Long-tailed thresher shark
Encyclopedia
The common thresher is the largest species of thresher shark
, family Alopiidae, attaining a maximum known length of 6 m (19.7 ft). Almost half of that length consists of the elongated upper lobe of its caudal fin. This structure, the source for many a fanciful tale about this shark through history, is employed by the thresher in a whip
-like fashion to deliver incapacitating blows to its prey. The common thresher resembles (and has often been confused with) the pelagic thresher
(A. pelagicus), which also has a streamlined body, short pointed snout, and modestly sized eyes. It can be distinguished from the latter species by the white of its belly extending in a band over the bases of its pectoral fins.
Common threshers inhabit both coastal and pelagic
waters in tropical and temperate
climate
s worldwide, from the surface to a depth of 550 m (1,804.5 ft). These sharks are seasonally migratory
and follow warm water to higher latitude
s in summer. The common thresher is a fast, strong swimmer that has been known to leap clear of the water. It possesses physiological adaptation
s that allow it to maintain an internal body temperature higher than that of the surrounding sea water. This species feeds primarily on small, schooling
forage fish
es. In common with other mackerel sharks
, the common thresher is ovoviviparous with the unborn embryo
s being sustained by undeveloped eggs ovulated
by their mother. Females give birth to litters of 2–7 pups following a gestation period
of nine months.
Although large, the common thresher has relatively small teeth and a timid disposition, posing minimal danger to humans. They are highly valued by commercial fishers
for their meat, fins
, hide, and liver oil
; large numbers are taken by longline and gillnet
fisheries throughout its range
. This shark is also esteemed by recreational big game anglers
for the exceptional fight it offers on hook-and-line. The common thresher has a low rate of reproduction and cannot sustain heavy fishing pressure for long, a case in point being the rapid collapse of the thresher fishery off the U.S. state
of California
in the 1980s. With commercial exploitation increasing in many parts of the world, the International Union for Conservation of Nature (IUCN) has assessed this species as Vulnerable
.
Pierre Joseph Bonnaterre
as Squalus vulpinus, in the 1788 Tableau encyclopédique et méthodique des trois règnes de la nature
. This species was later moved to the genus Alopias. The specific epithet is from the Latin
vulpes, meaning "fox
", and some sources give the scientific name incorrectly as Alopias vulpes. Other common name
s include Atlantic thresher, fox shark, grayfish, green thresher, sea fox, slasher, swiveltail, thintail thresher, thrasher/thresher, thresher shark, and whip-tailed shark.
Morphologically
, the common thresher and the pelagic thresher
(A. pelagicus) are united in having thin tails, smaller eyes, and no lateral grooves on the head. However, an allozyme
analysis conducted by Blaise Eitner in 1995 found that the pelagic thresher is most closely related to the bigeye thresher
(A. superciliosus), and that common thresher forms a separate clade
on its own. Its closest relative in the family
may be an unrecognized fourth thresher species from off southern California
.
it occurs from Newfoundland
to Cuba
, though is rare north of New England
, and from Brazil
to Argentina
. In the eastern Atlantic, it is found from Norway
and the British Isles
to Ghana
and the Ivory Coast, including the Mediterranean Sea
. In the Indo-Pacific
region, it has been reported from South Africa
, Tanzania
, Somalia
, Maldives
, Chagos Archipelago
, Gulf of Aden
, Pakistan
, India
, Sri Lanka
, Sumatra
, Japan
, Republic of Korea, Australia
, New Zealand
, and New Caledonia
. It occurs off the Society Islands
, Fanning Island, and Hawaiian Islands
in the central Pacific, and from British Columbia
to Baja California
and Panama
to Chile
in the eastern Pacific.
The common thresher is migratory
, moving to higher latitude
s following warm water masses. In the eastern Pacific, males travel further than females, reaching as far as Vancouver Island
in the late summer
and early fall. Juveniles tend to remain in warm nursery areas. There appear to be separate populations with different life history characteristics in the eastern Pacific and western Indian Ocean and possibly elsewhere; this species is not known to make transoceanic movements. In the northwestern Indian Ocean
, male
s and female
s segregate by location and depth during the pupping season from January to May. Analysis of mitochondrial DNA
has revealed substantial regional genetic variation within common threshers in all three oceans. This reaffirms the idea that, despite being high mobile, sharks from different areas rarely interbreed.
al waters and the open ocean. They tend to be most abundant in proximity to land, particularly the juvenile
s which frequent near-coastal habitats such as bays. Most individuals are encountered near the surface, but this species has been recorded to at least a depth of 550 m (1,804.5 ft).
Common threshers are the largest species of thresher shark; individuals 2–5 m (6.6–16.4 ft) long and weighing 230 kg (507.1 lb) are not uncommon, and they can grow upwards of 6 m (19.7 ft) long. The heaviest common thresher on record is a 4.8 m (15.7 ft) female weighing 510 kg (1,124.4 lb), caught in the English Channel
on November 22, 2007. The body is solidly built and torpedo
-shaped, with very long, falcate (sickle-shaped) pectoral fins. The first dorsal
and pelvic fins are large, while the second dorsal and anal fins are tiny. The distinctive upper caudal fin lobe is slender, bearing a moderate ventral notch near the tip, and can be nearly as long as the rest of the body.
The head is fairly short and broad, with a strongly convex dorsal profile and a pointed conical snout. The eyes are of medium size. The mouth is relatively small, with short furrows at the corners. The teeth are small, smooth-edged, and knife-like, lacking the small lateral cusplets of the pelagic thresher. There are 20 tooth rows on either side of the upper jaw and 21 tooth rows on either side of the lower jaw. The five pairs of gill slit
s are short, with the last two placed over the pectoral fin bases. The dermal denticles are minute and overlapping. The common thresher is dark brown to gray to almost black above, with a metallic luster. Dark spots are present around the pelvic fins and the caudal peduncle, and there may be a white spot at the tip of the pectoral fins. The underside is white, extending in a characteristic patch over the pectoral fin bases to the "cheeks". This pattern stands in contrast to that of the similar pelagic thresher, whose dark dorsal coloration extends uninterrupted to and over the pectoral fins.
, the common thresher has a strip of aerobic red muscle
along its flank that is able to contract powerfully and efficiently for long periods of time. In addition, they have slow-oxidative muscle
s centrally located within their bodies and a blood vessel
countercurrent exchange
system called the rete mirabile
("wonderful net"), allowing them to generate and retain body heat
. The temperature inside the red muscles of a common thresher averages 2°C (3.6°F) above that of the ambient seawater
, though there is significant individual variation. Unlike the pelagic and bigeye threshers, the common thresher lacks an orbital
rete mirabile to protect its eyes and brain from temperature changes.
