Smooth butterfly ray

Smooth butterfly ray
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Order: Myliobatiformes
Family: Gymnuridae
Genus: Gymnura
Species: G. micrura
Binomial name
Gymnura micrura
(Bloch & J. G. Schneider, 1801)

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 a diamond shape; giving them their common name of 'butterfly ray'.[3]

Taxonomy

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 and are characterized by their pectoral fins being widely expanded and fused to their heads.[4] The family Gymnuridae contains 2 genera which encompass 12 different species.[3]

Biology

Appearance

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 are 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 and 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

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 female's cloaca to fertilize the eggs.[3] The offspring take 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

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 Teleosts and crustaceans, but have also been noted to consume bivalve mussels and polychaetes.[1][10] They use a structure called the lateral line canal; it is located on the dorsal side from the head to the pectoral fins, and are arranged in a branching pattern.[11] The lateral line contains neuromasts that assists the rays in detecting changes in water movement.[11] The upper jaw consists of 6 to 120 teeth and the lower jaw has 52 to 106 teeth; each jaw contains 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

Gymnura micrura 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; this means they move their fins down and then quickly back up.[4] They pause after each stroke and then repeat.[4]

Distribution and habitat

Smooth butterfly rays are found in the western and eastern parts of the Atlantic ocean (Maryland to Brazil) and the Gulf of Mexico.[6] They are most commonly found in neurotic waters, but are also known to enter brackish estuaries and hypersaline lagoons.[6] They have a range that extends 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.[12]

Relationship to humans

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

This species does not have an extensive amount of information known about them.[1] There are no current conservation measures set in place.[1] They are usually taken as bycatch but generally released back into the waters alive.[1] Australia, Europe, and some parts of Asia do consumer this species of rays.[3]

References

  1. 1 2 3 4 5 6 7 8 9 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. 1 2 "Gymnura micrura summary page". FishBase. Retrieved 2016-03-14.
  3. 1 2 3 4 5 6 7 8 "Gymnuridae (Butterfly rays)". Animal Diversity Web. Retrieved 2016-03-14.
  4. 1 2 3 4 5 6 7 8 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. 1 2 "Smooth Butterfly Ray - Gymnura micrura - Details - Encyclopedia of Life". Encyclopedia of Life. Retrieved 2016-03-21.
  6. 1 2 3 4 5 6 7 8 "Gymnura micrura :: Florida Museum of Natural History". www.flmnh.ufl.edu. Retrieved 2016-03-20.
  7. 1 2 3 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. 1 2 Yokota, L; Goianeti, M (2012). "Reproductive Biology of the Smooth Butterfly Ray". Journal of Fish Biology 81: 1315–1326. Retrieved 22 Feb 2016.
  10. 1 2 3 4 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. 1 2 Hueter, Robert; Mann, David; Maruska, Karen; Sisneros, Joseph; Demski, Leo (2004). Biology of Sharks and Their Relatives. CRC Press LLC. pp. 335–348.
  12. ↑ "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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