in different spatial locations. This is possible evidence of a large-scale migration timed with the reproductive cycle of this species.

Humans and Conservation

The Portuguese dogfish is an important species in commercial fisheries of the eastern Atlantic and Japan. It is caught by trawl, hook and gillnet. This species has been taken for human consumption over a long period of time. Catches in Japan peaked during World War II, but then declined due to overfishing. The shark meat is dried or salted for storage, and used to make fishmeal.

Another reason for the active pursuit of this species is the high squalene content of the liver. Squalene is an organic compound found in plants and animals, but particularly in shark livers. It is used as an additive to foods, cosmetics, medication and health supplements, and in vaccines to help boost immune responses.

Information about the current status of Portuguese dogfish populations is sketchy, because it is difficult to separate data about this species from other dogfish sharks in fisheries records. However there is evidence that numbers are declining, and some stocks are considered to be depleted. The ongoing removal of this species is worrisome to begin with – having such a low rate of reproduction, it cannot logically withstand such fishing pressure.

Accordingly, the International Council for the Exploration of the Sea(ICES) recommends a zero catch of Portuguese dogfish. The IUCN Red List assesses this species as “Near Threatened”, based on its low fecundity and the lack of relevant data on population trends.

At the very least, available scientific information indicates that commercial exploitation of the Portuguese dogfish should proceed with caution.

Written By: Kara Lefevre


 

Sources

    • Carrassón M, Stefanescu C & Cartes JE (1992). Diets and bathymetric distributions of two bathyal sharks of the Catalan deep sea (western Mediterranean). Marine Ecology Progress Series 82:21-30.
    • Carrier JC, Musick JA & Heithaus MR (editors) (2010). Sharks and Their Relatives II: Biodiversity, Adaptive Physiology, and Conservation. CRC Press.
    • Castro JI (2011). The Sharks of North America. Oxford University Press.
    • Clarke MW, Connolly PL & Bracken JJ (2001). Aspects of reproduction of the deep water sharks Centroscymnus coelolepis and Centrophorus squamosus from west of Ireland and Scotland. Journal of the Marine Biological Association of the UK 81: 1019-1029.
    • Crawford D (2008). Shark. Reaktion Books.
    • Marine Girard & Marie-Henriette Du Buit. 1999. Reproductive biology of two deep-water sharks from the British Isles, Centroscymnus coelolepis and Centrophorus squamosus (Chondrichthyes: Squalidae). Journal of the Marine Biological Association of the UK 79: 923-931.
    • Stevens J & Correia JPS (2003). Centroscymnus coelolepis. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2.
    • Verissimo A, McDowell JR & Graves JE (2011). Population structure of a deep-water squaloid shark, the Portuguese dogfish (Centroscymnus coelolepis).ICES Journal of Marine Science 68: 555-563.

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