Smalleye hammerhead

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Smalleye hammerhead
Overhead view of a grayish shark with a hammer-shaped head and orange coloring on its head, sides, and fins

Critically Endangered  (IUCN 3.1)[1]
CITES Appendix II (CITES)[2]
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Elasmobranchii
Subdivision: Selachimorpha
Order: Carcharhiniformes
Family: Sphyrnidae
Genus: Sphyrna
Species:
S. tudes
Binomial name
Sphyrna tudes
(Valenciennes, 1822)
World map with blue shading along the eastern coast of South America from Venezuela to Uruguay
Range of the smalleye hammerhead[3]
Synonyms

Sphyrna bigelowi S. Springer, 1944

The smalleye hammerhead (Sphyrna tudes), also called the golden hammerhead or curry shark, is a small species of hammerhead shark in the family Sphyrnidae. This species was historically 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

critically endangered
in 2020.

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.

zoologist Achille Valenciennes' description of Zygaena tudes in the scientific journal Mémoires du Muséum 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 Guiana, and one from the Coromandel Coast of India.[5] For over two centuries, though, taxonomists believed Valenciennes' account matched the great hammerhead, which thus became known as Zygaena (later Sphyrna ) tudes.[3] 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.[6]

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.

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.[3][8]

In 1981, Jean Cadenat and Jacques Blache revisited the

whitefin hammerhead (S. couardi, likely a synonym of the scalloped hammerhead, S. lewini).[3][9] 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.[3] 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.[1]

Eusphyra blochii

Sphyrna mokarran

Sphyrna zygaena

Sphyrna lewini

Sphyrna tudes

Sphyrna media

Sphyrna tiburo

Sphyrna corona

Phylogenetic tree of hammerhead sharks:[10]

Until the first detailed study of the smalleye hammerhead was carried out in 1985–86 by José Castro of

sister species pair of the scalloped bonnethead (S. corona) and the bonnethead (S. tiburo).[10]

Description

Jaws
Upper teeth
Lower teeth

One of the smaller members of its family, the smalleye hammerhead can reach a length of 1.5 m (4.9 ft),[12] though 1.2–1.3 m (3.9–4.3 ft) is more typical,[13] and a weight of 9 kg (20 lb).[11] 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.[14] The cephalofoils of newborns are longer, more arched, and less indented in front than those of adults.[4] The eyes, placed at the ends of the cephalofoils, are proportionately smaller than in other hammerheads and equipped with nictitating membranes (protective third eyelids).[3][4] 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.[3][14]

The first

dermal denticles are oval with five horizontal ridges leading to marginal teeth.[15] 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 (18 in), which turns to orange by a length of 50 cm (20 in). The golden color is brightest in sharks 55–70 cm (22–28 in) long, and tends to fade with the onset of sexual maturity.[4]

Distribution and habitat

The smalleye hammerhead is found along the eastern coast of South America from Uruguay to Venezuela, though it seldom occurs further west than the

inshore murky waters 5–40 m (16–131 ft) deep, over muddy bottoms. Segregation occurs by sex and age; newborns and juveniles under 40 cm (16 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 (30–59 ft), while larger juveniles and adult males are mostly found at depths of 27–36 m (89–118 ft).[4] This species is tolerant of brackish water, and can be found over a salinity range of 20–34 ppt.[16]

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. Little competition occurs between these species because of their differing habitats and dietary preferences. The smalleye hammerhead is the dominant hammerhead in shallow, muddy areas, where high turbidity 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.[4][17]

Young smalleye hammerheads under 67 cm (26 in) long feed predominantly on

ectoparasites such as Echthrogaleus coleoptratus, Pandarus satyrus, and P. cranchii.[15]

Like all hammerhead sharks, the smalleye hammerhead is

Brazilian state of Maranhão are substantially larger, with males maturing at over 92 cm (36 in) long and females at over 101 cm (40 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.[16]

Human interactions

Timid and harmless to humans,

seine netting to trawling, and is unable to replenish this harvest. Smalleye hammerheads are also bycatch in commercial shrimp trawls, which are often run through the shark's shallow-water habitat. 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. The smalleye shark is federally protected in Brazil and Colombia.[1]

References

  1. ^
    doi:10.2305/IUCN.UK.2020-3.RLTS.T60202A3091946.en
    . Retrieved 19 November 2021.
  2. ^ "Appendices | CITES". cites.org. Retrieved 14 January 2022.
  3. ^
    ISBN 92-5-101384-5
    .
  4. ^
    S2CID 12510936
    .
  5. ^ Valenciennes, A. (1822). "Sur le sous-genre Marteau, Zygaena". Mémoires du Muséum National d'Histoire Naturelle. 9: 222–228.
  6. ^ Springer, S. (1944). "Sphyrna bigelowi, a new hammerhead shark from off the Atlantic coast of South America, with notes on Sphyrna mokarran from New South Wales". Journal of the Washington Academy of Sciences. 34 (8): 274–276.
  7. doi:10.1080/00222935008654116
    .
  8. doi:10.5479/si.00963801.119-3539.1
    .
  9. ISBN 2-7099-0576-0
    .
  10. ^
    PMID 20138218
    .
  11. ^ a b Martin, R.A. (August 4, 1998). In Search of the Golden Hammerhead. ReefQuest Centre for Shark Research. Retrieved on October 17, 2008.
  12. ^ a b Froese, Rainer; Pauly, Daniel (eds.) (2008). "Sphyrna tudes" in FishBase. January 2008 version.
  13. ^
    ISBN 1-55209-629-7
    .
  14. ^
    ISBN 0-292-75206-7
    .
  15. ^ a b c Gallagher, E. Biological Profiles: Smalleye Hammerhead. Florida Museum of Natural History Ichthyology Department. Retrieved on April 23, 2010.
  16. ^ a b Lessa, R.; Menni, R.C. & Lucena, F. (September 1998). "Biological observations on Sphyrna lewini and S. tudes (Chondrichthyes, Sphyrnidae) from northern Brazil". Vie et Milieu. 48 (3): 203–213.
  17. ^
    ISBN 2-84433-135-1
    .
  18. ISBN 0-8203-2592-9
    .
  19. ^ Suriano, D.M. & Labriola, J.B. (January 1998). "Erpocotyle VanBeneden et Hesse, 1863 (Monogenea, Hexabothriidae), parasite of carcharhiniform fishes from the southwestern Atlantic Ocean, with the description of E. schmitti sp. n". Acta Parasitologica. 43 (1): 4–10.

External links

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