Rio skate (Rioraja agassizii)

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Adult female Rio skate specimen
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Rio skate fact file

Rio skate description

KingdomAnimalia
PhylumChordata
ClassChondrichthyes
OrderRajiformes
FamilyArhynchobatidae
GenusRioraja (1)

The Rio skate (Rioraja agassizii) belongs to the family better known as the softnose skates (Arhynchobatidae), although in contrast to other members of the family this species has a heavily built area of cartilage at the base of its snout (3). It is the only member of its genus and displays the general characteristics of a skate, being greatly flattened and rhomboidal in shape, with a slender tail (4) (5). Its mouth is on the underside of the body, along with five pairs of gills (6). The male also possesses claspers, which are used during reproduction (7).

Spanish
Raya Lisa.
Size
Total length: 8 - 58 cm (2)
Maximum length: up to 71 cm (1)
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Rio skate biology

The Rio skate is a benthic feeder, hunting for its prey on the sea floor. Crustaceans such as shrimp are a staple part of its diet, but it also feeds on fish and polychaete worms, with its diet varying according to the abundance of prey (2). It locates its prey via a combination of smell, touch and the detection of electrical impulses (2).

Reproduction in the Rio skate takes place throughout the year, with peaks in egg laying in September and December (7). Females become reproductively active after reaching a body length of 40 centimetres and, after mating, lay pairs of eggs which are covered in a thick, leathery, brown membrane (7) (8).

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Rio skate range

The Rio skate is endemic to the southwest Atlantic Ocean, where it occurs along the coast of South America (1) (7).

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Rio skate habitat

The Rio skate can be found between depths of 10 and 130 metres, typically over a sand, mud or gravel substrate (1) (6) (7).

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Rio skate status

The Rio skate is classified as Vulnerable (VU) on the IUCN Red List (1).

IUCN Red List species status – Vulnerable

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Rio skate threats

A major threat to the Rio skate is the intensive level of trawl fishing which occurs throughout its range (1). It is taken extensively as bycatch but only used commercially when the numbers of other skate species are low (7). Although no species-specific information exists on population declines in the Rio skate, it is known that there has been an estimated 31 percent reduction in skate biomass due to commercial exploitation along the South American coast (1).

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Rio skate conservation

In Argentina, the Rio skate is included in a fishing quota defining the maximum annual permitted catch of skate per year (1).  However, the number of Rio skate caught in recent years has been higher than the permitted amount as the scheme has not been properly enforced, highlighting its inefficiency as a conservation measure (1). More specific catch data is needed for the Rio skate in order to better understand its conservation requirements (1).

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Find out more

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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

This species information was authored as part of the ARKive and Universities Scheme.
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Glossary

Benthic
Relating to the lowermost region of a body of water such as an ocean or lake, or to the organisms that live there.
Bycatch
In the fishing industry, the part of the catch made up of non-target species.
Crustaceans
Diverse group of animals with jointed limbs and a hard external skeleton, characterised by the possession of two pairs of antennae, one pair of mandibles (mouthparts used for handling and processing food) and two pairs of maxillae (appendages used in eating, which are located behind the mandibles). Includes crabs, lobsters, shrimps, woodlice and barnacles.
Genus
A category used in taxonomy, which is below ‘family’ and above ‘species’. A genus tends to contain species that have characteristics in common. The genus forms the first part of a ‘binomial’ Latin species name; the second part is the specific name.
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 (August, 2011)
    http://www.iucnredlist.org/
  2. Muto, E.Y., Soares, L.S.H. and Goitein,R. (2000) Food resource utilization of the skates Rioraja agassizii (Müller & Henle, 1841) and Psammobatis extenta (Garman, 1913) on the continental shelf off Ubatuba, south-eastern Brazil. Revista Brasileira de Biologia, 61(2): 217-238.
  3. Hamlett, W.C. (1999) Sharks, Skates, and Rays: The Biology of Elasmobranch Fishes. The Johns Hopkins University Press, Baltimore.
  4. Nelson, J.S. (2006) Fishes of the World. John Wiley & Sons, Inc., Hoboken.
  5. Williams, S.L., Dewees, C.M., Klingbeil, R. and Larson E.J. (Eds.) (2001) California's Living Marine Resources: A Status Report. California Department of Fish and Game, California. Available at:
    http://www.dfg.ca.gov/marine/status/status2001.asp
  6. FishBase - Rio skate (August, 2011)
    http://fishbase.org.cn/summary/SpeciesSummary.php?genusname=Rioraja&speciesname=agassizii
  7. Oddone, M.C., Amorin, A.F., Mancini, P.L., Norbis, W. and Velasco,G. (2007) The reproductive biology and cycle of Rioraja agassizi (Müller and Henle, 1841) (Chondrichthyes: Rajidae) in southeastern Brazil, SW Atlantic Ocean. Scientia Marina, 71(3): 593-604.
  8. Oddone, M.C., Mesa, A. and Ferreira de Amorim, A. (2006) The egg capsule of Rioraja agassizi (Müller & Henle) (Elasmobranchii, Rajidae), endemic to the SW Atlantic. Pan-American Journal of Aquatic Sciences, 1(2): 43-48.
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Image credit

Adult female Rio skate specimen  
Adult female Rio skate specimen

© María Cristina Oddone

Dr Maria Cristina Oddone
Universidad Federal de Rio Grande - FURG
Brazil
cristina_oddone@yahoo.com

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