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Rhinobatos blochii

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA CHONDRICHTHYES RAJIFORMES RHINOBATIDAE

Scientific Name: Rhinobatos blochii
Species Authority: Müller & Henle, 1841
Common Name/s:
English Bluntnose Guitarfish, Fiddlefish
Taxonomic Notes: Revision of the large genus Rhinobatos is proposing to elevate subgenera Acroteriobatus to generic status, thus Rhinobatos blochii will be referred to as Acroteriobatus blochii (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 blochii.

Commonly misidentified with Rhinobatos annulatus.

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. & Marshall, A.D.
Reviewer/s: Kyne, P.M., Heupel, M.R., Simpfendorfer, C.A. & Cavanagh, R.D. (Shark Red List Authority)
Justification:
A rare and very little known guitarfish with a narrow distribution limited to ~1,000 km of the western coast of Southern Africa from Walvis Bay, Namibia to Cape Point, South Africa. An inshore species, occurring in shallow bays and off sandy beaches. Reaches a maximum size of 96 cm total length, but nothing is known of its biology. The species? restricted range, apparent rarity, unknown population size, and occurrence in relatively shallow depths make it potentially vulnerable to fishing activities. However, there is only minimal fishing pressure in the species? area of occurrence and it is not taken in local fisheries with any regularity. The inaccessibility of parts of this species range due both to remoteness and diamond mine leases puts areas of the coast beyond most recreational fishing. Recreational fishermen along the Namibia coast are known to catch this species incidentally, with most individuals being released. Potential habitat degradation from local diamond mining activities also warrants consideration, however at the present time, all evidence considered, this species is Least Concern. Viable populations of this rare endemic should be assured into the future with the declaration of the proposed Namaqualand Marine Protected Area in South Africa, with continued monitoring of fishing activities throughout its range (to ensure inappropriate activities do not develop) and with effective enforcement of South African recreational line fishing regulations (which limits the catch of this species to one/person/day).

Geographic Range [top]

Range Description: Narrow range limited to ~1,000 km of the western coast of Southern Africa in Namibia and South Africa.
Countries:
Native:
Namibia; South Africa
FAO Marine Fishing Areas:
Native:
Atlantic – southeast
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: Reported to be a rare species (Compagno et al. 1989), however there is no knowledge of the species? population size or structure. Approximately 15?20% of rhinobatid species caught in light tackle ski boat competitions in Laangebaan Lagoon were R. blochii (D. Ebert, pers. comm.).
Population Trend: Unknown

Habitat and Ecology [top]

Habitat and Ecology: A little known species, R. blochii occurs in shallow bays and off sandy beaches. Aplacental viviparous, but its biology is unknown. Maximum recorded size 96 cm TL.

Life history parameters
Age at maturity (years): Unknown.
Size at maturity (total length cm): Unknown.
Longevity (years): Unknown.
Maximum size (total length): 96 cm TL.
Size at birth (cm): Unknown.
Average reproductive age (years): Unknown.
Gestation time (months): Unknown.
Reproductive periodicity: Unknown.
Average annual fecundity or litter size: Unknown.
Annual rate of population increase: Unknown.
Natural mortality: Unknown.
Systems: Marine

Threats [top]

Major Threat(s): Restricted range, apparent rarity, unknown population size, and occurrence in relatively shallow depths make this species potentially vulnerable to fishing activities. There is however minimal fishing pressure in the species area of occurrence and it is not being taken in any local fisheries with any regularity. Gillnet and beach seine fisheries in the Western Cape report bycatch of R. annulatus (Freer and Griffiths 1993, Hutchings and Lamberth 2002) and it is most likely that R. blochii forms a small component of this bycatch, but overall catches of Rhinobatos spp. are not significant. Some beach seine fishers have reported substantial landing of R. annulatus (up to 10t per year, likely 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 Rhinobatos spp. 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.

Recreational fishermen along the Namibia coast catch this species but they are not targeted nor are they used, with most individuals being released. The inaccessibility of parts of this species range due both to remoteness and diamond mine leases puts areas of the coast beyond recreational fishers. However, catch records from local fisheries should continue to be monitored.

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

Conservation Actions [top]

Conservation Actions: Monitoring of catch records from local fisheries is required and investigation into potential habitat degradation from local diamond mining activities warrants consideration.

In South Africa, the species? habitat is afforded some protection in the small West Coast National Park, which encompasses Laangebaan Lagoon. Fishing is prohibited in two management zones of the park. The declaration of the proposed Namaqualand Marine Protected Area (MPA), which would protect 9,700 km² between the Spoeg and Groen Rivers, would greatly benefit this and other species occurring off southwestern Africa. Given the fiddlefish?s apparent rarity and endemism this MPA would be of high conservation value for this species.

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

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.
Citation: Burgess, G.H. & Marshall, A.D. 2006. Rhinobatos blochii. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2. <www.iucnredlist.org>. Downloaded on 24 April 2014.
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