Immature common threshers fall prey to larger shark
s. Aside from observations of killer whales feeding on common threshers off New Zealand
, adults have no known natural predators. Known parasites of the common thresher include nine species of copepod
s in the genus Nemesis, which attach themselves to the sharks' gill filament
s, damaging tissue
and hindering respiration
. Other parasites include the protozoan Giardia intestinalis, the digenea
n Campula oblonga (not usual host), the tapeworms Paraorygmatobothrium exiguum and Sphyriocephalus tergetinus, and the copepod Kroeyerina benzorum.
Some 97% of the common thresher's diet is composed of bony fishes, mostly small schooling
forage fish
such as mackerel
, bluefish
, herring
, needlefish
, and lanternfish
. Before striking, the sharks compact schools of prey by swimming around them and splashing the water with its tail, often in pairs or small groups. Threshers are also known to take large, solitary fishes such as lancetfish
, as well as squid
and other pelagic invertebrate
s. Off California, common threshers feed mostly on the northern anchovy (Engraulis mordax), with Pacific hake (Merluccius productus), Pacific sardine (Sardinops sagax), Pacific mackerel (Scomber japonicus), market squid (Loligo opalescens), and pelagic red crab
(Pleuroncodes planipes) also being important food items. The sharks concentrate on a few prey species during cold water years, but become less discriminating during less productive, warmer El Niño periods.
There are numerous accounts of common threshers using the long upper lobes of their tail fins to stun prey, and they are often snagged on longlines by their tails after presumably striking at the bait. In July 1914, shark-watcher Russell J. Coles reported seeing a thresher shark use its tail to flip prey fish into its mouth, and that one fish that missed was thrown a "considerable distance". On April 14, 1923, noted oceanographer W.E. Allen observed a 2 m (6.6 ft) thresher shark pursuing a California smelt (Atherinopsis californiensis) off a pier
at the Scripps Institution of Oceanography
. The shark overtook the small fish and swung its tail above the water like a "coachwhip
" with "confusing speed", severely injuring its target. In the winter of 1865, Irish
ichthyologist Harry Blake-Knox claimed to have seen a thresher shark in Dublin Bay
use its tail to strike a wounded loon
(probably a great northern diver
, Gavia immer), which it then swallowed. Blake-Knox's account was subsequently disputed by other authorities, who asserted that the thresher's tail is not rigid or muscular enough to effect such a blow.
Like other thresher sharks, common threshers are ovoviviparous. They give birth to litters of two to four (rarely six) pups in the eastern Pacific, and three to seven pups in the eastern Atlantic. They are believed to reproduce throughout their range; one known nursery area is the Southern California Bight
. Breeding
occurs in the summer, usually July or August, and parturition occurs from March to June following a gestation period
of nine months. The developing embryo
s are oophagous
, feeding on eggs
ovulated
by the mother. The teeth of small embryos are peg-like and non-functional, being covered by a sheath of soft tissues. As the embryos mature, their series of teeth become progressively more like those of adults in shape, though they remain depressed and hidden until shortly before birth.
Newborn pups usually measure 114–160 cm (3.7–5.2 ft) long and weigh 5–6 kg (11–13.2 lb), depending on the size of the mother. The juveniles grow about 50 cm (1.6 ft) a year while adults grow about 10 cm (0.328083989501312 ft) a year. The size at maturation appears to vary between populations. In the eastern North Pacific males mature at 3.3 m (10.8 ft) and five years old, and females at around 2.6–4.5 m (8.5–14.8 ft) and seven years old. They are known to live to at least 15 years of age and their maximum lifespan has been estimated to be 45–50 years.
s, though they should be treated with respect as their powerful tails are easily capable of breaking bones. Most divers report that they are shy and difficult to approach underwater. The International Shark Attack File
lists a single provoked attack by the thresher shark and four attacks on boat
s, which were probably incidental from individuals fighting capture. There is an unsubstantiated report of a common thresher acting aggressively towards a spearfisherman off New Zealand
.
Famed big-game angler Frank Mundus
, in his book Sportsfishing for Sharks, recounted a tale in which a longline fisherman off the Carolinas leaned over the side of his boat to examine something large that he had hooked, and was decapitated
by the caudal fin of a thresher shark estimated to be 5 m (16.4 ft) long. The head supposedly fell into the water and was never recovered. This account is considered highly improbable by most authors.
The common thresher is widely caught by offshore longline and pelagic gillnet
fisheries, especially in the northwestern Indian Ocean, the western, central, and eastern Pacific, and the North Atlantic. Participating countries include the former USSR, Japan
, Taiwan
, Spain
, the United States
, Brazil
, Uruguay
, and Mexico
. The meat
is highly prized for human consumption cooked, dried and salted
, or smoked. In addition, their skin
is made into leather
, their liver oil
is processed for vitamin
s, and their fins are used for shark fin soup
. The United Nations
Food and Agricultural Organization (FAO) reported a worldwide common thresher take of 411 metric tons in 2006.
In the United States
, a drift gillnet fishery for the common thresher developed in southern California in 1977, beginning with 10 vessels experimenting with a larger-sized mesh. Within two years the fleet had increased to 40 vessels, and the fishery peaked in 1982 when 228 vessels landed 1,091 metric tons. The common thresher population rapidly collapsed from overfishing
, with landings decreasing to less than 300 metric tons a year by the late 1980s and larger size classes disappearing from the population. Common threshers are still taken commercially in the United States, with about 85% coming from the Pacific and 15% from the Atlantic. The largest catches remain from the California-Oregon gillnet fishery, which had shifted its focus to the more valuable swordfish
(Xiphius gladius) but still take threshers as bycatch
. Small numbers of Pacific threshers are also taken by harpoon
s, small-mesh driftnets, and longlines. In the Atlantic, threshers are primarily taken on longlines meant for swordfish and tuna
.
(Isurus oxyrhinchus), and are ranked as game fish
by the International Game Fish Association
(IGFA). They are pursued by anglers using rod and reel
off California, South Africa, and elsewhere. Frank Mundus has called thresher sharks "exceedingly stubborn" and "pound for pound, a harder fish to whip" than the mako. Fishing for the common thresher is similar to that for the mako; the recommended equipment is a 24 kg (52.9 lb) rod and a big-game reel holding at least 365 m (400 yd) of 24 kg (52.9 lb) line. The ideal method is trolling with baitfish, either deep or allowing it to drift.
