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Carcharhinus isodon

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA CHONDRICHTHYES CARCHARHINIFORMES CARCHARHINIDAE

Scientific Name: Carcharhinus isodon
Species Authority: (Müller & Henle, 1839)
Common Name(s):
English Fintooth Shark, Night Shark, Smoothtooth Shark, Eventooth Shark
French Requin à Petites Dents
Spanish Galana Dientefino, Tiburón de Noche, Tiburón Dentiliso
Synonym(s):
Carcharias isodon Müller & Henle, 1839

Assessment Information [top]

Red List Category & Criteria: Least Concern ver 3.1
Year Published: 2009
Date Assessed: 2008-12-01
Assessor(s): Carlson, J., Kyne, P.M. & Valenti, S.V.
Reviewer(s): Stevens, J.D., Dudley, S., Pollard, S., Soldo, A. & Kulka, D.W. (Shark Red List Authority)
Justification:
The Finetooth Shark (Carcharhinus isodon) is a coastal species occurring in shallow waters from the intertidal to depths of ~20 m. It is predominantly distributed in US waters in the western Atlantic and the northern Gulf of México where it is locally common. In South America, it is reported from São Paulo to Santa Catarina States in southern Brazil, Trinidad and Guyana. Stock assessments for the finetooth shark in US Atlantic waters and Gulf of Mexico indicate that the current status of the population is above maximum sustainable yield and no overfishing is occurring, therefore this population is assessed as Least Concern. This species is apparently rare throughout its reported range off South America, and virtually no information is available from this region. This rarity, together with its shallow inshore occurrence in a region which faces heavy coastal fishing pressure raises concern for the species' threat status in South America, particularly as significant declines have been documented in other elasmobranchs that occur in coastal waters of Brazil. However, due to infrequent records and a total lack of information on the species' full distribution and catches in fisheries, it is not possible to assess this population beyond Data Deficient at present. Further research is urgently required into the species' full distribution, catch levels, impact of fisheries and population trends off South America. Available information suggests that the majority of total global population occurs in the US Atlantic and Gulf of Mexico; thus the species is currently listed as Least Concern globally. With further information on the South American population of this species, this assessment may need to be revisited.

Geographic Range [top]

Range Description: Northwest, western central and southwest Atlantic: USA (Possibly north as a vagrant to New York, rare off North Carolina, and normally from off South Carolina, Georgia, the Atlantic coast of Florida and the Gulf of Mexico coast of Florida, Alabama, Mississippi and Texas). A record from Cuba is apparently erroneous (Compagno in prep, Castro 1993). However, Wiley and Simpfendorfer (2007) recently extended the US range to approximately 25°N which increases the likelihood of exchange between the US and Cuba. In South America, it is known with certainty from São Paulo to Santa Catarina States in southern Brazil (Soto 2001, Compagno et al. 2005). It is also reported from Trinidad and Guyana and may be more wide-ranging than currently documented (Garrick 1985, Castro 1993, Compagno in prep).

Records of the species from the eastern central Atlantic, from Senegal and Guinea-Bissau, are unconfirmed and probably incorrect (Compagno in prep, M. Ducrocq pers. comm. 2006).
Countries:
Native:
Brazil (Paraná, Santa Catarina, São Paulo); Guyana; Trinidad and Tobago; United States (Alabama, Florida, Georgia, Mississippi, North Carolina, South Carolina, Texas)
FAO Marine Fishing Areas:
Native:
Atlantic – eastern central; Atlantic – northwest; Atlantic – southwest; Atlantic – western central
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: The population structure of this species is poorly known throughout its range, but it is reasonable to assume that little to no exchange occurs between the population of this highly coastal species off the US Atlantic and Gulf of Mexico and the population off South America.

US Atlantic and Gulf of Mexico
Common in inshore waters off the eastern coast of the USA and the Gulf of Mexico. It is abundant along the coast of the southeastern United States and the Gulf of Mexico (Carlson et al. 2003, Wiley and Simpfendorfer 2007). Stock assessments for the US population of finetooth shark indicate that the current status of the population is above maximum sustainable yield and no overfishing is occurring (Cortés 2007).

South America
This species is poorly documented off South America, but is apparently rare throughout its range there (Castro 1993, Soto 2001, Compagno et al. 2005).
Population Trend: Unknown

Habitat and Ecology [top]

Habitat and Ecology: A coastal shark, occurring in shallow waters from the intertidal to depths of ~20 m (Compagno et al. 2005), which is common off beaches, in bays, estuaries and off river mouths. They often form large schools.

Throughout the southeastern USA and Gulf of Mexico, finetooth sharks use coastal bays and estuaries as nursery grounds (Carlson and Brusher 1999, McCandless et al. 2002). Adults and juveniles are common in shallow coastal waters off South Carolina, Georgia, northern states along the Gulf of Mexico during the warm summer months and migrate south when surface water temperatures drop below 68°F (20°C). In the Atlantic Ocean off the USA, they spend the winter months in the waters off the coast of Florida.

Estimates of size and age-at-maturity for male and female sharks from the Gulf of Mexico were different from those in the US Atlantic and northern Gulf of Mexico (Carlson et al. 2003, Drymon et al. 2006). Fork length at which 50% of the population reached maturity is 1,022 mm in the US South Atlantic and 990 mm in the Gulf of Mexico for females and was found to be significantly different. Median fork length at maturity for males is 988 mm and 935 mm for the US South Atlantic and Gulf of Mexico, respectively. Median age-at-maturity was 6.2 and 4.2 years for females, and 4.9 and 3.5 years for males for sharks in the US Atlantic and Gulf of Mexico, respectively (Carlson et al. 2003, Drymon et al. 2006).

