Winghead shark

{{Short description|Species of shark}} {{Speciesbox | image = Eusphyra blochii csiro-nfc.jpg | status = CR | status_system = IUCN3.1 | status_ref = <ref name="iucn status 10 October 2025">{{cite iucn |author=Smart, J.J. |author2=Simpfendorfer, C. |date=2025 |title=''Eusphyra blochii'' |volume=2025 |article-number=e.T41810A124417935 |doi=10.2305/IUCN.UK.2025-2.RLTS.T41810A124417935.en |access-date=10 October 2025}}</ref> | status2 = CITES_A2 | status2_system = CITES | status2_ref = <ref name="CITESAppendices">{{Cite web|title=Appendices {{!}} CITES|url=https://cites.org/eng/app/appendices.php|access-date=14 January 2022|website=cites.org}}</ref> | genus = Eusphyra | parent_authority = T. N. Gill, 1862 | species = blochii | authority = (G. Cuvier, 1816) | range_map = Range_map_winhghead.png | range_map_caption = Range of the winghead shark (IUCN)<ref name="last and stevens"/> | synonyms = * ''Zygaena blochii'' {{small|G. Cuvier, 1816}} * ''Zygaena laticeps'' {{small|Cantor, 1837}} * ''Zygaena latycephala'' {{small|van Hasselt, 1823}} }}

The '''winghead shark''' ('''''Eusphyra blochii''''') is a species of hammerhead shark, and part of the family Sphyrnidae. It is the sole member of the genus '''''Eusphyra'''''. Reaching a length of {{convert|1.9|m|ft|abbr=on}}, this small brown to gray shark has a slender body with a tall, sickle-shaped first dorsal fin. Its name comes from its exceptionally large "hammer", or cephalofoil, which can be as wide as half of the shark's total length. The function of this structure is unclear, but may relate to the shark's senses. The wide spacing of its eyes grants superb binocular vision, while the extremely long nostrils on the leading margin of the cephalofoil may allow for better detection and tracking of odor trails in the water. The cephalofoil also provides a large surface area for its ampullae of Lorenzini and lateral line, with potential benefits for electroreception and mechanoreception, respectively.

Inhabiting the shallow coastal waters of the central and western Indo-Pacific, the winghead shark feeds on small bony fishes, crustaceans, and cephalopods. It gives birth to live young, with the developing embryos receiving nourishment through a placental connection. Females produce annual litters of six to 25 pups; depending on region, birth may occur from February to June after a gestation period of 8–11 months. This harmless species is widely fished for meat, fins, liver oil, and fishmeal. The International Union for Conservation of Nature has assessed it as endangered in 2016, as it is thought to have declined in some parts of its range due to overfishing.

==Taxonomy== In 1785, German naturalist Marcus Elieser Bloch described a shark that he referred to ''Squalus zygaena'' (a synonym of ''Sphyrna zygaena'', the smooth hammerhead). French zoologist Georges Cuvier, as a brief footnote to the account of ''S. zygaena'' in his 1817 ''Le Règne animal distribué d'après son organisation, pour servir de base à l'histoire naturelle des animaux et d'introduction à l'anatomie comparée'', observed that Bloch's specimen (which he labeled "''z. nob. Blochii''") was not a smooth hammerhead, but rather a different species. Although Cuvier did not propose a proper binomial name, his colleague Achille Valenciennes interpreted it as such in 1822 when he described another specimen of the same species in detail, calling it ''Zygaena Blochii nobis'' and attributing the name to Cuvier.<ref name="cuvier"/><ref name="compagno"/>

In 1862, Theodore Gill placed the winghead shark in its own genus ''Eusphyra'', derived from the Greek ''eu'' ("good" or "true") and ''sphyra'' ("hammer").<ref name="gill"/><ref name="fishbase"/> However, subsequent authors did not accept ''Eusphyra'' and preferred to keep this species with the other hammerheads in the genus ''Sphyrna''. ''Eusphyra'' was resurrected by Henry Bigelow and William Schroeder in 1948, and came into wider usage after additional taxonomic research was published by Leonard Compagno in 1979 and 1988. Nevertheless, some sources still refer to this species as ''Sphyrna blochii''.<ref name="compagno"/><ref name="martin"/> Other common names for the winghead shark include arrowhead, arrow-headed hammerhead shark, and slender hammerhead.<ref name="fishbase"/>

