Portuguese dogfish

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Portuguese dogfish
A small, dark brown, heavy-bodied shark with large green eyes and small fins, lying on the ground next to a meterstick

Near Threatened  (IUCN 3.1)[1]
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Elasmobranchii
Subdivision: Selachimorpha
Order: Squaliformes
Family: Somniosidae
Genus: Centroscymnus
Species:
C. coelolepis
Binomial name
Centroscymnus coelolepis
World map with blue shading in the northern Atlantic Ocean, western Mediterranean Sea, southern Indian Ocean, and off Japan
Range of the Portuguese dogfish
Synonyms

Centroscymnus macrops* Hu & Li, 1982
Scymnodon melas Bigelow, Schroeder & Springer, 1953

* ambiguous synonym

The Portuguese dogfish (Centroscymnus coelolepis) or Portuguese shark, is a

bony fish. This species typically reaches 0.9–1 m (3.0–3.3 ft) in length; sharks in the Mediterranean Sea
are much smaller and have distinct depth and food preferences.

Relatively common, the Portuguese dogfish is an active hunter capable of tackling fast, large prey. It feeds mainly on

Near Threatened
.

Taxonomy

Black and white drawing of a dogfish from the side
Early illustration of a Portuguese dogfish.

The first

type specimen, caught off Portugal, has since been destroyed in a fire.[2]

Distribution and habitat

One of the widest-ranging deepwater sharks, the Portuguese dogfish is patchily distributed around the world.

Beachport, South Australia, including Tasmania.[1]

The deepest-living shark known,

benthic in nature, though young sharks can be found a considerable distance off the bottom.[2][10] There is depth segregation by size and sex; pregnant females are found in shallower water, above 1,200–1,500 m (3,900–4,900 ft), while juveniles are found deeper.[1][8][11] There may be several separate populations in the Atlantic, and sharks in the Mediterranean and off Japan appear to be distinct as well.[12]

Description

Side view of a dark brown shark
The Portuguese dogfish can be distinguished from similar species by its tiny dorsal fin spines.
Dorsal and ventral view of the Portuguese dogfish's head, showing the broad, flattened snout and wide mouth.

The Portuguese dogfish typically reaches a length of 0.9 m (3.0 ft) for males and 1.0 m (3.3 ft) for females, though specimens up to 1.2 m (3.9 ft) long have been recorded.[13] Sharks in the Mediterranean are smaller, growing no more than 65 cm (26 in) long.[4] This species has a flattened, broadly rounded snout that is shorter than the mouth is wide. The nostrils are preceded by short flaps of skin.[2] The eyes are large and oval in shape, positioned laterally on the head and equipped with a reflective tapetum lucidum that produces a yellow-green "eye shine".[14] The mouth is wide and slightly arched, with moderately thick, smooth lips and short furrows at the corners extending onto both jaws. The upper teeth are slender and upright with a single cusp, numbering 43–68 rows. The lower teeth have a short, strongly angled cusp and number 29–41 rows; their bases interlock to form a continuous cutting surface.[13] The five pairs of gill slits are short and nearly vertical.[15]

The body of the Portuguese dogfish is thick and cylindrical except for the flattened belly. The two dorsal fins are small and of similar size and shape, each bearing a tiny grooved spine in front. The first dorsal fin originates well behind the

bony fishes.[16] Young sharks are a uniform blue-black in color, while adults are brown-black; there are no prominent fin markings.[13] In 1997, a partially albino individual, with a pale body but normal eyes, was caught in the northeastern Atlantic. This represented the first documented case of albinism in a deep-sea shark.[17]

Biology and ecology

Living almost exclusively in the

tapeworms Sphyriocephalus viridis,[21] S. richardi, and Anthobothrium sp.[22]

An active predator of mobile, relatively large

lens, and a tapetum lucidum, its eyes also contain a high concentration of ganglion cells mostly concentrated in a horizontal streak that is densest at the center; these cells impart highly sensitive motion detection along the horizontal plane. The visual system of this species appears adapted for detecting bioluminescence: the maximum absorption of its opsins correspond to the wavelengths of light emitted by favored prey, such as the squids Heteroteuthis dispar, Histioteuthis spp., Lycoteuthis lorigera, and Taningia danae.[14]

In the Mediterranean sea, the Portuguese dogfish is one of the most common deepwater sharks along with the

velvet belly lantern shark (Etmopterus spinax), and the only shark abundant below a depth of 1,500 m (4,900 ft).[8] By inhabiting deeper water, Portuguese dogfish in the Mediterranean may reduce competition with the other two species.[4] The smaller size of Mediterranean sharks relative to those from the rest of the world may be due to limited food availability and/or the warmer, saltier environment. Some 87% of the diet of Portuguese dogfish in the Mediterranean consists of cephalopods. Bony fishes are a secondary food source, while immature sharks favor the shrimp Acanthephyra eximia, the most common decapod crustacean in their environment.[9] Unlike in other regions, Mediterranean sharks seldom scavenge.[8]

Life history

The Portuguese dogfish is

testis on its left.[12]

