Smalltail shark
Encyclopedia
The smalltail shark is a species
of requiem shark
, family
Carcharhinidae, found in the western Atlantic Ocean
from the northern Gulf of Mexico
to southern Brazil
. It inhabits shallow waters close to shore, particularly over mud
dy bottoms around estuaries. It tends to swim low in the water column and forms large aggregations segregated by sex. A slim species generally not exceeding 1.1 m (3.6 ft) in length, the smalltail shark has a rather long, pointed snout, a broad, triangular first dorsal fin
, and a second dorsal fin that originates over the midpoint of the anal fin base. It is plain gray in color, without prominent markings on its fins.
The diet of the smalltail shark consists mainly of bony fishes such as croakers
, while crustacean
s, cephalopod
s, and smaller sharks and rays may also be consumed. It is viviparous, meaning that the developing embryo
s are sustained by a placenta
l connection. Females bear litters of 2–9 young on a biennial cycle, following an approximately 12-month gestation period
. The smalltail shark is often caught as bycatch
and may be used for meat, fins
, liver oil
, cartilage
, and fishmeal. The impact of fishing on its population is largely unknown except off northern Brazil, where it seems to have declined significantly since the 1980s. Therefore, the International Union for Conservation of Nature (IUCN) has listed it as Data Deficient
overall and as Vulnerable
in Brazil.
Camillo Ranzani
published the first scientific description of the smalltail shark, in an 1839 volume of Novi Commentarii Academiae Scientiarum Instituti Bononiensis. He named the new shark Carcharias porosus from the Greek porus ("pore"), referring to the prominent pores behind its eyes. The type specimen, a 1.2 m (3.9 ft) long male from Brazil, has since been lost. This species was moved to the genus
Carcharhinus
by later authors. Its Trinidad
ian name is puppy shark.
The evolutionary relationships of the smalltail shark are uncertain. Based on morphology
, Jack Garrick in 1982 and Leonard Compagno
in 1988 tentatively placed it in a group defined by the whitecheek shark
(C. dussumieri) and the blackspot shark
(C. sealei). This grouping was equivocally supported by Gavin Naylor's 1992 allozyme
-based phylogenetic analysis. Alternately, a 2011 phylogenetic study by Ximena Vélez-Zuazoa and Ingi Agnarsson, based on nuclear
and mitochondrial
gene
s, found close relationships between the smalltail shark, the daggernose shark
(Isogomphodon oxyrhynchus), the blacknose shark
(C. acronotus), and the finetooth shark
(C. isodon). The Pacific smalltail shark
(C. cerdale) was once mistakenly synonymized
with C. porosus, until 2011 when José Castro resurrected it as a distinct taxon
. An undescribed species closely similar to C. porosus is known from Southeast Asia
.
s, and behind them are a series of prominent pores. The mouth bears short furrows at the corners and contains 13–15 tooth rows on either side of both jaws (usually 14 upper and 13 lower). The upper teeth are tall and triangular with strong serrations, becoming increasing oblique towards the sides. The lower teeth are comparatively narrower and more upright, with finer serrations. The five pairs of gill slit
s are short.
The small pectoral fins are falcate (sickle-shaped) with relatively pointed tips. The first dorsal fin
is broad, forming nearly an equilateral triangle in adults, with a blunt apex; it originates over the pectoral fin rear tips. The second dorsal fin is small and originates over the midpoint of the anal fin base. There is no ridge between the dorsal fins. The pelvic fins are small with pointed to narrowly rounded tips, and the anal fin has a deep notch in its trailing margin. The asymmetrical caudal fin has a strong lower lobe and a longer upper lobe with a ventral notch near the tip. The dermal denticles are mostly non-overlapping; each has 3–5 horizontal ridges leading to posterior teeth, with the central one the longest. This shark is plain gray to slate above and whitish below, with a faint lighter stripe on the flanks. The pectoral, dorsal, and caudal fins may darken toward the tips. The smalltail shark reaches a maximum known length of 1.5 m (4.9 ft), though 0.9–1.1 m (3–3.6 ft) is typical. Females grow larger than males.
