Largetooth cookiecutter shark
Encyclopedia
The largetooth cookiecutter shark (Isistius plutodus) is a rare species
of dogfish shark
in the family
Dalatiidae
, reported from depths of 60–200 m (196.9–656.2 ft) at scattered locations in the Atlantic and Pacific Ocean
s. As its common name
suggests, it is similar in appearance to the cookiecutter shark
(I. brasiliensis) but has much larger lower teeth. Most individuals also lack the dark "collar" of I. brasiliensis. This species reaches a maximum known length of 42 cm (16.5 in). The largetooth cookiecutter shark feeds by gouging out chunks of flesh from larger animals, including bony fishes, sharks, and marine mammal
s, and is able to take larger bites than I. brasiliensis. Little is known of its life history; it is thought to be a weaker swimmer than I. brasiliensis, and is presumably aplacental viviparous like the rest of its family. This shark is an infrequent bycatch
of commercial trawl and longline fisheries, but is not thought to be much threatened by these activities.
, in a 1964 issue of the scientific journal
Copeia. Their description was based on a 42 cm (16.5 in) long adult female caught in a midwater trawl in the Gulf of Mexico
, some 160 km (99.4 mi) south of Dauphin Island, Alabama
. The specific epithet plutodus is derived from the Greek
ploutos ("wealth" or "abundance") and odous ("tooth"). This species may also be referred to as the bigtooth or longtooth cookiecutter shark, or the Gulf dogfish.
in Brazil
, the Azores
, and Western Sahara
in the Atlantic Ocean
, and off Okinawa and New South Wales
in the Pacific. Those captures were made in the epipelagic zone 60–200 m (196.9–656.2 ft) down, close to land over continental shelves, continental slopes, or oceanic trench
es that may descend as far as 6.44 km (4 mi). The shark's rarity may be due to a restricted distribution or, more likely, it normally preferring deeper waters.
, and are followed by wide, angled spiracle
s. The nostril
s are small, each with a low, pointed skin lobe in front. The mouth is transverse, with a deep fold enclosing its corners and fleshy suctorial
lips. The jaws are larger and more powerful than those of I. brasiliensis, and contain fewer tooth rows, numbering around 29 in the upper jaw and 19 in the lower jaw. The upper teeth are small, narrow, and smooth-edged, upright at the center of the jaw and becoming more angled towards the corners. The lower teeth are massive, the largest teeth relative to body size of any living shark. They are triangular in shape, with minutely serrated edges and interlocking rectangular bases. The five pairs of gill slit
s are minute.
The small dorsal fin
s have rounded apices and are placed far back, on the last third of the body. The first dorsal fin originates slightly ahead of the pelvic fins, while the second dorsal originates closely behind and measures almost a third again the height of the first. The pectoral fins are small and rounded, and positioned relatively high on the body behind the fifth gill slit. The pelvic fins are tiny, and there is no anal fin. The caudal fin is very short, with the upper lobe twice as long as the lower and bearing a prominent ventral notch near the tip. The coloration is a plain dark brown, with translucent margins on the fins and sparsely scattered light-emitting
photophore
s on the belly. Most specimens have lacked the dark "collar" found on the throat of I. brasiliensis. However, a specimen caught in 2004 off the Azores did possess the collar. The maximum recorded length is 42 cm (16.5 in).
-filled liver
, which allows it to maintain neutral buoyancy
in the water column with little effort. Unlike I. brasiliensis, this shark possesses binocular vision, which may allow it to target its prey with greater precision. Virtually nothing is known of its biology; it is presumed to be aplacental viviparous.
