Smalleye hammerhead
Encyclopedia
The smalleye hammerhead or golden hammerhead (Sphyrna tudes) is a small species
of hammerhead shark
, family
Sphyrnidae, common in the shallow coastal waters of the western Atlantic Ocean
from Venezuela
to Uruguay
. It favors muddy habitats with poor visibility, reflected by its relatively small eyes. Adult males and juveniles are schooling
and generally found apart from the solitary adult females. Typically reaching 1.2–1.3 m (3.9–4.3 ft) in length, this shark has a unique, bright golden color on its head, sides, and fins, which was only scientifically documented in the 1980s. As in all hammerheads, its head is flattened and laterally expanded into a hammer-shaped structure called the "cephalofoil", which in this species is wide and long with an arched front margin bearing central and lateral indentations.
The yellow-orange pigment
s of the smalleye hammerhead seem to be acquired from the penaeid shrimp
Xiphopenaeus kroyeri
, the main food of juvenile sharks, and from sea catfish
and their eggs
, the main food of adults. The golden color may serve to conceal it from predators such as larger sharks. This species is viviparous, with the developing embryo
s sustained by a placenta
l connection formed from the depleted yolk sac
. Females bear litters of 5–19 pups every year following a gestation period
of 10 months. Reproductive seasonality, litter size, and size at maturity
vary between geographical regions. Because of its abundance, the smalleye hammerhead is an economically important bycatch
of artisanal
gillnet
fisheries throughout its range and is utilized as food. In recent years, overfishing
has caused marked declines in its numbers off Trinidad
, northern Brazil
, and probably elsewhere. Coupled with its low reproductive rate, this has led the International Union for Conservation of Nature (IUCN) to list it under Vulnerable
.
' description of Zygaena tudes in the scientific journal
Memoires du Museum National d'Histoire Naturelle; the specific epithet tudes is Latin
for "hammer". Valenciennes made reference to three specimens: one from Nice
in France
, one from Cayenne
in French Guyana, and one from the Coromandel Coast
of India
. However, for over two centuries taxonomists believed Valenciennes' account matched the great hammerhead
, which thus became known as Zygaena (later Sphyrna) tudes. The smalleye hammerhead was known by a different name, Sphyrna bigelowi, coined by Stewart Springer
in a 1944 issue of Journal of the Washington Academy of Sciences.
In 1950, Enrico Tortonese examined the Nice and Cayenne specimens of S. tudes (the Coromandel specimen having been lost in the interim) and concluded that they were not great hammerheads but rather the same species as S. bigelowi. Carter Gilbert concurred in his 1967 revision of the hammerhead sharks, noting that while the lost Coromandel specimen was probably a great hammerhead, none of the existing material belonged to that species. Thus, Sphyrna tudes became the accepted name for the smalleye hammerhead, taking precedence over S. bigelowi because it was published earlier, and the great hammerhead received the next available name Sphyrna mokarran. Gilbert designated the Nice specimen as the lectotype
that would define S. tudes, having priority over the Cayenne specimen (the paralectotype). This was meant to stabilize the name but had the opposite effect.
In 1981, Jean Cadenat and Jacques Blache revisited the type specimens of S. tudes and found that the lectotype from Nice is likely not a smalleye hammerhead but rather a fetal
whitefin hammerhead
(S. couardi, likely a synonym
of the scalloped hammerhead
, S. lewini). This would also explain the anomalous locality of the Nice specimen, as the smalleye hammerhead is not otherwise known outside of the Americas. By the rules of binomial nomenclature
, Sphyra tudes should then become the valid name for the whitefin hammerhead, taking precedence over S. couardi, and the smalleye hammerhead would revert to being Sphyrna bigelowi. Taxonomists though have been reluctant to change the names again, preferring to keep the smalleye hammerhead as S. tudes. For this solution to have official status would require a decision by the International Commission on Zoological Nomenclature
(ICZN), to reject the Nice specimen as the lectotype and designate the Cayenne specimen in its place. The relevant petition to the ICZN has not yet been put forth.
