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Smooth Butterfly Ray

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The Smooth Butterfly Ray (Gymnura micrura) is a species of cartilaginous fish in the Gymnuridae family.[1] They are a member of the Order Myliobatiformes, which contains 10 total families.[2] Its natural habitats are shallow seas, subtidal aquatic beds, estuarine waters, and coastal saline lagoons.[1] They are distinguished by having a body that is compressed, pectoral fins that are wider than their length, and having a diamond shape; giving them their common name of 'butterfly rays'.[3]

Smooth butterfly ray
Scientific classification
Kingdom:
Phylum:
Class:
Order:
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Genus:
Species:
G. micrura
Binomial name
Gymnura micrura

Taxonomy

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Gymnura is derived from greek roots and is translated into 'naked tail' (Gymnos=Naked, Oura=Tail).[2] They belong to a monophyletic group of Batoid fish.[4] This group contains over 500 other elasmobranch fishes which includes electric rays, sawfishes, guitarfishes, skates, and stingrays.[4] They are a part of Order Myliobatiformes which are characterized by their pectoral fins being widely expanded and fused to their heads.[4] The family Gymnuridae contains 2 genera which encompasses 12 different species.[3]

Biology

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Appearance

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These are broad-diamond shaped rays with a short tail that has low dorsal and ventral fin folds.[5] The tail has 3 to 4 dark lines that are referred to as crossbars.[6] The edges of the disc concave.[5] The caudal fin is never present and a variable number of tubercles can be found on larger specimens.[7] The smooth butterfly rays have disc widths nearly twice the size of their body lengths and are very flat-bodied (compressed).[8] The width of the rays are between 16 and 22 centimeters when they are born, they are about 50 cm when mature for a female and about 42 cm for a male.[1] Females are bigger than their male counterparts; this allows them to carry larger embryos and a greater abundance of embryos.[9] They have a maximum size of 120 cm.[1]

Dorsal view of a Smooth Butterfly Ray

Lifecycle

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These rays invest a large amount of energy into reproduction and only give birth to a few offspring; however, they give birth on a yearly basis.[3] They use internal fertilization which is the process of the male inserting his claspers into the females Cloaca to fertilize the eggs.[3] The offspring takes between two to four months to develop inside the mother.[3] They use aplacental uterine viviparity and the young are histotrophs.[9]

Behavior and ecology

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The ventral side is lightly colored while the dorsal side is variable in color.[6] The ventral side is usually white but can contain a rusty or bronze coloration.[7] The dorsal side can be grey, light green, brown, and also not uniform in color.[6] They tend to use countershading to blend in with the bottom of their environments in order to hide from predators and to catch prey.[6]

The foraging strategy that these rays use is dependent on the abundance of prey in their environments.[10] They either use opportunistic feeding where they eat what is available, or they use specialized feeding where they eat a specific organism.[10] They tend to feed on larger prey items and swallow them whole; then they enter a long digestion time period where they feed very little or not at all.[10] They prey mainly on Teleost and crustaceans, but have also been noted to consume bivalve muscles and polychaetes.[10][1] They use a structure called the lateral line canal that contains ampullae of lorenzini that is located on their ventral side to detect prey.[4][3] Their upper jaw consists of 6 to 120 teeth and the lower jaw has 52 to 106 teeth; each jaw containing 6 to 8 simultaneously functioning rows.[6]

They are hunted by larger predators, such as sharks.[3] The great hammerhead (Sphyrna mokarran) specializes in feeding on these butterfly rays and are their main predator in some areas.[3]

Locomotion

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They alter their swimming habits depending on where they are swimming in the water column.[4] They tend to change between an Undulation pattern and an Oscillation pattern.[4] They use small amplitude undulations of their fins when they are swimming along the bottom, but switch to an oscillatory approach when they are swimming freely in the water.[4] When swimming freely in the water column, they use a quick, powerful downstroke to increase their speed; which means they move their fins down and then quickly back up.[4] They pause after each stroke and then repeat.[4]

Distribution and habitat

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They are found in the western and eastern parts of the Atlantic ocean (Maryland to brazil) and the Gulf of Mexico.[6] Most commonly found in neritic waters but are known to enter brackish estuaries and hypersaline lagoons.[6] They live in a range from the continental shelf to 40 meters deep in tropical and warm waters.[1][7] They prefer habitats that have either sandy or muddy bottoms.[11]

Relation to humans

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The dorsal spine on the tail is absent, therefore no stinging can occur to harm humans.[6]

This species does not have a sufficient amount of information known about them, but there are no current conservation measures set in place.[1] They are usually takes as bycatch but generally released back into the waters alive.[1] Australia, Europe, and some parts of Asia do consume this species of rays and consider them to be food.[3]

References

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  1. ^ a b c d e f g h IUCN. "Gymnura micrura: Grubbs, R.D. & Ha, D.S." IUCN Red List of Threatened Species. doi:10.2305/iucn.uk.2006.rlts.t60115a12305055.en.
  2. ^ a b "Gymnura micrura summary page". FishBase. Retrieved 2016-03-14.
  3. ^ a b c d e f g h i "Gymnuridae (Butterfly rays)". Animal Diversity Web. Retrieved 2016-03-14.
  4. ^ a b c d e f g h i Rosenberger, Lisa (2001). "Pectoral fin locomotion in Batoid fishes: Undulation verses oscillation" (PDF). The Journal of Experimental Biology. 204: 379–394. Retrieved 23 February 2016.
  5. ^ a b "Smooth Butterfly Ray - Gymnura micrura - Details - Encyclopedia of Life". Encyclopedia of Life. Retrieved 2016-03-21.
  6. ^ a b c d e f g h "Gymnura micrura :: Florida Museum of Natural History". www.flmnh.ufl.edu. Retrieved 2016-03-20.
  7. ^ a b c McEachran, J. "Gymnuridae: Butterfly Rays" (PDF). Retrieved 22 Feb 2016.
  8. ^ Smith, W. D.; Bizzarro, J. J.; Richards, V. P.; Nielsen, J.; Márquez-Flarías, F.; Shivji, M. S. (2009-09-01). "Morphometric convergence and molecular divergence: the taxonomic status and evolutionary history of Gymnura crebripunctata and Gymnura marmorata in the eastern Pacific Ocean". Journal of Fish Biology. 75 (4): 761–783. doi:10.1111/j.1095-8649.2009.02300.x. ISSN 1095-8649. PMID 20738578.
  9. ^ a b Yokota, L; Goianeti, M (2012). "Reproductive Biology of the Smooth Butterfly Ray". Journal of Fish Biology. 81: 1315–1326. Retrieved 22 Feb 2016.
  10. ^ a b c d Yokota, L.; Goitein, R.; Gianeti, M. D.; Lessa, R. T. P. (2013-12-01). "Diet and feeding strategy of smooth butterfly ray Gymnura micrura in northeastern Brazil". Journal of Applied Ichthyology. 29 (6): 1325–1329. doi:10.1111/jai.12213. ISSN 1439-0426.
  11. ^ "A dorsal fold in Gymnura micrura (Bloch and Scheneider, 1801) (Chondrichthyes: Gymnuridae)". ResearchGate. doi:10.1590/S1516-89132009000200027. Retrieved 2016-03-21.

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