to southern Brazil
, excluding the Caribbean
islands (aside from Trinidad and Tobago
). Its center of abundance is along the northern Brazilian coast, off Pará
and Maranhão
, where it is the most common shark. This species has not been reported east of the Mississippi River
in the past 50 years, despite historical evidence of a nursery area off Louisiana
. The smalltail shark can usually be found close the bottom in inshore waters no deeper than 36 m (118.1 ft). Off northern Brazil, its environment is characterized by tide
s up to 7 m (23 ft) high and reaching 7.5 knots; the salinity
fluctuates between 14 ppt in the rainy season and 34 ppt in the dry season
and the temperature ranges from 25 to 32 °C (77 to 89.6 F). It favors estuarine
areas with muddy bottoms.
, croakers
, jacks
, and grunts
. Shrimp
, crab
s, and squid
are secondary food sources, while adults are also capable of taking young sharpnose shark
s (Rhizoprionodon), hammerhead shark
s (Sphyrna), and stingray
s (Dasyatis). Opportunistic in habits, the dietary composition of this shark generally reflects what is most available in its environment; off northern Brazil the most important prey species are the croakers Macrodon ancylodon and Stellifer naso. Juveniles consume a wider variety of prey than adults. In turn, the smalltail shark may potentially be preyed upon by larger sharks.
Like other members of its family, the smalltail shark is viviparous: once the developing embryo
s exhaust their supply of yolk, the yolk sac
develops into a placenta
l connection through which the mother delivers nourishment. Females produce litters of 2–9 (typically 4–6) young every other year; litter size increases with the size of the female. The gestation period
lasts approximately 12 months. Reproduction occurs throughout the year, with a peak in birthing from September to November. There are known nursery areas in shallow, murky waters off northern Brazil and Trinidad, where many bay
s and estuaries provide shelter and food. The newborns measure 30–33 cm (11.8–13 in) long and grow an average of 7 cm (2.8 in) per year in their first four years of life. Males and females mature sexually
at 70–93 cm (27.6–36.6 in) and 71–85 cm (28–33.5 in) long respectively, corresponding to six years of age for both sexes. The average growth rate slows to 4 cm (1.6 in) per year after maturation. The maximum lifespan is at least 12 years.
by gillnet
and longline fisheries
throughout its range. The meat is sold fresh, frozen, or dried and salted. In addition, the dried fins are exported for use in shark fin soup
, the liver oil
and cartilage
are used medicinally, and the carcass is processed into fishmeal. No fishery data are available on this species in most of its range, leading it to be listed under Data Deficient
by the International Union for Conservation of Nature (IUCN). In Trinidad, its abundance makes it the most economically important shark. Off northern Brazil, substantial numbers of smalltail sharks are caught by gillnet fisheries targeting the Serra Spanish mackerel
(Scomberomorus brasiliensis). In the 1980s this species constituted roughly 43% of the shark and ray catch, but since then its share has declined to around 17%. This apparent decline is thought to have resulted from increasing fishing effort, the large proportion of juveniles captured, and the shark's low reproductive rate. Consequently, the IUCN has assessed the smalltail shark in Brazil as Vulnerable
, and noted the urgent need for conservation measures given that northern Brazil represents the center of the the species' range. Although the smalltail shark was ostensibly given protection by inclusion on the 2004 Official List of Endangered Animals in Brazil, fishing remains effectively unmanaged.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of requiem shark
Requiem shark
Requiem sharks are a family, Carcharhinidae, of sharks in the order Carcharhiniformes, containing migratory, live-bearing sharks of warm seas such as the tiger shark, the blue shark, the bull shark, and the milk shark.The name may be related to the French word for shark, "requin", itself of...