All three thresher shark species were reassessed from Data Deficient
to Vulnerable
by the International Union for Conservation of Nature (IUCN) in 2007. The rapid collapse of the Californian subpopulation (over 50% within three generations) prompted concerns regarding the species' susceptibility to overfishing in other areas, where fishery data is seldom reported and aspects of life history and population structure are little-known. In addition to continued fishing pressure, common threshers are also taken as bycatch
in other gear such as bottom trawls and fish traps, and are considered a nuisance by mackerel fishers as they become entangled in the nets.
The United States manages common thresher fisheries via regulations such as commercial quotas and trip limits, and recreational minimum sizes and retention limits. Shark finning
is illegal under U.S. federal law. The Atlantic common thresher fishery is regulated by the National Marine Fisheries Service
(NMFS) Highly Migratory Species Management Division through the 2006 Consolidated Atlantic Highly Migratory Species (HMS) Fishery Management Plan (FMP), and the Pacific common thresher fishery is regulated by the Pacific Fishery Management Council through the Fishery Management Plan (FMP) for U.S. West Coast Fisheries for Highly Migratory Species (HMS). In the 1990s, after the depletion of common thresher stocks by the California gillnet fishery, the fleet was limited to 70 boats and restrictions were placed on season, operation range, and landings. There is evidence that the California subpopulation is recovering, and the potential population growth rate has been estimated to be 4–7% per year.
(384–322 BCE) wrote some of the earliest observations about the common thresher. In his Historia Animalia, he claimed that hooked threshers had a propensity for freeing themselves by biting through fishing line
s, and that they protected their young by swallowing them. These "clever" behaviors, which have not been borne out by science, led the ancient Greeks to call it alopex (meaning "fox"), on which its modern scientific name is based.
An oft-repeated myth about the common thresher is that they cooperate with swordfish to attack whale
s. In one version of events, the thresher shark circles the whale and distracts it by beating the sea to a froth with its tail, thereby allowing the swordfish to impale it in a vulnerable spot with its rostrum
. In an alternate account, the swordfish positions itself beneath the whale, while the thresher leaps out of the water and lands on top of the whale, hammering it onto the swordfish's rostrum. Yet other authors describe the thresher "cutting huge gashes" in the side of the whale with its tail. Neither threshers nor swordfish however are known to feed on whales or indeed possess the dentition
to do so. The story may have arisen from mariners mistaking the tall dorsal fins of killer whales, which do attack large cetaceans, for thresher shark tails. Swordfish bills have also been found embedded in blue
and fin whale
s (likely accidents due to the fast-moving fish's inertia
), and thresher sharks do exhibit some of the aforementioned behaviors independent of whales.
Thresher shark
Thresher sharks are large lamniform sharks of the family Alopiidae. Found in all temperate and tropical oceans of the world, the family contains three species all within the genus Alopias.-Taxonomy:...
, family Alopiidae, attaining a maximum known length of 6 m (19.7 ft). Almost half of that length consists of the elongated upper lobe of its caudal fin. This structure, the source for many a fanciful tale about this shark through history, is employed by the thresher in a whip
Whip
A whip is a tool traditionally used by humans to exert control over animals or other people, through pain compliance or fear of pain, although in some activities whips can be used without use of pain, such as an additional pressure aid in dressage...
-like fashion to deliver incapacitating blows to its prey. The common thresher resembles (and has often been confused with) the pelagic thresher
Pelagic thresher
The pelagic thresher is a species of thresher shark, family Alopiidae; this group of sharks are characterized by the greatly elongated upper lobes of their caudal fins. The pelagic thresher occurs in the tropical and subtropical waters of the Indian and Pacific Oceans, usually far from shore but...
(A. pelagicus), which also has a streamlined body, short pointed snout, and modestly sized eyes. It can be distinguished from the latter species by the white of its belly extending in a band over the bases of its pectoral fins.
Common threshers inhabit both coastal and pelagic
Pelagic zone
Any water in a sea or lake that is not close to the bottom or near to the shore can be said to be in the pelagic zone. The word pelagic comes from the Greek πέλαγος or pélagos, which means "open sea". The pelagic zone can be thought of in terms of an imaginary cylinder or water column that goes...
waters in tropical and temperate
Temperate
In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold...
climate
Climate
Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elemental measurements in a given region over long periods...
s worldwide, from the surface to a depth of 550 m (1,804.5 ft). These sharks are seasonally migratory
Fish migration
Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousands of kilometres...
and follow warm water to higher latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...
s in summer. The common thresher is a fast, strong swimmer that has been known to leap clear of the water. It possesses physiological adaptation
Adaptation
An adaptation in biology is a trait with a current functional role in the life history of an organism that is maintained and evolved by means of natural selection. An adaptation refers to both the current state of being adapted and to the dynamic evolutionary process that leads to the adaptation....
s that allow it to maintain an internal body temperature higher than that of the surrounding sea water. This species feeds primarily on small, schooling
Shoaling and schooling
In 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...
forage fish
Forage fish
Forage fish, also called prey fish or bait fish, are small fish which are preyed on by larger predators for food. Predators include other larger fish, seabirds and marine mammals. Typical ocean forage fish feed near the base of the food chain on plankton, often by filter feeding...
es. In common with other mackerel sharks
Lamniformes
Lamniformes is an order of sharks commonly known as mackerel sharks . It includes some of the most familiar species of sharks, such as the great white shark, as well as more unusual representatives, such as the goblin shark and the megamouth shark.Members of the order are distinguished by...
, the common thresher is ovoviviparous with the unborn 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 being sustained by undeveloped eggs ovulated
Ovulation
Ovulation is the process in a female's menstrual cycle by which a mature ovarian follicle ruptures and discharges an ovum . Ovulation also occurs in the estrous cycle of other female mammals, which differs in many fundamental ways from the menstrual cycle...
by their mother. Females give birth to litters of 2–7 pups following a 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:...
of nine months.
Although large, the common thresher has relatively small teeth and a timid disposition, posing minimal danger to humans. They are highly valued by commercial fishers
Commercial fishing
Commercial fishing is the activity of catching 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 conditions...
for their 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...
, hide, and 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...
; large numbers are taken by longline and 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...
fisheries throughout its range
Range (biology)
In biology, the range or distribution of a species is the geographical area within which that species can be found. Within that range, dispersion is variation in local density.The term is often qualified:...
. This shark is also esteemed by recreational big game anglers
Recreational fishing
Recreational fishing, also called sport fishing, is fishing for pleasure or competition. It can be contrasted with commercial fishing, which is fishing for profit, or subsistence fishing, which is fishing for survival....
for the exceptional fight it offers on hook-and-line. The common thresher has a low rate of reproduction and cannot sustain heavy fishing pressure for long, a case in point being the rapid collapse of the thresher fishery off the U.S. state
U.S. state
A U.S. state is any one of the 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. Four states use the official title of...
of California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
in the 1980s. With commercial exploitation increasing in many parts of the world, the International Union for Conservation of Nature (IUCN) has assessed this species 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:...
