|Scientific Name:||Carcharhinus signatus|
|Species Authority:||(Poey, 1868)|
|Infra-specific Taxa Assessed:|
|Red List Category & Criteria:||Vulnerable A2abd+3bd+4abd ver 3.1|
|Assessor(s):||Santana, F.M., Lessa, R. & Carlson, J.|
|Reviewer(s):||Cavanagh, R.D., Kyne, P.M., Walker, T.I., Stevens, J., Dudley, S. & Pollard, D. (Shark Red List Authority)|
Concern for the status of Carcharhinus signatus off South America arises from uncontrolled fishing effort on the species and from its comparatively low biological productivity. Under intense fishing pressure off parts of Brazil, C. signatus is a target species (for fins and meat) regularly caught in commercial fisheries on seamounts off northeastern Brazil where the species aggregates. The Night Shark is the most important elasmobranch species in the seamount area where it makes up 90% of catches from over shallow banks. Estimates of age composition indicated that 89.2% of individuals were below the age at 50% maturity. Demographic analysis indicates declines due to fishing mortality rate and early recruitment to the fishery. It is likely that there are no significant natural refuges for the species and that there is little or no exchange with other populations of C. signatus. Formerly common in Caribbean fisheries, this species is now apparently rare. Historically, night sharks comprised a significant proportion of the artisanal Cuban shark fishery, making up to 60 to 75% of the catch from 1937 to 1941. However, beginning in the 1970s with the development of the swordfish fishery, anecdotal evidence has indicated a substantial decline in the abundance of this species. Night sharks comprised 26.1% of the shark catch in the pelagic US longline fishery from 1981 to 1983, but observer data showed this to decline to 0.3% and 3.3% of the shark catch in 1993 and 1994. Further, photographic evidence from marlin tournaments in south Florida in the 1970s shows that large Night Sharks were caught daily, but today they are rarely captured. However, recent trends in catch rates from the pelagic logbook data indicate that the trend has stabilized since 1992, the Fishery Management Plan of the Atlantic tunas, swordfish and sharks currently lists the Night Shark as a Prohibited Species and recent time/area closures should help to reduce any further increases in bycatch. All this considered, the Night Shark is assessed as Vulnerable globally based on significant population declines throughout its Western Atlantic range due to target and bycatch exploitation by fisheries, which although now managed in US waters, is not the case elsewhere in the region.
There is currently no available information from the Eastern Atlantic distribution of C. signatus off West Africa, and until further research and enquiries in this region, the species cannot be assessed beyond Data Deficient for this part of its range, although coastal fisheries in the region are known to be intense and its apparent disjunct distribution could easily lead to localised depletions.
|Range Description:||Studies on the species have been carried out at several localities along the Brazilian coast during the past five years. Whether or not specimens examined from the different localities belong to the same population or whether there is exchange between the animals off Brazil with those in other parts of its range is unknown. Pregnant females are observed in northeastern Brazil, although full-term embryos and new-born specimens are never caught, perhaps due to size-selectivity of gear used. On the shelf break in the southern region of its distribution (latitude ~34° South) (Hellebrandt and Vooren 2000) the animals are predominantly juveniles, and the area is thought to be an important nursery area.
The night shark makes up 90% of elasmobranchs caught by longline over seamounts off northeastern Brazil (Amorim et al. 1998). About 89% of individuals in landings are below age-at-50%-maturity. Recruitment to the seamount longline fisheries occurs at five years. Demographic analysis carried out using data collected over seamounts off northeastern Brazil indicates declines due to a high fishing mortality rate (F=0.117) and early recruitment causing an annual loss of 4.4% (Santana da Silva 2001). Fishing mortality is double that required to maintain population equilibrium (Z'=0.287). Estimates of total mortality (Z), natural mortality (M), initial natural mortality (Z0) and equilibrium fishing mortality (F') are 0.355, 0.238, 0.362 and 0.049, respectively. Further, the reproductive net rate (R0) is estimated to be 0.59 and generation time (G) 11.71. Average fecundity is 9.5 embryos and the sex ratio of embryos is 1:1 (Santana da Silva 2001).
Native:Angola (Angola); Argentina; Benin; Brazil; Cameroon; Congo, The Democratic Republic of the; Côte d'Ivoire; Cuba; Gambia; Ghana; Guinea; Guinea-Bissau; Guyana; Liberia; Nigeria; Senegal; Sierra Leone; Togo; United States (Delaware, District of Columbia, Florida, Georgia, Maryland, North Carolina, South Carolina, Virginia); Uruguay
|FAO Marine Fishing Areas:||
Present - origin uncertain:
Atlantic – eastern central; Atlantic – southeast; Atlantic – southwest; Atlantic – western central; Pacific – southeast
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||Formerly common in Caribbean fisheries, this species is now apparently rare (Compagno et al. 2005).|
|Current Population Trend:||Decreasing|
|Habitat and Ecology:||Castro (1983) reports that this species is usually found at depths between 275 and 366 m during the day and <183 m at night. Compagno (in prep b) reports that the species prefers waters 50 to 100 m deep, but that it ranges from the surface to at least 600 m depth. In northeastern Brazil C. signatus is caught in commercial landings on deep (Aracati, Dois Irmaos Fundo, Sirius) and shallow (Pequeno, Leste and Sueste) seamounts at depths of 38 to 370 m on the summits. In these areas mating occurs throughout the austral summer; embryos measuring 10 to 40 cm TL were collected in February, whereas 31 to 37 cm TL embryos were found in June. Parturition occurs during several months in a protracted birthing season. Size-at-birth is estimated to be 66.8 cm TL. The gestation period is assumed to be about one year. Whether or not there is a resting break between two reproductive seasons is unclear. Gravid females have between 4 and 15 pups. Peak gonadosomatic index (GSI) occurs in spring and ovulation occurs shortly after that. Copulation is assumed to occur in summer. Average fecundity is 9.5 embryos and the sex ratio of embryos is 1:1 (Santana da Silva 2001).