, family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Carcharhinidae, found in the western Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
from the northern Gulf of Mexico
Gulf of Mexico
The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...
to southern Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
. It inhabits shallow waters close to shore, particularly over mud
Mud
Mud is a mixture of water and some combination of soil, silt, and clay. Ancient mud deposits harden over geological time to form sedimentary rock such as shale or mudstone . When geological deposits of mud are formed in estuaries the resultant layers are termed bay muds...
dy bottoms around estuaries. It tends to swim low in the water column and forms large aggregations segregated by sex. A slim species generally not exceeding 1.1 m (3.6 ft) in length, the smalltail shark has a rather long, pointed snout, a broad, triangular first dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
, and a second dorsal fin that originates over the midpoint of the anal fin base. It is plain gray in color, without prominent markings on its fins.
The diet of the smalltail shark consists mainly of bony fishes such as croakers
Sciaenidae
Sciaenidae is a family of fish commonly called drums, croakers, or hardheads for the repetitive throbbing or drumming sounds they make...
, while crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s, cephalopod
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...
s, and smaller sharks and rays may also be consumed. It is viviparous, meaning that the developing embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
s are sustained by a placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...
l connection. Females bear litters of 2–9 young on a biennial cycle, following an approximately 12-month gestation period
Gestation period
For mammals the gestation period is the time in which a fetus develops, beginning with fertilization and ending at birth. The duration of this period varies between species.-Duration:...
. The smalltail shark is often caught as bycatch
Bycatch
The term “bycatch” is usually used for fish caught unintentionally in a fishery while intending to catch other fish. It may however also indicate untargeted catch in other forms of animal harvesting or collecting...
and may be used for meat, fins
Shark fin soup
Shark fin soup is a popular soup item of Chinese cuisine usually served at special occasions such as weddings and banquets, or as a luxury item in Chinese culture. The shark fins provide texture while the taste comes from the other soup ingredients.There is controversy over the practice of shark...
, liver oil
Shark liver oil
Shark liver oil is obtained from sharks that are caught for food purposes and are living in cold, deep oceans. The liver oil from sharks has been used by fishermen for centuries as a folk remedy for general health...
, cartilage
Shark cartilage
Shark cartilage is a dietary supplement made from the dried and powdered cartilage of a shark; that is, from the tough material that composes a shark's skeleton. Shark cartilage is claimed to combat and/or prevent a variety of illnesses, most notably cancer. It is often marketed under the names...
, and fishmeal. The impact of fishing on its population is largely unknown except off northern Brazil, where it seems to have declined significantly since the 1980s. Therefore, the International Union for Conservation of Nature (IUCN) has listed it as Data Deficient
Data Deficient
Data Deficient is a category applied by the IUCN, other agencies, and individuals to a species when the available information is not sufficient for a proper assessment of conservation status to be made...
overall and as Vulnerable
Vulnerable species
On 30 January 2010, the IUCN Red List of Threatened Species identified 9694 Vulnerable species, subspecies and varieties, stocks and sub-populations.-References:...
in Brazil.
Taxonomy and phylogeny
Italian naturalistNaturalist
Naturalist may refer to:* Practitioner of natural history* Conservationist* Advocate of naturalism * Naturalist , autobiography-See also:* The American Naturalist, periodical* Naturalism...
Camillo Ranzani
Camillo Ranzani
Camillo Ranzani was an Italian priest and a naturalist. He was director of the Museum of Natural History of Bologna from 1803 to 1841...
published the first scientific description of the smalltail shark, in an 1839 volume of Novi Commentarii Academiae Scientiarum Instituti Bononiensis. He named the new shark Carcharias porosus from the Greek porus ("pore"), referring to the prominent pores behind its eyes. The type specimen, a 1.2 m (3.9 ft) long male from Brazil, has since been lost. This species was moved to the genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
Carcharhinus
Carcharhinus
Carcharhinus is the type genus of the requiem shark family, Carcharhinidae.- Species :* Carcharhinus acarenatus * Carcharhinus acronotus...
by later authors. Its Trinidad
Trinidad
Trinidad is the larger and more populous of the two major islands and numerous landforms which make up the island nation of Trinidad and Tobago. It is the southernmost island in the Caribbean and lies just off the northeastern coast of Venezuela. With an area of it is also the fifth largest in...
ian name is puppy shark.
