Giant guitarfish  (Rhynchobatus djiddensis)

Classified as Vulnerable (VU) on the IUCN Red List. However, the publication of a taxonomic revision is pending (1).

Its large, elongated, greyish-coloured body, two tall dorsal fins, and a large scythe-like tail give this fish its remarkable shark-like appearance (3) (4) (5). Large black eyespots occur at the base of each pectoral fin; there is a distinctive black cross between the eyes and the upper body is marked by rows of small white spots. The snout is pointed and the mouth is small, with flattened, pavement-like teeth (2).

Widely distributed in the tropical Indo-west Pacific (6), ranging from South Africa to the Red Sea, and from Japan to New South Wales, Australia (7). However, this distribution is thought by many to in fact refer to several closely-related species that require taxonomic revision, with the true Rhynchobatus djiddensis thought to be confined to the Western Indian Ocean, and those ranging from the north-western Indian Ocean to the Western Pacific constituting separate species (1).

This bottom-dwelling fish is found in muddy and sandy substrates in estuaries, lagoons and near coral and rocky reefs (5) (7), at intertidal depths to 50 metres (2) (8).

The giant guitarfish swims onto reef flats at high tide to feed and find refuge (7). Diet comprises crabs, lobsters, clams, small fish and squid (2).

Males mature at a length of around 156 centimetres, females at around 177 centimetres. Reproduction is ovoviviparous, and litters of between four and ten live young are usual. In South African waters, birth takes place in summer (7).

The fins of the giant guitarfish are among the most sought-after of any species in Asian markets - used for making shark-fin soup - and consequently there are concerns about over-fishing (1) (6). Its value makes this species an important fish to be directly targeted as well as retained as bycatch, and substantial declines in abundance have been recorded in Indonesian fisheries, and are also thought likely to be occurring elsewhere (1). Additionally, this unusual fish is highly prized by sport anglers in southern Africa for its size and powerful fight when hooked (7).

There are currently no conservation measures targeting this species. More research is certainly needed into current levels of harvesting and the direct impact this is having on population sizes (1).

For further information on the conservation of sharks and rays see:

• Save Our Seas Foundation:
  http://www.saveourseas.com
• Project Aware:
  http://www.projectaware.org/

Authenticated (19/06/2006) by R. Aidan Martin, Director of the ReefQuest Centre for Shark Research.
http://www.elasmo-research.org/

• Bycatch: in the fishing industry, the part of the catch made up of non-target species.
• Dorsal fin: the unpaired fin found on the back of the body of fish, or the raised structure on the back of most cetaceans.
• Ovovivipary: method of reproduction whereby the egg shell is weakly formed and young hatch inside the female; they are nourished by their yolk sac and then ‘born’ live.
• Pectoral fins: in fish, the pair of fins that are found one on each side of the body just behind the gills. They are generally used for balancing and braking.

1. IUCN Red List of Threatened Species (April, 2006)
   http://www.redlist/org
2. FishBase (April, 2006)
   http://www.fishbase.org
3. Marine Themes (April, 2006)
   http://www.marinethemes.com
4. Sundive: the marine life of Julian Rocks and Byron Bay (April, 2006)
   http://www.julianrocks.net/index.htm
5. Ministry of Natural Resources, Environment and Meteorology: Samoa’s Biodiversity (April, 2006)
   http://www.mnre.gov.ws/biodiversity/popup_Marine.cfm?RecordID=101
6. ReefQuest Centre for Shark Research (April, 2006)
   http://www.elasmo-research.org/education/shark_profiles/rhynchobatiformes.htm
7. The Life and Times of Long Dead Sharks (April, 2006)
   http://www.elasmo.com/frameMe.html?file=batoids/extant/rhynchobatus_sp.html&menu=bin/menu_batoid-alt.html
8. Martin, R.A. (2006) Pers. comm.