Until the first detailed study of the smalleye hammerhead was carried out in 1985–86 by José Castro of Clemson University
for the Food and Agriculture Organization of the United Nations (FAO), its distinctive golden coloration was unknown to science. The color fades after death and the pigment
s leech into the preservative
, resulting in the "yellowish cast" of museum specimens being regarded as an artifact of preservation. The names "yellow hammerhead" or "golden hammerhead" are used by fishermen in Trinidad
for this shark, and the latter was promoted for wider usage by Castro. Another common name
for this species is the curry shark. Recent phylogenetic analyses, based on morphological
, isozyme
, and mitochondrial DNA
data, have found that the hammerheads with the smallest cephalofoils are the most derived
members of their lineage. A hammerhead "supertree
" (a composite of several independent phylogenetic trees) published by Mauro José Cavalcanti in 2005 found the closest relatives of the smalleye hammerhead to be the sister species pair of the scalloped bonnethead
(S. corona) and the scoophead
(S. media), and that the three form a clade
with the bonnethead
(S. tiburo).
from Uruguay
to Venezuela
, though it seldom occurs further west than the Orinoco Delta southeast of Trinidad
. There are unconfirmed reports of this species from off Panama
, Mexico
, and western Florida
; records from other parts of the world are most likely erroneous, resulting from its tangled taxonomic history. It is among the most abundant sharks within its range. This species inhabits inshore murky waters 5–40 m (16.4–131.2 ft) deep, over muddy bottoms. There is segregation by sex and age: newborns and juveniles under 40 cm (15.7 in) long are found in the shallowest waters, moving deeper after a few months of life. Adult females are mostly found at depths of 9–18 m (29.5–59.1 ft), while larger juveniles and adult males are mostly found at depths of 27–36 m (88.6–118.1 ft). This species is tolerant of brackish water
and can be found over a salinity
range of 20–34 ppt.
s (protective third eyelids). The nostrils are positioned just inside of the eyes, each with a well-developed groove running towards the center of the cephalofoil. The mouth is strongly curved, containing on either side 15–16 upper tooth rows and 15–17 lower tooth rows. The teeth have single narrow cusps with smooth or weakly serrated edges, that are angled in the upper jaw and upright in the lower jaw.
The first dorsal fin
is tall and slightly falcate (sickle-shaped), originating behind the pectoral fin bases; its free rear tip lies over the origin of the pelvic fins. The second dorsal fin is smaller than the first but still rather large, with a concave trailing margin. The pelvic fins have nearly straight trailing margins. The anal fin is taller and longer than the second dorsal fin. The caudal fin has a well-developed lower lobe and a notch near the tip of the upper lobe. The dermal denticles are oval with five horizontal ridges leading to marginal teeth. The most distinctive trait of this species is its coloration: the back and dorsal fins are gray to yellowish gray, and the cephalofoil margins, flanks, underside, pectoral fins, pelvic fins, and anal fin are bright yellow to orange with a metallic or iridescent sheen. Newborn sharks are gray above, darkening on the first dorsal fin and upper caudal fin lobe, and whitish below. They gain a bright yellow cast on their undersides by a length of 45 cm (17.7 in), which turns to orange by a length of 50 cm (19.7 in). The golden color is brightest in sharks 55–70 cm (21.7–27.6 in) long, and tends to fade with the onset of sexual maturity
.
limits the utility of vision (hence its smaller eyes). Adult males and juveniles of both sexes form schools
of uniform body size; these schools do not appear to relate to reproduction or migration
. Adult females are apparently solitary.
Young smalleye hammerheads under 67 cm (26.4 in) long feed predominantly on penaeid shrimp
, mostly Xiphopenaeus kroyeri
. Larger sharks feed mainly on bony fishes, especially ariid sea catfish
and their eggs
. The shrimp and the surface mucus
layer and eggs of the catfish contain carotenoid
pigments that appear to be the source of the sharks' golden color; it is uncertain whether the pigments in the catfish also ultimately come from the shrimp. Another shark species in the region, the yellow smooth-hound (Mustelus higmani), also feeds on shrimp and has a yellowish color, albeit not nearly as bright. This species has also been known to consume swimming crabs, squid
, grunts
, and newborn scalloped hammerheads. The smalleye hammerhead may fall prey to larger sharks such as the bull shark
(Carcharhinus leucas), while smaller individuals may also be taken by bony fishes. Its coloration may provide camouflage
. A known parasite of this species is the monogenea
n Erpocotyle schmitti; it may also serve as a host to common copepod
ectoparasites such as Echthrogaleus coleoptratus, Pandarus saturus and P. cranchii.