.
Taxonomy and phylogeny
The common thresher was first described by French naturalistNaturalist
Naturalist may refer to:* Practitioner of natural history* Conservationist* Advocate of naturalism * Naturalist , autobiography-See also:* The American Naturalist, periodical* Naturalism...
Pierre Joseph Bonnaterre
Pierre Joseph Bonnaterre
Abbé Pierre Joseph Bonnaterre was a French naturalist who contributed sections on cetaceans, mammals, birds, reptiles, amphibians, and insects to the Tableau encyclopédique et méthodique...
as Squalus vulpinus, in the 1788 Tableau encyclopédique et méthodique des trois règnes de la nature
Tableau encyclopédique et méthodique
The Tableau encyclopédique et méthodique des trois regnes de la nature was an illustrated encyclopedia of plants, animals and minerals, notable for including the first scientific descriptions of many species, and for its attractive engravings. It was published in Paris by Charles Joseph Panckoucke,...
. This species was later moved to the genus Alopias. The specific epithet is from the Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
vulpes, meaning "fox
Fox
Fox is a common name for many species of omnivorous mammals belonging to the Canidae family. Foxes are small to medium-sized canids , characterized by possessing a long narrow snout, and a bushy tail .Members of about 37 species are referred to as foxes, of which only 12 species actually belong to...
", and some sources give the scientific name incorrectly as Alopias vulpes. Other common name
Common name
A common name of a taxon or organism is a name in general use within a community; it is often contrasted with the scientific name for the same organism...
s include Atlantic thresher, fox shark, grayfish, green thresher, sea fox, slasher, swiveltail, thintail thresher, thrasher/thresher, thresher shark, and whip-tailed shark.
Morphologically
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....
, the common thresher and the pelagic thresher
Pelagic thresher
The pelagic thresher is a species of thresher shark, family Alopiidae; this group of sharks are characterized by the greatly elongated upper lobes of their caudal fins. The pelagic thresher occurs in the tropical and subtropical waters of the Indian and Pacific Oceans, usually far from shore but...
(A. pelagicus) are united in having thin tails, smaller eyes, and no lateral grooves on the head. However, an 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....
analysis conducted by Blaise Eitner in 1995 found that the pelagic thresher is most closely related to the bigeye thresher
Bigeye thresher
The bigeye thresher is a species of thresher shark, family Alopiidae, found in temperate and tropical oceans worldwide. Like other thresher sharks, nearly half its total length consists of the elongated upper lobe of the tail fin. Its common name comes from its enormous eyes, which are placed in...
(A. superciliosus), and that common thresher forms a separate clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
on its own. Its closest relative in the 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...
may be an unrecognized fourth thresher species from off southern California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
.
Distribution
The distribution of the common thresher is virtually circumglobal in warm waters. In the western AtlanticAtlantic 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...
it occurs from Newfoundland
Newfoundland and Labrador
Newfoundland and Labrador is the easternmost province of Canada. Situated in the country's Atlantic region, it incorporates the island of Newfoundland and mainland Labrador with a combined area of . As of April 2011, the province's estimated population is 508,400...
to Cuba
Cuba
The Republic of Cuba is an island nation in the Caribbean. The nation of Cuba consists of the main island of Cuba, the Isla de la Juventud, and several archipelagos. Havana is the largest city in Cuba and the country's capital. Santiago de Cuba is the second largest city...
, though is rare north of New England
New England
New England is a region in the northeastern corner of the United States consisting of the six states of Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, and Connecticut...
, and from 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...
to Argentina
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...
. In the eastern Atlantic, it is found from Norway
Norway
Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...
and the British Isles
British Isles
The British Isles are a group of islands off the northwest coast of continental Europe that include the islands of Great Britain and Ireland and over six thousand smaller isles. There are two sovereign states located on the islands: the United Kingdom of Great Britain and Northern Ireland and...
to Ghana
Ghana
Ghana , officially the Republic of Ghana, is a country located in West Africa. It is bordered by Côte d'Ivoire to the west, Burkina Faso to the north, Togo to the east, and the Gulf of Guinea to the south...
and the Ivory Coast, including the Mediterranean Sea
Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...
. In the Indo-Pacific
Indo-Pacific
The Indo-Pacific is a biogeographic region of the Earth's seas, comprising the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the seas connecting the two in the general area of Indonesia...
region, it has been reported from South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
, Tanzania
Tanzania
The United Republic of Tanzania is a country in East Africa bordered by Kenya and Uganda to the north, Rwanda, Burundi, and the Democratic Republic of the Congo to the west, and Zambia, Malawi, and Mozambique to the south. The country's eastern borders lie on the Indian Ocean.Tanzania is a state...
, Somalia
Somalia
Somalia , officially the Somali Republic and formerly known as the Somali Democratic Republic under Socialist rule, is a country located in the Horn of Africa. Since the outbreak of the Somali Civil War in 1991 there has been no central government control over most of the country's territory...
, Maldives
Maldives
The Maldives , , officially Republic of Maldives , also referred to as the Maldive Islands, is an island nation in the Indian Ocean formed by a double chain of twenty-six atolls oriented north-south off India's Lakshadweep islands, between Minicoy Island and...
, Chagos Archipelago
Chagos Archipelago
The Chagos Archipelago , is a group of seven atolls comprising more than 60 individual tropical islands in the Indian Ocean; situated some due south of the Maldives archipelago. This chain of islands are the southernmost archipelago of the Chagos-Laccadive Ridge a long submarine mountain range...
, Gulf of Aden
Gulf of Aden
The Gulf of Aden is located in the Arabian Sea between Yemen, on the south coast of the Arabian Peninsula, and Somalia in the Horn of Africa. In the northwest, it connects with the Red Sea through the Bab-el-Mandeb strait, which is about 20 miles wide....
, Pakistan
Pakistan
Pakistan , officially the Islamic Republic of Pakistan is a sovereign state in South Asia. It has a coastline along the Arabian Sea and the Gulf of Oman in the south and is bordered by Afghanistan and Iran in the west, India in the east and China in the far northeast. In the north, Tajikistan...
, India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
, Sri Lanka
Sri Lanka
Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka is a country off the southern coast of the Indian subcontinent. Known until 1972 as Ceylon , Sri Lanka is an island surrounded by the Indian Ocean, the Gulf of Mannar and the Palk Strait, and lies in the vicinity of India and the...
, Sumatra
Sumatra
Sumatra is an island in western Indonesia, westernmost of the Sunda Islands. It is the largest island entirely in Indonesia , and the sixth largest island in the world at 473,481 km2 with a population of 50,365,538...
, Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
, Republic of Korea, Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
, and New Caledonia
New Caledonia
New Caledonia is a special collectivity of France located in the southwest Pacific Ocean, east of Australia and about from Metropolitan France. The archipelago, part of the Melanesia subregion, includes the main island of Grande Terre, the Loyalty Islands, the Belep archipelago, the Isle of...
. It occurs off the Society Islands
Society Islands
The Society Islands are a group of islands in the South Pacific Ocean. They are politically part of French Polynesia. The archipelago is generally believed to have been named by Captain James Cook in honor of the Royal Society, the sponsor of the first British scientific survey of the islands;...
, Fanning Island, and Hawaiian Islands
Hawaiian Islands
The Hawaiian Islands are an archipelago of eight major islands, several atolls, numerous smaller islets, and undersea seamounts in the North Pacific Ocean, extending some 1,500 miles from the island of Hawaii in the south to northernmost Kure Atoll...
in the central Pacific, and from British Columbia
British Columbia
British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...
to Baja California
Baja California
Baja California officially Estado Libre y Soberano de Baja California is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is both the northernmost and westernmost state of Mexico. Before becoming a state in 1953, the area was known as the North...
and Panama
Panama
Panama , officially the Republic of Panama , is the southernmost country of Central America. Situated on the isthmus connecting North and South America, it is bordered by Costa Rica to the northwest, Colombia to the southeast, the Caribbean Sea to the north and the Pacific Ocean to the south. The...
to Chile
Chile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...
in the eastern Pacific.
The common thresher is migratory
Fish migration
Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousands of kilometres...
, moving to higher latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...
s following warm water masses. In the eastern Pacific, males travel further than females, reaching as far as Vancouver Island
Vancouver Island
Vancouver Island is a large island in British Columbia, Canada. It is one of several North American locations named after George Vancouver, the British Royal Navy officer who explored the Pacific Northwest coast of North America between 1791 and 1794...
in the late summer
Summer
Summer is the warmest of the four temperate seasons, between spring and autumn. At the summer solstice, the days are longest and the nights are shortest, with day-length decreasing as the season progresses after the solstice...
and early fall. Juveniles tend to remain in warm nursery areas. There appear to be separate populations with different life history characteristics in the eastern Pacific and western Indian Ocean and possibly elsewhere; this species is not known to make transoceanic movements. In the northwestern Indian Ocean
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
, male
Male
Male refers to the biological sex of an organism, or part of an organism, which produces small mobile gametes, called spermatozoa. Each spermatozoon can fuse with a larger female gamete or ovum, in the process of fertilization...
s and female
Female
Female is the sex of an organism, or a part of an organism, which produces non-mobile ova .- Defining characteristics :The ova are defined as the larger gametes in a heterogamous reproduction system, while the smaller, usually motile gamete, the spermatozoon, is produced by the male...
s segregate by location and depth during the pupping season from January to May. Analysis of mitochondrial DNA
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...
has revealed substantial regional genetic variation within common threshers in all three oceans. This reaffirms the idea that, despite being high mobile, sharks from different areas rarely interbreed.
Habitat
Common threshers are inhabitants of both continentContinent
A continent is one of several very large landmasses on Earth. They are generally identified by convention rather than any strict criteria, with seven regions commonly regarded as continents—they are : Asia, Africa, North America, South America, Antarctica, Europe, and Australia.Plate tectonics is...
al waters and the open ocean. They tend to be most abundant in proximity to land, particularly the juvenile
Juvenile (organism)
A juvenile is an individual organism that has not yet reached its adult form, sexual maturity or size. Juveniles sometimes look very different from the adult form, particularly in terms of their colour...
s which frequent near-coastal habitats such as bays. Most individuals are encountered near the surface, but this species has been recorded to at least a depth of 550 m (1,804.5 ft).
Description
English Channel
The English Channel , often referred to simply as the Channel, is an arm of the Atlantic Ocean that separates southern England from northern France, and joins the North Sea to the Atlantic. It is about long and varies in width from at its widest to in the Strait of Dover...
on November 22, 2007. The body is solidly built and torpedo
Torpedo
The modern torpedo is a self-propelled missile weapon with an explosive warhead, launched above or below the water surface, propelled underwater towards a target, and designed to detonate either on contact with it or in proximity to it.The term torpedo was originally employed for...
-shaped, with very long, falcate (sickle-shaped) pectoral fins. The first dorsal
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 pelvic fins are large, while the second dorsal and anal fins are tiny. The distinctive upper caudal fin lobe is slender, bearing a moderate ventral notch near the tip, and can be nearly as long as the rest of the body.
The head is fairly short and broad, with a strongly convex dorsal profile and a pointed conical snout. The eyes are of medium size. The mouth is relatively small, with short furrows at the corners. The teeth are small, smooth-edged, and knife-like, lacking the small lateral cusplets of the pelagic thresher. There are 20 tooth rows on either side of the upper jaw and 21 tooth rows on either side of the lower jaw. 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, with the last two placed over the pectoral fin bases. The dermal denticles are minute and overlapping. The common thresher is dark brown to gray to almost black above, with a metallic luster. Dark spots are present around the pelvic fins and the caudal peduncle, and there may be a white spot at the tip of the pectoral fins. The underside is white, extending in a characteristic patch over the pectoral fin bases to the "cheeks". This pattern stands in contrast to that of the similar pelagic thresher, whose dark dorsal coloration extends uninterrupted to and over the pectoral fins.
Biology and ecology
Common threshers are active, strong swimmers; there are infrequent reports of them leaping completely out of the water. Like the fast-swimming sharks of the family LamnidaeLamnidae
Lamnidae is a family of sharks, commonly known as mackerel sharks or white sharks. They are large, fast-swimming sharks, found in oceans worldwide....
, the common thresher has a strip of aerobic red muscle
Muscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...
along its flank that is able to contract powerfully and efficiently for long periods of time. In addition, they have slow-oxidative muscle
Muscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...
s centrally located within their bodies and a blood vessel
Blood vessel
The blood vessels are the part of the circulatory system that transports blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and...
countercurrent exchange
Countercurrent exchange
Countercurrent exchange is a mechanism occurring in nature and mimicked in industry and engineering, in which there is a crossover of some property, usually heat or some component, between two flowing bodies flowing in opposite directions to each other. The flowing bodies can be liquids, gases, or...
system called the rete mirabile
Rete mirabile
A rete mirabile is a complex of arteries and veins lying very close to each other, found in some vertebrates. The rete mirabile utilizes countercurrent blood flow within the net...
("wonderful net"), allowing them to generate and retain body heat
Thermoregulation
Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different...
