The
finetooth shark,
Carcharhinus isodon, is a species of
requiem sharkRequiem sharks refers to all members of the family Carcharhinidae: this includes migratory, live-bearing sharks of warm seas such as the tiger shark, the blue shark, the bull shark, and the milk shark. The name comes from the French word for shark, "requin". Family members have the usual...
,
familyIn 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...
Carcharhinidae, found in the western
Atlantic OceanThe Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about 106.4 million square kilometres , it covers approximately one-fifth of the Earth's surface and about one-quarter of its water surface area. The first part of its name refers to the Atlas of Greek...
from
North CarolinaNorth Carolina is a state located on the Atlantic Seaboard in the southeastern United States. The state borders South Carolina and Georgia to the south, Tennessee to the west and Virginia to the north. North Carolina contains 100 counties...
to
BrazilBrazil , officially the Federative Republic of Brazil , is a country in South America. It is the fifth largest country by geographical area, occupying nearly half of South America, the fifth most populous country, and the fourth most populous democracy in the world. Bounded by the Atlantic Ocean...
. It forms large
schoolsIn biology, any group of fish that stay together for social reasons are said to be shoaling , and if, in addition, the group is swimming in the same direction in a coordinated manner, they are said to be schooling . In common usage, the terms are sometimes used rather loosely...
in shallow, coastal waters and
migrateMany types of fish migrate on a regular basis, on time scales ranging from daily to annual, and over distances ranging from a few meters to thousands of kilometers...
s seasonally following warm water. A relatively small, slender-bodied shark, the finetooth shark can be identified by its needle-like teeth, dark blue-gray dorsal coloration, and long
gill slitGill 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. It attains a maximum length of 1.9 m (6.2 ft). The diet of this species consists primarily of small bony fishes, in particular
menhadenMenhaden, also known as mossbunker, bunker and pogy, are forage fish of the genera Brevoortia and Ethmidium, two genera of marine fish in the family Clupeidae.-Description:...
. Like other members of its family, it is viviparous with females giving birth to 2–6 pups in
estuarineAn estuary is a semi-enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries are thus subject to both marine influences, such as tides, waves, and the influx of saline water; and riverine influences, such as flows of...
nursery areas every other year.
Valued for its meat, the finetooth shark forms an important component of the
commercialCommercial fishing is the activity of capturing fish and other seafood for commercial profit, mostly from wild fisheries. It provides a large quantity of food to many countries around the world, but those who practice it as an industry must often pursue fish far into the ocean under adverse...
gillnetGillnetting is a common fishing method used by commercial fishermen of all the oceans and in some freshwater and estuary areas. Because gillnets can be so effective their use is closely monitored and regulated by fisheries management and enforcement agencies. Mesh size, twine strength, as well as...
shark
fisheryGenerally, a fishery is an entity engaged in raising and/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...
operating off the southeastern
United StatesThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
. A population assessment conducted by the U.S.
National Marine Fisheries ServiceThe U.S. National Marine Fisheries Service is a United States federal agency. A division of the National Oceanic and Atmospheric Administration and the Department of Commerce, NMFS is responsible for the stewardship and management of the nation's living marine resources and their habitat within...
(NMFS) in 2002 concluded that although the finetooth shark population in this region has not yet been depleted, fishing is occurring at unsustainable levels and additional conservation measures would be advisable. The finetooth shark is not known to pose a danger to humans, though it snaps vigorously when captured and should be handled with caution.
Taxonomy and phylogeny
The finetooth shark was originally described as
Carcharias (Aprion) isodon by French zoologist
Achille ValenciennesAchille Valenciennes was a French zoologist.Valenciennes was born in Paris, and studied under Georges Cuvier. Valenciennes' study of parasitic worms in humans made an important contribution to the study of parasitology...