Size at birth is 55-58 cm TL and fecundity is 4.0 (SD=0.79) pups for sharks in the US South Atlantic (Castro 1993). Off Louisiana, Neer and Thompson (2004) observed three gravid females with litters of three, four and five pups, respectively. The reproductive cycle is currently assumed to be biennial (Castro 1993).

Significant differences between von Bertalanffy growth curves were found between sharks in the US Atlantic and northern Gulf of Mexico for females but not males (Carlson et al. 2003, Drymon et al. 2006). In the US Atlantic, growth coefficients (K) were 0.19 yr-1 for females and 0.33 yr-1 for males whereas female growth coefficient were 0.24 yr-1 and males were 0.41 yr-1 in the Gulf of Mexico. The maximum observed ages, based on vertebral band counts, were 8.2 and 10.3 years for male sharks from the Gulf of Mexico and US Atlantic, respectively (Carlson et al. 2003).

Castro (1993) published descriptive diet data for the finetooth shark in the northwest Atlantic off the coasts of South Carolina and Daytona Beach, FL, and found teleosts (Atlantic Menhaden (Brevoortia tyrannus), Spot Croaker (Leiostomus xanthurus), Spanish Mackerel (Scomberomorus maculatus), and Mugil species) to be the primary prey. In northwest Florida, Finetooth Sharks fed almost entirely on menhaden and showed no ontogenetic shift in diet (Bethea et al. 2004).
Systems: Marine

Threats [top]

Major Threat(s): US Atlantic and Gulf of Mexico
Targeted by recreational fishers, small gillnet fisheries and occasionally taken as bycatch in demersal shrimp trawls that occur along the southeast coast of the USA and Gulf of Mexico. Estimated commercial landings were 69,258 lbs dressed weight in 2000 while recreational catches of small coastal sharks were 86,167 lbs (Cortés 2002). Finetooth Shark makes up a small proportion of these landings but the actual number is unknown. The group "small coastal sharks" includes Atlantic Sharpnose Shark (Rhizoprionodon terraenovae), Blacknose Shark (Carcharhinus acronotus) and Bonnethead Shark (Sphyrna tiburo), as well as Finetooth Shark (Carcharhinus isodon).

The Finetooth Shark is vulnerable to overfishing and depletion because of targeted fishing in gillnet fisheries in the southeastern United States (Carlson and Bethea 2007). Despite this, recent stock assessments have shown that the US population of this species is above maximum sustainable yield, with current fishing levels not threatening its viability (Cortés 2007). This species is also restricted by its limited distribution (both bathymetric and geographic), with the majority of individuals living in shallow inshore waters adjacent to built-up areas, with extensive habitat degradation and some fisheries. However, the coastal nature of this species affords it some protection because many gillnet fisheries in US state waters have been banned (NMFS 2007).

South America
Shark fisheries have increased dramatically in the southern part of the Finetooth Shark's range during the past half-century (L.J.V. Compagno pers. comm. 2008). The species' apparent rarity is of concern in the southern part of its range because rare species captured as bycatch of coastal shark fisheries may become even rarer to the point of local extirpation as the fisheries continue, supported by the more common species (L.J.V. Compagno pers. comm. 2008).

Coastal species are the most important commercial elasmobranchs in the Southwest Atlantic, and inshore fisheries are generally very intense off southern Brazil (Bonfil et al. 2005). Intensive fishing by pair trawl, shrimp trawl, gillnet and beach seine in near-shore waters is documented off Rio Grande do Sul State (Vooren and Klippel 2005). Although this species' range does not extend to Rio Grande do Sul, similar fisheries are likely to operate throughout much of the coast of Santa Catarina to São Paulo States, from which it is known.

Fisheries in Guyana and Trinidad and Tobago are generally inshore and artisanal (Chan A Shing 1999). Intensive trawling occurs in Trinidad and Tobago's waters (Mohammed and Chan A Shing 2003). Bycatch of the shrimp trawl fleet is considerably higher than the target catches. Total bycatch in these fisheries declined from 13,712 t in 1987 to 4,099 t in 2001 although the species composition of this bycatch has not yet been examined (Mohammed and Chan A Shing 2003). An artisanal gillnet and line fishery targets mackerel in coastal waters off Trinidad and Tobago and takes sharks as bycatch. This is the most widespread fishing method, accounting for over 85% of artisanal shark landings (Chan A Shing 1999).

In Guyana, there is a partially directed gillnet fishery for sharks (~600 vessels) which captures both demersal and pelagic inshore species. This fishery operates in estuarine and shallow coastal waters (at depths of <40 m) (Chan A Shing 1999). About 100 industrial shrimp trawlers also take sharks and finfish as bycatch, but no details are available on the composition of the bycatch. An artisanal demersal longline fishery targets sharks and catfish at depths of 9-20 m (Chan A Shing 1999).

Conservation Actions [top]

Conservation Actions: US Atlantic and Gulf of Mexico
Finetooth sharks are managed under the US Fishery Management Plan for Atlantic tunas, swordfish, and sharks and management actions are underway to limit potential increases in fishing. Moreover, gillnet bans in state waters of Florida, Georgia, South Carolina, and Texas will give added protection to this species, as it primarily occurs in state waters. See http://www.nmfs.noaa.gov/sfa/hms/hmsdocument_files/sharks.htm for up-to-date information and the regulations that apply to the small coastal shark complex.

South America
No measures in place. Recommended: The status of this species in South American waters should be investigated. Research is needed into distribution, catch levels, impact of fisheries and population trends.

Citation: Carlson, J., Kyne, P.M. & Valenti, S.V. 2009. Carcharhinus isodon. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 02 September 2014.
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