Patagonian skate (Rhinoraja macloviana)

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Patagonian skate, specimen
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Patagonian skate fact file

Patagonian skate description

KingdomAnimalia
PhylumChordata
ClassChondrichthyes
OrderRajiformes
FamilyArhynchobatidae
GenusRhinoraja (1)

A rather poorly known, medium-sized skate (1), the Patagonian skate (Rhinoraja macloviana) has a dark grey to brown body, covered in faint white spots of differing sizes. There are often two large, pale spots in the centre of the body, and the entire upper surface is covered with small spines, particularly along the midline of the body. The underparts are white (2) (3).

As in other skates, the body of the Patagonian skate is flattened and fused to the enlarged pectoral fins, forming a broad, flat, diamond-shaped disc (4) (5). The eyes are positioned on top of the body, just in front of openings known as spiracles, through which the skate can take in water while lying flat on the seabed (4). The Patagonian skate has a soft, blunt snout (2) and a relatively slender tail, which bears a single dorsal fin (4) (5).

The female Patagonian skate may grow slightly larger than the male (2) (3) (6) (7). Mature males can also be distinguished by the presence of slender, rod-like ‘claspers’, which are used in mating (2). Males also have a slightly different tooth shape to the female (7) and have patches of spines, known as ‘alar thorns’, towards the edges of the pectoral fins (2).

Synonyms
Bathyraja macloviana, Raja macloviana.
Spanish
Raya Espinosa.
Size
Total length: up to 77 cm (1)
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Patagonian skate biology

The Patagonian skate specialises in feeding on polychaete worms (1) (7) (8), particularly species such as Travisia kerguelensis (8). It also takes some amphipods, isopods and crabs (1) (7) (8). Juveniles may feed largely on amphipods before switching to polychaetes as they mature (2).

All skate species lay eggs inside tough, rectangular egg cases (5). The egg cases of the Patagonian skate measure around 6.9 to 7.5 centimetres in length and are dark brown (6), with stiff ‘horns’ at the corners (4) (6). The male Patagonian skate reaches sexual maturity at a body length of around 53 centimetres, while the female matures at a length of about 52 to 55 centimetres (6) (7).

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Patagonian skate range

The Patagonian skate is found in the southwest Atlantic Ocean, where it occurs around Uruguay, Argentina and the Falkland Islands. It has also been recorded in the southeast Pacific Ocean, off southern Chile (1).

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Patagonian skate habitat

Like other skates, the Patagonian skate lives on the seabed (4). Little information is available on its habitat preferences, but it has been recorded at depths of 53 to 514 metres (1), and is reported to be most common between 150 and 200 metres (2).

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Patagonian skate status

The Patagonian skate is classified as Near Threatened (NT) on the IUCN Red List (1).

IUCN Red List species status – Near Threatened

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Patagonian skate threats

Although it is only of moderate commercial importance (2), the Patagonian skate is taken by multi-species skate and ray fisheries, and also occurs as bycatch in other fisheries (1) (9) (10) (11). Few species-specific data are available on the catch rates of this species, but fishing pressure has increased in its range in recent decades and some general declines in skate and ray catches have been reported (1).

Like many skates, sharks and rays, the Patagonian skate is likely to have a long lifespan and relatively slow reproductive rate, making it particularly vulnerable to overfishing (4).

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Patagonian skate conservation

A number of fishing regulations are in place in Argentina, but are not regularly enforced (1). The Falkland Islands skate fishery is relatively well managed, and since 1994 there have been limits on the number of licences issued to limit the total fishing effort. Due to declining catches, direct fishing of skates around the south of the Falkland Islands has been prohibited since 1996, but to the north of the islands it is believed to be occurring at sustainable levels (1) (11). Illegal fishing does sometimes occur, but may only be a relatively minor problem (11).

Perhaps the most important conservation measure for the Patagonian skate would be more detailed assessments of the skate fishery, as species-specific data are lacking and management measures do not take into account the differing biology of each species (1) (11). Species-specific bycatch data will also be important, allowing researchers to better assess the status of the Patagonian skate, as well as that of other skate species in the area (1).