, in
MüllerJohannes Müller, Johann Müller or Hans Müller may refer to:* Johannes Müller von Königsberg , aka Regiomontanus, German mathematician, astronomer...
and Henle's 1839
Systematische Beschreibung der Plagiostomen. The type specimen is a 65 cm (26 in) juvenile male, possibly caught off the
U.S. stateA U.S. state is any one of 50 federated states of the United States of America that share sovereignty with the federal government . Because of this shared sovereignty, an American is a citizen both of the federal entity and of his or her state of domicile...
of
New YorkNew York is a state in the Mid-Atlantic and Northeastern regions of the United States and is the nation's third most populous. The state is bordered by New Jersey and Pennsylvania to the south, and Connecticut, Massachusetts and Vermont to the east...
. This species was later moved to the genus
Carcharhinus. The specific epithet
isodon means "equal teeth" in Greek, and refers to the similar number of teeth in the upper and lower jaws. This species may also be referred to as the eventooth shark, smoothtooth shark, or night shark (usually used for
C. signatusThe night shark, Carcharhinus signatus, is a species of requiem shark, family Carcharhinidae, found in the temperate and tropical waters of the Atlantic Ocean...
).
As is the case for most
Carcharhinus species, attempts to analyze the finetooth shark's phylogenetic relationships have yielded variable results. In 1988,
Leonard CompagnoLeonard J. V. 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, Stanford...
grouped this species with the
spinner sharkThe spinner shark, Carcharhinus brevipinna, is a species of requiem shark, family Carcharhinidae, named for the spinning leaps it makes as a part of its feeding strategy. This species occurs in tropical and warm temperate waters worldwide, except for in the eastern Pacific Ocean...
(
C. brevipinna),
blacktip sharkThe blacktip shark, Carcharhinus limbatus, is a species of requiem shark, family Carcharhinidae. It is common to coastal tropical and subtropical waters around the world, including brackish habitats. Genetic analyses have revealed substantial variation within this species, with populations from the...
(
C. limbatus),
graceful sharkThe graceful shark, Carcharhinus amblyrhynchoides, is a requiem shark of the family Carcharhinidae, found in the Indo-Pacific oceans between latitudes 21° N and 25° S, from the surface to 50 m. Its length is up to about 1.6 m....
(
C. amblyrhynchoides), and the
smooth tooth blacktip sharkThe smooth tooth blacktip shark, Carcharhinus leiodon, is a species of requiem shark, family Carcharhinidae, known only from a single immature male caught in the Gulf of Aden by W. Hein in 1902. The locality of the holotype was given as "Gischin", which may be an old spelling or misspelling of...
(
C. leiodon), on the basis of
morphologicalIn biology morphology is the form, structure and configuration of an organism.This includes aspects of the outward appearance as well as the form and structure of the internal parts like bones and organs...
characters. Gavin Naylor's 1992
allozymeVariant forms of an enzyme that are not coded for by different alleles at the same locus are called allozymes as opposed to isozymes which are enzymes that perform the same function, but which are coded for by genes located at different loci....
analysis found that the finetooth shark is the second-most
basalIn phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
member of the genus next to the
blacknose sharkThe blacknose shark, Carcharhinus acronotus, 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...
(
C. acronotus). Mine Dosay-Akbulut's 2008 study, based on
ribosomal DNARibosomal DNA are sequences encoding ribosomal RNA. These sequences regulate amplification and transcription initiation and contain transcribed and nontranscribed spacer segments. The nucleolus consists of expanded chromosomal loops that carry transcriptional units encoding ribosomal RNA. These...
, suggested that the closest relative of the finetooth shark is the
smalltail sharkThe smalltail shark, Carcharhinus porosus, is a requiem shark of the family Carcharhinidae, found in the western Atlantic Ocean between latitudes 32° N and 36° S. Its length is up to about 1.5 m....
(
C. porosus), and that the two species form a
cladeA clade is a term used in modern alpha taxonomy, the scientific classification of living and fossil organisms, to describe a monophyletic group, defined as a group consisting of a single common ancestor and all its descendants.[The term "monophyletic group" is used in this article...]
apart from other
Carcharhinus species.
