|Scientific Name:||Carcharhinus porosus|
|Species Authority:||(Ranzani, 1839)|
|Red List Category & Criteria:||Data Deficient ver 3.1|
|Assessor/s:||Lessa, R., Almeida, Z., Santana, F.M., Siu, S. & Perez, M.|
|Reviewer/s:||Cavanagh, R.D., Kyne, P.M., Stevens, J., Dudley, S. & Pollard, D. (Shark Red List Authority)|
This small (<150 cm TL) shark occurs in the Western Atlantic (Gulf of Mexico to southern Brazil) and Eastern Pacific (Gulf of California to Peru). Apparently Data Deficient throughout much of its range. For example, although it is a known bycatch component of artisanal gillnet fisheries in Central America, there are no data on catch or effort for this species. Information on Carcharhinus porosus in the Gulf of Mexico and much of its range down to Brazil is scarce. Considered rare in the south of Brazil, but detailed information is available for the population in the north (considered to be the centre of abundance for this species) where it was previously common, particularly off the Maranhão Coast. Carcharhinus porosus is a bycatch in gillnet fisheries directed at Spanish Mackerel Scomberomorus brasiliensis and declines in abundance have been observed off Maranhão Coast when comparing the catches from the 1980?s to the present. Previously an important component of the catch, (43% of the elasmobranch catch, with 88% of these comprising juveniles), C. porusus was recently recorded as a much lower component (17%) of the catch by the same gear (Almeida 1998). Increasing directed fishing effort by artisanal fisheries is considered to be the primary reason for this species? decline. Furthermore, the species has an early age of recruitment to the fishery and an apparent low fecundity. Given the increasing fishing pressure, and evidence of decline in the main part of its distribution, its vulnerability and overall lack of management, this species is considered to be Vulnerable in Brazil. Close monitoring of catches is necessary and there is concern that the species could become more threatened if conservation and management measures are not urgently addressed. Information is required from elsewhere in its range to complete the picture.
|Range Description:||Not known to occur in high numbers elsewhere throughout its range, Northern Brazil is in fact considered to be the centre of abundance for this species, with the highest abundance occurring in shallow waters off the Maranhão Coast, between Tubarão and Turiacu Bays (44° to 45°W) in gillnet fisheries targeting Spanish Mackerel Scomberomorus brasiliensis (in 8 to 32 m). Overall salinity in the area ranges from 13.96 ppm during the rainy season to 33.6 ppm during the dry season; temperature ranges from 25.1?31.5°C. The most important feature in this area is the tidal range that reaches up to 7 m bringing about tidal currents that attain speeds of 7.5 knots (Lessa 1997). The abundance of the species apparently decreases gradually easterly to this area. However, some specimens are still taken in gillnet fisheries targeting Spanish mackerel off Ceara (4°S) and Pernambuco States (8°S). The species is considered rare in the southern part of its Brazilian range.
Pregnant females, adult males and new-born sharks of this species have been observed in studies off northern Brazil (Lessa and Menni 1994). Of 1,128 Smalltail Sharks collected from June 1984 to November 1987 in gillnets from coastal waters, about 78% of females and 82% of males were immature in catches (Lessa and Santana 1998, Lessa et al.1999). Neonate males and females are commonly caught (30 to 35 cm TL /150 to 235 g). The coastline has mangroves and is deeply indented because of the large number of islands, rivers, estuaries, sandy beaches and cliffs, called ?Reentrancias?, which encompasses the coast of Para and Maranhão States. The area is considered a nursery area for this species as well as for other elasmobranchs, providing shelter and abundant food for initial phases of development.
Native:Belize; Brazil; Colombia; Costa Rica; Ecuador; El Salvador; French Guiana; Guatemala; Guyana; Honduras; Mexico (Baja California, Baja California Sur, Campeche, Chiapas, Colima, Guerrero, Jalisco, Michoacán, Nayarit, Oaxaca, Quintana Roo, Sinaloa, Sonora, Tabasco, Tamaulipas, Veracruz, Yucatán); Nicaragua; Panama; Peru; Suriname; United States (Texas); Venezuela
|FAO Marine Fishing Areas:||
Atlantic – southwest; Atlantic – western central; Pacific – eastern central; Pacific – southeast
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||BRAZIL: Analyses of the catch in northern Brazil indicate that the age of recruitment to the fisheries is two years (45 cm TL for males and 50 cm TL for females). Maturity length (50%) corresponds to six year-old individuals. The estimated mortality rate (Z) is 0.41; natural mortality is 0.217 and fishing mortality 0.193. Although the exploitation rate is 0.47, there are a high number of juveniles (88%, both sexes) and the estimated equilibrium fishing mortality (F?) is 0.051.|
|Habitat and Ecology:||
Common in waters over continental shelves, the Smalltail Shark prefers muddy bottoms in estuarine habitats. It swims along the bottom to depths of 36 m.
