• Lisa

Guitarfishes, Wedgefishes & Sharkrays (Rhinobatiformes)


In some regions they are referred to as sandsharks and at first sight they look very similar to shark, but in fact Guitarfishes and their relatives (Rhinobatiformes) are Rays. They are divided into three separate families: Guitarfishes (Rhinobatidae), Wedgefishes (Rhynchobatidae) and Sharkrays (Rhinidae). For the untrained eye it is not always easy to tell them apart.


Wedgefishes and Sharkrays prefer tropical waters and their South African distribution is limited to KwaZulu Natal, whereas Guitarfishes can be encountered virtually anywhere along the South African coast. If you would like to see a Sharkray, Wedge- or Guitarfish, you will need to look carefully as their flat shape and their often speckled yellow to brown skin, is a perfect camouflage in their preferred habitat: The sandy or muddy seafloor. Occasionally you can also encounter them on a coral reef or in estuaries, but you won’t find them in freshwater.


Although Rhinobatiformes are not particularly fast swimmers, they have a powerful dorsal fin which can help them leap forward when an unsuspecting flatfish or invertebrate swims by while they are couching in the sand. Guitarfish can even thrust their jaw forward to catch their prey and use their blunt, pebble-like teeth to crush it.


Guitarfish, Wedgefish and Sharkrays don’t lay eggs but they give birth to live pups. The young are nourished with yolk from a yolk-sac for ca. 10 months until they are born, which usually occurs in the late South African summer (March-April).


Did you know? Guitarfish, Wedgefish and Sharkrays can’t breath through their mouth when they are buried in the sand, so instead they use a pair of spiracles, which are located behind their eyes. After drawing the water through their spiracles, it is pumped through the gill chambers and expelled through the gills on their underside.


Rhinobatiformes are not only commonly caught as bycatch in both, local inshore as well as offshore trawling fisheries, but they are often actively targeted for their fins and flesh. Wedgefish are the third most endangered Elasmobranch family and Guitarfish rank sixth. The only Sharkray occurring in South Africa, the Bowmouth Guitarfish, is listed as vulnerable.


Morphology


Rhinobatiformes have flattened, shark-like bodies, small to moderate-sized pectoral discs and an elongated stout tail without a sting or electric organs. Their snout can be short or elongated, tapering or round. Rhinobatiformes have small pectoral fins which are fused to the disc. They have two large dorsal and one large shark-like caudal fin. The spiracles, which are used for breathing, are located close to their eyes (Compagno & Last 1999).


Distinguishing Sharkrays from Wedgefishes and Guitarfishes is relatively easy whereas the differentiation between the latter two families can be a bit tricky.


  • Broadly rounded head and snout, indent clearly separates the head from the pectoral fin origins, shoulders with clusters of large thorns (Compagno & Last 1999)

Rhinidae (Sharkrays)


  • Body thicker and more shark-like, dorsal fin is larger, more curved like a sickle and located about opposite their pelvic fins (Compagno & Last 1999, Smith 1950)

Rhynchobatidae (Wedgefishes)


  • Body less thick and less shark-like, dorsal fin is smaller and well behind pelvic fins (Compagno & Last 1999, Smith 1950)

Rhinobatidae (Guitarfish)



RHINIDAE (SHARKRAYS)

Species List & IUCN Redlist Status

  • Bowmouth guitarfish (Rhina ancylostoma) - Vulnerable


Distribution: Tropical Eastern hemisphere, Indian Ocean and western Pacific. South African East coast: Durban to Mozambique


Habitat: Close inshore in shallow waters, mainly over sandy or muddy substrates, enclosed bays, estuaries and off river mouths, coral reefs, do not enter freshwater


Behaviour: Bottom-dwellers, slow but powerful swimmers, inoffensive to people


Diet: Benthic invertebrates (crabs, shrimps)


Reproduction: Ovoviviparous (live-bearing, young nourished through yolk in yolk-sac)


Status: Vulnerable, commonly caught as bycatches in small local inshore fisheries and targeted in gill net fisheries for their fins and flesh, habitat destruction and lossWedgefish (Rhynchobatidae)


RHYNCHOBATIDAE (WEDGEFISHES)

Species List & IUCN Redlist Status

  • Giant guitarfish (Rhynchobatus djiddensis) - Vulnerable

  • Whitespotted guitarfish - (Rhynchobatus australiae) - Vulnerable


Distribution: Tropical Eastern hemisphere, Indian Ocean and western Pacific. South African East coast: Durban to Mozambique


