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Rhinobatos annulatus

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA CHONDRICHTHYES RAJIFORMES RHINOBATIDAE

Scientific Name: Rhinobatos annulatus
Species Authority: Müller & Henle, 1841
Common Name(s):
English Lesser Guitarfish, Lesser Sandshark
French Poison-guitare
Spanish Guitarra Del Cabo
Taxonomic Notes: Revision of the large genus Rhinobatos is proposing to elevate subgenera Acroteriobatus to generic status, thus Rhinobatos annulatus will be referred to as Acroteriobatus annulatus (L.J.V. Compagno pers. comm.). However, these changes are not yet published and until such time as they are the species should continue to be referred to as Rhinobatos annulatus.

Commonly misidentified with Rhinobatos blochii.

Assessment Information [top]

Red List Category & Criteria: Least Concern ver 3.1
Year Published: 2006
Date Assessed: 2006-01-31
Assessor(s): Burgess, G.H., Holtzhausen, H.A. & Smale, M.J.
Reviewer(s): Kyne, P.M., Heupel, M.R., Simpfendorfer, C.A. & Cavanagh, R.D. (Shark Red List Authority)
Justification:
An inshore guitarfish distributed from southern Angola, through Namibia to KwaZulu-Natal in South Africa. This is the most abundant guitarfish in the sub-equatorial African region and is found in inshore waters from the shoreline to 50 to 100 m depth, including estuaries, the surf zone and enclosed bays. Maximum size recorded is 140 cm total length, reaching sexual maturity relatively quickly for an elasmobranch (50% maturity at three years), with a maximum lifespan of seven years and an annual fecundity for 3 to 9 young. Shallow sandy habitats are important nursery areas. Although it is caught by recreational beach anglers, gillnets, beach seines and in benthic trawls it is abundant and is not subjected to significant fishing mortality. As such, it is assessed as Least Concern. There is still a need however to monitor catch levels and to collect more information, particularly from Namibia and Angola where relatively little is known about this species.

Geographic Range [top]

Range Description: Endemic to southern Africa from southern Angola to KwaZulu-Natal, South Africa.
Countries:
Native:
Angola (Angola); Namibia; South Africa (Eastern Cape Province, KwaZulu-Natal, Northern Cape Province, Western Cape)
FAO Marine Fishing Areas:
Native:
Atlantic – southeast; Indian Ocean – western
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: A common species, the most abundant rhinobatid in southern African waters. Stocks of the species are not characterized, but there are possibly two separate stocks, one in the Western Cape area, South Africa and northward into southern Angolan waters, and the other along the southeastern African coast.
Population Trend: Unknown

Habitat and Ecology [top]

Habitat and Ecology: Found in inshore waters from the shoreline to 50 to 100 m depth, including estuaries, the surf zone and enclosed bays, where it burrows beneath the sand. Sandy areas are used as nursery areas (Rossouw 1983). Possible offshore migration during winter and longshore migration of juveniles is also an unverified possibility (Rossouw 1983, Buxton et al. 1984).

Copulation occurs in shallow inshore waters off sandy beaches. Aplacental viviparous, with females bearing litters of 2 to 10 young (Compagno et al. 1989), which in South Africa, are born in the late summer (March-April). Offspring remain in shallows for at least one year. Maximum documented age is seven years and reaches 140 cm TL (Rossouw 1984, Compagno et al. 1989).

Consumes infaunal invertebrates such as swimming crabs, mole crabs, small fishes, polychaete annelid worms, amphipods, and isopods.

Life history parameters
Age at maturity: 50% maturity: 3 years (male and female).
Size at maturity (total length): Female: 50% maturity: 61.5 to 65 cm TL; Male: 50% maturity: 58 cm TL.
Longevity: 7 years.
Maximum size (total length): 140 cm TL.
Size at birth: 23 cm TL.
Average reproductive age: 2 to 3 years.
Gestation time: 10 months.
Reproductive periodicity: Annual.
Average annual fecundity or litter size: 2 to 10 pups/litter.
Annual rate of population increase: Unknown.
Natural mortality: Unknown.
Systems: Marine

Threats [top]

Major Threat(s): This guitarfish is subject to fishing mortality from recreational beach anglers and commercial fisheries, being commonly caught during shore angling tournaments, and being taken as bycatch in commercial gillnet, beach seine and trawl fisheries in South Africa and Namibia. No information is available on catches in Angola.

Gillnet and beach seine fisheries in the Western Cape of South Africa report bycatch of R. annulatus, but overall these catches are not significant (Freer and Griffiths 1993, Hutchings and Lamberth 2002). Some beach seine fishers have reported substantial landings of R. annulatus (up to 10t per year, likely also including R. blochii due to identification issues), but surveying suggests that this is uncommon and overall effort from this fishery is small (Hutchings and Lamberth 2002). Bycatch of R. annulatus in the gillnet fishery appears to be negligible (Hutchings and Lamberth 2002) with Freer and Griffiths (1993) reporting that R. annulatus are returned live to the water. Rhinobatos annulatus forms an irregular component of the bycatch of commercial prawn trawlers on the Tugela Bank, KwaZulu-Natal, occurring in 2.4% of trawls surveyed (Fennessy 1994). Those recorded in that fishery were primarily immature (Fennessy 1994).

Potential habitat degradation from local diamond mining activities also warrants consideration.

Conservation Actions [top]

Conservation Actions: Monitoring of bycatch levels in various fisheries (recreational, commercial beach seine, gillnet and trawl) in all parts of the species' range is required. Investigation into potential habitat degradation from local diamond mining activities warrants consideration.

In South Africa, the species' habitat is afforded some protection in a number of smaller Marine Protected Areas (MPA) including the West Coast National Park which encompasses Laangebaan Lagoon, Pondoland MPA, Table Mountain National Park and others. The declaration of the proposed Namaqualand MPA, which would protect 9,700 km² between the Spoeg and Groen Rivers, would provide further protection for the habitat of this and other species occurring off southwestern Africa.

The recreational line fishery in South Africa is managed by a bag limit of one per species per person per day for unspecified chondrichthyans, which includes R. annulatus.

The development and implementation of management plans (national and/or regional e.g., under the FAO International Plan of Action for the Conservation and Management of Sharks: IPOA-Sharks) are required to facilitate the conservation and sustainable management of all chondrichthyan species in the region. Namibia's National Plan of Action for Sharks (NPOA-Sharks) has been approved by the government, South Africa's is stalled, still awaiting government approval and this process should occur as a matter of urgency. At the time of writing Angola had expressed its intention to begin to develop an NPOA (Anon. 2004).

Citation: Burgess, G.H., Holtzhausen, H.A. & Smale, M.J. 2006. Rhinobatos annulatus. The IUCN Red List of Threatened Species. Version 2014.3. <www.iucnredlist.org>. Downloaded on 26 November 2014.
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