The evolutionary relationships of the smalltail shark are uncertain. Based on morphology
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
, Jack Garrick in 1982 and Leonard Compagno
Leonard Compagno
Leonard Joseph Victor Compagno is an international authority on shark taxonomy and the author of many scientific papers and books on the subject, best known of which is his 1984 catalogue of shark species produced for the Food and Agriculture Organization of the United Nations.-Career:*Ph.D,...
in 1988 tentatively placed it in a group defined by the whitecheek shark
Whitecheek shark
The whitecheek shark, Carcharhinus dussumieri, is a requiem shark of the family Carcharhinidae, found in the Indo-West Pacific Ocean between latitudes 34° N and 25° S. Its length is up to about 1.2 m....
(C. dussumieri) and the blackspot shark
Blackspot shark
The blackspot shark, Carcharhinus sealei, is a requiem shark of the family Carcharhinidae, found in the Indo-West Pacific oceans between latitudes 24° N and 30° S, from the surface to 40 m. Its length is up to about 1.5 m....
(C. sealei). This grouping was equivocally supported by Gavin Naylor's 1992 allozyme
Allozyme
Variant forms of an enzyme that are coded by different alleles at the same locus are called allozymes. These are opposed to isozymes, which are enzymes that perform the same function, but which are coded by genes located at different loci....
-based phylogenetic analysis. Alternately, a 2011 phylogenetic study by Ximena Vélez-Zuazoa and Ingi Agnarsson, based on nuclear
Nuclear DNA
Nuclear DNA, nuclear deoxyribonucleic acid , is DNA contained within a nucleus of eukaryotic organisms. In mammals and vertebrates, nuclear DNA encodes more of the genome than the mitochondrial DNA and is composed of information inherited from two parents, one male, and one female, rather than...
and mitochondrial
Mitochondrial DNA
Mitochondrial DNA is the DNA located in organelles called mitochondria, structures within eukaryotic cells that convert the chemical energy from food into a form that cells can use, adenosine triphosphate...
gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
s, found close relationships between the smalltail shark, the daggernose shark
Daggernose shark
The daggernose shark is a little-known species of requiem shark, family Carcharhinidae, and the only extant member of its genus. It occurs in shallow tropical waters off northeastern South America from Trinidad to northern Brazil, favoring muddy habitats such as mangroves, estuaries, and river...
(Isogomphodon oxyrhynchus), the blacknose shark
Blacknose shark
The blacknose shark is a species of requiem shark, family Carcharhinidae, common in the tropical and subtropical waters of the western Atlantic Ocean. This species generally inhabits coastal seagrass, sand, or rubble habitats, with adults preferring deeper water than juveniles...
(C. acronotus), and the finetooth shark
Finetooth shark
The finetooth shark is a species of requiem shark, family Carcharhinidae, found in the western Atlantic Ocean from North Carolina to Brazil. It forms large schools in shallow, coastal waters and migrates seasonally following warm water...
(C. isodon). The Pacific smalltail shark
Pacific smalltail shark
The Pacific smalltail shark is a species of requiem shark, family Carcharhinidae....
(C. cerdale) was once mistakenly synonymized
Synonym (taxonomy)
In scientific nomenclature, a synonym is a scientific name that is or was used for a taxon of organisms that also goes by a different scientific name. For example, Linnaeus was the first to give a scientific name to the Norway spruce, which he called Pinus abies...
with C. porosus, until 2011 when José Castro resurrected it as a distinct taxon
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
. An undescribed species closely similar to C. porosus is known from Southeast Asia
Southeast Asia
Southeast Asia, South-East Asia, South East Asia or Southeastern Asia is a subregion of Asia, consisting of the countries that are geographically south of China, east of India, west of New Guinea and north of Australia. The region lies on the intersection of geological plates, with heavy seismic...