==Phylogeny== {{cladogram|title=|align=left|caption=Phylogenetic tree of hammerhead sharks based on mitochondrial and nuclear DNA<ref name="lim et al"/> |clades={{clade|style=font-size:80%;line-height:80% |1={{clade |1='''''Eusphyra blochii''''' |2={{clade |1={{clade |1=''Sphyrna mokarran'' |2=''Sphyrna zygaena'' }} |2={{clade |1=''Sphyrna lewini'' |2={{clade |1={{clade |1=''Sphyrna tudes'' |2=''Sphyrna media'' }} |2={{clade |1=''Sphyrna tiburo'' |2=''Sphyrna corona'' }} }} }} }} }} }} }} The traditional view of hammerhead shark evolution is that species with smaller cephalofoils evolved first from a requiem shark ancestor, and later gave rise to species with larger cephalofoils. Under this interpretation, the winghead shark is the most derived hammerhead, as it has the most extreme cephalofoil morphology. However, molecular phylogenetic research based on isozymes, mitochondrial DNA, and nuclear DNA have found the opposite pattern, with the winghead shark as the most basal member of the hammerhead family. This result supports the counterintuitive idea that the first hammerhead shark to evolve had a large cephalofoil. It also supports the separation of ''Eusphyra'' from ''Sphyrna'' by keeping the latter monophyletic (including all descendants of a single ancestor). The winghead shark lineage is estimated to have diverged from the rest of the hammerheads some 15–20 million years ago during the Miocene.<ref name="martin"/><ref name="lim et al"/><ref name="cavalcanti"/>

==Description== thumb|upright=1.2|Winghead shark, X-ray image True to its name, the winghead shark's cephalofoil consists of a pair of long, narrow, and gently swept-back blades. The width of the cephalofoil is equal to 40–50% of the shark's total length. The front of the cephalofoil has a slight indentation in the middle and a gentle bump on each side in front of the nostrils. Each nostril is roughly twice as long as the width of the mouth and extends along almost the entire leading margin of each blade. The circular eyes, located at the forward outer corners of the cephalofoil, are equipped with protective nictitating membranes. The relatively small, arched mouth contains 15–16 upper and 14 lower tooth rows on each side, and sometimes also a single row of tiny teeth at the upper and/or lower symphyses (jaw midpoints). The teeth are small and smooth-edged, with angled triangular cusps. Five pairs of gill slits are seen, with the fifth pair over the pectoral fin origins.<ref name="last and stevens"/><ref name="compagno"/><ref name="last et al"/><ref name="randall"/>

The body is slim and streamlined, with a very tall, narrow, and falcate (sickle-shaped) first dorsal fin that originates over the bases of the rather small pectoral fins. The second dorsal fin is much smaller and originates over the caudal third of the anal fin base. The anal fin is about half again as long as the second dorsal fin. A lengthwise groove is on the caudal peduncle at the dorsal origin of the caudal fin. The upper caudal fin lobe is longer than the lower lobe, and bears a notch in the trailing margin near the tip.<ref name="last and stevens"/><ref name="randall"/> The skin is covered by overlapping dermal denticles, each with three horizontal ridges leading to marginal teeth.<ref name="mello et al"/> This species is brownish gray to gray above and off-white below, and lacks fin markings.<ref name="last and stevens"/> It grows up to {{convert|1.9|m|ft|abbr=on}} long.<ref name="last et al"/>

==Distribution and habitat== The winghead shark is found in the tropical central and western Indo-Pacific, from the Persian Gulf eastward across South and Southeast Asia to New Guinea and northern Queensland. Its range extends as far north as Taiwan and as far south as the Montebello Islands off Western Australia.<ref name="last and stevens"/><ref name="compagno"/> This species inhabits shallow waters close to shore and has been known to enter estuaries.<ref name="fishbase"/>

==Biology and ecology== thumb|upright=1.2|Illustration of a winghead shark from ''Fauna of British India'' (1889), showing the remarkably wide cephalofoil: The function of this structure is yet unclear. Several nonexclusive hypotheses have been proposed to explain the extreme size of the winghead shark's cephalofoil. The placement of the eyes at the ends of the cephalofoil provides a binocular field of view of 48°, the most of any hammerhead and four times that of a requiem shark; this species thus has excellent depth perception, which may aid in hunting.<ref name="mccomb et al"/> This species also has proportionately the longest nostrils among the hammerheads; longer nostrils contain more chemosensory receptors and can sample more water at a time, increasing the chances of detecting an odor molecule. A winghead shark {{convert|1|m|ft|abbr=on}} long is theoretically capable of sampling over {{convert|2300|cm3|in3|abbr=on}} of water per second. Another potential olfactory benefit of the cephalofoil is increased separation between the midpoints of the left and right nostrils, which enhances the shark's ability to resolve the direction of a scent trail.<ref name="kajiura et al"/> Finally, the cephalofoil may increase the shark's ability to detect the electric fields and movements of its prey, by providing a larger surface area for its electroreceptive ampullae of Lorenzini and mechanoreceptive lateral line.<ref name="compagno"/> The lateral blades seem too large to function in maneuvering, which has been suggested for other hammerheads.<ref name="nakaya"/>

