Friday 17 May
Rio skate (Rioraja agassizii)
Rio skate fact file
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Rio skate description
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).
- Raya Lisa.
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).Top
Rio skate rangeTop
Rio skate habitatTop
Rio skate status
The Rio skate is classified as Vulnerable (VU) on the IUCN Red List (1).Top
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).Top
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).Top
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Find out more about the Rio skate:
FishBase - Rio skate:
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- Relating to the lowermost region of a body of water such as an ocean or lake, or to the organisms that live there.
- In the fishing industry, the part of the catch made up of non-target species.
- 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.
- 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).
IUCN Red List (August, 2011)
- 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.
- Hamlett, W.C. (1999) Sharks, Skates, and Rays: The Biology of Elasmobranch Fishes. The Johns Hopkins University Press, Baltimore.
- Nelson, J.S. (2006) Fishes of the World. John Wiley & Sons, Inc., Hoboken.
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:
FishBase - Rio skate (August, 2011)
- 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.
- 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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