.
Description
The smalltail shark is a slender-bodied species with a fairly long, pointed snout. The leading margin of each nostril is enlarged into a narrow, pointed lobe. The large, circular eyes are equipped with nictitating membraneNictitating membrane
The nictitating membrane is a transparent or translucent third eyelid present in some animals that can be drawn across the eye for protection and to moisten it while maintaining visibility. Some reptiles, birds, and sharks have a full nictitating membrane; in many mammals, there is a small...
s, and behind them are a series of prominent pores. The mouth bears short furrows at the corners and contains 13–15 tooth rows on either side of both jaws (usually 14 upper and 13 lower). The upper teeth are tall and triangular with strong serrations, becoming increasing oblique towards the sides. The lower teeth are comparatively narrower and more upright, with finer serrations. The five pairs of gill slit
Gill slit
Gill slits are individual openings to gills, i.e., multiple gill arches, which lack a single outer cover. Such gills are characteristic of Cartilaginous fish such as sharks, rays, sawfish, and guitarfish. Most of these have five pairs, but a few species have 6 or 7 pairs...
s are short.
The small pectoral fins are falcate (sickle-shaped) with relatively pointed tips. The first dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
is broad, forming nearly an equilateral triangle in adults, with a blunt apex; it originates over the pectoral fin rear tips. The second dorsal fin is small and originates over the midpoint of the anal fin base. There is no ridge between the dorsal fins. The pelvic fins are small with pointed to narrowly rounded tips, and the anal fin has a deep notch in its trailing margin. The asymmetrical caudal fin has a strong lower lobe and a longer upper lobe with a ventral notch near the tip. The dermal denticles are mostly non-overlapping; each has 3–5 horizontal ridges leading to posterior teeth, with the central one the longest. This shark is plain gray to slate above and whitish below, with a faint lighter stripe on the flanks. The pectoral, dorsal, and caudal fins may darken toward the tips. The smalltail shark reaches a maximum known length of 1.5 m (4.9 ft), though 0.9–1.1 m (3–3.6 ft) is typical. Females grow larger than males.
Distribution and habitat
The known range of the smalltail shark extends from the northern Gulf of MexicoGulf of Mexico
The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...
to southern Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
, excluding the Caribbean
Caribbean
The Caribbean is a crescent-shaped group of islands more than 2,000 miles long separating the Gulf of Mexico and the Caribbean Sea, to the west and south, from the Atlantic Ocean, to the east and north...
islands (aside from Trinidad and Tobago
Trinidad and Tobago
Trinidad and Tobago officially the Republic of Trinidad and Tobago is an archipelagic state in the southern Caribbean, lying just off the coast of northeastern Venezuela and south of Grenada in the Lesser Antilles...
). Its center of abundance is along the northern Brazilian coast, off Pará
Pará
Pará is a state in the north of Brazil. It borders the Brazilian states of Amapá, Maranhão, Tocantins, Mato Grosso, Amazonas and Roraima. To the northwest it also borders Guyana and Suriname, and to the northeast it borders the Atlantic Ocean. The capital is Belém.Pará is the most populous state...
and Maranhão
Maranhão
Maranhão is a northeastern state of Brazil. To the north lies the Atlantic Ocean. Maranhão is neighbored by the states of Piauí, Tocantins and Pará. The people of Maranhão have a distinctive accent...
, where it is the most common shark. This species has not been reported east of the Mississippi River
Mississippi River
The Mississippi River is the largest river system in North America. Flowing entirely in the United States, this river rises in western Minnesota and meanders slowly southwards for to the Mississippi River Delta at the Gulf of Mexico. With its many tributaries, the Mississippi's watershed drains...
in the past 50 years, despite historical evidence of a nursery area off Louisiana
Louisiana
Louisiana is a state located in the southern region of the United States of America. Its capital is Baton Rouge and largest city is New Orleans. Louisiana is the only state in the U.S. with political subdivisions termed parishes, which are local governments equivalent to counties...