Like all hammerhead sharks, the smalleye hammerhead is viviparous: when the developing embryo
s exhaust their supply of yolk, the depleted yolk sac
develops into a placenta
l connection through which the mother delivers nourishment. Mature females have a single functional ovary
and two functional uterus
es. Ovulation
occurs at the same time as gestation
, allowing females to bear young every year. The details of the smalleye hammerhead's life history vary across its range. Off Trinidad, reproduction occurs on a well-defined annual cycle with mating in August and September, and birthing in late May and June of the following year. The females carry between 5 and 12 pups for 10 months, and make use of food-rich, shallow coastal bay
s as nursery areas. The newborns measure around 30 cm (0.984251968503937 ft) long, and males and females attain sexual maturity at 80 cm (31.5 in) and 98 cm (38.6 in) long respectively. By contrast, smalleye hammerheads off the northern Brazilian state of Maranhão
are substantially larger, with males maturing at over 92 cm (36.2 in) long and females at over 101 cm (39.8 in) long. As the litter size increases with female size, Maranhão sharks have been recorded carrying up to 19 pups. The seasonality of breeding also differs, with pregnant females found from June to October and January to April, and males in apparent reproductive condition from May to November and in March.
by inshore artisanal
multi-species fisheries throughout its range, and marketed as food. It is the most or second-most important shark caught by such fisheries off Trinidad, Guyana, and Brazil. Because of its head shape, individuals of all ages are readily caught in gillnet
s; small numbers are also caught on line gear and in bottom trawls. The International Union for Conservation of Nature (IUCN) has assessed this species as Vulnerable
, as it is subjected to intense fishing pressure and its low reproductive rate renders it susceptible to population depletion. Anecdotal evidence suggests that smalleye hammerhead catches have declined significantly off Trinidad and northern Brazil, which are likely indicative of population trends in the rest of its range. It is not the target of any conservation or management schemes.
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 hammerhead shark
Hammerhead shark
The hammerhead sharks are a group of sharks in the family Sphyrnidae, so named for the unusual and distinctive structure of their heads, which are flattened and laterally extended into a "hammer" shape called a "cephalofoil". Most hammerhead species are placed in the genus Sphyrna while the...
, 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...
Sphyrnidae, common in the shallow coastal waters of the western Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
from Venezuela
Venezuela
Venezuela , officially called the Bolivarian Republic of Venezuela , is a tropical country on the northern coast of South America. It borders Colombia to the west, Guyana to the east, and Brazil to the south...
to 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...
. It favors muddy habitats with poor visibility, reflected by its relatively small eyes. Adult males and juveniles are 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...
and generally found apart from the solitary adult females. Typically reaching 1.2–1.3 m (3.9–4.3 ft) in length, this shark has a unique, bright golden color on its head, sides, and fins, which was only scientifically documented in the 1980s. As in all hammerheads, its head is flattened and laterally expanded into a hammer-shaped structure called the "cephalofoil", which in this species is wide and long with an arched front margin bearing central and lateral indentations.
The yellow-orange pigment
Pigment
A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...
s of the smalleye hammerhead seem to be acquired from the penaeid shrimp
Penaeidae
Penaeidae is a family of prawns, although they are often referred to as penaeid shrimp. It contains many species of economic importance, such as the tiger prawn , whiteleg shrimp, Atlantic white shrimp and Indian prawn. Many prawns are the subject of commercial fishery, and farming, both in marine...
Xiphopenaeus kroyeri
Xiphopenaeus kroyeri
Xiphopenaeus kroyeri, commonly called the Atlantic seabob, is a commercially important prawn. It is up to long and is the most intensely fished prawn species in the Guianas and along much of the Gulf Coast of the United States.-Description:...
, the main food of juvenile sharks, and from sea catfish
Ariidae
The Ariidae or ariid catfish are a family of catfish that mainly live in marine waters with many freshwater and brackish water species. They are found worldwide in tropical to warm temperate zones.-Taxonomy:...
and their eggs
Roe
Roe or hard roe is the fully ripe internal egg masses in the ovaries, or the released external egg masses of fish and certain marine animals, such as shrimp, scallop and sea urchins...
