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Carcharhinus cautus

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA CHONDRICHTHYES CARCHARHINIFORMES CARCHARHINIDAE

Scientific Name: Carcharhinus cautus
Species Authority: (Whitley, 1945)
Common Name(s):
English Nervous Shark

Assessment Information [top]

Red List Category & Criteria: Data Deficient ver 3.1
Year Published: 2003
Date Assessed: 2003-04-30
Annotations:
Needs updating
Assessor(s): Bennett, M.B. & Kyne, P.M. (SSG Australia & Oceania Regional Workshop, March 2003)
Reviewer(s): Fowler, S. & Cavanagh, R.D. (Shark Red List Authority)
Justification:
This species is apparently common in shallow warm coastal waters and embayments within its range (northern Australia, Papua New Guinea and Solomon Islands). Females mature at 5 to 6 years and reach maximum size at 16 years. Litters of 2 to 6 are produced at two-year intervals. Relatively little is known about its population structure and dynamics. It occurs in areas of northern Australia that are targeted by a moderate level of prawn trawling and coastal/estuarine gillnetting. This species is probably taken as a bycatch in both fisheries, but with a greater likelihood of being caught in the inshore gillnet fishery. Discard/release mortality is probably significant but these fisheries are not thought to be detrimental to the Australian population (where this species is assessed as Least Concern). It will also be taken (and presumably not discarded) in shallow coastal gillnet and line fisheries elsewhere in its range, where no data are available.

Geographic Range [top]

Range Description: Occurs on continental and insular shelves in shallow water in sub-tropical and tropical waters of northern Australia, Papua New Guinea (P.N.G.) and the Solomon Islands. It seems likely that this species may also be found in the intervening waters around east P.N.G. The southern extent of its range on the east coast of Australia has been recently extended following the capture of mature adults and young sharks in Moreton Bay, Queensland (Kyne et al., in prep.). It is the most common carcharhinid in Darwin Harbour (Northern Territory), which lies at the centre of this species' range. It is one of the six most common near-shore species on the eastern side of the Gulf of Carpentaria (Queensland) and is also common in Shark Bay (Western Australia).
Countries:
Native:
Australia (Northern Territory, Queensland, Western Australia); Papua New Guinea; Solomon Islands
FAO Marine Fishing Areas:
Native:
Indian Ocean – eastern; Pacific – western central
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: There are no data on the populations of this species.
Population Trend: Unknown

Habitat and Ecology [top]

Habitat and Ecology: This species occurs in shallow warm, coastal waters including large embayments. They may be more common in areas that are fringed by mangroves, possibly preferring a sand/mud substrate, although they are also found in areas away from mangroves (Lyle 1987, White et al. 2002). The species is often found in association with C. melanopterus, C. dussumieri, C. amblyrhynchos, C. sorrah, C. tilsoni, C. fitzroyensis and Rhizoprionodon acutus. Very similar to C. melanopterus (but lacks conspicuous black tips to the first dorsal and anal fins) and may have been confused in parts of its range. It is reported to reach 150 cm total length (TL) (Last and Stevens 1994) although other data suggest males reach about 120 cm and females 140 cm TL (White et al. 2002). Males are thought to mature at about 79 to 84 cm TL and females at about 91 cm TL from Darwin, Northern Territory (Lyle 1987), but at 91 cm TL and 101 cm TL respectively from Shark Bay, Western Australia (White et al. 2002). Testes mass peaks in January, with sperm present in seminal vesicles in February/March (Lyle 1987). White et al. (2002) report ovulation and conception occurring in December. It seems likely that copulation occurs over a period of two or three months in mid/late-summer (December to March). Gestation lasts 10 months with a litter size of 2 to 6, produced every other year. Young are born at 33-39 cm TL. Males mature at 4 to 5 years of age and reach maximum body size by about 12 years. Females mature at 6 to 7 years, reaching a maximum size at about 16 years. Carcharhinus cautus has a varied diet, primarily consisting of teleost fishes, followed in importance by crustaceans (prawns, crabs, mantid shrimps) and molluscs (Lyle 1987, Salini et al. 1992). There are records of this species taking terrestrial snakes, indicating an opportunistic feeding behaviour (Lyle and Timms 1987).
Systems: Marine

Threats [top]

Major Threat(s): This species is threatened primarily by inshore gill-net fisheries throughout its range. In Australia it is the barramundi (Lates calcarifer) fishery that poses the greatest threat. Smaller individuals may also be taken as bycatch in the prawn trawl fisheries to the north of Australia. It will also be taken in shallow coastal gill net and line fisheries elsewhere in its range, where no data are available.

Conservation Actions [top]

Conservation Actions: The broad distribution and common occurrence of C. cautus is offset by the susceptibility of the species to inshore gill-net fisheries. Future research should examine the level of bycatch in these fisheries, together with their attendant mortalities. An education program aimed at encouraging release of sharks would have a limited effect, as individual sharks caught in nets die quickly of hypoxia. Practical action in the form of net restrictions will be the only effective measure. Research into population sizes and movements of individuals, via tag-release-recapture studies, is required to better understand this species.

Citation: Bennett, M.B. & Kyne, P.M. (SSG Australia & Oceania Regional Workshop, March 2003) 2003. Carcharhinus cautus. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 31 July 2014.
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