ARKive is supported by OTEP, a joint programme of funding from the UK FCO and DFID which provides support to address priority environmental issues in the Overseas Territories, and Defra
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Find out more

Find out more about the conservation of sharks, rays and skates:

Find out more about conservation in the Falkland Islands:

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Authentication

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:
arkive@wildscreen.org.uk

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Glossary

Amphipods
A group of small shrimp-like crustaceans that includes sandhoppers, beach hoppers, and water lice.
Bycatch
In the fishing industry, the part of the catch made up of non-target species.
Dorsal fin
The unpaired fin found on the back of the body of fish, or the raised structure on the back of most cetaceans (whales, dolphins and porpoises).
Isopods
A diverse group of crustaceans, with flattened, segmented bodies, that includes pill bugs and woodlice.
Pectoral fins
In fish, the pair of fins that are found one on each side of the body just behind the gills. They are generally used for balancing and braking.
Polychaete worms
Polychaeta means ‘many bristled’; this class of worms are segmented and bear many ‘chaetae’ (bristles).
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References

  1. IUCN Red List (March, 2011)
    http://www.iucnredlist.org/
  2. Bizikov, V.A., Arkhipkin, A.I., Laptikhovsky, V.V. and Pompert, J. (2004) Identification Guide and Biology of the Falkland Islands Skates. Falkland Islands Fisheries Department, Falkland Islands. Available at:
    http://www.fis.com/falklandfish/pdf/ray2004.pdf
  3. Cousseau, M.B., Figueroa, D.E. and Díaz de Astarloa, J.M. (2000) Clave de Identificación de las Rayas del Litoral Maritimo de Argentina y Uruguay (Chondrichthyes, Familia Rajidae). Publicaciones Especiales, INIDEP, Mar del Plata, Argentina.
  4. Campbell, A. and Dawes, J. (2004) Encyclopedia of Underwater Life. Oxford University Press, Oxford.
  5. ReefQuest Centre for Shark Research - Batoids: Sawfishes, Guitarfishes, Electric Rays, Skates, and Sting Rays (March, 2011)
    http://www.elasmo-research.org/education/shark_profiles/batoids.htm
  6. Paesch, L. and Oddone, M.C. (2009) Size at maturity and egg capsules of the softnose skates Bathyraja brachyurops (Fowler, 1910) and Bathyraja macloviana (Norma, 1937) (Elasmobranchii: Rajidae) in the SW Atlantic (37º00’-39º30’S). Journal of Applied Ichthyology, 25: 66-71.
  7. Scenna, L.B., García de la Rosa, S.B. and Díaz de Astarloa, J.M. (2006) Trophic ecology of the Patagonian skate, Bathyraja macloviana, on the Argentine continental shelf. ICES Journal of Marine Science, 63: 867-874.
  8. Mabragaña, E., Giberto, D.A. and Bremec, C.S. (2005) Feeding ecology of Bathyraja macloviana (Rajiformes: Arhynchobatidae): a polychaete-feeding skate from the South-west Atlantic. Scientia Marina, 69(3): 405-413.
  9. Laptikhovsky, V.V. (2004) Survival rates for rays discarded by the bottom trawl squid fishery off the Falkland Islands. Fishery Bulletin, 102(4): 757-759.
  10. Wakeford, R.C., Agnew, D.J., Middleton, D.A.J., Pompert, J.H.W. and Laptikhovsky, V.V. (2004) Management of the Falkland Islands multispecies ray fishery: Is species-specific management required? Journal of Northwest Atlantic Fishery Science, 35: 309-324.
  11. Fowler, S.L., Cavanagh, R.D., Camhi, M., Burgess, G.H., Cailliet, G.M., Fordham, S.V., Simpfendorfer, C.A. and Musick, J.A. (2005) Sharks, Rays and Chimaeras: The Status of the Chondrichthyan Fishes. IUCN/SSC Shark Specialist Group, IUCN, Gland. Available at:
    http://data.iucn.org/dbtw-wpd/edocs/2005-029.pdf
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Image credit

Patagonian skate, specimen  
Patagonian skate, specimen

© Dr Daniel E. Figueroa

Dr Daniel E. Figueroa
Laboratorio de Ictiología
Departamento de Ciencias Marinas
Facultad de Ciencias Exactas y Naturales
Universidad Nacional de Mar del Plata
Funes 3350
Mar del Plata
Argentina
Tel: +54 (223) 4751107
Fax: +54 (223) 4753150
dfiguer@mdp.edu.ar

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