, the main food of adults. The golden color may serve to conceal it from predators such as larger sharks. This species is viviparous, with 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 sustained by a placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...
l connection formed from the depleted yolk sac
Yolk sac
The yolk sac is a membranous sac attached to an embryo, providing early nourishment in the form of yolk in bony fishes, sharks, reptiles, birds, and primitive mammals...
. Females bear litters of 5–19 pups every year 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 10 months. Reproductive seasonality, litter size, and size at maturity
Sexual maturity
Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...
vary between geographical regions. Because of its abundance, the smalleye hammerhead is an economically important 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 artisanal
Artisan fishing
Artisan fishing is a term used to describe small scale low-technology commercial or subsistence fishing practices. The term particularly applies to coastal or island ethnic groups using traditional techniques such as rod and tackle, arrows and harpoons, throw nets and drag nets, and traditional...
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 and is utilized as food. In recent years, 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....
has caused marked declines in its numbers off Trinidad
Trinidad
Trinidad is the larger and more populous of the two major islands and numerous landforms which make up the island nation of Trinidad and Tobago. It is the southernmost island in the Caribbean and lies just off the northeastern coast of Venezuela. With an area of it is also the fifth largest in...
, northern 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...
, and probably elsewhere. Coupled with its low reproductive rate, this has led the International Union for Conservation of Nature (IUCN) to list it under 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
Despite being one of the most easily recognizable sharks, the smalleye hammerhead has had a long history of taxonomic confusion that still remains to be fully resolved. Its scientific name originated in 1822, with French zoologist Achille ValenciennesAchille Valenciennes
Achille Valenciennes was a French zoologist.Valenciennes was born in Paris, and studied under Georges Cuvier. Valenciennes' study of parasitic worms in humans made an important contribution to the study of parasitology...
' description of Zygaena tudes in 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...
Memoires du Museum National d'Histoire Naturelle; the specific epithet tudes is 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...
for "hammer". Valenciennes made reference to three specimens: one from Nice
Nice
Nice is the fifth most populous city in France, after Paris, Marseille, Lyon and Toulouse, with a population of 348,721 within its administrative limits on a land area of . The urban area of Nice extends beyond the administrative city limits with a population of more than 955,000 on an area of...
in France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
, one from Cayenne
Cayenne
Cayenne is the capital of French Guiana, an overseas region and department of France located in South America. The city stands on a former island at the mouth of the Cayenne River on the Atlantic coast. The city's motto is "Ferit Aurum Industria" which means "Work brings wealth"...
in French Guyana, and one from the Coromandel Coast
Coromandel Coast
The Coromandel Coast is the name given to the southeastern coast of the Indian Subcontinent between Cape Comorin and False Divi Point...
of 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...
. However, for over two centuries taxonomists believed Valenciennes' account matched the great hammerhead
Great hammerhead
The great hammerhead is the largest species of hammerhead shark, family Sphyrnidae, attaining a maximum length of 6.1 m . It is found in tropical and warm temperate waters worldwide, inhabiting coastal areas and the continental shelf...
, which thus became known as Zygaena (later Sphyrna) tudes. The smalleye hammerhead was known by a different name, Sphyrna bigelowi, coined by Stewart Springer
Stewart 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 1944 issue of Journal of the Washington Academy of Sciences.
In 1950, Enrico Tortonese examined the Nice and Cayenne specimens of S. tudes (the Coromandel specimen having been lost in the interim) and concluded that they were not great hammerheads but rather the same species as S. bigelowi. Carter Gilbert concurred in his 1967 revision of the hammerhead sharks, noting that while the lost Coromandel specimen was probably a great hammerhead, none of the existing material belonged to that species. Thus, Sphyrna tudes became the accepted name for the smalleye hammerhead, taking precedence over S. bigelowi because it was published earlier, and the great hammerhead received the next available name Sphyrna mokarran. Gilbert designated the Nice specimen as the lectotype
Lectotype
In botanical nomenclature and zoological nomenclature, a lectotype is a kind of name-bearing type. When a species was originally described on the basis of a name-bearing type consisting of multiple specimens, one of those may be designated as the lectotype...
that would define S. tudes, having priority over the Cayenne specimen (the paralectotype). This was meant to stabilize the name but had the opposite effect.