Habitat: Close inshore in shallow waters, mainly over sandy or muddy substrates, enclosed bays, estuaries and off river mouths, coral reefs, do not enter freshwater


Behaviour: Bottom-dwellers, slow but powerful swimmers, inoffensive to people


Diet: Benthic invertebrates (crabs, shrimps)


Reproduction: Ovoviviparous (live-bearing, young nourished through yolk in yolk-sac)


Status: Third most endangered Elasmobranch family (Dulvy et al. 2014), commonly caught as bycatches in small local inshore fisheries and targeted in gill net fisheries for their fins and flesh, habitat destruction and lossGuitarfish (Rhinobatidae)



RHINOBATIDAE (GUITARFISHES)

Species List & IUCN Redlist Status


  • Lesser guitarfish (Rhinobatos annulatus) - Least concern

  • Bluntnose guitarfish / Fiddlefish (Rhinobatos blochii) - Least concern

  • Blackchin guitarfish (Rhinobatos cemiculus) - Endangered

  • Slender guitarfish (Rhinobatos holcorhynchus) - Data deficient

  • Spineback guitarfish (Rhinobatos irvinei) - Vulnerable

  • Greyspot guitarfish (Rhinobatos leucospilus) - Data deficient

  • Speckled guitarfish (Rhinobatos ocellatus) - Data deficient

  • Common guitarfish / Violinfish (Rhinobatos rhinobatos) - Endangered


Distribution: Globally in warm-temperate waters


Habitat: Mostly inshore, over sandy or muddy substrates, enclosed bays, estuaries and off river mouths, coral reefs, do not enter freshwater, few species found in off-shore deeper water


Behaviour: Bottom-dwellers, slow but powerful swimmers, inoffensive to people


Diet: Benthic invertebrates, use protrusible jaw to pick up prey


Reproduction: Ovoviviparous (live-bearing, young nourished through yolk in yolk-sac)


Status: Sixth most endangered Elasmobranch family (Dulvy et al. 2014), commonly caught as bycatches in small local inshore fisheries and offshore trawl fisheries, targeted for their fins and meat



References


Compagno, L.J.V., Last, P.W. Rhinobatiformes: Rhinidae. ORDER RHINOBATIFORMES in Carpenter, K.E., Niem, V.H. (eds). 1999. FAO species identification guide for fishery purposes. The living marine resources of the Western Central Pacific. Volume 3. Batoid fishes, chimaeras and bony fishes part 1 (Elopidae to Linophrynidae). Rome, FAO, pp. 1418-1430.


Compagno, L.J.V., Ebert, D.A., Smale, M.J. Guide to southern African cartilaginous fish (sharks, rays and chimaeras). http://www.biodiversityexplorer.org/chondrichthyes/classification.htm (accessed on 20/01/2016).


Dulvy et al. 2014. Extinction risk and conservation of the world’s sharks and rays. eLife 3: e00590. DOI:10.7554/eLife.00590


Smith, J.L.B. 1950. The Sea Fishes of Southern Africa. Central News Agency, LTD. South Africa. pp. 62-64.


Illustrations by Lena Freund (freund.lena@gmail.com)


Test your Guitarfish Knowledge


1. Are Guitarfish Sharks or Rays?

  • Sharks

  • Rays


2. List the three families of the suborder Rhinobatiformes:



3. What is the main difference between a Guitarfish and a Wedgefish?



4. What kind of habitat do Rhinobatiformes usually prefer?

  • Sandy seafloor

  • Rocky reef


5. Pick typical Guitarfish prey items from the list:

  • Clams

  • Seagrass

  • Small fishes

  • Large fishes

  • Crabs

  • Worms



6. Do Guitarfish lay eggs?

  • Yes

  • No


7. How do guitarfish breathe when they are buried in the ground?



Would you like to see the answers to the quiz or save this article? Download the PDF here!

#Guitarfish #Elasmobranchs #Wedgefish #Sharkray

Subscribe to the ELMO Newsletter

© 2020 by ELMO (South African Elasmobranch Monitoring). 

  • 1440283104_Aquicon-Facebook
  • 1456757215_Aquicon-Twitter
  • 1440283168_Aquicon-Linkedin
This site was designed with the
.com
website builder. Create your website today.
Start Now