. The smalltail shark can usually be found close the bottom in inshore waters no deeper than 36 m (118.1 ft). Off northern Brazil, its environment is characterized by tide
Tide
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the moon and the sun and the rotation of the Earth....
s up to 7 m (23 ft) high and reaching 7.5 knots; the salinity
Salinity
Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...
fluctuates between 14 ppt in the rainy season and 34 ppt in the dry season
Dry season
The dry season is a term commonly used when describing the weather in the tropics. The weather in the tropics is dominated by the tropical rain belt, which oscillates from the northern to the southern tropics over the course of the year...
and the temperature ranges from 25 to 32 °C (77 to 89.6 F). It favors estuarine
Estuary
An estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea....
areas with muddy bottoms.
Biology and ecology
The smalltail shark forms large aggregations segregated by sex, with the males generally found deeper than the females. It feeds mainly on bony fishes, including sea catfishAriidae
The Ariidae or ariid catfish are a family of catfish that mainly live in marine waters with many freshwater and brackish water species. They are found worldwide in tropical to warm temperate zones.-Taxonomy:...
, croakers
Sciaenidae
Sciaenidae is a family of fish commonly called drums, croakers, or hardheads for the repetitive throbbing or drumming sounds they make...
, jacks
Carangidae
Carangidae is a family of fish which includes the jacks, pompanos, jack mackerels, and scads.They are marine fish found in the Atlantic, Indian and Pacific Oceans...
, and grunts
Haemulidae
The grunts are a family, Haemulidae, of fishes in the order Perciformes. They are numerous and widespread, with about 150 species in 19 genera, found in tropical fresh, brackish and salt waters around the world...
. Shrimp
Shrimp
Shrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...
, crab
Crab
True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...
s, and squid
Squid
Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...
are secondary food sources, while adults are also capable of taking young sharpnose shark
Rhizoprionodon
Rhizoprionodon is a genus of requiem sharks, family Carcharhinidae, commonly known as sharpnose sharks because of their long, pointed snouts.-Species:* Rhizoprionodon acutus...
s (Rhizoprionodon), hammerhead shark
Hammerhead shark
The hammerhead sharks are a group of sharks in the family Sphyrnidae, so named for the unusual and distinctive structure of their heads, which are flattened and laterally extended into a "hammer" shape called a "cephalofoil". Most hammerhead species are placed in the genus Sphyrna while the...
s (Sphyrna), and stingray
Dasyatis
Dasyatis is a genus of stingray. The members of the genus Neotrygon were formerly included in Dasyatis.-Species:...
s (Dasyatis). Opportunistic in habits, the dietary composition of this shark generally reflects what is most available in its environment; off northern Brazil the most important prey species are the croakers Macrodon ancylodon and Stellifer naso. Juveniles consume a wider variety of prey than adults. In turn, the smalltail shark may potentially be preyed upon by larger sharks.
Like other members of its family, the smalltail shark is viviparous: once the developing embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
s exhaust their supply of yolk, the yolk sac
Yolk sac
The yolk sac is a membranous sac attached to an embryo, providing early nourishment in the form of yolk in bony fishes, sharks, reptiles, birds, and primitive mammals...
develops into a placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...
l connection through which the mother delivers nourishment. Females produce litters of 2–9 (typically 4–6) young every other year; litter size increases with the size of the female. The gestation period
Gestation period
For mammals the gestation period is the time in which a fetus develops, beginning with fertilization and ending at birth. The duration of this period varies between species.-Duration:...
lasts approximately 12 months. Reproduction occurs throughout the year, with a peak in birthing from September to November. There are known nursery areas in shallow, murky waters off northern Brazil and Trinidad, where many bay
Bay
A bay is an area of water mostly surrounded by land. Bays generally have calmer waters than the surrounding sea, due to the surrounding land blocking some waves and often reducing winds. Bays also exist as an inlet in a lake or pond. A large bay may be called a gulf, a sea, a sound, or a bight...