. The temperature inside the red muscles of a common thresher averages 2°C (3.6°F) above that of the ambient seawater
Seawater
Seawater is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% . This means that every kilogram of seawater has approximately of dissolved salts . The average density of seawater at the ocean surface is 1.025 g/ml...
, though there is significant individual variation. Unlike the pelagic and bigeye threshers, the common thresher lacks an orbital
Orbit (anatomy)
In anatomy, the orbit is the cavity or socket of the skull in which the eye and its appendages are situated. "Orbit" can refer to the bony socket, or it can also be used to imply the contents...
rete mirabile to protect its eyes and brain from temperature changes.
Immature common threshers fall prey to larger shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....
s. Aside from observations of killer whales feeding on common threshers off New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
, adults have no known natural predators. Known parasites of the common thresher include nine species of copepod
Copepod
Copepods are a group of small crustaceans found in the sea and nearly every freshwater habitat. Some species are planktonic , some are benthic , and some continental species may live in limno-terrestrial habitats and other wet terrestrial places, such as swamps, under leaf fall in wet forests,...
s in the genus Nemesis, which attach themselves to the sharks' gill filament
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...
s, damaging tissue
Tissue (biology)
Tissue is a cellular organizational level intermediate between cells and a complete organism. A tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. These are called tissues because of their identical functioning...
and hindering respiration
Respiration (physiology)
'In physiology, respiration is defined as the transport of oxygen from the outside air to the cells within tissues, and the transport of carbon dioxide in the opposite direction...
. Other parasites include the protozoan Giardia intestinalis, the digenea
Digenea
Digenea is a subclass within the Platyhelminthes consisting of parasitic flatworms with a syncytial tegument and, usually, two suckers, one ventral and one oral. Adults are particularly common in the digestive tract, but occur throughout the organ systems of all classes of vertebrates...
n Campula oblonga (not usual host), the tapeworms Paraorygmatobothrium exiguum and Sphyriocephalus tergetinus, and the copepod Kroeyerina benzorum.
Feeding
Shoaling and schooling
In 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...
forage fish
Forage fish
Forage fish, also called prey fish or bait fish, are small fish which are preyed on by larger predators for food. Predators include other larger fish, seabirds and marine mammals. Typical ocean forage fish feed near the base of the food chain on plankton, often by filter feeding...
such as mackerel
Mackerel
Mackerel 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...
, bluefish
Bluefish
The bluefish , called tailor in Australia, is a species of popular marine gamefish found in all climates. It is the sole species of the Pomatomidae family....
, herring
Herring
Herring is an oily fish of the genus Clupea, found in the shallow, temperate waters of the North Pacific and the North Atlantic oceans, including the Baltic Sea. Three species of Clupea are recognized. The main taxa, the Atlantic herring and the Pacific herring may each be divided into subspecies...
, needlefish
Needlefish
Needlefish are piscivorous fishes primarily associated with very shallow marine habitats or the surface of the open sea. Some genera include species found in marine, brackish, and freshwater environments while a few genera are confined to freshwater rivers and streams, including Belonion,...
, and lanternfish
Lanternfish
Cooper Lanternfishes are small mesopelagic fish of the large family Myctophidae. One of two families in the order Myctophiformes, the Myctophidae are represented by 246 species in 33 genera, and are found in oceans worldwide. They are aptly named after their conspicuous use of bioluminescence...
. Before striking, the sharks compact schools of prey by swimming around them and splashing the water with its tail, often in pairs or small groups. Threshers are also known to take large, solitary fishes such as lancetfish
Lancetfish
Lancetfishes are large oceanic predatory fishes in the genus Alepisaurus , the only living genus in the family Alepisauridae....
, as well as 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...
and other pelagic invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
s. Off California, common threshers feed mostly on the northern anchovy (Engraulis mordax), with Pacific hake (Merluccius productus), Pacific sardine (Sardinops sagax), Pacific mackerel (Scomber japonicus), market squid (Loligo opalescens), and pelagic red crab
Pleuroncodes planipes
Pleuroncodes planipes, sometimes called the pelagic red crab , tuna crab or , is a species of squat lobster from the eastern Pacific Ocean.-Description:...
(Pleuroncodes planipes) also being important food items. The sharks concentrate on a few prey species during cold water years, but become less discriminating during less productive, warmer El Niño periods.
There are numerous accounts of common threshers using the long upper lobes of their tail fins to stun prey, and they are often snagged on longlines by their tails after presumably striking at the bait. In July 1914, shark-watcher Russell J. Coles reported seeing a thresher shark use its tail to flip prey fish into its mouth, and that one fish that missed was thrown a "considerable distance". On April 14, 1923, noted oceanographer W.E. Allen observed a 2 m (6.6 ft) thresher shark pursuing a California smelt (Atherinopsis californiensis) off a pier
Pier
A pier is a raised structure, including bridge and building supports and walkways, over water, typically supported by widely spread piles or pillars...
at the Scripps Institution of Oceanography
Scripps Institution of Oceanography
Scripps Institution of Oceanography in La Jolla, California, is one of the oldest and largest centers for ocean and earth science research, graduate training, and public service in the world...
. The shark overtook the small fish and swung its tail above the water like a "coachwhip
Whip
A whip is a tool traditionally used by humans to exert control over animals or other people, through pain compliance or fear of pain, although in some activities whips can be used without use of pain, such as an additional pressure aid in dressage...
" with "confusing speed", severely injuring its target. In the winter of 1865, Irish
Irish people
The Irish people are an ethnic group who originate in Ireland, an island in northwestern Europe. Ireland has been populated for around 9,000 years , with the Irish people's earliest ancestors recorded having legends of being descended from groups such as the Nemedians, Fomorians, Fir Bolg, Tuatha...
ichthyologist Harry Blake-Knox claimed to have seen a thresher shark in Dublin Bay
Dublin Bay
Dublin Bay is a C-shaped inlet of the Irish Sea on the east coast of Ireland. The bay is about 10 kilometres wide along its north-south base, and 7 km in length to its apex at the centre of the city of Dublin; stretching from Howth Head in the north to Dalkey Point in the south...
use its tail to strike a wounded loon
Loon
The loons or divers are a group of aquatic birds found in many parts of North America and northern Eurasia...
(probably a great northern diver
Great Northern Diver
The Great Northern Loon, Great Northern Diver, or Common Loon , is a large member of the loon, or diver, family of birds...
, Gavia immer), which it then swallowed. Blake-Knox's account was subsequently disputed by other authorities, who asserted that the thresher's tail is not rigid or muscular enough to effect such a blow.