Distribution and habitat
The finetooth shark is found in the western Atlantic from
North CarolinaNorth Carolina is a state located on the Atlantic Seaboard in the southeastern United States. The state borders South Carolina and Georgia to the south, Tennessee to the west and Virginia to the north. North Carolina contains 100 counties...
south to the
Gulf of MexicoThe Gulf of Mexico is the ninth largest body of water in the world. Considered a smaller part of the Atlantic Ocean, it is an 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...
, and is rare in the
Caribbean SeaThe Caribbean Sea is a sea of the Atlantic Ocean situated in the tropics of the Western hemisphere, bounded to the south and west by the American landmass, with the North Atlantic Ocean proper to the northeast and the Gulf of Mexico to the northwest...
. It also occurs off southern
BrazilBrazil , officially the Federative Republic of Brazil , is a country in South America. It is the fifth largest country by geographical area, occupying nearly half of South America, the fifth most populous country, and the fourth most populous democracy in the world. Bounded by the Atlantic Ocean...
and on rare occasions it strays as far north as New York. There are old records of this species in the eastern Atlantic off
SenegalSenegal , officially the Republic of Senegal, is a country south of the Sénégal River in western Africa. Senegal is bounded by the Atlantic Ocean to the west, Mauritania to the north, Mali to the east, and Guinea and Guinea-Bissau to the south, and it also encircles The Gambia on its three sides,...
and
Guinea-BissauThe Republic of Guinea-Bissau is a country in western Africa, and one of the smallest states in continental Africa. It is bordered by Senegal to the north, and Guinea to the south and east, with the Atlantic Ocean to its west....
, but these may represent misidentifications of
spinner sharkThe spinner shark, Carcharhinus brevipinna, is a species of requiem shark, family Carcharhinidae, named for the spinning leaps it makes as a part of its feeding strategy. This species occurs in tropical and warm temperate waters worldwide, except for in the eastern Pacific Ocean...
s (
C. brevipinna).
An inhabitant of coastal waters, the finetooth shark occurs no deeper than 10 m (30 ft) deep in the summer and 20 m (70 ft) deep in the winter. Historically it was known to venture into rivers in the
Gulf Coastal PlainThe Gulf Coastal Plain extends from the Florida Parishes of Louisiana over most of Mississippi, some of western Tennessee and Kentucky, the southwestern 2/3 of Alabama, and the western Florida Panhandle and Southern Texas. Its southern boundary is the Gulf of Mexico and its western boundary the...
of
TexasTexas is the second-largest U.S. state in both area and population, and the largest state in the contiguous United States.The name had wide usage among native Americans, meaning "friends" or "allies"...
, though most of paths into this area are now blocked by
damA dam is a barrier that impounds water or underground streams. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees are used to manage or prevent water flow into specific land regions...
s. The northwestern Atlantic population of this species is strongly
migratoryMany types of fish migrate on a regular basis, on time scales ranging from daily to annual, and over distances ranging from a few meters to thousands of kilometers...
: juveniles, followed by adults, arrive off
South CarolinaSouth Carolina is a U.S. state that borders Georgia to the south and North Carolina to the north. Originally part of the Province of Carolina, the Province of South Carolina was one of the 13 colonies that declared independence from the British Crown during the American Revolution. The colony was...
from late March to early May, when the water temperature rises above 20° C (68° F). They remain until September to mid-October, at which point the water temperature drops and they move south to
FloridaFlorida is a state located in the southeastern region of the United States, bordering Alabama to the northwest and Georgia to the north. It was the 27th state admitted to the United States...
. The movements of the Gulf of Mexico population are unknown.
Description
The body of the finetooth shark is slender and streamlined. The snout is long and pointed, with the nares preceded by short, broadly triangular flaps of skin. The eyes are large and round, with
nictitating membraneThe 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 the eye while also keeping visibility...
s (protective third
eyelidAn eyelid is a thin fold of skin that covers and protects an eye. With the exception of the prepuce and the labia minora, it has the thinnest skin of the whole body. The levator palpebrae superioris muscle retracts the eyelid to "open" the eye. This can be either voluntarily or involuntarily...
s). The mouth is broad with well-defined furrows at the corners. There are 12–15 tooth rows on either side of the upper jaw and 13–14 tooth rows on either side of the lower jaw. Each tooth is small and needle-like, with a narrow central cusp and smooth to minutely serrated edges. The five pairs of gill slits are long, measuring about half the length of the
dorsal finA dorsal fin is a fin located on the backs of some fish, whales, dolphins, and porpoises, as well as the ichthyosaurs. Depending on the species, an animal can have up to three of them. Its main purpose is to stabilize the animal against rolling and assist in sudden turns...
base.