BRAZIL: The largest specimen ever caught in northern Brazil was a 128.5 cm TL female. However, the largest specimen analyzed in the literature cited here was a female measuring 120.5 cm TL and the smallest a 29.4 cm TL male (Lessa et al. 1999). The modal class in samples was 50 to 60 cm TL for both sexes. Age ranged from zero (newborns) to 12 years for individuals between 30 and 101 cm TL. Developed embryos of 28.5 cm TL were observed in the area; the average size at birth is 30 cm TL. The average fecundity is six embryos per female (Lessa et al. 1999). A resting break is suggested between successive pregnancies, implying a biennial cycle. The length- weight relationship did not differ significantly between the sexes. Diameter of ovarian follicles, presence of eggs/embryos and nidamental gland traits in female point to a major physiological change toward maturity at about 70.0 cm. Vitellogenesis was first observed at 63.0 cm, and the smallest of the six pregnant females was 70.0 cm; there was a significant relationship between the number of embryos and female size (Lessa et al. 1999) The size at 50% of maturity is 71 cm TL (males) and 70 cm TL (females) (Lessa et al.1999). Age and growth were estimated from vertebral analysis for individuals ranging from zero to twelve years. Von Bertalanffy growth parameters were: L? = 136.4 cm TL, K= 0.077 year-1 and t0 = -3.27 year.
The Smalltail Shark is an opportunistic predator, feeding primarily on small fishes including sea catfish, croakers, jacks and grunts, it also consumes aquatic invertebrates including crabs and shrimps. Adults may prey upon elasmobranchs, whereas juveniles show a wider food spectrum. Ontogenetic differences in diet were observed for both males and females. There is evidence of size selection of prey related to predator size (Lessa and Almeida 1997).
Life history parameters
Age at maturity: Male & Female: 6 years (Lessa and Santana 1998).
Size at maturity (total length): Female: 70 cm (Lessa and Santana 1988), 72 to 78 cm (Compagno et al. 2005); Male: 71 cm (Lessa and Santana 1998), 84 cm (Compagno et al. 2005)
Longevity: 12 years (Lessa and Santana 1998).
Maximum size (total length): 128.5 cm (Maranhão - Lessa et al. 1999); 134 cm (São Paulo - Sadowsky 1967); <150 cm (Compagno et al. 2005).
Size at birth: 30 cm (observed) and 31.1 cm (back-calculated) (Lessa and Santana 1998); 31-40 cm (Compagno et al. 2005).
Average reproductive age: 6 years (Lessa and Santana 1998).
Gestation time: ~12 months (Lessa et al. 1999).
Reproductive periodicity: Biannual cycle (Lessa et al. 1999).
Average annual fecundity or litter size: Average 6 embryos; maximum 9 (Lessa et al. 1999, Stride et al. 1992).
Annual rate of population increase: Unknown.
Natural mortality: 0.20 (Hoening´s Model); 0.23 (Pauly´s Model) (Santana da Silva 2001)..
BRAZIL: The species is a bycatch in gillnet fisheries directed at Spanish Mackerel Scomberomorus brasiliensis. Declines in populations have been observed in Maranhão Coast (northern Brazil ? the centre of abundance for this species) from comparing the species abundance in catches in the 1980?s to the present. The species represented about 43% of elasmobranch catches in the 1980?s. These catches were mainly composed of juveniles (88%). The proportion of the species in catches today using the same gear (recent National Research Program on EEZ Living Resources, REVIZEE Program) is about 17% of the total elasmobranch catch in numbers (Almeida 1998, Santana da Silva 2001). Ongoing research is being undertaken by Zafira Almeida.
PERU: Information on C. porosus in Peru is extremely scarce, other than reports of its presence off the north coast (to Chimbote, 09° 04.4´S) and occasionally rare off the south coast (Callao 12° 00´S and Ilo 17° 38.4´S). Landings of this species are not specifically reported in Peru (M. Romero, Unidad de Investigaciones en Biodiversidad, Instituto del Mar del Peru (IMARPE) pers.comm.).
No information for the rest of its range, for example, although a known bycatch component of artisanal gillnet fisheries in Central America, there is no data on catch or effort for this species. Information on C. porosus in the Gulf of Mexico is also scarce.
CENTRAL AMERICA: in general, sharks are utilized for human consumption (fillets), medicine (cartilages, liver oil) and dried fins are exported.
The Smalltail Shark is of little commercial importance, primarily caught as incidental bycatch in the gillnets of other fisheries. The flesh is marketed fresh for human consumption while the fins are valuable for use in soup fin soup. This shark is also processed into fishmeal and the oil is extracted from the liver (http://www.flmnh.ufl.edu).
BRAZIL: No effective measures in place at the present. The species was assessed as Vulnerable and included in the Official List of Endangered Animals in Brazil (published 26/05/2004); according to this status no captures are allowed. There have been recommendations from the Brazilian Society for the Study of Elasmobranchs (SBEEL) to the Brazilian Ministry of Environment to expand conservation areas along the Maranhão State in order to include coastal areas.
CENTRAL AMERICA: Other than steps being taken to ban finning in Costa Rica and Nicaragua, there are no regulations for shark species in particular, and where they are in place the monitoring, control and surveillance system is deficient. Studies are required to investigate population size and threats.
GENERAL: Development and effective 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 in order to facilitate the conservation and sustainable management of all chondrichthyan species in the region.
|Citation:||Lessa, R., Almeida, Z., Santana, F.M., Siu, S. & Perez, M. 2006. Carcharhinus porosus. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. <www.iucnredlist.org>. Downloaded on 24 May 2013.|
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