|Scientific Name:||Isogomphodon oxyrhynchus (Müller & Henle, 1839)|
|Red List Category & Criteria:||Critically Endangered A2ad+3d+4ad ver 3.1|
|Assessor(s):||Lessa, R., Charvet-Almeida, P., Santana, F.M. & Almeida, Z.|
|Reviewer(s):||Musick, J.A., Stevens, J.D., Kyne, P.M. & Cavanagh, R.D. (Shark Red List Authority)|
This inshore tropical species is endemic to the coastal waters off northern South America with a restricted distribution. Studies on the Daggernose Shark's biology, ecology and fisheries have been carried out only in parts of its area of occurrence. It has limiting biological parameters (fecundity 2 to 8 pups; gestation 12 months; reproductive cycle possibly biennial) and a resultant low intrinsic population growth rate, making it highly susceptible to declines. The species is caught incidentally in floating gillnet artisanal fisheries. Recruitment to fisheries occurs about two years after maturity, limiting reproductive potential. In Brazil, fishing pressure in its habitat continues to increase. Recent demographic analyses suggest that the population has been decreasing at 18.4% per year with very large declines (>90%) resulting over the past 10 years (Santana and Lessa 2002). Although data are currently lacking for Venezuela, Trinidad, Guyana, Suriname and French Guiana, it is highly likely that similar declines have also occurred there given that the species is taken primarily in artisanal fisheries. Such fishing pressure is intense across its range, will continue to increase into the future and its restricted movements may limit re-colonisation to depleted areas. These factors, together with limited distribution, life history traits and dramatic population declines result in the Daggernose Shark being considered a Critically Endangered species for which urgent conservation and management action is required.
|Range Description:||Compagno (1984) mentions the occurrence of the Daggernose Shark off the eastern (central) Brazilian coast (Valenca, Bahia, 13°S). However, this species has never been collected in fishery surveys and, is unknown to local fishermen in this area. In surveys carried out from 1998 to 2000 by the REVIZEE Program (Brazilian national program for the assessment of living resources of the exclusive economic zone) this species was also not recorded.|
Native:Brazil; French Guiana; Guyana; Suriname; Trinidad and Tobago; Venezuela, Bolivarian Republic of
|FAO Marine Fishing Areas:|
Atlantic – western central; Atlantic – southwest
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||Nursery areas have been observed in shallow areas such as estuaries and shallow coastal areas. Pregnant females were caught during the Amazonian summer (July-December) (Lessa et al. 1999).|
|Current Population Trend:||Decreasing|
|Habitat and Ecology:||The whole area where the Daggernose Shark occurs is characterized by a humid, tropical climate, coasts covered by extensive mangrove systems, wide continental shelves, intense draining by numerous rivers (including the Amazon), muddy bottoms and highly turbid waters. This species is found mainly in a deeply indented coastline with a large number of rivers, islands, estuaries and some beaches. Tidal amplitude in this region reaches up to 7 m and salinity ranges from 20 to 34 ppt (Lessa et al. 1999). Depth is shallow waters to 40 m (Lessa 1986, Lessa and Menni 1994). |
The elasmobranch fish fauna in the area is made up of two dominant-resident species, Carcharhinus porosus and Sphyrna tiburo and 11 other common species. The daggernose shark spends most of its life cycle within the same area and no long distance movements have been recorded, however some local seasonal movements possibly occur (Lessa and Menni 1994).
Off the northern Brazilian coast, females mature at an age of 6 to 7 years (115 cm TL) and males at 5 to 6 years (103 cm TL) (Lessa et al. 2000). Placental viviparous with the litter size varying between two and eight pups. The gestation period is 12 months and reproductive periodicity is possibly biennial (Lessa 1987, Lessa et al. 1999, Stride et al. 1999).
This species recruits to fisheries at 8.6 years (Marcante and Lessa 2002). Von Bertalanffy parameters obtained from vertebral analysis are: L? = 171.4 cm TL; k = 0.12 yr -1; t0 = -2.61. The oldest female specimen that had vertebrae analyzed was 12 years and the oldest male was seven years old. In the length frequency sample, the maximum size of 160 cm TL would correspond to a 20 year-old female and the maximum size of 144 cm TL would correspond to a 12 year-old male. Size at birth ~42 cm TL (Lessa et al. 2000).
Life history parameters
Age at maturity: Female: 6?7 years; Male: 5?6 years.
Size at maturity (total length): Female: 115 cm TL; Male: 103 cm TL.
Longevity: Female: 20 years; Male: 12 years.
Maximum size (total length): Female: 160 cm TL; Male: 144 cm TL.
Size at birth: ~42 cm TL.
Average reproductive age (years): Unknown.
Gestation time: 12 months.
Reproductive periodicity: Possibly biennial.
Average annual fecundity or litter size: 2?8 pups/litter, therefore average annual fecundity may equal 1?4 young if reproductive periodicity is biennial.
Annual rate of population increase: Unknown.
Natural mortality: Unknown.
The Daggernose Shark is caught incidentally in artisanal floating gillnets targeting both Spanish mackerel Scomberomorus brasiliensis and King Weakfish Cynoscium acoupa inside or near estuary mouths mainly during the dry season, representing about 10% of the catch in the State of Maranhao, Brazil (Lessa 1986, Lessa et al. 1999). Stride et al. (1992) recorded a CPUE of 71 kg/km/h for the Daggernose Shark, however, fishing efforts for target bony fish have increased in recent years due to the increase of the price of byproducts, mainly swim bladders. Observations have indicated that a commercial fishery targeting sharks is also presently taking place in this area (P. Charvet-Almeida, personal observation). Recent demographic analyses suggest that the population has been decreasing at 18.4% per year and very large population declines (>90%) have been observed over the past 10 years (Santana and Lessa 2002).
This species does not compensate for the high natural and fishing mortality due to its limited biological characteristics, including intrinsic population growth rate. The high mortality rates for such a biologically limited species are resulting in it not being able to support sustained fishing pressure (Lessa et al. 2000, Santana and Lessa 2002). This entire situation indicates a high risk of extinction for this species particularly given that it is an endemic species with a restricted range, and that fishing pressure is still increasing.
Data are lacking for the other countries in its range, but because the species is taken primarily in artisanal fisheries, which are intense throughout its range there is no reason to believe that a similar decline has not occurred there as well.
The Daggernose Shark is commercialised as human food but fins have a low price.
The following measures are recommended for this species:
It is suggested that the conservation area of Reentrâncias Maranhenses (Brazil) and adjacent regions is extended to encompass marine areas and seamounts where this species spends part of its life cycle.
Monitoring of the fishing efforts of vessels that use gillnets in the area of occurrence is also recommended. Encourage the release of live specimens landed.
Inclusion of this species in the Brazilian National list of Endangered Species (IBAMA). Creation and enforcement of specific laws/restrictions in the number of landings with the aim of conserving the species.
Studies and monitoring of this species in the other countries in its range outside Brazil.
|Citation:||Lessa, R., Charvet-Almeida, P., Santana, F.M. & Almeida, Z. 2006. Isogomphodon oxyrhynchus. The IUCN Red List of Threatened Species 2006: e.T60218A12323498.Downloaded on 11 December 2017.|