The first dorsal fin is high and triangular with a pointed apex, originating forward of the free rear tips of the pectoral fins. The second dorsal fin is relatively large and originates over the anal fin. There is no ridge running between the dorsal fins. The pectoral fins are small and falcate (sickle-shaped), with pointed tips. The
dermal denticleDenticles are body surface structures found on some fish and insects. Literally, the term means "small tooth" and refer to the structures' shape....
s are small and overlapping, each bearing three horizontal ridges leading to marginal teeth. Living finetooth sharks are a distinctive dark bluish-gray above and white below, with a faint pale stripe on the flanks and no prominent fin markings. Some individuals from Florida have green eyes. Males average 1.6 m (5.2 ft) in length and females 1.7 m (5.4 ft); the largest shark on record was 1.9 m (6.2 ft) long.
Biology and ecology
Despite being common in the northwestern Atlantic and the Gulf of Mexico, the finetooth shark is one of the least-known requiem sharks off the southeastern United States. Both adults and juveniles form large
schoolsIn biology, any group of fish that stay together for social reasons are said to be shoaling , and if, in addition, the group is swimming in the same direction in a coordinated manner, they are said to be schooling . In common usage, the terms are sometimes used rather loosely...
. This energetic, fast-moving predator feeds mainly on small bony fishes, often entering the
surf zoneAs ocean surface waves come closer to shore they break, forming the foamy, bubbly surface we call surf. The region of breaking waves defines the surf zone. After breaking in the surf zone, the waves continue to move in, and they run up onto the sloping front of the beach, forming an uprush of...
during the day to hunt. The most important prey of this species off the U.S. East Coast is the
Atlantic menhadenThe Atlantic menhaden is a silvery, highly compressed fish in the herring family, Clupeidae. A filter feeder, it lives on plankton caught in midwater. Adult fish can filter up to four gallons of water a minute; and they play an important role in clarifying ocean water...
(
Brevoortia tyrannus), which the sharks swallow whole after removing the head. Other known food items include
spotThe spot croaker or simply spot is a small saltwater fish. The species inhabits estuary and coastal waters from Massachusetts to Texas, and derives its name from the prominent dark spot behind each gill. It is the only species in the genus Leiostomus...
,
mackerelMackerel is a common name applied to a number of different species of fish, mostly, but not exclusively, from the family Scombridae. They may be found in all tropical and temperate seas. Most live offshore in the oceanic environment but a few, like the Spanish mackerel , enter bays and can be...
,
mulletThe mullets or grey mullets are a family of ray-finned fish found worldwide in coastal temperate and tropical waters, and in some species in fresh water also. Mullets have served as an important source of food in Mediterranean Europe since Roman times...
,
shrimpShrimp 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...
, and in one case a juvenile
Atlantic sharpnose sharkThe Atlantic sharpnose shark, Rhizoprionodon terraenovae, is a requiem shark of the family Carcharhinidae, found in the subtropical waters of the western Atlantic Ocean between latitudes 43° N and 25° S, at depths of from 10 to 280 m. Its length is up to about 1.1 m....
(
Rhizoprionodon terraenovae), which may have been
scavengedScavenging, or necrophagy, is a carnivorous feeding behaviour in which a predator consumes corpses or carrion that were not killed to be eaten by the predator or others of its species. Scavengers play an important role in the ecosystem by contributing to the decomposition of dead animal remains...
from the bycatch discard of a shrimp
trawlerA fishing trawler is a commercial fishing vessel designed to operate fishing trawls. Trawling is a method of fishing that involves actively pulling a trawl through the water behind one or more trawlers. Trawls are fishing nets that are dragged along the bottom of the sea or in midwater at a...