In 1981, Jean Cadenat and Jacques Blache revisited the type specimens of S. tudes and found that the lectotype from Nice is likely not a smalleye hammerhead but rather a fetal
Fetus
A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...
whitefin hammerhead
Whitefin hammerhead
The whitefin hammerhead is a species of hammerhead shark, family Sphyrnidae, found in the tropical waters of the northeastern Atlantic Ocean, from Senegal to the Congo region...
(S. couardi, likely a synonym
Synonym (taxonomy)
In scientific nomenclature, a synonym is a scientific name that is or was used for a taxon of organisms that also goes by a different scientific name. For example, Linnaeus was the first to give a scientific name to the Norway spruce, which he called Pinus abies...
of the scalloped hammerhead
Scalloped hammerhead
The scalloped hammerhead is a species of hammerhead shark, family Sphyrnidae. Originally Zygaena lewini, it was later moved to its current name. The Greek word sphyrna translates into "hammer" in English, referring to the shape of this shark's head.This shark is also known as the bronze,...
, S. lewini). This would also explain the anomalous locality of the Nice specimen, as the smalleye hammerhead is not otherwise known outside of the Americas. By the rules of binomial nomenclature
Binomial nomenclature
Binomial nomenclature is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin grammatical forms, although they can be based on words from other languages...
, Sphyra tudes should then become the valid name for the whitefin hammerhead, taking precedence over S. couardi, and the smalleye hammerhead would revert to being Sphyrna bigelowi. Taxonomists though have been reluctant to change the names again, preferring to keep the smalleye hammerhead as S. tudes. For this solution to have official status would require a decision by the International Commission on Zoological Nomenclature
International Commission on Zoological Nomenclature
The International Commission on Zoological Nomenclature is an organization dedicated to "achieving stability and sense in the scientific naming of animals". Founded in 1895, it currently comprises 28 members from 20 countries, mainly practicing zoological taxonomists...
(ICZN), to reject the Nice specimen as the lectotype and designate the Cayenne specimen in its place. The relevant petition to the ICZN has not yet been put forth.
Until the first detailed study of the smalleye hammerhead was carried out in 1985–86 by José Castro of Clemson University
Clemson University
Clemson University is an American public, coeducational, land-grant, sea-grant, research university located in Clemson, South Carolina, United States....
for the Food and Agriculture Organization of the United Nations (FAO), its distinctive golden coloration was unknown to science. The color fades after death and the pigment
Pigment
A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...
s leech into the preservative
Preservative
A preservative is a naturally occurring or synthetically produced substance that is added to products such as foods, pharmaceuticals, paints, biological samples, wood, etc. to prevent decomposition by microbial growth or by undesirable chemical changes....
, resulting in the "yellowish cast" of museum specimens being regarded as an artifact of preservation. The names "yellow hammerhead" or "golden hammerhead" are used by fishermen in Trinidad
Trinidad
Trinidad is the larger and more populous of the two major islands and numerous landforms which make up the island nation of Trinidad and Tobago. It is the southernmost island in the Caribbean and lies just off the northeastern coast of Venezuela. With an area of it is also the fifth largest in...
for this shark, and the latter was promoted for wider usage by Castro. Another 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...
for this species is the curry shark. Recent phylogenetic analyses, based on morphological
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....
, isozyme
Isozyme
Isozymes are enzymes that differ in amino acid sequence but catalyze the same chemical reaction. These enzymes usually display different kinetic parameters Isozymes (also known as isoenzymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction. These enzymes...
, and 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...
data, have found that the hammerheads with the smallest cephalofoils are the most derived
Derived
In phylogenetics, a derived trait is a trait that is present in an organism, but was absent in the last common ancestor of the group being considered. This may also refer to structures that are not present in an organism, but were present in its ancestors, i.e. traits that have undergone secondary...
members of their lineage. A hammerhead "supertree
Supertree
A supertree is a single phylogenetic tree assembled from a combination of smaller phylogenetic trees, which may have been assembled using different datasets or a different selection of taxa. Supertree algorithms can highlight areas where additional data would most usefully resolve any ambiguities...
" (a composite of several independent phylogenetic trees) published by Mauro José Cavalcanti in 2005 found the closest relatives of the smalleye hammerhead to be the sister species pair of the scalloped bonnethead
Scalloped bonnethead
The scalloped bonnethead, Sphyrna corona, is a rare, little-known species of hammerhead shark, family Sphyrnidae. Its other common names include the mallethead shark and the crown shark. It is found in tropical and subtropical waters in the eastern Pacific Ocean, from Mexico to Peru, and possibly...
