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Rhinobatos jimbaranensis

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA CHONDRICHTHYES RAJIFORMES RHINOBATIDAE

Scientific Name: Rhinobatos jimbaranensis
Species Authority: Last, White & Fahmi, 2006
Synonym/s:
Rhinobatos sp. nov. [Indonesia – blotched] subspecies
Taxonomic Notes: Prior to its description in 2006, this species was referred to as Rhinobatos sp. nov. [Indonesia ? blotched].

This newly recognised species of Rhinobatos is landed frequently in southern Bali by gillnet fisherman. It differs markedly from the other co-occurring newly recognised species of, Rhinobatos penggali and also from other Rhinobatos species in this region.

Assessment Information [top]

Red List Category & Criteria: Vulnerable A2cd+3cd+4cd; B1ab(iii,v) ver 3.1
Year Published: 2006
Date Assessed: 2006-01-31
Assessor/s: White, W.T.
Reviewer/s: Kyne, P.M., Heupel, M.R., Simpfendorfer, C.A. & Cavanagh, R.D. (Shark Red List Authority)
Justification:
Rhinobatos jimbaranensis is landed in substantial numbers by demersal gillnet fisherman targeting small rays in southern Bali in eastern Indonesia. This species appears to be restricted to the inner continental shelf (inshore, <60 m depth), primarily around the island of Bali but individuals have also been observed in Lombok. The present known range is limited to <20,000 km², all of which is intensively fished. A continuing decline in the number of mature individuals is inferred from intensive fishing pressure and a decline in the area, extent and/or quality of habitat is inferred from destructive fishing practices and pollution. Fishing practices catch a large number of juveniles as well as adults, limiting recruitment to reproductive age. Indonesia has an extremely high level of exploitation on its marine resources, and this is only likely to increase into the future in this region. Overall, since this species appears to be endemic to a small part of eastern Indonesia and occurs in a habitat that is heavily exploited by subsistence and small-scale commercial fisherman, it is categorized as Vulnerable. However, further data may indicate that this species falls within a higher threatened category. The large numbers of individuals of this ray that are landed and utilized for human consumption in southern Bali should be monitored into the future.

Geographic Range [top]

Range Description: Known only from off Bali and Lombok in eastern Indonesia. Restricted extent of occurrence of <20,000 km². May occur further east into Nusa Tenggara and possibly west into Java with additional sampling.
Countries:
Native:
Indonesia (Bali)
FAO Marine Fishing Areas:
Native:
Pacific – western central
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: Common in gillnet catches off Jimbaran Bay in southern Bali. Only several observed in eastern Lombok (White, unpubl. data) and unknown elsewhere.
Population Trend: Decreasing

Habitat and Ecology [top]

Habitat and Ecology: Demersal on the upper continental shelf, <60 m depth on relatively sandy substratum (White, unpubl. data).

Females attain a larger maximum size (93 cm TL) than males (82 cm TL) and males mature at about 70 cm TL. The litter size of four pregnant females ranged from 6 to 11 with the largest embryos 12.5 cm TL (White, unpubl. data).

Age compositions, growth rates and diets not known. Age at maturity unknown. Size at maturity ~70 cm total length (TL) (male). Longevity unknown. Maximum size 82 cm TL (males), 93 cm TL (female) (White, unpubl. data). Size at birth unknown. Average reproductive age unknown. Gestation time unknown. Reproductive periodicity unknown. Average annual fecundity or litter size: four pregnant females had 6 to 11 embryos (White, unpubl. data). Annual rate of population increase unknown. Natural mortality unknown.
Systems: Marine

Threats [top]

Major Threat(s): This species is a common component of the small-scale demersal gillnet fishery for batoids operating out of Jimbaran Bay in southern Bali. Approximately 50% of the catches of this species consist of immature individuals, thus a large number of rays that have not had prior opportunity to reproduce are being landed on a regular basis at the landing site of Kedonganan in Jimbaran Bay (Bali) (White, unpubl. data).

There is little or no trawling close inshore around Bali and Lombok, thus pressure from this fishing practice is not a factor for this species. However, since the actual extent of occurrence of this species is not fully understood, it may be under more severe fishing pressure in other areas with more heavily fished waters, e.g., east Java.

The seemingly small geographic range of this species is of concern, particularly in the context of the fact that this region has a very high level of exploitation of marine resources. Destructive fishing practices and pollution are also significant factors affecting marine resources in the region.

Conservation Actions [top]

Conservation Actions: None currently in place. The implementation of the National Plan of Action under the FAO International Plan of Action for the Conservation and Management of Sharks will assist in enacting measures for the conservation of this and other elasmobranchs in Indonesia.

Further research into the population structure, biology and ecology of this species is required to assess the extent to which fishing pressure, and habitat destruction is influencing this species within its range. Improved species composition data from all fisheries that take shovelnose rays and guitarfish is necessary.

Future management may involve hard decisions affecting communities adjacent to these areas.

Bibliography [top]

IUCN. 2006. 2006 IUCN Red List of Threatened Species. www.iucnredlist.org. Downloaded on 04 May 2006.

IUCN SSC Shark Specialist Group. Specialist Group website. Available at: http://www.iucnssg.org/.

Last, P.R., White, W.T. and Fahmi 2006. Rhinobatos jimbaranensis and R. penggali, two new shovelnose rays (Batoidea: Rhinobatidae) from eastern Indonesia. Cybium 30(3): 261-271.

Citation: White, W.T. 2006. Rhinobatos jimbaranensis. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2. <www.iucnredlist.org>. Downloaded on 16 April 2014.
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