Life history
Southern California Bight
The Southern California Bight includes coastal southern California, the Channel Islands and part of the Pacific Ocean.Within the Southern California bight lie the traditional territories of the Chumash and the Gabrieliño. These two cultures are considered the epitome of hunter-gatherer complexity...
. Breeding
Breeding in the wild
Breeding in the wild is the natural process of animal reproduction occurring in the natural habitat of a given species. This terminology is distinct from animal husbandry or breeding of species in captivity...
occurs in the summer, usually July or August, and parturition occurs from March to June following a 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:...
of nine months. 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 oophagous
Oophagy
Oophagy , literally "egg eating", is the practice of embryos feeding on eggs produced by the ovary while still inside the mother's uterus. The word oophagy is formed from the classical Greek ᾠόν and classical Greek φᾱγεῖν ....
, feeding on eggs
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
ovulated
Ovulation
Ovulation is the process in a female's menstrual cycle by which a mature ovarian follicle ruptures and discharges an ovum . Ovulation also occurs in the estrous cycle of other female mammals, which differs in many fundamental ways from the menstrual cycle...
by the mother. The teeth of small embryos are peg-like and non-functional, being covered by a sheath of soft tissues. As the embryos mature, their series of teeth become progressively more like those of adults in shape, though they remain depressed and hidden until shortly before birth.
Newborn pups usually measure 114–160 cm (3.7–5.2 ft) long and weigh 5–6 kg (11–13.2 lb), depending on the size of the mother. The juveniles grow about 50 cm (1.6 ft) a year while adults grow about 10 cm (0.328083989501312 ft) a year. The size at maturation appears to vary between populations. In the eastern North Pacific males mature at 3.3 m (10.8 ft) and five years old, and females at around 2.6–4.5 m (8.5–14.8 ft) and seven years old. They are known to live to at least 15 years of age and their maximum lifespan has been estimated to be 45–50 years.
Human interactions
Despite their large size, common threshers pose little danger to humanHuman
Humans are the only living species in the Homo genus...
s, though they should be treated with respect as their powerful tails are easily capable of breaking bones. Most divers report that they are shy and difficult to approach underwater. The International Shark Attack File
International Shark Attack File
The International Shark Attack File is a global database of shark attacks. It began as an attempt to catalogue shark attacks on servicemen during World War II. The Office of Naval Research funded it from 1958 until 1968. During that time a panel of shark experts developed a standard system for...
lists a single provoked attack by the thresher shark and four attacks on boat
Boat
A boat is a watercraft of any size designed to float or plane, to provide passage across water. Usually this water will be inland or in protected coastal areas. However, boats such as the whaleboat were designed to be operated from a ship in an offshore environment. In naval terms, a boat is a...
s, which were probably incidental from individuals fighting capture. There is an unsubstantiated report of a common thresher acting aggressively towards a spearfisherman off New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
.
Famed big-game angler Frank Mundus
Frank Mundus
Frank Mundus was a sport fisherman at Montauk, New York who is said to be the inspiration for the character Quint in the movie and book Jaws...
, in his book Sportsfishing for Sharks, recounted a tale in which a longline fisherman off the Carolinas leaned over the side of his boat to examine something large that he had hooked, and was decapitated
Decapitation
Decapitation is the separation of the head from the body. Beheading typically refers to the act of intentional decapitation, e.g., as a means of murder or execution; it may be accomplished, for example, with an axe, sword, knife, wire, or by other more sophisticated means such as a guillotine...
by the caudal fin of a thresher shark estimated to be 5 m (16.4 ft) long. The head supposedly fell into the water and was never recovered. This account is considered highly improbable by most authors.
Commercial fishing
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...
fisheries, especially in the northwestern Indian Ocean, the western, central, and eastern Pacific, and the North Atlantic. Participating countries include the former USSR, Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
, Taiwan
Taiwan
Taiwan , also known, especially in the past, as Formosa , is the largest island of the same-named island group of East Asia in the western Pacific Ocean and located off the southeastern coast of mainland China. The island forms over 99% of the current territory of the Republic of China following...
, Spain
Spain
Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...
, the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, 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...
, Uruguay
Uruguay
Uruguay ,officially the Oriental Republic of Uruguay,sometimes the Eastern Republic of Uruguay; ) is a country in the southeastern part of South America. It is home to some 3.5 million people, of whom 1.8 million live in the capital Montevideo and its metropolitan area...
, and Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
. The meat
Meat
Meat is animal flesh that is used as food. Most often, this means the skeletal muscle and associated fat and other tissues, but it may also describe other edible tissues such as organs and offal...
is highly prized for human consumption cooked, dried and salted
Salting (food)
Salting is the preservation of food with dry edible salt. It is related to pickling . It is one of the oldest methods of preserving food, and two historically significant salt-cured foods are dried and salted cod and salt-cured meat.Salting is used because most bacteria, fungi and other potentially...
, or smoked. In addition, their skin
Skin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
is made into leather
Leather
Leather is a durable and flexible material created via the tanning of putrescible animal rawhide and skin, primarily cattlehide. It can be produced through different manufacturing processes, ranging from cottage industry to heavy industry.-Forms:...
, their 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...
is processed for vitamin
Vitamin
A vitamin is an organic compound required as a nutrient in tiny amounts by an organism. In other words, an organic chemical compound is called a vitamin when it cannot be synthesized in sufficient quantities by an organism, and must be obtained from the diet. Thus, the term is conditional both on...
s, and their fins are used for 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 United Nations
United Nations
The United Nations is an international organization whose stated aims are facilitating cooperation in international law, international security, economic development, social progress, human rights, and achievement of world peace...
Food and Agricultural Organization (FAO) reported a worldwide common thresher take of 411 metric tons in 2006.
In the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, a drift gillnet fishery for the common thresher developed in southern California in 1977, beginning with 10 vessels experimenting with a larger-sized mesh. Within two years the fleet had increased to 40 vessels, and the fishery peaked in 1982 when 228 vessels landed 1,091 metric tons. The common thresher population rapidly collapsed from overfishing
Overfishing
Overfishing 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....
, with landings decreasing to less than 300 metric tons a year by the late 1980s and larger size classes disappearing from the population. Common threshers are still taken commercially in the United States, with about 85% coming from the Pacific and 15% from the Atlantic. The largest catches remain from the California-Oregon gillnet fishery, which had shifted its focus to the more valuable swordfish
Swordfish
Swordfish , also known as broadbill in some countries, are large, highly migratory, predatory fish characterized by a long, flat bill. They are a popular sport fish of the billfish category, though elusive. Swordfish are elongated, round-bodied, and lose all teeth and scales by adulthood...
(Xiphius gladius) but still take threshers 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...