The winghead shark usually hunts close to the sea floor. Its diet consists mainly of small bony fishes, followed by crustaceans and cephalopods.<ref name="last and stevens"/><ref name="stevens and lyle"/> Known parasites of this species include the tapeworms ''Callitetrarhynchus blochii'',<ref name="pramanik and manna"/> ''Heteronybelinia heteromorphi'',<ref name="palm"/> ''Otobothrium carcharidis'', ''O. mugilis'',<ref name="schaeffner and beveridge"/> ''Phoreiobothrium puriensis'',<ref name="srivastav and capoor"/> and ''Phyllobothrium blochii'',<ref name="srivastav and srivastava"/> the nematodes ''Hysterothylacium ganeshi'',<ref name="lakshmi and sreeramulu"/> ''Pseudanisakis'' sp.,<ref name="arthur and ahmed"/> ''Raphidascaroides blochii'',<ref name="bruce et al"/> and ''Terranova'' sp.,<ref name="arthur and ahmed"/> the copepod ''Caligus furcisetifer'',<ref name="margolis et al"/> and the protozoan ''Eimeria zygaenae''.<ref name="chakravarty and mandal"/>

===Life history=== The winghead shark is viviparous like the rest of its family, with the developing young sustained to term by a placental connection to the mother. Adult females have a single functional ovary, on the right, and two functional uteri. Compartments form inside the uteri during pregnancy, one for each embryo. In the waters around Mumbai, the mating season is in July and August during the monsoon.<ref name="appukuttan"/> The males bite at the sides of the females as a prelude to copulation. Females can reproduce every year; the litter size ranges from six to 25 pups, and increases with the size of the female. The gestation period lasts 8–9 months off western India, and 10–11 months off northern Australia.<ref name="last and stevens"/><ref name="stevens and lyle"/><ref name="devadoss"/> Pregnant females have been reported to quarrel with each other.<ref name="compagno"/>

Initially, the embryo is nourished by yolk and develops in a similar fashion to other sharks. At a length of {{convert|4.0|-|4.5|cm|in|abbr=on}}, the cephalofoil and the fins begin to form. When the embryo is {{convert|12|-|16|cm|in|abbr=on}} long, the yolk supply begins to run low and folds appear on the yolk sac and uterine wall, which later interlock to form the placenta. At this stage, the embryo has most of the features of an adult, albeit rudimentary and colorless. The blades of the cephalofoil are folded back along the body, and long external gill filaments protrude from the gill slits. At a length of {{convert|20|-|29|cm|in|abbr=on}}, the placenta has formed; the first teeth, dermal denticles, and skin pigmentation appear on the embryo, and the external gills are much reduced in size. By the time the embryo is {{convert|30|cm|in|abbr=on}} long, it resembles a miniature version of the adult.<ref name="appukuttan"/><ref name="devadoss"/>

Birthing takes place in May and June off Mumbai and Parangipettai, in March and April in the Gulf of Mannar, and in February and March off northern Australia. The pups emerge tail first, and their cephalofoils remain folded until after birth to facilitate passage through the cloaca.<ref name="stevens and lyle"/><ref name="appukuttan"/><ref name="devadoss"/> The newborns measure {{convert|32|-|47|cm|in|abbr=on}} in length.<ref name="last et al"/> Sexual maturity is reached around {{convert|1.0|-|1.1|m|ft|abbr=on}} long for males and {{convert|1.1|-|1.2|m|ft|abbr=on}} long for females.<ref name="last et al"/><ref name="devadoss"/> Their maximum lifespan is at least 21 years.<ref name="smart et al"/>

==Human interactions== Harmless to humans, the winghead shark is caught throughout its range using gillnets, seines, stake nets, longlines, and hook-and-line. The meat is sold fresh, the fins are exported to Asia for shark fin soup, the liver is a source of vitamin oil, and the offal is processed into fishmeal.<ref name="last and stevens"/><ref name="compagno"/> This species is taken in large numbers in some areas, such as in the Gulf of Thailand and off India and Indonesia, and anecdotal evidence indicates its population has suffered as a result. The International Union for Conservation of Nature has listed the winghead shark as endangered. This species is only infrequently caught in Australian waters, where it has been assessed regionally as least concern by the IUCN.<ref name="iucn status 19 November 2021">{{cite iucn |author=Smart, J.J. |author2=Simpfendorfer, C. |date=2016 |title=''Eusphyra blochii'' |volume=2016 |article-number=e.T41810A68623209 |doi=10.2305/IUCN.UK.2016-1.RLTS.T41810A68623209.en |access-date=19 November 2021}}</ref>

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==External links== *[http://shark-references.com/species/view/Eusphyra-blochii "Species description of ''Eusphyra blochii''" at Shark-References.com] *[http://fishesofaustralia.net.au/home/species/3143 Fishes of Australia : ''Eusphyra blochii'']

{{Carcharhiniformes}} {{Taxonbar|from=Q890336}} {{Good article}}

winghead shark Category:Marine fauna of South Asia Category:Marine fish of Southeast Asia Category:Extant Miocene first appearances winghead shark Category:Taxa named by Georges Cuvier