Family Gymnuridae – The Butterfly Rays

Sara McCutcheon

Order: Mlyliobatiformes– stingrays

Family: Gymnuridae – butterfly rays

Genus: 2 Genera – Aetoplatea and Gymnura

Species: 12-14 species

Diagnostic Characteristics

  • Broad, diamond shaped ray
  • Disc extremely broad (>1.5x)
  • Short tail, no caudal fin
  • Low dorsal and ventral finfolds
  • Some with poisonous tail spine
  • Dorsal fin present or absent
  • Skin relatively smooth with small denticles
  • Teeth with high conical cusp
  • Teeth get larger as the ray grows
  • 8-12 rows of functional teeth
  • Dental bands take up ~70% jaw width
  • Maximum disk width over 4m (13 feet; G. altavela)

Distribution and Habitat

  • Atlantic, Indian, and Pacific
  • Marine, rarely brackish
  • Tropical to temperate
  • Continental shelves
  • Demersal, benthic
  • Depths range from intertidal to100m
  • Prefers sandy and muddy substrates
  • Also found inbrackish estuaries, hyper-saline lagoons, coastal and neritic waters, bays, sandy beaches, and salt marshes

Size, Age, and Growth

  • Maximum disk with 4m (13.1ft; G. altavela)
  • Maximum weight 60kg (132lbs)
  • Maximum total length 1.4m (4.6ft)
  • Females are larger than males

Reproduction

  • Two functional uteri
  • Aplacental viviparous
  • Embryos initially fed with yolk, then uterine milk
  • "A number of the glandular villi, which clothe the uterine walls of the mother, are always found inserted into the spiracular openings of the embryos, suggesting that some of the uterine "milk" is absorbed this way" (Wallace 1967)
  • Gestation ~4-9 months
  • One reproductive cycle per year
  • Fecundity assumed to be <10
  • Some species with reported litters of 2-6, 4-7, 6-8, and 4-16 embryos
  • Females commonly abort fetuses upon capture (G. poecilura)

Diet

  • Teleosts
  • Crustaceans(benthic copepods, crabs, shrimps, prawns)
  • Mollusks (Bivalves, cephalopods, and gastropods)
  • Plankton
  • Polychaete worms

Predators

  • Larger fishes, marine mammals, and hammerhead sharks

Status

  • IUCN status
  • 6 spp not in IUCN
  • 2 spp data deficient
  • 1 sp vulnerable – A. zonura(declines of at least 30%)
  • 1 sp near threatened – G. poecilura
  • Population doubling time >14 years
  • Artisanal fisheries, commercial fisheries, high exploitation of habitat, caught as bycatch, and wings can be used as bait, low recruitment/reproduction, high juvenile mortality, and habitat degradation/loss

Danger to Humans

  • Not aggressive
  • Species without spines are harmless
  • Those with venomous spines are considered dangerous

Bibliography

Bauchot, M.-L., 1987. Raies et autres batoides. p. 845-886. In W. Fischer, M.L. Bauchot and M. Schneider (eds.) Fiches FAO d'identificationpour les besoins de la pêche. (rev. 1). Mèditerranée et mer Noire. Zone de pêche 37. Vol. II. Commission des Communautés Européennes and FAO, Rome.

Bizzarro, J.J. & White, W.T. 2006. Gymnura poecilura. In: IUCN 2007. 2007 IUCN Red List of Threatened Species. Downloaded on 28 November 2007.

Compagno, L.J.V., 1999. Checklist of living elasmobranchs. p. 471-498. In W.C. Hamlett (ed.) Sharks, skates, and rays: the biology of elasmobranch fishes. JohnHopkinsUniversity Press, Maryland.

Grubbs, R.D. & Ha, D.S. 2006. Gymnura micrura. In: IUCN 2007. 2007 IUCN Red List of Threatened Species. Downloaded on 28 November 2007.

Last, P.R. and J.D. Stevens, 1994. Sharks and rays of Australia. CSIRO, Australia. 513 p.

McEachran, J.D. and B. Seret, 1990. Gymnuridae. p. 64-66. In J.C. Quero, J.C. Hureau, C. Karrer, A. Post and L. Saldanha (eds.) Check-list of the fishes of the eastern tropical Atlantic (CLOFETA). JNICT, Lisbon; SEI, Paris; and UNESCO, Paris. Vol. 1.

Nelson, J.S. 2006. Fishes of the World, 4th ed. John Wiley and Sons, Inc, NJ. p 80.

Smith, W.D. & Bizzarro, J.J. 2006. Gymnura marmorata. In: IUCN 2007. 2007 IUCN Red List of Threatened Species. Downloaded on 28 November 2007.

White, W.T. 2006. Aetoplatea zonura. In: IUCN 2007. 2007 IUCN Red List of Threatened Species. Downloaded on 28 November 2007.

Wintner, S.P. 2006. Gymnura natalensis. In: IUCN 2007. 2007 IUCN Red List of Threatened Species. Downloaded on 28 November 2007.