(S. corona) and the scoophead
Scoophead
The scoophead is a little-known species of hammerhead shark, family Sphyrnidae, occurring in the tropical waters of the western Atlantic Ocean from Panama to southern Brazil, and in the eastern Pacific Ocean from the Gulf of California to Ecuador and probably northern Peru...
(S. media), and that the three form a 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...
with the bonnethead
Bonnethead
The bonnethead shark or shovelhead, Sphyrna tiburo, is a member of the hammerhead shark genus Sphyrna. The Greek word sphyrna translates as hammer, referring to the shape of this shark's head - tiburo is the Taino word for shark....
(S. tiburo).
Distribution and habitat
The smalleye hammerhead is found along the eastern coast of South AmericaSouth America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
from 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...
to Venezuela
Venezuela
Venezuela , officially called the Bolivarian Republic of Venezuela , is a tropical country on the northern coast of South America. It borders Colombia to the west, Guyana to the east, and Brazil to the south...
, though it seldom occurs further west than the Orinoco Delta southeast of Trinidad
Trinidad
Trinidad is the larger and more populous of the two major islands and numerous landforms which make up the island nation of Trinidad and Tobago. It is the southernmost island in the Caribbean and lies just off the northeastern coast of Venezuela. With an area of it is also the fifth largest in...
. There are unconfirmed reports of this species from off 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...
, 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...
, and western Florida
Florida
Florida is a state in the southeastern United States, located on the nation's Atlantic and Gulf coasts. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia and to the east by the Atlantic Ocean. With a population of 18,801,310 as measured by the 2010 census, it...
; records from other parts of the world are most likely erroneous, resulting from its tangled taxonomic history. It is among the most abundant sharks within its range. This species inhabits inshore murky waters 5–40 m (16.4–131.2 ft) deep, over muddy bottoms. There is segregation by sex and age: newborns and juveniles under 40 cm (15.7 in) long are found in the shallowest waters, moving deeper after a few months of life. Adult females are mostly found at depths of 9–18 m (29.5–59.1 ft), while larger juveniles and adult males are mostly found at depths of 27–36 m (88.6–118.1 ft). This species is tolerant of brackish water
Brackish water
Brackish water is water that has more salinity than fresh water, but not as much as seawater. It may result from mixing of seawater with fresh water, as in estuaries, or it may occur in brackish fossil aquifers. The word comes from the Middle Dutch root "brak," meaning "salty"...
and can be found over a salinity
Salinity
Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...
range of 20–34 ppt.
Description
One of the smaller members of its family, the smalleye hammerhead can reach a length of 1.5 m (4.9 ft), though 1.2–1.3 m (3.9–4.3 ft) is more typical, and a weight of 9 kg (19.8 lb). The body is streamlined and fairly slender. The mallet-shaped cephalofoil is wide and long, with a span measuring 28–32% of the body length; the leading margin forms a broad arch with indentations in the middle and on either side. The cephalofoil of newborns are longer, more arched, and less indented in front than those of adults. The eyes, placed at the ends of the cephalofoil, are proportionately smaller than in other hammerheads and equipped with nictitating membraneNictitating membrane
The nictitating membrane is a transparent or translucent third eyelid present in some animals that can be drawn across the eye for protection and to moisten it while maintaining visibility. Some reptiles, birds, and sharks have a full nictitating membrane; in many mammals, there is a small...
s (protective third eyelids). The nostrils are positioned just inside of the eyes, each with a well-developed groove running towards the center of the cephalofoil. The mouth is strongly curved, containing on either side 15–16 upper tooth rows and 15–17 lower tooth rows. The teeth have single narrow cusps with smooth or weakly serrated edges, that are angled in the upper jaw and upright in the lower jaw.