As mentioned above, about 89% of individuals in landings in the seamount fishery are below age-at-50%-maturity (eight years for males and 10 years for females). Recruitment to the seamount longline fisheries occurs at five years (157 cm TL for males and 202 cm TL for females). Maximum size in the area is 260 cm TL, and size-at-50%-maturity is 185 cm TL for males and 202 cm TL for females. Maximum age in this area is 17 years (Santana and Lessa 2004).
Age and growth were determined for the northeastern Brazil region from vertebral sections from 317 animals. Von Bertalanffy growth functions showed no significant differences between sexes. Growth parameter estimates were L∞ = 270 cm TL, k = 0.11 yr?1; t0 = -2.71 yr (Santana and Lessa 2004).
Carcharhinus signatus is a target species and is regularly caught in commercial landings on deep (Aracati, Dois Irmaos Fundo, Sirius) and shallow (Pequeno, Leste and Sueste) seamounts off northeastern Brazil (Ceara and Rio Grande do Norte), at depths of 38-370 m on the summits. Exploitation started in 1991 for the highly prized fins, the increasing value of shark meat in the local market, and the species' accessibility to fisheries. Carcharhinus signatus is the most abundant elasmobranch species in the seamount fisheries where it makes up 90% of catches in number over shallow banks (CPUE, in number 2.94/100 hooks) but only 15% of catches on the surrounding deep areas (CPUE 0.04/100 hooks) using the traditional Japanese-style multifilament longline (Amorim et al. 1998). Estimates of age composition for the whole sample indicated that 89.2% of individuals were below age-at-50%-maturity (eight years for males and 10 years for females). Recruitment to the fisheries is at five years of age. The population is highly aggregated over the seamounts and shelf break and, thus, highly "available" to fisheries. It is likely that there are no natural refuges for the species and that there is little or no exchange with other populations of C. signatus. One possible respite for the population is re-targeting away from C. signatus to Swordfish Xiphias gladius and Bigeye Tuna Thunnus obesus.
Historically, Night Sharks comprised a significant proportion of the artisanal Cuban shark fishery, making up to 60-75% of the catch from 1937-1941 (Martinez 1947). However, beginning in the 1970s with the development of the swordfish fishery, anecdotal evidence has demonstrated a substantial decline in the abundance of this species. Guitart-Manday (1975) documented a decline in the mean weight per unit of effort for night sharks from 53.4 kg in 1971 to 21.1 kg in 1973.
Night sharks comprised 26.1% of the shark catch in the pelagic U.S. longline fishery from 1981-1983 (Berkeley and Campos 1988), but this declined to 0.3% and 3.3% of the shark catch in 1993 and 1994 based on observer data (L. Beerkircher, unpublished data). Further, photographic evidence from marlin tournaments in south Florida in the 1970s shows that large night sharks were caught daily but today they are rarely captured (J.I. Castro, personal observation). However, recent trends in catch rates from the pelagic logbook data indicate that the trend has stabilized since 1992 (Brown and Cramer 2002). Night sharks are still caught incidentally as bycatch in the US Longline Fishery although the species currently makes up only 2% of the shark catch. Recent time/area closures off the Florida Straits and the Charleston Bump should help to reduce any further increases in bycatch because most night shark catches occur in these areas (L. Beerkircher, NOAA Fisheries, pers. comm.).
Brazil: There are controls on the number of vessels in the fishery and the use of drift nets is prohibited, but there needs to be enforcement of existing laws that ban the transport of shark fins without corresponding carcasses, better monitoring of landings, and declaration of closed fishing areas over some of the seamounts off northeastern Brazil. The Brazilian National Plan of Action for Sharks (NPOA-Sharks) is in urgent need of implementation under the FAO International Plan of Action for the Conservation and Management of Sharks (IPOA-Sharks).
US: In US waters, under the Fishery Management Plan of the Atlantic tunas, swordfish and sharks (NMFS 1999), the Night Shark, Carcharhinus signatus, is currently listed as a Prohibited Species but was originally petitioned and added to the Candidate Species List under the Endangered Species Act in 1997. Recent time/area closures off the Florida Straits and the Charleston Bump should help to reduce any further increases in bycatch (L. Beerkircher, NOAA Fisheries, pers. comm).
|Citation:||Santana, F.M., Lessa, R. & Carlson, J. 2006. Carcharhinus signatus. The IUCN Red List of Threatened Species 2006: e.T60219A12323765. http://dx.doi.org/10.2305/IUCN.UK.2006.RLTS.T60219A12323765.en . Downloaded on 09 October 2015.|