s and estuaries provide shelter and food. The newborns measure 30–33 cm (11.8–13 in) long and grow an average of 7 cm (2.8 in) per year in their first four years of life. Males and females mature sexually
Sexual maturity
Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...
at 70–93 cm (27.6–36.6 in) and 71–85 cm (28–33.5 in) long respectively, corresponding to six years of age for both sexes. The average growth rate slows to 4 cm (1.6 in) per year after maturation. The maximum lifespan is at least 12 years.
Human interactions
Harmless to humans, the smalltail shark is caught incidentallyBycatch
The term “bycatch” is usually used for fish caught unintentionally in a fishery while intending to catch other fish. It may however also indicate untargeted catch in other forms of animal harvesting or collecting...
by gillnet
Gillnet
Gillnetting is a common fishing method used by commercial and artisanal fishermen of all the oceans and in some freshwater and estuary areas. The gillnet also is used by fisheries scientists to monitor fish populations. Because gillnets can be so effective their use is closely monitored and...
and longline fisheries
Fishery
Generally, a fishery is an entity engaged in raising or harvesting fish which is determined by some authority to be a fishery. According to the FAO, a fishery is typically defined in terms of the "people involved, species or type of fish, area of water or seabed, method of fishing, class of boats,...
throughout its range. The meat is sold fresh, frozen, or dried and salted. In addition, the dried fins are exported for use in shark fin soup
Shark fin soup
Shark fin soup is a popular soup item of Chinese cuisine usually served at special occasions such as weddings and banquets, or as a luxury item in Chinese culture. The shark fins provide texture while the taste comes from the other soup ingredients.There is controversy over the practice of shark...
, the liver oil
Shark liver oil
Shark liver oil is obtained from sharks that are caught for food purposes and are living in cold, deep oceans. The liver oil from sharks has been used by fishermen for centuries as a folk remedy for general health...
and cartilage
Shark cartilage
Shark cartilage is a dietary supplement made from the dried and powdered cartilage of a shark; that is, from the tough material that composes a shark's skeleton. Shark cartilage is claimed to combat and/or prevent a variety of illnesses, most notably cancer. It is often marketed under the names...
are used medicinally, and the carcass is processed into fishmeal. No fishery data are available on this species in most of its range, leading it to be listed under Data Deficient
Data Deficient
Data Deficient is a category applied by the IUCN, other agencies, and individuals to a species when the available information is not sufficient for a proper assessment of conservation status to be made...
by the International Union for Conservation of Nature (IUCN). In Trinidad, its abundance makes it the most economically important shark. Off northern Brazil, substantial numbers of smalltail sharks are caught by gillnet fisheries targeting the Serra Spanish mackerel
Serra Spanish mackerel
The ', Scomberomorus brasiliensis, is a species of fish in the family Scombridae. Specimens have been recorded at up to 125 cm in length, and weighing up to 6,710 g. It is found in the western Atlantic, along the Caribbean and Atlantic coasts of Central and South America from Belize to Rio Grande...
(Scomberomorus brasiliensis). In the 1980s this species constituted roughly 43% of the shark and ray catch, but since then its share has declined to around 17%. This apparent decline is thought to have resulted from increasing fishing effort, the large proportion of juveniles captured, and the shark's low reproductive rate. Consequently, the IUCN has assessed the smalltail shark in Brazil as Vulnerable
Vulnerable species
On 30 January 2010, the IUCN Red List of Threatened Species identified 9694 Vulnerable species, subspecies and varieties, stocks and sub-populations.-References:...
, and noted the urgent need for conservation measures given that northern Brazil represents the center of the the species' range. Although the smalltail shark was ostensibly given protection by inclusion on the 2004 Official List of Endangered Animals in Brazil, fishing remains effectively unmanaged.