Carcharias taurus (Southwest Atlantic subpopulation)http://dx.doi.org/10.2305/IUCN.UK.2007.RLTS.T63163A12625032.en
|Scientific Name:||Carcharias taurus (Southwest Atlantic subpopulation)|
|Species Authority:||Rafinesque, 1810|
|Taxonomic Notes:||See Compagno (1984, 2001) for a detailed discussion of the taxonomical background for this species and for its separation from the genus Odontaspis. Off India it appears to have been referred to as C. tricuspidatus (Compagno 1984) but this name was synonymized with C. taurus (Compagno 2001).|
|Red List Category & Criteria:||Critically Endangered A2abcd ver 3.1|
|Assessor(s):||Chiaramonte, G., Domingo, A. & Soto, J.|
|Reviewer(s):||Musick, J., Dudley, S., Soldo, A., Francis, M., Valenti, S.V. & Kyne, P.M. (Shark Red List Authority)|
A large migratory coastal shark with one of the lowest reproductive rates known among chondrichthyans, giving birth to only one or two large young every two years. As a result, annual rates of population increase and ability to sustain fishing pressure are extremely low. Although the species is widespread in subtropical and temperate waters of the Atlantic, Indian and western Pacific Oceans, as well as the Mediterranean Sea, regional populations are isolated and are not thought to mix. In the Southwest Atlantic, the species ranges from Rio de Janeiro, Brazil (21°S) to San Matías Gulf, Argentina (41°30’S). Although it is not directly fished in this region, it does have commercial value as a bycatch in benthic trawling and gillnet fisheries and is harvested throughout this range by commercial, artisanal and recreational (mainly in Argentina) fishing. In Uruguay, this species has been taken for over 50 years by the artisanal fleet and it formed an important component of gillnet catches off southern Brazil in the 1980s. Catches have declined dramatically off Uruguay from 784 kg per fishing day in 1985 to 32 kg per fishing day in 2001 and off southern Brazil from a CPUE of 11.7 to 0.3 sharks per 1,000 meters of net during the 1980s and 1990s, respectively. Recent surveys (2005) also appear to indicate that catches in the gillnet fisheries off southern Brazil have declined considerably relative to levels in the 1980s. Aggregations off Brazil were also targeted by spear-fishers for sport in the 1970s and 1980s. This species is assessed as Critically Endangered due to a combination of a severe depletion along the Brazilian coast since the 1970s and declining trends in the Uruguayan coastal fisheries. Coastal fishing pressure is intense and continuing within its range along the South Atlantic coast of South America. The species is listed as threatened with over-exploitation on Annex II of the Brazilian federal law of Threatened and Overexploited Aquatic Species. However there are no known species-specific management measures in place for it within the region and protection measures are urgently required.
Carcharias taurus has a broad but disjunct distribution in littoral and sub-littoral waters, primarily in subtropical to warm temperate regions around the main continental landmasses, except in the eastern and central Pacific (Compagno 1984, 2001; Gilmore et al. 1983). It is not known from deepwater, unlike Odontaspis ferox.
Southwest Atlantic subpopulation: in the Southwest Atlantic C. taurus ranges from Rio de Janeiro, Brazil (21°S) to San Matías Gulf, Argentina (41°30’S) (Menni 1986, Soto 2001).
Native:Argentina (Buenos Aires, Rio Negro); Brazil (Paraná, Rio de Janeiro, Rio Grande do Sul, Santa Catarina, São Paulo); Uruguay
|FAO Marine Fishing Areas:||
Atlantic – southwest
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||Morphometric and meristic analysis indicate that the Southwest Atlantic subpopulation is a probable “closed group” with common characteristics, but not a distinct species (Sadowsky 1970, Compagno 2001). Although there is no information on the population size of C. taurus in the Southwest Atlantic, past and present fishing pressures have led to significant declines in catches (see Threats section below).|
|Current Population Trend:||Decreasing|
|Habitat and Ecology:||
Carcharias taurus generally occurs in warm-temperate and subtropical waters, ranging from the surf zone and shallow bays to approximately 200 m depth on the outer continental shelf. The species is most usually found on or near the bottom in reef areas but may occasionally occur in midwater or at the surface (Compagno 1984). Embryonic oviphagy and intra-uterine cannibalism occurs in this species and only two large pups are produced per litter every second year (Gilmore et al. 1983, Goldman 2002, Goldman et al. in press). As a result, annual rates of population increase are very low, greatly reducing its ability to sustain fishing pressure. Size at birth is about 95 to 105 cm TL (Gilmore et al. 1983).