The first dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
is tall and slightly falcate (sickle-shaped), originating behind the pectoral fin bases; its free rear tip lies over the origin of the pelvic fins. The second dorsal fin is smaller than the first but still rather large, with a concave trailing margin. The pelvic fins have nearly straight trailing margins. The anal fin is taller and longer than the second dorsal fin. The caudal fin has a well-developed lower lobe and a notch near the tip of the upper lobe. The dermal denticles are oval with five horizontal ridges leading to marginal teeth. The most distinctive trait of this species is its coloration: the back and dorsal fins are gray to yellowish gray, and the cephalofoil margins, flanks, underside, pectoral fins, pelvic fins, and anal fin are bright yellow to orange with a metallic or iridescent sheen. Newborn sharks are gray above, darkening on the first dorsal fin and upper caudal fin lobe, and whitish below. They gain a bright yellow cast on their undersides by a length of 45 cm (17.7 in), which turns to orange by a length of 50 cm (19.7 in). The golden color is brightest in sharks 55–70 cm (21.7–27.6 in) long, and tends to fade with the onset of sexual maturity
Sexual maturity
Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...
.
Biology and ecology
Four other species of hammerhead sharks overlap in range with the smalleye hammerhead: the small-sized scoophead and bonnethead, and the large-sized scalloped hammerhead and great hammerhead. There is little competition between these species because of their differing habitat and dietary preferences. The smalleye hammerhead is the dominant hammerhead in shallow muddy areas, where high turbidityTurbidity
Turbidity is the cloudiness or haziness of a fluid caused by individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality....
limits the utility of vision (hence its smaller eyes). Adult males and juveniles of both sexes form schools
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...
of uniform body size; these schools do not appear to relate to reproduction or migration
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...
. Adult females are apparently solitary.
Young smalleye hammerheads under 67 cm (26.4 in) long feed predominantly on penaeid shrimp
Penaeidae
Penaeidae is a family of prawns, although they are often referred to as penaeid shrimp. It contains many species of economic importance, such as the tiger prawn , whiteleg shrimp, Atlantic white shrimp and Indian prawn. Many prawns are the subject of commercial fishery, and farming, both in marine...
, mostly Xiphopenaeus kroyeri
Xiphopenaeus kroyeri
Xiphopenaeus kroyeri, commonly called the Atlantic seabob, is a commercially important prawn. It is up to long and is the most intensely fished prawn species in the Guianas and along much of the Gulf Coast of the United States.-Description:...
. Larger sharks feed mainly on bony fishes, especially ariid sea catfish
Ariidae
The Ariidae or ariid catfish are a family of catfish that mainly live in marine waters with many freshwater and brackish water species. They are found worldwide in tropical to warm temperate zones.-Taxonomy:...
and their eggs
Roe
Roe or hard roe is the fully ripe internal egg masses in the ovaries, or the released external egg masses of fish and certain marine animals, such as shrimp, scallop and sea urchins...
. The shrimp and the surface mucus
Mucus
In vertebrates, mucus is a slippery secretion produced by, and covering, mucous membranes. Mucous fluid is typically produced from mucous cells found in mucous glands. Mucous cells secrete products that are rich in glycoproteins and water. Mucous fluid may also originate from mixed glands, which...
layer and eggs of the catfish contain carotenoid
Carotenoid
Carotenoids are tetraterpenoid organic pigments that are naturally occurring in the chloroplasts and chromoplasts of plants and some other photosynthetic organisms like algae, some bacteria, and some types of fungus. Carotenoids can be synthesized fats and other basic organic metabolic building...
pigments that appear to be the source of the sharks' golden color; it is uncertain whether the pigments in the catfish also ultimately come from the shrimp. Another shark species in the region, the yellow smooth-hound (Mustelus higmani), also feeds on shrimp and has a yellowish color, albeit not nearly as bright. This species has also been known to consume swimming crabs, 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...
, grunts
Sciaenidae
Sciaenidae is a family of fish commonly called drums, croakers, or hardheads for the repetitive throbbing or drumming sounds they make...
, and newborn scalloped hammerheads. The smalleye hammerhead may fall prey to larger sharks such as the bull shark
Bull shark
The bull shark, Carcharhinus leucas, also known as Zambezi shark or unofficially known as Zambi in Africa and Nicaragua shark in Nicaragua, is a shark common worldwide in warm, shallow waters along coasts and in rivers...
(Carcharhinus leucas), while smaller individuals may also be taken by bony fishes. Its coloration may provide camouflage
Crypsis
In ecology, crypsis is the ability of an organism to avoid observation or detection by other organisms. It may be either a predation strategy or an antipredator adaptation, and methods include camouflage, nocturnality, subterranean lifestyle, transparency, and mimicry...