Like I. brasiliensis, the largetooth cookiecutter shark is an ectoparasite that feeds by excising plugs of flesh from larger animals. While I. brasiliensis is theorized to latch onto the surface of its prey and bite with a twisting motion, producing a circular wound containing spiral grooves inside from its lower teeth, the largetooth cookiecutter shark seems to employ a "sweeping" bite that produces a larger, more elongate (twice as long as the width of the mouth), oval wound containing parallel tooth grooves. This shark has been known to bite bony fishes, sharks, and marine mammals. One study has found that the largetooth cookiecutter shark is responsible for 80% of the cookiecutter wounds found on cetaceans off Bahia, Brazil. The flank was the most often-attacked area, followed by the head and abdomen. In at least three cases, bites to dolphin
s appeared to have resulted in their subsequent deaths by stranding. Another prey species in the area is the subantarctic fur seal
(Arctocephalus tropicalis); at least two cases of juveniles fatally stranding after being bitten have also been recorded.
es or other valued species, the largetooth cookiecutter shark is of no import to commercial fisheries
. All but one of the known specimens have been caught as bycatch
in commercial trawls or longlines. However, given the infrequency of these catches and this species' probable wide distribution, the International Union for Conservation of Nature (IUCN) has assessed it as of Least Concern
.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of dogfish shark
Squaliformes
Squaliformes is an order of sharks that includes about 97 species in seven families.Members of the order have two dorsal fins, which usually possess spines, no anal fin or nictitating membrane, and five gill slits. In most other respects, however, they are quite variable in form and size...
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...
Dalatiidae
Dalatiidae
Dalatiidae is a family of sharks in the order Squaliformes, commonly known as kitefin sharks . Members of this family are small, under long, and are found worldwide. They have cigar-shaped bodies with narrow heads and rounded snouts...
, reported from depths of 60–200 m (196.9–656.2 ft) at scattered locations in the Atlantic and Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
s. As its 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...
suggests, it is similar in appearance to the cookiecutter shark
Cookiecutter shark
The cookiecutter shark , also called the cigar shark, is a species of small dogfish shark in the family Dalatiidae. This shark occurs in warm, oceanic waters worldwide, particularly near islands, and has been recorded from as deep as . It migrates vertically up to every day, approaching the...
(I. brasiliensis) but has much larger lower teeth. Most individuals also lack the dark "collar" of I. brasiliensis. This species reaches a maximum known length of 42 cm (16.5 in). The largetooth cookiecutter shark feeds by gouging out chunks of flesh from larger animals, including bony fishes, sharks, and marine mammal
Marine mammal
Marine mammals, which include seals, whales, dolphins, and walruses, form a diverse group of 128 species that rely on the ocean for their existence. They do not represent a distinct biological grouping, but rather are unified by their reliance on the marine environment for feeding. The level of...
s, and is able to take larger bites than I. brasiliensis. Little is known of its life history; it is thought to be a weaker swimmer than I. brasiliensis, and is presumably aplacental viviparous like the rest of its family. This shark is an infrequent 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...
of commercial trawl and longline fisheries, but is not thought to be much threatened by these activities.
Taxonomy
The largetooth cookiecutter shark was originally described by Jack Garrick and Stewart SpringerStewart Springer
Stewart Springer, was a world renowned expert on shark behavior, classification , and distribution of shark populations. There are more than 35 species of sharks, skates, rays, and other animals either classified originally by him or named after him.-Education:Springer was a field naturalist,...
, in a 1964 issue of the scientific journal
Scientific journal
In academic publishing, a scientific journal is a periodical publication intended to further the progress of science, usually by reporting new research. There are thousands of scientific journals in publication, and many more have been published at various points in the past...
Copeia. Their description was based on a 42 cm (16.5 in) long adult female caught in a midwater trawl in the Gulf of Mexico
Gulf of Mexico
The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...
, some 160 km (99.4 mi) south of Dauphin Island, Alabama
Alabama
Alabama is a state located in the southeastern region of the United States. It is bordered by Tennessee to the north, Georgia to the east, Florida and the Gulf of Mexico to the south, and Mississippi to the west. Alabama ranks 30th in total land area and ranks second in the size of its inland...
. The specific epithet plutodus is derived from the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
ploutos ("wealth" or "abundance") and odous ("tooth"). This species may also be referred to as the bigtooth or longtooth cookiecutter shark, or the Gulf dogfish.