Maximum size attained is 300 to 320 cm TL (females) and 220 to 270 cm TL (males) (Compagno 2001). Age and size at maturity varies regionally. Age at maturity is reported at 7.7 years (females) and 4.5 years (males) in the Southwest Atlantic by Lucifora (2003). Lucifora (2003) reports size at maturity in the Southwest Atlantic as 218 to 235 cm TL (females) and 193 cm TL (males). Longevity is estimated at 18.3 years in females and 12.8 years in males in the Southwest Atlantic (Lucifora 2003).
Average reproductive age is 17.1 yrs from demographic analysis (Goldman 2002). Natural mortality is MHoenig = 0.205, MJensen = 0.211 and MPauly = 0.198 from analyses from the Southwest Atlantic (Lucifora 2003).
Because this species typically inhabits shallow inshore areas it is rarely, if ever caught by large-scale industrial fisheries operating on the high seas. However, its nearshore distribution makes it susceptible to small-scale multi-species and artisanal fisheries as well as recreational fisherman, spearfishers and shark control programs. As a bycatch in other fisheries it is often reported as unidentified shark or not reported at all and as such the extent of the impact that these fisheries have had on C. taurus is unknown for most of its geographic range. Consequently this species could be at a high risk of unrecognized depletion in many countries.
The sand tiger is not subjected to directed fishing in South America, but nevertheless does have commercial value (including the jaws) as a non target catch in benthic trawling and gillnet fisheries and is harvested throughout its regional range by commercial, artisanal and recreational (mainly in Argentina) fishing (Chiaramonte 1998, Nion 1999, Lucifora et al. 2002). Coastal species are the most important commercial elasmobranchs in the Southwest Atlantic and coastal fishing pressure is intense in this region (Bonfil et. al. 2005). The exposure of its coastal habitat to fisheries and its vulnerable life-history characteristics provide little capacity for recovery.
Captures of C. taurus from Central-North Rio Grande do Sul, southern Brazil have declined dramatically throughout the 1980s and 1990s from a CPUE of 11.7 to 0.3 sharks per 1000 meters of net (Soto 2001) (a decline of approximately 97%). In Rio Grande do Sul C. taurus were fished with gillnets during the 1980s, at which time the species was considered abundant and could be captured in aggregations (Vooren et al. 2005). However there are no records of the species from monitoring of the shore based fishery during the summer of 2003, and the species occurred in only 3 of 43 fishing trips (11 individuals captured in total) by the Passo de Torres gillnet fishery monitored during November-March 2005 (Vooren et al. 2005). Vooren et al. (2005) note that this species is now considered rare in this area and that the scarcity of recent records of neonates is of great concern. Adult C. taurus can still be found inshore along the coast between Tramandaí and Saint Simão (30 to 31°S) (Vooren et al. 2005). Although no information exists on the population size of C. taurus, fishing pressure is intense and continuing within its coastal habitat off southern Brazil. Large aggregations of C. taurus were also systematically wiped out in Santa Catarina state, Brazil, by spear fishermen in the 1970s and 1980s.
In Uruguay, this species has been taken for over 50 years by the artisanal fleet. Captures increased in the late 1970s, mainly in summer, reaching a peak in the mid 1980s. Thereafter there was a continued decline, with catches decreasing from 784 kg per fishing day in 1985 to 32 kg per fishing day in 2001 (A. Domingo pers. obs). Only occasional captures are recorded from 2000 to the present. There are also occasional captures in the trawl net and longline fisheries.
Lucifora (2003) estimated that 889 sharks (CI 95%=625 to 1,140) were captured by anglers during three consecutive summers (1999-2001) in Anegada Bay, Argentina. Out of 175 sharks observed, 153 suffered serious injuries of the internal organs caused by hooks. Crespo and Corcuera (1990) report extensive damage to shark catches in gillnets by marine mammals (sea lions bite out the belly of entangled sharks and eat the liver).
|Conservation Actions:||Further studies of the biology and reproduction of this species in the Southwest Atlantic are needed. This species has been listed as a species threatened with over-exploitation on Annex II of the Brazilian federal law of Threatened and Overexploited Aquatic Species since 2004 (Vooren and Klippel 2005). Also the prohibition of trawl fishing within three nautical miles from the coast of southern Brazil is now being enforced satisfactorily. However, the species is still caught as bycatch in the legally permitted coastal gillnet fisheries and offshore trawl and gillnet fisheries. It is recommended that the species is protected throughout its inshore range along the Southwest Atlantic coast of South America, particularly in areas of critical habitat and areas where the adult population still exists. A management plan is being considered for development for this species in the Bahía San Blas Reserve (Anegada Bay, Argentina).|
|Citation:||Chiaramonte, G., Domingo, A. & Soto, J. 2007. Carcharias taurus (Southwest Atlantic subpopulation). The IUCN Red List of Threatened Species 2007: e.T63163A12625032. http://dx.doi.org/10.2305/IUCN.UK.2007.RLTS.T63163A12625032.en . Downloaded on 04 October 2015.|