. The finetooth shark may be preyed upon by larger sharks.
Life history
Like other requiem sharks, the finetooth shark is viviparous, with the females bearing litters of 2–6 pups every other year. Courtship involves the male biting the female to hold her for copulation. The
semenSemen is an organic fluid, also known as seminal fluid, that usually contains spermatozoa. It is secreted by the gonads and other sexual organs of male or hermaphroditic animals and can fertilize female ova...
exuded by the male congeals into a large spongy mass called a "spermatozeugma", in which the individual spermatozoa are embedded, inside the female's
uterusThe uterus is a major female hormone-responsive reproductive sex organ of most mammals, including humans. It is within the uterus that the fetus develops during gestation. The term uterus is used consistently within the medical and related professions; the Germanic term, womb is more common in...
; the function of this short-lived structure is unknown. Mating occurs from early May to early June, with the young born the following year at around the same time after a
gestation periodFor mammals the gestation period is the time in which a fetus develops, beginning with fertilization and ending at the embryo stage. The duration of this period varies between species.-Duration:...
of about a year. The
embryoAn 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
yolk sacThe 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...
for the first fifteen weeks, after which the depleted yolk sac develops into a
placentaThe placenta is an organ unique to mammals that connects the developing fetus to the uterine wall. The placenta supplies the fetus with oxygen and food, and allows fetal waste to be disposed of via the maternal kidneys...
l connection through which the mother provides nourishment. Females make use of shallow estuarine nursery areas, such as Bull's Bay, South Carolina, to give birth. The newborns measure 48–64 cm (19–25 in) long Estuaries are critical habitat for newborns and juveniles.
Females grow at a slower rate and to a larger ultimate size than males. The life history characteristics of this species differs between the northwestern Atlantic and Gulf of Mexico populations, with sharks in the northwestern Atlantic being larger and slower to mature. The northwestern Atlantic males mature at a fork length (length from snout tip to tail fin fork) of 99 cm (39 in) and females at 102 cm (40 in), corresponding to ages of 5 and 6 years respectively. The Gulf of Mexico males mature at a fork length of 94 cm (37 in) and females at 99 cm (39 in), corresponding to ages of 4 and 5 years respectively. The maximum lifespan has been estimated to be at least 9 years for males and 14 years for females.
Human interactions
The finetooth shark has never been implicated in an attack on humans. However, when caught this shark will thrash and snap at anything within range, and people have been bitten attempting to handle it. Finetooth sharks are utilized for human consumption fresh or dried and salted. Other than off the southeastern United States, this species is of little commercial importance: it is small and occurs in water too shallow for most commercial and recreational fisheries, and is too fast-swimming to be caught by shrimp trawlers. Small numbers are taken incidentally by floating longlines and on hook-and-line.
Substantial numbers of finetooth sharks are caught in drift
gillnetGillnetting is a common fishing method used by commercial fishermen of all the oceans and in some freshwater and estuary areas. Because gillnets can be so effective their use is closely monitored and regulated by fisheries management and enforcement agencies. Mesh size, twine strength, as well as...
s operated by the shark fishery off southeastern United States, which peaked in 1999 at about landed. This fishery is managed under the U.S.
National Marine Fisheries ServiceThe U.S. National Marine Fisheries Service is a United States federal agency. A division of the National Oceanic and Atmospheric Administration and the Department of Commerce, NMFS is responsible for the stewardship and management of the nation's living marine resources and their habitat within...
(NMFS) 1993 Fisheries Management Plan (FMP) for Atlantic and Gulf of Mexico sharks. The finetooth shark is classified as a "Small Coastal Shark" (SCS) for the purposes of commercial quotas and recreational bag limits. In 2002, the NMFS determined that the finetooth shark population in United States waters was not yet
overfishedOverfishing occurs when fishing activities reduce fish stocks below an acceptable level. This can occur in any body of water from a pond to the oceans....
, but also that the catch rate had exceeded sustainable levels and additional conservation measures were needed. The conservation status of this species has not been evaluated by the International Union for Conservation of Nature (IUCN).