Distribution and habitat
Much rarer than I. brasiliensis, only ten specimens of largetooth cookiecutter shark are known, caught from a handful of widely scattered localities: off Alabama in the United States, BahiaBahia
Bahia is one of the 26 states of Brazil, and is located in the northeastern part of the country on the Atlantic coast. It is the fourth most populous Brazilian state after São Paulo, Minas Gerais and Rio de Janeiro, and the fifth-largest in size...
in 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...
, the Azores
Azores
The Archipelago of the Azores is composed of nine volcanic islands situated in the middle of the North Atlantic Ocean, and is located about west from Lisbon and about east from the east coast of North America. The islands, and their economic exclusion zone, form the Autonomous Region of the...
, and Western Sahara
Western Sahara
Western Sahara is a disputed territory in North Africa, bordered by Morocco to the north, Algeria to the northeast, Mauritania to the east and south, and the Atlantic Ocean to the west. Its surface area amounts to . It is one of the most sparsely populated territories in the world, mainly...
in the Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
, and off Okinawa and New South Wales
New South Wales
New South Wales is a state of :Australia, located in the east of the country. It is bordered by Queensland, Victoria and South Australia to the north, south and west respectively. To the east, the state is bordered by the Tasman Sea, which forms part of the Pacific Ocean. New South Wales...
in the Pacific. Those captures were made in the epipelagic zone 60–200 m (196.9–656.2 ft) down, close to land over continental shelves, continental slopes, or oceanic trench
Oceanic trench
The oceanic trenches are hemispheric-scale long but narrow topographic depressions of the sea floor. They are also the deepest parts of the ocean floor....
es that may descend as far as 6.44 km (4 mi). The shark's rarity may be due to a restricted distribution or, more likely, it normally preferring deeper waters.
Description
The largetooth cookiecutter shark has a long, cigar-shaped body with an extremely short, blunt head and snout. The large, oval eyes are positioned to allow binocular visionBinocular vision
Binocular vision is vision in which both eyes are used together. The word binocular comes from two Latin roots, bini for double, and oculus for eye. Having two eyes confers at least four advantages over having one. First, it gives a creature a spare eye in case one is damaged. Second, it gives a...
, and are followed by wide, angled spiracle
Spiracle
Spiracles are openings on the surface of some animals that usually lead to respiratory systems.-Vertebrates:The spiracle is a small hole behind each eye that opens to the mouth in some fishes. In the primitive jawless fish the first gill opening immediately behind the mouth is essentially similar...
s. The nostril
Nostril
A nostril is one of the two channels of the nose, from the point where they bifurcate to the external opening. In birds and mammals, they contain branched bones or cartilages called turbinates, whose function is to warm air on inhalation and remove moisture on exhalation...
s are small, each with a low, pointed skin lobe in front. The mouth is transverse, with a deep fold enclosing its corners and fleshy suctorial
Suctorial
Suctorial pertains to the adaptation for sucking or suction, as possessed by marine parasites such as the Cookiecutter shark, specifically in a specialised lip organ enabling attachment to the host....
lips. The jaws are larger and more powerful than those of I. brasiliensis, and contain fewer tooth rows, numbering around 29 in the upper jaw and 19 in the lower jaw. The upper teeth are small, narrow, and smooth-edged, upright at the center of the jaw and becoming more angled towards the corners. The lower teeth are massive, the largest teeth relative to body size of any living shark. They are triangular in shape, with minutely serrated edges and interlocking rectangular bases. 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 minute.