. Small numbers of Pacific threshers are also taken by harpoon
Harpoon
A harpoon is a long spear-like instrument used in fishing to catch fish or large marine mammals such as whales. It accomplishes this task by impaling the target animal, allowing the fishermen to use a rope or chain attached to the butt of the projectile to catch the animal...
s, small-mesh driftnets, and longlines. In the Atlantic, threshers are primarily taken on longlines meant for swordfish and tuna
Tuna
Tuna is a salt water fish from the family Scombridae, mostly in the genus Thunnus. Tuna are fast swimmers, and some species are capable of speeds of . Unlike most fish, which have white flesh, the muscle tissue of tuna ranges from pink to dark red. The red coloration derives from myoglobin, an...
.
Recreational fishing
Common threshers are well regarded by sports fishers as one of the strongest fighting sharks alongside the shortfin mako sharkShortfin mako shark
The shortfin mako shark, Isurus oxyrinchus , is a large mackerel shark. Along with the closely related longfin mako it is commonly referred to as a "mako shark".-Etymology:...
(Isurus oxyrhinchus), and are ranked as game fish
Game fish
Game fish are fish pursued for sport by recreational anglers. They can be freshwater or marine fish. Game fish can be eaten after being caught, though increasingly anglers practise catch and release to improve fish populations. Some game fish are also targeted commercially, particularly...
by the International Game Fish Association
International Game Fish Association
The International Game Fish Association is the leading authority on angling pursuits and the keeper of the most current World Record fishing catches by fish categories. Fishermen who are sport fishers are careful to follow their stringent rules for fair play and line requirements in order to...
(IGFA). They are pursued by anglers using rod and reel
Fishing rod
A fishing rod or a fishing pole is a tool used to catch fish, usually in conjunction with the pastime of angling, and can also be used in competition casting. . A length of fishing line is attached to a long, flexible rod or pole: one end terminates in a hook for catching the fish...
off California, South Africa, and elsewhere. Frank Mundus has called thresher sharks "exceedingly stubborn" and "pound for pound, a harder fish to whip" than the mako. Fishing for the common thresher is similar to that for the mako; the recommended equipment is a 24 kg (52.9 lb) rod and a big-game reel holding at least 365 m (400 yd) of 24 kg (52.9 lb) line. The ideal method is trolling with baitfish, either deep or allowing it to drift.
Conservation
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...
to 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:...
by the International Union for Conservation of Nature (IUCN) in 2007. The rapid collapse of the Californian subpopulation (over 50% within three generations) prompted concerns regarding the species' susceptibility to overfishing in other areas, where fishery data is seldom reported and aspects of life history and population structure are little-known. In addition to continued fishing pressure, common threshers are also taken 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...
in other gear such as bottom trawls and fish traps, and are considered a nuisance by mackerel fishers as they become entangled in the nets.
The United States manages common thresher fisheries via regulations such as commercial quotas and trip limits, and recreational minimum sizes and retention limits. Shark finning
Shark finning
Shark finning refers to the removal and retention of shark fins and the discarding of the rest of the fish. Shark finning takes place at sea so the fishers only have to transport the fins.Shark finning is widespread, and largely unmanaged and unmonitored...
is illegal under U.S. federal law. The Atlantic common thresher fishery is regulated by the National Marine Fisheries Service
National Marine Fisheries Service
The 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 the...
(NMFS) Highly Migratory Species Management Division through the 2006 Consolidated Atlantic Highly Migratory Species (HMS) Fishery Management Plan (FMP), and the Pacific common thresher fishery is regulated by the Pacific Fishery Management Council through the Fishery Management Plan (FMP) for U.S. West Coast Fisheries for Highly Migratory Species (HMS). In the 1990s, after the depletion of common thresher stocks by the California gillnet fishery, the fleet was limited to 70 boats and restrictions were placed on season, operation range, and landings. There is evidence that the California subpopulation is recovering, and the potential population growth rate has been estimated to be 4–7% per year.
Historical perceptions
The Greek philosopher AristotleAristotle
Aristotle was a Greek philosopher and polymath, a student of Plato and teacher of Alexander the Great. His writings cover many subjects, including physics, metaphysics, poetry, theater, music, logic, rhetoric, linguistics, politics, government, ethics, biology, and zoology...
(384–322 BCE) wrote some of the earliest observations about the common thresher. In his Historia Animalia, he claimed that hooked threshers had a propensity for freeing themselves by biting through fishing line
Fishing line
A fishing line is a cord used or made for angling. Important parameters of a fishing line are its length, material, and weight...
s, and that they protected their young by swallowing them. These "clever" behaviors, which have not been borne out by science, led the ancient Greeks to call it alopex (meaning "fox"), on which its modern scientific name is based.
An oft-repeated myth about the common thresher is that they cooperate with swordfish to attack whale
Whale
Whale is the common name for various marine mammals of the order Cetacea. The term whale sometimes refers to all cetaceans, but more often it excludes dolphins and porpoises, which belong to suborder Odontoceti . This suborder also includes the sperm whale, killer whale, pilot whale, and beluga...
s. In one version of events, the thresher shark circles the whale and distracts it by beating the sea to a froth with its tail, thereby allowing the swordfish to impale it in a vulnerable spot with its rostrum
Rostrum (anatomy)
The term rostrum is used for a number of unrelated structures in different groups of animals:*In crustaceans, the rostrum is the forward extension of the carapace in front of the eyes....
. In an alternate account, the swordfish positions itself beneath the whale, while the thresher leaps out of the water and lands on top of the whale, hammering it onto the swordfish's rostrum. Yet other authors describe the thresher "cutting huge gashes" in the side of the whale with its tail. Neither threshers nor swordfish however are known to feed on whales or indeed possess the dentition
Dentition
Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, the characteristic arrangement, kind, and number of teeth in a given species at a given age...
to do so. The story may have arisen from mariners mistaking the tall dorsal fins of killer whales, which do attack large cetaceans, for thresher shark tails. Swordfish bills have also been found embedded in blue
Blue Whale
The blue whale is a marine mammal belonging to the suborder of baleen whales . At in length and or more in weight, it is the largest known animal to have ever existed....
and fin whale
Fin Whale
The fin whale , also called the finback whale, razorback, or common rorqual, is a marine mammal belonging to the suborder of baleen whales. It is the second longest whale and the sixth largest living animal after the blue whale, bowhead whale, and right whales, growing to nearly 27 metres long...
s (likely accidents due to the fast-moving fish's inertia
Inertia
Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion. It is proportional to an object's mass. The principle of inertia is one of the fundamental principles of classical physics which are used to...
), and thresher sharks do exhibit some of the aforementioned behaviors independent of whales.