. A known parasite of this species is the monogenea
Monogenea
Monogenea are a group of largely ectoparasitic members of the flatworm phylum Platyhelminthes, class Monogenea.-Characteristics:Monogenea are very small parasitic flatworms mainly found on skin or gills of fish....
n Erpocotyle schmitti; it may also serve as a host to common 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,...
ectoparasites such as Echthrogaleus coleoptratus, Pandarus saturus and P. cranchii.
Like all hammerhead sharks, the smalleye hammerhead is viviparous: when the developing embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
s exhaust their supply of yolk, the depleted yolk sac
Yolk sac
The yolk sac is a membranous sac attached to an embryo, providing early nourishment in the form of yolk in bony fishes, sharks, reptiles, birds, and primitive mammals...
develops into a placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...
l connection through which the mother delivers nourishment. Mature females have a single functional ovary
Ovary
The ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in anatomically female individuals are analogous to testes in anatomically male individuals, in that they are both gonads and endocrine glands.-Human anatomy:Ovaries...
and two functional uterus
Uterus
The uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...
es. Ovulation
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...
occurs at the same time as gestation
Gestation
Gestation is the carrying of an embryo or fetus inside a female viviparous animal. Mammals during pregnancy can have one or more gestations at the same time ....
, allowing females to bear young every year. The details of the smalleye hammerhead's life history vary across its range. Off Trinidad, reproduction occurs on a well-defined annual cycle with mating in August and September, and birthing in late May and June of the following year. The females carry between 5 and 12 pups for 10 months, and make use of food-rich, shallow coastal bay
Bay
A bay is an area of water mostly surrounded by land. Bays generally have calmer waters than the surrounding sea, due to the surrounding land blocking some waves and often reducing winds. Bays also exist as an inlet in a lake or pond. A large bay may be called a gulf, a sea, a sound, or a bight...
s as nursery areas. The newborns measure around 30 cm (0.984251968503937 ft) long, and males and females attain sexual maturity at 80 cm (31.5 in) and 98 cm (38.6 in) long respectively. By contrast, smalleye hammerheads off the northern Brazilian state of Maranhão
Maranhão
Maranhão is a northeastern state of Brazil. To the north lies the Atlantic Ocean. Maranhão is neighbored by the states of Piauí, Tocantins and Pará. The people of Maranhão have a distinctive accent...
are substantially larger, with males maturing at over 92 cm (36.2 in) long and females at over 101 cm (39.8 in) long. As the litter size increases with female size, Maranhão sharks have been recorded carrying up to 19 pups. The seasonality of breeding also differs, with pregnant females found from June to October and January to April, and males in apparent reproductive condition from May to November and in March.
Human interactions
Timid and harmless to humans, the smalleye hammerhead is caught incidentallyBycatch
The term “bycatch” is usually used for fish caught unintentionally in a fishery while intending to catch other fish. It may however also indicate untargeted catch in other forms of animal harvesting or collecting...
by inshore artisanal
Artisan fishing
Artisan fishing is a term used to describe small scale low-technology commercial or subsistence fishing practices. The term particularly applies to coastal or island ethnic groups using traditional techniques such as rod and tackle, arrows and harpoons, throw nets and drag nets, and traditional...
multi-species fisheries throughout its range, and marketed as food. It is the most or second-most important shark caught by such fisheries off Trinidad, Guyana, and Brazil. Because of its head shape, individuals of all ages are readily caught in 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...
s; small numbers are also caught on line gear and in bottom trawls. 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:...
, as it is subjected to intense fishing pressure and its low reproductive rate renders it susceptible to population depletion. Anecdotal evidence suggests that smalleye hammerhead catches have declined significantly off Trinidad and northern Brazil, which are likely indicative of population trends in the rest of its range. It is not the target of any conservation or management schemes.
External links
- Sphyrna tudes, Smalleye hammerhead at FishBase
- Sphyrna tudes (Curry Shark, Golden Hammerhead, Smalleye Hammerhead Shark) at IUCN Red List
- Biological Profiles: Smalleye Hammerhead at Florida Museum of Natural History Ichthyology Department
- In Search of the Golden Hammerhead at ReefQuest Centre for Shark Research