The small dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
s have rounded apices and are placed far back, on the last third of the body. The first dorsal fin originates slightly ahead of the pelvic fins, while the second dorsal originates closely behind and measures almost a third again the height of the first. The pectoral fins are small and rounded, and positioned relatively high on the body behind the fifth gill slit. The pelvic fins are tiny, and there is no anal fin. The caudal fin is very short, with the upper lobe twice as long as the lower and bearing a prominent ventral notch near the tip. The coloration is a plain dark brown, with translucent margins on the fins and sparsely scattered light-emitting
Bioluminescence
Bioluminescence is the production and emission of light by a living organism. Its name is a hybrid word, originating from the Greek bios for "living" and the Latin lumen "light". Bioluminescence is a naturally occurring form of chemiluminescence where energy is released by a chemical reaction in...
photophore
Photophore
A photophore is a light-emitting organ which appears as luminous spots on various marine animals, including fish and cephalopods. The organ can be simple, or as complex as the human eye; equipped with lenses, shutters, color filters and reflectors...
s on the belly. Most specimens have lacked the dark "collar" found on the throat of I. brasiliensis. However, a specimen caught in 2004 off the Azores did possess the collar. The maximum recorded length is 42 cm (16.5 in).
Biology and ecology
Based on its smaller dorsal and caudal fins, the largetooth cookiecutter shark is believed to be less active than I. brasiliensis and an overall weak swimmer. Much of its body cavity is occupied by an enormous oilShark 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...
-filled liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
, which allows it to maintain neutral buoyancy
Neutral buoyancy
Neutral buoyancy is a condition in which a physical body's mass equals the mass it displaces in a surrounding medium. This offsets the force of gravity that would otherwise cause the object to sink...
in the water column with little effort. Unlike I. brasiliensis, this shark possesses binocular vision, which may allow it to target its prey with greater precision. Virtually nothing is known of its biology; it is presumed to be aplacental viviparous.
Like I. brasiliensis, the largetooth cookiecutter shark is an ectoparasite that feeds by excising plugs of flesh from larger animals. While I. brasiliensis is theorized to latch onto the surface of its prey and bite with a twisting motion, producing a circular wound containing spiral grooves inside from its lower teeth, the largetooth cookiecutter shark seems to employ a "sweeping" bite that produces a larger, more elongate (twice as long as the width of the mouth), oval wound containing parallel tooth grooves. This shark has been known to bite bony fishes, sharks, and marine mammals. One study has found that the largetooth cookiecutter shark is responsible for 80% of the cookiecutter wounds found on cetaceans off Bahia, Brazil. The flank was the most often-attacked area, followed by the head and abdomen. In at least three cases, bites to dolphin
Dolphin
Dolphins are marine mammals that are closely related to whales and porpoises. There are almost forty species of dolphin in 17 genera. They vary in size from and , up to and . They are found worldwide, mostly in the shallower seas of the continental shelves, and are carnivores, mostly eating...
s appeared to have resulted in their subsequent deaths by stranding. Another prey species in the area is the subantarctic fur seal
Subantarctic Fur Seal
The subantarctic fur seal is a fur seal found in the southern parts of the Indian and Atlantic Oceans. It was first described by Gray in 1872 from a specimen recovered in northern Australia—hence the inappropriate tropicalis specific name.- Description :The subantarctic fur seal is...
(Arctocephalus tropicalis); at least two cases of juveniles fatally stranding after being bitten have also been recorded.
Human interactions
Other than possibly damaging billfishBillfish
The term billfish is applied to a number of different large, predatory fish characterised by their large size and their long, sword-like bill. Billfish include the sailfish and marlin, which make up the family Istiophoridae, and the swordfish, sole member of the family Xiphiidae...
es or other valued species, the largetooth cookiecutter shark is of no import to commercial fisheries
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...
. All but one of the known specimens have been caught as bycatch
Bycatch
The term “bycatch” is usually used for fish caught unintentionally in a fishery while intending to catch other fish. It may however also indicate untargeted catch in other forms of animal harvesting or collecting...
in commercial trawls or longlines. However, given the infrequency of these catches and this species' probable wide distribution, the International Union for Conservation of Nature (IUCN) has assessed it as of Least Concern
Least Concern
Least Concern is an IUCN category assigned to extant taxon or lower taxa which have been evaluated but do not qualify for any other category. As such they do not qualify as threatened, Near Threatened, or Conservation Dependent...
.