Early in development, the embryos are sexually undifferentiated, unpigmented, and possess filamentous external gills; the external

ovarian atresia (regression of the follicles), suggesting that they enter a resting period afterwards.[24] The litter size ranges from 1 to 29 (typically 12), and is not correlated with female size.[1][12] Parturition may occur in a yet-unknown nursery area, as newborns are rarely ever caught.[12] The length at birth has been reported as 23–30 cm (9.1–11.8 in) in the Atlantic,[12][25] and 30–35 cm (12–14 in) in the Pacific.[26][27]

Aside from the distinctive Mediterranean population, Portuguese dogfish attain sexual maturity at similar sizes around the world: males and females mature at 90–101 cm (35–40 in) and 85–115 cm (33–45 in) respectively off the Iberian Peninsula,[12][24][25] 86 cm (34 in) and 102 cm (40 in) respectively west of the British Isles,[28] 70 cm (28 in) and 95–100 cm (37–39 in) respectively in Suruga Bay, Japan,[26] and 82–90 cm (32–35 in) and 99–110 cm (39–43 in) respectively off southeastern Australia.[27][29] In the Mediterranean, males mature at around 53 cm (21 in) long.[30]

Human interactions

Black and white photo of a row of small sharks lying side by side on the deck of a fishing boat
The Portuguese dogfish is an important component of several deepwater fisheries.

The Portuguese dogfish is too small and occurs too deep to pose a danger to humans.

fishmeal.[1][7] An important fishery for the Portuguese dogfish exists in Suruga Bay for liver oil; catches peaked during World War II, but declined soon after from over-exploitation.[1] In the past few years, catches by the South East Trawl Fishery off Australia have been increasing, as fishers have been seeking out species not covered by commercial quotas following the relaxation of seafood mercury regulations. Shark landings in this fishery are affected by a prohibition on landing livers without the rest of the carcass.[1]

Until recently, Portugal was the only European country to utilize the Portuguese dogfish. An important

Near Threatened, because of its commercial value and low reproductive productivity.[1]

In June 2018 the New Zealand Department of Conservation classified the Portuguese dogfish as "Not Threatened" with the qualifier "Data Poor" under the New Zealand Threat Classification System.[31]

References

  1. ^
    doi:10.2305/IUCN.UK.2003.RLTS.T41747A10552910.en.{{cite journal}}: CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link
    )
  2. ^
    ISBN 978-92-5-101384-7
    .
  3. ^ Lineaweaver, T.H. & R.H. Backus (1970). The Natural History of Sharks. Lippincott. p. 239.
  4. ^
    S2CID 86109497
    .
  5. doi:10.1560/N4KU-AV5L-0VFE-83DL
    .
  6. PMID 16777734
    .
  7. ^ a b Froese, Rainer; Pauly, Daniel (eds.) (2009). "Centroscymnus coelolepis" in FishBase. November 2009 version.
  8. ^
    hdl:10261/5645
    .
  9. ^
    doi:10.3354/meps082021
    .
  10. ^
    doi:10.2960/J.v35.m516.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  11. ^
    S2CID 83052597
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  12. ^
    doi:10.1016/S1054-3139(03)00146-2
    .
  13. ^ a b c d e f Burgess, G. and Bester, C. Biological Profiles: Portuguese Shark. Florida Museum of Natural History Ichthyology Department. Retrieved on October 17, 2009.
  14. ^
    doi:10.3989/scimar.2004.68s3185
    .
  15. ^ Yano, K. & S. Tanaka (1983). "Portuguese shark, Centroscymnus coelolepis from Japan, with notes on C. owstoni". Japanese Journal of Ichthyology. 30 (3): 208–216.
  16. S2CID 198492003
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  17. ^ Deynat, P.P. (September 30, 2003). "Partial albinism in the Portuguese dogfish Centroscymnus coelolepis (Elasmobranchii, Somniosidae)". Cybium. 27 (3): 233–236.
  18. doi:10.1071/MF01035
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  19. S2CID 84555258
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  20. S2CID 84642290
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  21. doi:10.1051/parasite/1970451005
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  22. ^ Guitart, J. (1935). "Cestodes parasites provenant des campagnes scientifiquesde S.A.S. le Prince Albert ler de Monaco (1886–1913)". Résultats des Campagnes Scientifiques Accomplies Sur Son Yacht Par Albert Ier Prince Souverain de Monaco Publiés Sous Sa Direction Avec le Concours de M. Jules Richard. 91: 1–100.
  23. S2CID 84676692
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  24. ^
    doi:10.1111/j.1095-8649.2008.01927.x
    .
  25. ^
    S2CID 86283124
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  26. ^
    doi:10.2331/suisan.54.167
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  27. ^ a b Daley, R., J. Stevens and K. Graham. (2002). Catch analysis and productivity of the deepwater dogfish resource in southern Australia. FRDC Final Report, 1998/108. Canberra: Fisheries Research and Development Corporation.
  28. S2CID 84868639
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  29. ^ Irvine, S.B. (2004). Age, growth and reproduction of deepwater dogfishes from southeastern Australia. PhD Thesis, Deakin University.
  30. ^ Cló, S., M. Dalú, R. Danovaro and M. Vacchi (2002). Segregation of the Mediterranean population of Centroscymnus coelolepis (Chondrichthyes: Squalidae): a description and survey. NAFO SCR Doc. 02/83
  31. OCLC 1042901090
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