Angular roughshark

Angular roughshark
Conservation status
Vulnerable  (IUCN 3.1)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Chondrichthyes
Subclass:	Elasmobranchii
Order:	Squaliformes
Family:	Oxynotidae
Genus:	Oxynotus
Species:	O. centrina
Binomial name
Oxynotus centrina (Linnaeus, 1758)
Range of the angular roughshark (in blue)

The angular roughshark, Oxynotus centrina, is a rough shark of the family Oxynotidae.^[1]

Taxonomy

Biologist Carl Linnaeus founded the Angular Roughshark, O. centrina, in 1758. This name was later finalized and accepted by the scientific community as the official name for the species in 1976.^[2]

Description and Feeding

At birth they are less than 25 cm (10 in) and they mature at about 50 cm (20 in). Most records are of individuals less than 1 m (3.28 ft), but they can reach up to about 1.5 m (4.9 ft). Their litter size is from 7-8 pups off Angola to 23 in the Mediterranean. They have ridges over their eyes that expand into large rounded knobs, which are covered with enlarged denticles – these are absent in other species of rough shark. They possess very large spiracles that are vertically elongated, being almost as high as the length of their eye. Their first dorsal spine is orientated slightly forward. They feed on worms, crustaceans, and mollusks.^[3]

O. centrina has a compressed body, triangular in cross section, with a broad and flattened head. The snout is flat and blunt. Just like all of the Oxynotus species, they have two relatively large dorsal fins that are sail-like and no anal fin. Their color scheme is grey or grey-brown dorsally with dark blotched on its head and sides. However, one identifying feature is the light horizontal line below the eyes on the cheek.^[4]

Since it shares the northeast Atlantic with another species of Oxynotus, another distinguishing feature, mentioned above, are the extremely large spiracles, their dorsal fins, and their large dermal denticles above their eyes. Although, like most of the Oxynotus species, O. centrina has lanceolate upper teeth and blade-like lower teeth, with 12 rows of teeth on either side.^[4]

O. centrina usually moves by gliding on the bottom of the sea, sometimes hovering over the sandy or muddy surfaces of the seabed.^[5]

Range and habitat

They occur in the eastern Atlantic from Norway to South Africa, including the entire Mediterranean. They may also occur off Mozambique. They prefer coralline algal and muddy bottoms on continental shelves and upper slopes at depths of 50 to 660 m (165 to 2165 ft), but occur mostly below 100 m (328 ft).^[3]

Reproduction

Male and female angular roughsharks are reported to mature at about 50–70 cm. Although, some studies have shown that females mature at a slightly larger size than males. Being an ovoviviparous species, O. centrina produce 10-12 pups usually between the sizes of 21 and 24 cm in length.^[4]

Population

Some data has been gathered on this species of Oxynotus in the period from 1994 to 1999 in the Mediterranean. O. centrina was only present in 0.6% of the tows during this period at a depth of 100 to 200 m. Regional indexes indicate this species is more common in the western central Mediterranean and lower index in the western and eastern Mediterranean. However, O. centrina was completely absent from the Eastern central Mediterranean.^[2]

In 1948, trawl surveys indicated that O. centrina was once present, but uncommon, in the Adriatic. Although, the species has been absent in subsequent studies in the Adriatic, suggesting a possible extinction of that species in the area. However, recent studies, done by Lipej in 2004, show that some juveniles have been caught in the central Adriatic. Also, some data collected during the surveys in the Balearic Sea and the Ionian Sea found one specimen at 800 m in the western Ionian Sea, suggesting that the population of O. centrina, in the Eastern central Mediterranean, has an unknown population.^[2]

However, this species was absent in the Northeast Atlantic in a study of deepwater longline fishing for sharks near the Canary Islands. This is important because this species was abundant in this region until 1997.^[2]

Threat and Conservation

O. centrina in a minor bycatch of offshore fisheries such as trawl fleets. Although this can have a negative impact on the species, as stated above, the species has been extinct in Adriatic for some time, but due to decreased fisheries in the Adriatic, the species seems to be refurbished.^[2]

This species, sometimes caught by fisherman in the Mediterranean, has little to no commercial value. Also, it is thought to bring bad luck to fisherman if caught and kept. Although, released, it has never been reported of this fish to survive.^[2]

The IUCN Red List of Threatened Species has deemed this species of Oxynotus as vulnerable due to consistent landings by fisherman and bycatch by deepsea fisheries. The implementation of management plans is to require conserving and sustaining management of all chondrichthyes species in the region.^[2]

References